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  • Electron microscopy  (1,530)
  • NMR  (1,047)
  • Springer  (1,572)
  • Elsevier  (1,003)
  • Oxford University Press
  • 1
    Electronic Resource
    Electronic Resource
    The effect of flexible lattice aluminium in zeolite beta during the nitration of toluene with nitric acid and acetic anhydride (2000)
    Springer
    Catalysis letters 70 (2000), S. 61-65 
    Details
    ISSN: 1572-879X
    Keywords: flexible lattice aluminium ; zeolite beta ; nitration ; regio‐control ; para‐selectivity ; toluene ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The nitration of toluene with nitric acid and acetic anhydride using zeolite H‐beta as catalyst was studied with multi‐nuclear solid‐state NMR spectroscopy in order to investigate the causes for the observed enhanced para‐selectivity. The reversible transformation of framework aluminium from a tetrahedral into an octahedral environment was observed by 27Al NMR upon interaction of the zeolite with the different components of the nitrating system. The octahedral co‐ordination complex between lattice aluminium and acetylnitrate might explain the surface‐catalysed para‐selective nitration reaction and suggests that the lattice flexibility plays an important role in determining the regio‐selectivity of the nitration catalysed by zeolites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019015216483
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  • 2
    Electronic Resource
    Electronic Resource
    A comparative CP/MAS 13C-NMR study of cellulose structure in spruce wood and kraft pulp (2000)
    Springer
    Cellulose 7 (2000), S. 35-55 
    Details
    ISSN: 1572-882X
    Keywords: cellulose ; hemicellulose ; kraft pulp ; NMR ; spruce wood
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract CP/MAS 13C-NMR spectroscopy in combination with spectral fitting was used to study the supermolecular structure of the cellulose fibril in spruce wood and spruce kraft pulp. During pulping, structures contributing to inaccessible surfaces in the wood cellulose are converted to the cellulose Iβ allomorph, that is, the degree of order is increased. This increase is also accompanied by a conversion of cellulose Iα to cellulose Iβ. Cellulose from wood composed of different cell types, that is, compression wood, juvenile wood, earlywood, latewood and normal wood exhibited a similar supermolecular structure. Assignments were made for signals from hemicellulose which contribute significantly to the spectral C-4 region (80–86 ppm) in kraft pulp spectra but substantially less to the corresponding region in wood spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009236932134
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  • 3
    Electronic Resource
    Electronic Resource
    A 29Si MAS-NMR study of Cd7[Ge6Si]O21 pyroxmangite (2000)
    Springer
    Physics and chemistry of minerals 27 (2000), S. 713-718 
    Details
    ISSN: 1432-2021
    Keywords: Key words Cd-pyroxmangite ; NMR ; Pyroxenoids ; Ordering ; Superperiods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  Synthetic (SiGe)-pyroxenoids are often observed to have superperiods. Whether or not these superperiods grow in connection with Si-Ge ordering is a fundamental question. The size difference between Ge and Si tetrahedra leads to CdGeO3 having the pyroxmangite structure, whereas CdSiO3 has the wollastonite structure. Consequently, considerable strain is expected for a pyroxenoid with a disordered Ge-Si distribution. A 29Si MAS-NMR study of a Cd-pyroxmangite of nominal composition Cd7[Ge6Si]O7 points to considerable Si clustering, probably as GeSiSiSiGe triples corresponding to the wollastonite-like units of the siebener chain. It is proposed that such ordering relieves strain within the tetrahedral chain. Residual strain is also relieved by insertion of an extra pair of GeO4 tetrahedra into the pyroxene-like component of the siebener-chain units, leading to single neuner-chain units which terminate the superperiods. This growth pattern is cyclic. The presence of several types of superperiod may reflect similar energetics for different Ge-Si-ordering patterns within the siebener chains. Ordering of Si-rich unit cells and of unit cells having no Si is proposed as the reason for the occurrence of the superperiods in Cd-pyroxmangite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690000115
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  • 4
    Electronic Resource
    Electronic Resource
    Defect structure of the low temperature α-cristobalite phase and the cristobalite ⇆ tridymite transformation in (Si-Ge)O2 (2000)
    Springer
    Physics and chemistry of minerals 27 (2000), S. 386-397 
    Details
    ISSN: 1432-2021
    Keywords: Key words Cristobalite ; Tridymite ; Phase transformation ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Using minimum exposure techniques, it is feasible to perform high resolution electron microscopy on the α-cristobalite phase of (Si0.9 Ge0.1)O2, which is extremely radiation sensitive. Such images reveal atomic scale information of twins and tridymite-like stacking faults on (1 1 1)β planes, as well as of domain boundaries resulting from the β→α transition. Polytype structures are formed in certain cases. Morphological features suggest that the phase transformation cristobalite → tridymite proceeds by means of a zonal dislocation mediated synchro-shear process on (1 1 1)β planes; the geometry of this process is analyzed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002699900082
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  • 5
    Electronic Resource
    Electronic Resource
    The need for a shared database infrastructure: combining X-ray crystallography and electron microscopy (2000)
    Springer
    European biophysics journal 29 (2000), S. 457-462 
    Details
    ISSN: 1432-1017
    Keywords: Key words X-ray crystallography ; Electron microscopy ; Biological databases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Advances in structural biology are opening greater opportunities for understanding biological structures from the cellular to the atomic level. Particularly promising are the links that can be established between the information provided by electron microscopy and the atomic structures derived from X-ray crystallography and nuclear magnetic resonance spectroscopy. Combining such different kinds of structural data can result in novel biological information on the interaction of biomolecules in large supramolecular assemblies. As a consequence, the need to develop new databases in the field of structural biology that allow for an integrated access to data from all the experimental techniques is becoming critical. Pilot studies performed in recent years have already established a solid background as far as the basic information that an integrated macromolecular structure database should contain, as well as the basic principles for integration. These efforts started in the context of the BioImage project, and resulted in a first complete database prototype that provided a versatile platform for the linking of atomic models or X-ray diffraction data with electron microscopy information. Analysis of the requirements needed to combine data at different levels of resolution have resulted in sets of specifications that make possible the integration of all these different types in the context of a web environment. The case of a structural study linking electron microscopy and X-ray data, which is already contained within the BioImage data base and in the Protein Data Bank, is used here to illustrate the current approach, while a general discussion highlights the urgent need for integrated databases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002490000089
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  • 6
    Electronic Resource
    Electronic Resource
    NMR Structure Determination and Structure-Based Functional Characterization of Conserved Hypothetical Protein MTH1175 from Methanobacterium thermoautotrophicum (2000)
    Springer
    Journal of structural and functional genomics 1 (2000), S. 15-25 
    Details
    ISSN: 1570-0267
    Keywords: structural genomics ; RNase H ; NMR ; methanobacterium thermoautotrophicum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The solution structure of MTH1175, a 124-residue protein from the archaeon Methanobacterium thermoautotrophicum has been determined by NMR spectroscopy. MTH1175 is part of a family of conserved hypothetical proteins (COG1433) with unknown functions which contains multiple paralogs from all complete archaeal genomes and the archaeal gene-rich bacterium Thermotoga maritima. Sequence similarity indicates this protein family may be related to the nitrogen fixation proteins NifB and NifX. MTH1175 adopts an α/β topology with a single mixed β-sheet, and contains two flexible loops and an unstructured C-terminal tail. The fold resembles that of Ribonuclease H and similar proteins, but differs from these in several respects, and is not likely to have a nuclease activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011348803324
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  • 7
    Electronic Resource
    Electronic Resource
    Structure and Morphology of a Polyether/Polyacrylate Semi-interpenetrating Polymer Network (2000)
    Springer
    Journal of thermal analysis and calorimetry 59 (2000), S. 83-92 
    Details
    ISSN: 1572-8943
    Keywords: cationic and photoinitiated polymerization ; DSC ; interfacial mixing ; interpenetrating polymer network (IPN) ; glass transition temperature ; NMR ; quantitative thermal analysis of phases ; reactive epoxy and acrylate systems ; Tg broadening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In this study NMR and DSC are used to probe the structure, thermal characteristics and morphology of a network formed from a diepoxide/acrylate system. Separate chemistries are employed to polymerize the diepoxide and acrylate components. The cationic polymerization of the diepoxide exhibits excellent selectivity in producing a crosslinked polyether network without affecting the acrylate monomer. Subsequent photoinitiated free-radical polymerization of the acrylate produces a phase separated, semi-interpenetrating polymer network (SIPN).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010123610324
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  • 8
    Electronic Resource
    Electronic Resource
    [13C]Dynamic NMR and Molecular Modeling of 2,4-Bis(N-Pyrrolidinyl)-6-chloro-s-triazine (2000)
    Springer
    Structural chemistry 11 (2000), S. 303-306 
    Details
    ISSN: 1572-9001
    Keywords: NMR ; [13C]NMR ; 2,4-bis(N-pyrrolidinyl)6-chloro-s-triazine ; variable temperature ; molecular modeling ; rotational barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The room temperature [13C]NMR spectrum of 2,4-bis(N-pyrrolidinyl)-6-chloro-s-triazine shows doubled signals for the pyrrolidine rings, which suggests restricted rotation about the Ar-C—N bond. The rotational barrier around this bond was determined by [13C]dynamic NMR (DNMR) spectra run at different increasing temperatures and also by the PM3 Hamiltonian contained in the MOPAC package. The values thus obtained, 16.6 and 13.6 kcal mol−1, respectively, are in good agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009238326751
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  • 9
    Electronic Resource
    Electronic Resource
    An NMR Study of MeTMS Based Coatings Filled with Colloidal Silica (2000)
    Springer
    Journal of sol gel science and technology 19 (2000), S. 131-135 
    Details
    ISSN: 1573-4846
    Keywords: coatings ; colloids ; NMR ; organosilanes ; adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Coatings were prepared by mixing MeTMS and an aqueous colloidal silica. Mixing of an MeTMS hydrolysis mixture with the aqueous colloidal silica is only possible, without flocculation of the colloidal silica particles, within a certain time window. 29Si NMR was used to follow the hydrolysis/condensation reactions of MeTMS, whereas 1H NMR was used to monitor the reaction of the MeTMS monomers and oligomers with the silica surface in the coating liquid. The reaction of MeTMS with the surface of the SiO2 particles is determined by the oligomer size. Typical SiO2 surface coverage is less than 3 molecules/nm2 (approximately one monolayer). Large MeTMS oligomers and/or cyclic species do not react with the SiO2 surface. These species are probably too apolar to react or absorb at the SiO2 surface. Flocculation of the aqueous colloidal silica occurs due to the low polarity of the hydrolysis mixture. The water content and the degree of condensation of the MeTMS determine the width of the time window.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008795113990
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  • 10
    Electronic Resource
    Electronic Resource
    Non-Hydrolytic Routes for the Synthesis of NASICON (2000)
    Springer
    Journal of sol gel science and technology 19 (2000), S. 463-467 
    Details
    ISSN: 1573-4846
    Keywords: NASICON ; NMR ; non-hydrolytic synthesis ; precursor chemistry ; solid electrolyte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The study of non-hydrolytic reactions for the synthesis of NASICON is reported. Different procedures have been considered, changing the precursors and their addition order, and varying the reaction solvent; dichloromethane, acetonitrile and tetrahydrofuran (THF). The most promising results in terms of homogeneous reactivity were obtained using PO(On-C4H9)3, Zr(Ot-C4H9)4, SiCl4 and Na(Ot-C4H9) in acetonitrile. The reactions were followed using heteronuclear Nuclear Magnetic Resonance (NMR) spectroscopy (13C, 31P). NASICON powders were prepared by the thermal decomposition of the gels between 900 and 1200°C. The powders were analyzed by XRD to check the formation of the NASICON phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008707815750
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  • 11
    Electronic Resource
    Electronic Resource
    Comparative Study of Structure of Silica Gels from Different Sources (2000)
    Springer
    Journal of sol gel science and technology 19 (2000), S. 495-499 
    Details
    ISSN: 1573-4846
    Keywords: sol-gel ; silicas ; biology ; X-ray diffraction ; IR ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The medium-range-network structure of silicas from different sources was comparatively examined by X-ray diffraction, IR and NMR analyses. Silica gels made through the conventional sol-gel route were found to have a different structure from silica glass, and considered to be composed of 4-fold siloxane ring units, irrespective of preparation conditions. Amorphous silicas in rice-hulls and bamboo leaves showed structure data close to silica glass, being suggested to consist mainly of 6-fold siloxane ring units. The modified sol-gel method, in which siloxane oligomers containing cyclic siloxane tetramers may have been ring-opened and polymerized under the catalytic reaction of NaOH or NH4F in the water-free solution, provided the silica gel of which structure was very similar to silica glass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008720118475
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  • 12
    Electronic Resource
    Electronic Resource
    Low Temperature Sol-Gel Preparation of β-Al2TiO5 Thin Films: Spectroscopic Analysis of the Precursors (2000)
    Springer
    Journal of sol gel science and technology 19 (2000), S. 577-580 
    Details
    ISSN: 1573-4846
    Keywords: aluminum titanate ; NMR ; MS ; thin films ; precursor chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Two sol-gel syntheses allowed the preparation of β-Al2TiO5 thin films on silicon substrates at 700°C, reacting aluminum and titanium alkoxides with and without acetylacetone as a chelating agent. Nuclear magnetic resonance (NMR) and mass spectra of the sols allowed identification of the intermediate species formed and to show the formation of an Al-Ti containing polymer establishing that the synthesis without acetylacetone leads to the most extensive polymerization. The formation of β-Al2TiO5 at low temperatures is attributed to diffusion-limited crystallization process, which takes place in the conditions of high homogeneity at molecular level reached in the sol-gel synthesis. The crystallization of the films was studied as a function of the firing time and temperature and confirmed that β-Al2TiO5 with better thermal stability was obtained with the synthesis without chelating agent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008705109815
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  • 13
    Electronic Resource
    Electronic Resource
    The Structure of Hybrid Gels by Drift and NMR Spectroscopies (2000)
    Springer
    Journal of sol gel science and technology 19 (2000), S. 403-407 
    Details
    ISSN: 1573-4846
    Keywords: hybrid gels ; silica ; polytetrahydrofuran ; DRIFTS ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Hybrid inorganic-organic gels have been prepared by the sol-gel process using tetraethoxysilane (TEOS) as precursor, mixed with a low concentration of polytetrahydrofuran (PTHF), under acid catalysis. The hybrid xerogels were characterized by DRIFTS and Solid State 1H, 13C and 29Si NMR. The DRIFT spectra indicate that the polymer is responsible for decreasing the number of free silanol groups in comparison to pure silica. Solid-state NMR spectra reveal the types of silicate structures formed and the conditions for establishing chemical bonds between the two phases, which are responsible for the silica network flexibility. We have concluded that it is possible to design a hybrid gel with tailored properties, even at very low polymer concentration, by selecting the appropriate preparation route.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008783010298
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  • 14
    Electronic Resource
    Electronic Resource
    The Effect of Nanoscaled Metal Oxide Sols on the Structure and Properties of Glycidoxypropyltrimethoxysilane Derived Sols and Gels (2000)
    Springer
    Journal of sol gel science and technology 19 (2000), S. 305-309 
    Details
    ISSN: 1573-4846
    Keywords: epoxide ; ring-opening ; condensation ; NMR ; hardness ; nanoparticles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Glycidoxypropyltrimethoxysilane (GPTS) is frequently used as precursor for the preparation of sol-gel derived nanoscaled hybrid polymers. The influence of nanoscaled metal oxide sols of silica, boehmite, zirconia and ceria on reactions of GPTS in ethanolic hydrolysates and in corresponding gels (epoxide ring-opening, condensation degree) was examined by liquid- and solid-state 13C and 29Si NMR with regard to a better correlation between structure and material properties. Generally, a higher condensation degree of RSi(O0.5)3 units of GPTS is found after addition of metal oxide sols compared to GPTS without additives. The metal oxide sols (10 mole% series) cause an epoxide ring-opening up to 20% in GPTS hydrolysates after 24 h. A nearly complete ring opening was found in the boehmite and silica containing hybrid gels whereas gels containing ceria and other types of silica only show a low degree of ring-opening. The results show an accelerated ring-opening with increasing content of AlO/OH-species in silica sols. 13C NMR studies reveal that the epoxide ring-opening does not completely lead to polyether structures but to considerable amounts (up to 40%) of ethylether groups which can influence the material properties (hardness).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008777414416
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  • 15
    Electronic Resource
    Electronic Resource
    Conformational Studies of a Melittin—Inhibitor Complex (2000)
    Springer
    The protein journal 19 (2000), S. 529-534 
    Details
    ISSN: 1573-4943
    Keywords: Melittin ; inhibitor ; NMR ; peptide ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The conformation of a melittin—inhibitor complex was studied by solution NMR, solid-state NMR, and circular dichroism. In solution, binding was studied by titrating inhibitor against melittin in dimethyl sulfoxide, methanol, aqueous buffer, and dodecylphosphocholine micelles. The change in chemical shift of Trp19 resonances and the formation of a precipitate at 1:1 molar ratio indicated that the inhibitor was bound to melittin. Solid-state NMR also showed a change in chemical shift of two labeled carbons of melittin near Pro14 and a change in 1H T 1 relaxation times when complexed with inhibitor. Rotational resonance experiments of melittin labeled in the proline region indicated a change in conformation for melittin complexed with inhibitor. This observation was also supported by circular dichroism measurements, indicating a reduction in α-helical structure for increasing ratios of inhibitor bound to melittin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026561701338
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  • 16
    Electronic Resource
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    Temperature, pH, and Solvent Isotope Effects on Cytochrome c Peroxidase Mutant N82A Studied by Proton NMR (2000)
    Springer
    The protein journal 19 (2000), S. 535-542 
    Details
    ISSN: 1573-4943
    Keywords: Cytochrome c peroxidase ; CcP ; NMR ; A82CcP mutant ; solvent isotope effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The mutant of baker's yeast cytochrome c peroxidase-CN with Ala82 in place of Asn82, [N82A]CcPCN, exhibits a complex solution behavior featuring dynamic interconversion among three enzyme forms that so far have only been detected by NMR spectroscopy. Proton NMR studies of [N82A]CcPCN reveal resonances from each of the three enzyme forms and show that the interconversion among forms is controlled by the pH, temperature, and isotope composition (H2O vs. D2O) of the buffer solution. No evidence for a key hydrogen bond between His52 and heme-coordinated cyanide is found in any of the enzyme forms, indicating that disruption of the extensive distal hydrogen bonding network is the source of this phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026513818176
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  • 17
    Electronic Resource
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    Evidence for stable grain boundary melt films in experimentally deformed olivine-orthopyroxene rocks (2000)
    Springer
    Physics and chemistry of minerals 27 (2000), S. 480-494 
    Details
    ISSN: 1432-2021
    Keywords: Key words Olivine ; Grain boundary ; Partial melt ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The microstructure of olivine-olivine grain boundaries has been studied in experimentally deformed (1200–1227 °C, 300 MPa) partially molten olivine and olivine-orthopyroxene rocks. In-situ melting produced ∼1 vol% melt in all samples studied. Grain boundary analyses were carried out using a number of transmission electron microscopy techniques. The grain boundary chemistry in undeformed olivine-orthopyroxene starting material showed evidence for the presence of an intergranular phase along some, but not all, of the olivine-olivine boundaries. In the deformed samples, ultrathin Si-rich, Al- and Ca-bearing amorphous films have been observed along all investigated olivine-olivine grain boundaries. The chemistry of the grain boundaries, which is considered to be indicative for the presence of a thin film, was measured with energy-dispersive X-ray spectroscopy (EDX) and energy-filtering imaging. The amorphous nature of the films was confirmed with diffuse dark field imaging, Fresnel fringe imaging, and high-resolution electron microscopy. The films range in thickness from 0.6 to 3.0 nm, and EDX analyses show that the presence of Al and Ca is restricted to this ultrathin film along the grain boundaries. Because thin melt films have been observed in all the samples, they are thought to be stable features of the melt microstructure in deformed partially molten rocks. The transition from the occasional presence of films in the undeformed starting material to the general occurrence of the films in deformed materials suggests that deformation promotes the formation and distribution of the films. Alternatively, hot-pressing may be too short for films to develop along all grain boundaries. A difference in creep strength between the studied samples could not be attributed to grain boundary melt films, as these have been found in all deformed samples. However, a weakening effect of grain boundary melt films on olivine rheology could not be ruled out due to the lack of confirmed melt-film free experiments.
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    URL: http://dx.doi.org/10.1007/s002690000090
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  • 18
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    Analysis of the structure of lignin-carbohydrate complexes by the specific13C tracer method (2000)
    Springer
    Journal of wood science 46 (2000), S. 130-136 
    Details
    ISSN: 1611-4663
    Keywords: Lignin-carbohydrate complexes ; NMR ; 13C tracer ; Coniferin ; Ketal linkage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In the present study the specifically13C-enriched lignin precursors of biosynthesis (i.e., coniferin-[side chainα−13C], coniferin-[side chain-β−13C] and coniferin-[side chain-γ−13C]) were synthesized and administered exogeneously to ginkgo shoots (Ginkgo biloba L.) to obtain13C-enriched lignin-carbohydrate complexes (LCCs). The specifically13C-enriched LCCs were isolated from the newly formed xylem of ginkgo shoots administered with the13C-enriched precursors and degraded by enzymes. Lignin-rich fractions, so called enzyme-degraded LCCs (EDLCCs), were obtained. By determining their13C-NMR spectra, information related to the chemical structure of lignin building units and linkages between phenylpropane units of lignin and carbohydrates were obtained. It was found that these precursors were incorporated in natural lignin successfully. Three lignin-carbohydrates linkages (i.e., ether type, ester type, ketal type) were found at the C α -position of the side chain of phenylpropane units in ginkgo LCC. No lignin-carbohydrate bond at the Cβ- or Cγ-position of the lignin side chain was observed in the13C-NMR spectra of the13C-enriched LCCs. This fact indicates that a specific13C tracer technique can be useful in NMR study of the chemical structure of LCCs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00777359
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  • 19
    Electronic Resource
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    Modeling ganglioside headgroups by conformational analysis and molecular dynamics (2000)
    Springer
    Glycoconjugate journal 17 (2000), S. 283-299 
    Details
    ISSN: 1573-4986
    Keywords: ganglioside conformation ; NMR ; molecular mechanics ; molecular dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The conformations and dynamics of gangliosides GM1, GM2, 6′-GM2 and GM4 have been studied by computational means, and the results compared to NMR data. Unconstrained conformational searches were run using the AMBER* force field augmented by MNDO derived parameters for the Neu5Ac anomeric torsion, the GB/SA water solvation model, and the MC/EM alogorithm; extended (10–12[emsp4 ]ns) dynamic simulations in GB/SA water were performed with the MC/SD protocol, and the stored structures were minimized. The overall mobility of the Neu5Acα2,3Gal linkage and the position of its minimum energy conformation have been shown to depend mainly on the presence or the absence of a GalNAc residue at the adjacent position. The best quantitative agreement with the available NOE data was achieved after minimization of the structures stored during the MC/SD dynamic runs. The latter protocol appears to reproduce satisfactorily the available experimental data, and can be used with confidence to build three-dimensional models of ganglioside headgroups.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007161319700
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  • 20
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    Glycosylations versus conformational preferences of cancer associated mucin core (2000)
    Springer
    Glycoconjugate journal 17 (2000), S. 835-848 
    Details
    ISSN: 1573-4986
    Keywords: cancer vaccine ; glycopeptide ; MUC-1 ; immunotherapy ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Synthetic oligosaccharide vaccines based on core STn (sialyl α2-6 GalNAc) carbohydrate epitopes are being evaluated by a number of biopharmaceutical firms as potential immunotherapeutics in the treatment of mucin-expressing adenocarcinomas. The STn carbohydrate epitopes exist as discontinuous clusters, O-linked to proximal serine and threonine residues within the mucin sequence. In an effort to probe the structure and dynamics of STn carbohydrate clusters as they may exist on the cancer-associated mucin, we have used NMR spectroscopy and MD simulations to study the effect of O-glycosylation of adjacent serine residues in a repeating (Ser)n sequence. Three model peptides/glyco-peptides were studied: a serine trimer containing no carbohydrate groups ((Ser)3 trimer); a serine trimer containing three Tn (GalNAc) carbohydrates α-linked to the hydroxyls of adjacent serine sidechains ((Ser.Tn)3 trimer); and a serine trimer containing three STn carbohydrates α-linked to the hydroxyls of adjacent serine sidechains ((Ser.STn)3 trimer). Our results demonstrate that clustering of carbohydrates shifts the conformational equilibrium of the underlying peptide backbone into a more extended and rigid state, an arrangement that could function to optimally present the clustered carbohydrate antigen to the immune system. Steric effects appear to drive these changes since an increase in the size of the attached carbohydrate (STn versus Tn) is accompanied by a stronger shift in the equilibrium toward the extended state. In addition, NMR evidence points to the formation of hydrogen bonds between the peptide backbone NH protons and the proximal GalNAc groups in the (Ser.Tn)3 and (Ser.STn)3 trimers. The putative peptide-sugar hydrogen bonds may also play a role in influencing the conformation of the underlying peptide backbone, as well as the orientation of the O-linked carbohydrate. The significance of these results will be discussed within the framework of developing clustered STn-based vaccines, capable of targeting the clustered STn epitopes on the cancer-associated mucin.
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    URL: http://dx.doi.org/10.1023/A:1010909011496
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    Biocompatibility of MPC: in vivo evaluation for clinical application (2000)
    Springer
    Journal of artificial organs 3 (2000), S. 39-46 
    Details
    ISSN: 1619-0904
    Keywords: Poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) (MPC) ; In vivo biocompatibility ; Artificial endocrine pancreas ; Electron microscopy ; Glucose sensor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Biocompatibility is important to assure a mild body reaction to an implanted device and its long-term stability and functionality. In diabetes research, subcutaneously implanted glucose monitoring systems need biocompatible surfaces for long-term application. The biocompatibility of poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) (MPC), a material similar to the phospholipid layer of a cell membrane, was compared in vivo with the biocompatibility of polyurethane (PU), polyvinyl alcohol (PVA), and cuprophane (CUP). Needle-type glucose sensors and hollow-fiber probes used for microdialysis were coated with these four different biomaterials and implanted subcutaneously in 18 rats and 7 healthy volunteers. At set intervals, the implants and, in the case of the rats, also the surrounding tissue were removed and characterized by light and electron microscopy. MPC-coated sensors and hollow-fiber probes showed smooth and thin deposits in flat layers, whereas the surface deposits on PU- and PVA-coated sensors and those on CUP hollow-fiber probes appeared as rough, irregular, and dense attachments of aggregated cells and protein. This study confirmed results from earlier in vitro tests by showing the biocompatibility and reliability of MPC. Even though the amount of protein and cells attached to the MPC surface was not as low as expected from in vitro experiments, the biocompatibility and long-term stability of the implanted devices were superior to those of PU, PVA, and CUP.
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    URL: http://dx.doi.org/10.1007/BF02479925
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    Energy metabolism and re-establishment of intercellularadhesion complexes of gel entrapped hepatocytes (2000)
    Springer
    Cytotechnology 32 (2000), S. 219-228 
    Details
    ISSN: 1573-0778
    Keywords: alginate ; bioreactor ; energy metabolism ; hepatocytes ; microscopy ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract We studied the effect of continuous medium flow on the viabilityand structural organization of hepatocytes high density entrapped inalginate gel beads in the first few hours after isolation.The metabolic energy status of the entrapped cells, monitored invivo by 31P NMR spectroscopy, was stable during theexperimental time and a physiological redox ratio was reachedafter the first three hours of culture. The morphologicalanalysis revealed that the entrapped hepatocytes placed in a fixed-bed bioreactor under continuous flow showed a polyhedricalshape with numerous microvilli on cell surface and reconstitutedtight junctions as well as bile canalicular structures, closelyresembling those present in the liver.These results suggest that continuous flow allows the culture ofhepatocytes at very high cell density within a matrix withoutloss of viability and accelerates cellular tissue reconstructionat very short times after isolation. This type of culture couldrepresent a very useful model for physiological andtoxicological studies as well as a promising approach toward thedevelopment of a bioartificial hybrid support device in acuteliver failure.
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    Structural studies of the glycopeptides of B-chain of cinnamomin – a type II ribosome-inactivating protein by nuclear magnetic resonance (2000)
    Springer
    Glycoconjugate journal 17 (2000), S. 749-759 
    Details
    ISSN: 1573-4986
    Keywords: cinnamomin ; glycopeptides ; NMR ; primary structure ; ribosome-inactivating protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Cinnamomin is a plant type II ribosome-inactivating protein (RIP) isolated from the seeds of Cinnamomum camphora. It consists of two nonidentical polypeptide chains (A- and B-chain) held together through one disulfide linkage. Its A- and B-chain contain 0.3% and 3.9% sugars respectively. The B-chain of cinnamomin was digested by pronase E and then the liberated glycopeptides were separated from non-glycopeptides by gel filtration chromatography on a Bio-Gel P-4 column. Three crude glycopeptides were obtained by continuing chromatography over anion-exchange resin (AG1-X2) in the buffer of 2% pyridine-acetic acid (pH 8.3) with a polygradient elution system. Through further purification by the gel filtration chromatography and HPLC, three major glycopeptides, GP1, GP2 and GP3 were obtained. Mainly by two-dimensional Nuclear Magnetic Resonance (NMR) including TOCSY, DQF-COSY, NOESY, HMQC and HMBC, their primary structures were analyzed as: Manα1,3Manα1,6(Manα1,3)(Xylβ1,2)Manβ1,4GlcNAcβ1,4GlcNAcβ1-(Gly-)Asn-Asn-Thr(GP1), Manα1,6(Manα1,3)(Xylβ1,2)Manβ1,4GlcNAcβ1,4(Fucα1,3)GlcNAcβ1-Asn-Ala-Thr(GP2),Manα1,6(Manα1,3)Manα1,6(Manα1,2 Manα1,3)Manβ1,4GlcNAcβ1,4GlcNAcβ1-(Ala-)Asn-Gly-Thr(GP3).
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    URL: http://dx.doi.org/10.1023/A:1010957007038
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    Alkaloids of Peganum harmala (2000)
    Springer
    Chemistry of natural compounds 36 (2000), S. 602-605 
    Details
    ISSN: 1573-8388
    Keywords: Peganum harmala ; alkaloid ; dipegine ; dipeginol ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Dipegine (1) and dipeginol (2) were isolated fromPeganum harmala.The structures of these alkaloids were established by mass and IR spectra
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    URL: http://dx.doi.org/10.1023/A:1017524027513
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    Effects of photic and thermal stress on distal and proximal rhabdomeres in the crayfish eye: why are the visual membranes of the 8th retinula cell more resilient than the others? (2000)
    Springer
    Protoplasma 210 (2000), S. 156-163 
    Details
    ISSN: 1615-6102
    Keywords: Electron microscopy ; Photoreceptor ; Visual membrane ; Photic radiation damage ; Retina ; Crustacea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Visual membranes of the crayfish eye either belong to the small, distally placed rhabdomere of retinula cell R8 or are part of the much more voluminous proximal rhabdom, made up of rhabdomeres belonging to cells R1–R7. Under various conditions of environmental stress (e.g., prolonged darkness, elevated temperature, bright light with and without a concomitant rise in temperature, flickering lights) the visual membranes of R8 prove far more resistant to structural damage than those of R1–R7. Membrane damage is known to occur when dormant lipoxygenases become activated, for example through heat. Since R8 is the only type of visual cell in the crayfish retina that does not contain grains of screening pigment, the view that screening-pigment granules could “aggravate” or even “trigger” membrane damage in times of stress is strengthened. Functionally, R8's strong resistance to physical damage when exposed to flickering lights points to a role of the distal rhabdom in the movement detection system of the crayfish eye.
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    URL: http://dx.doi.org/10.1007/BF01276855
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    The Oligomeric Subunit c Rotor in the Fo Sector of ATP Synthase: Unresolved Questions in Our Understanding of Function (2000)
    Springer
    Journal of bioenergetics and biomembranes 32 (2000), S. 433-439 
    Details
    ISSN: 1573-6881
    Keywords: FoF1-ATP synthase ; Fo rotary motor ; subunit c ; subunit a ; transmembrane helices ; NMR ; cross linking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract We have proposed a model for the oligomeric c-rotor of the Fo sector of ATP synthase and its interaction with subunit a during H+-transport driven rotation. The model is based upon the solution structure of monomeric subunit c, determined by NMR, and an extensive series of cross-linking distance constraints between c subunits and between subunits c and a. To explain the complete set of cross-linking data, we have suggested that the second transmembrane helix rotates during its interaction with subunit a in the course of the H+-translocation cycle. The H+-transport coupled rotation of this helix is proposed to drive the stepwise movement of the c-oligomeric rotor. The model is testable and provides a useful framework for addressing questions raised by other experiments.
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    URL: http://dx.doi.org/10.1023/A:1005604722178
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    Fluorometric and NMR Studies of the Naproxen–Cyclodextrin Inclusion Complexes in Aqueous Solutions (2000)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 37 (2000), S. 383-394 
    Details
    ISSN: 1573-1111
    Keywords: naproxen ; cyclodextrins ; complexation ; association constants ; fluorescence ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Inclusion complexation processesinvolving four cyclodextrins and naproxen have beenstudied for the protonated and unprotonated forms ofthe guest molecule. The association constants havebeen evaluated from changes in the fluorescenceintensity of naproxen following addition of acyclodextrin to an aqueous naproxen solution. 1HNMR NOESY and ROESY spectra have shown that twoorientations of the guest molecule relative toβ-cyclodextrin are possible.
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    URL: http://dx.doi.org/10.1023/A:1008114815223
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    Thermal Behavior of Dispersed Vanadium Dioxide Particles in Polyethylene Glycol Matrix Containing Tetraethylammonium Bromide (2000)
    Springer
    Journal of thermal analysis and calorimetry 62 (2000), S. 473-478 
    Details
    ISSN: 1572-8943
    Keywords: metal-semiconductor phase transitions ; NMR ; polyethylene glycol matrix ; vanadiumdioxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A study has been made on samples of dispersed vanadium dioxide (VO2) in a matrix of polyethylene glycol (PEG) doped with a quaternary ammonium salt (QAS), namely tetraethylammonium bromide. It has been established that under the influence of the dopant the heating of a sample up to the temperature of the metal-semiconductor phase transition (MSPT) results in a phase in homogeneity of the sample. On the basis of the results of this study it is possible to conclude that small concentrations of QAS in a PEG matrix can exert a strong effect on the electronic structure of dispersed VO2 particles. This is accompanied by the appearance of phase heterogeneity of VO2 which manifests itself in the fact that - with the onset of MSPT with increasing temperature - one portion of the substance passes into the metallic state, and the other remains in the semiconductive state.
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    URL: http://dx.doi.org/10.1023/A:1010166903988
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    The primary electron acceptor of green sulfur bacteria, bacteriochlorophyll 663, is chlorophyll a esterified with Δ 2,6-phytadienol (2000)
    Springer
    Photosynthesis research 63 (2000), S. 269-280 
    Details
    ISSN: 1573-5079
    Keywords: bacteriochlorophyll a epimer ; bacteriochlorophyll 663 ; chlorophyll a ; green sulfur bacteria ; FAB-mass ; NMR ; phytadienol ; primary electron acceptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The primary electron acceptor of green sulfur bacteria, bacteriochlorophyll (BChl) 663, was isolated at high purity by an improved purification procedure from a crude reaction center complex, and the molecular structure was determined by fast atom bombardment mass spectroscopy (FAB-mass), 1H- and 13C-NMR spectrometry, double quantum filtered correlation spectroscopy (DQF-COSY), heteronuclear multiple-quantum coherence (HMQC) and heteronuclear multiple-bond correlation (HMBC) spectral measurements. BChl 663 was 2.0 mass units smaller than plant Chl a. The NMR spectra showed that the macrocycle was identical to that of Chl a. In the esterifying alcohol, a singlet P71 signal was observed at the high-field side of the singlet P31 signal in BChl 663, while a doublet peak of P71 overlapped that of P111 in Chl a. A signal of P7-proton, seen in Chl a, was lacking, and the P6-proton appeared as a triplet signal near the triplet P2-proton signal in BChl 663. These results indicate the presence in BChl 663 of a C=C double bond between P6 and P7 in addition to that between P2 and P3. The structure of BChl 663 was hence concluded to be Chl a esterified with 2,6-phytadienol instead of phytol. In addition to BChl 663, two molecules of the 132-epimer of BChl a, BChl a′, were found to be present per reaction center, which may constitute the primary electron donor.
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    URL: http://dx.doi.org/10.1023/A:1006480629059
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    Volume dependence of NMR of ordered correlated electron systems (2000)
    Springer
    Hyperfine interactions 128 (2000), S. 167-181 
    Details
    ISSN: 1572-9540
    Keywords: NMR ; high pressure ; phase transitions ; magnetic materials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The importance of NMR high pressure studies of ordered magnetic materials for the understanding of the ground and excited states of magnetic conductors is discussed with examples from recent work on the manganese perovskites and the rare earth compounds SmMn2Ge2 and CeIn3. A brief discussion is given of the difference between true pressure experiments and the “chemical pressure” introduced by changing the composition of a material.
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    URL: http://dx.doi.org/10.1023/A:1012631515382
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    Study of single crystal surfaces with polarized 8Li (2000)
    Springer
    Hyperfine interactions 127 (2000), S. 463-468 
    Details
    ISSN: 1572-9540
    Keywords: NMR ; surfaces ; Si(1 1 1) (7×7) ; Ru(0 0 1) ; Li adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract NMR experiments on 8Li adsorbed on semiconductor and metallic surfaces are described (Si(1 1 1)−(7×7) and Ru(0 0 1)). They yield detailed information on LDOS (EF), the local density of states at the nucleus and at Fermi energy.
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    An apparatus for NMR of laser polarized 129Xe on single crystal surfaces (2000)
    Springer
    Hyperfine interactions 127 (2000), S. 469-474 
    Details
    ISSN: 1572-9540
    Keywords: NMR ; single crystal surfaces ; optical pumping of Rb ; hyperpolarized 129Xe ; laser polarized 129Xe
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Due to a lack of at least 2 orders of magnitude in the amount of sample nuclei, single crystal surfaces are out of reach for conventional NMR measurements. Our aim is to prove that highly polarized 129Xe provides a technique to overcome this restriction. Therefore an apparatus for polarizing 129Xe up to 0.7 by spin transfer from optically pumped Rb has been designed as well as an NMR spectrometer in combination with a UHV chamber with sample cleaning, cooling and characterization abilities and a special manifold of glass stopcocks with a liquid nitrogen cooled trap for dosing nitrogen free polarized Xe into the chamber onto the surface.
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    Anisotropy of the Hyperfine Field on 57Fe in Pure and Substituted Yttrium Iron Garnet (2000)
    Springer
    Hyperfine interactions 131 (2000), S. 3-19 
    Details
    ISSN: 1572-9540
    Keywords: NMR ; hyperfine field ; ferrites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using NMR, anisotropy of the hyperfine field on 57Fe nuclei was measured in Y3Fe5O12 with nonmagnetic, trivalent substitutions on d (Ga3+) and a (Y3+ - yttrium antisite defect) sites which are occupied by ferric ions in a pure, stoichiometric system. The measurements were performed by the spin-echo method at liquid helium temperature. Thorough analysis of the hyperfine field anisotropy on the 57Fe nuclei in an ideal environment and in an environment where one of Fe3+ nearest cation neighbours is replaced by the nonmagnetic impurity is given. When the Fe3+ on which the NMR is measured is on the a site and the impurity is Ga3+(d), the results may be interpreted in terms of the superposition model. On the other hand, the results for Fe3+ on the d site and Y3+(a) are in clear disagreement with the predictions of this model.
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    Nuclear Magnetic Resonance and Infrared Spectroscopic Analysis of Nedocromil Hydrates (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 619-624 
    Details
    ISSN: 1573-904X
    Keywords: NMR ; infrared ; nedocromil ; hydrates ; solvate ; methanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Nedocromil sodium (NS), which is used in the treatment ofreversible obstructive airway diseases, such as asthma, has been foundto exist in the following solid phases: the heptahemihydrate, thetrihydrate, a monohydrate, an amorphous phase, which contains variableamounts of water, and a recently discovered methanol + water (MW)solvate. Our aim was to apply 13C solid-state nuclear magneticresonance (NMR) spectroscopy and solid-state Fourier transform infrared(FTIR) spectroscopy to the study of specific interactions in the varioussolid forms of NS. Methods. The 13 solid-state NMR and FTIR spectra of the varioussolid forms of NS were obtained and were related to the crystalstructures of NS, the conformations of the nedocromil anion, and theinteractions of the water molecules in these crystals. Results. The 13C solid-state NMR spectrum is sensitive to theconformation of the nedocromil anion, while the solid-state FTIR spectrumis sensitive to interactions of water molecules in the solid state. In NSmonohydrate, for which the crystal structure has not yet been solved,and in the amorphous phase, the information about the conformationsof the nedocromil anion and the interactions of the water moleculesare deduced from the 13C solid-state NMR spectra and solid-state FTIRspectra, respectively. Conclusions. 13C solid-state NMR spectroscopy and solid-state FTIRspectroscopy are shown to be powerful complementary tools forprobing the chemical environment of molecules in the solid state,specifically the conformation of the nedocromil anion and the interactions ofwater-molecules, respectively.
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    The Molecular Complexes of Calix[4]resorcinolarene with Diglycidylmethyl Phosphonate (2000)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 36 (2000), S. 153-162 
    Details
    ISSN: 1573-1111
    Keywords: calix[4]resorcinolarene ; diglycidylmethyl phosphonate ; complexation ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The formation of strong molecular complexes of calix[4]recorcinolarene with the polyfunctional phosphoorganic compound diglycidylmethyl phosphonate was observed in organic media. Complexes of different compositions were obtained with the ratio of the initial reagents of 1 : 1 and 1 : 4. Three complexes were isolated and characterized by elemental analysis; their 1H and 13C NMR spectroscopic parameters are also discussed.
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    Synthesis and Conformational Studies of an Asymmetrical Dibenzo-16-crown-5 Carboxylic Acid (2000)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 36 (2000), S. 287-299 
    Details
    ISSN: 1573-1111
    Keywords: crown ether ; NMR ; complexation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Asymmetrical cis-5,6-dimethyl-6-oxyacetoxy-(2,3)(9,10)-dibenzo-16-crown-5 was synthesized by a multi-step sequence and its stereochemistry determined by NOE experiments. Introduction of the 6-methyl group markedly reduces the stability constant for complexation of Na+ and K+ by the ionized form of the lariat ether carboxylic acid.
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    The structure and conformation of the tryptophanyl diketopiperazines cyclo(Trp–Trp)·C2H6SO and cyclo(Trp–Pro) (1999)
    Springer
    Journal of chemical crystallography 29 (1999), S. 435-447 
    Details
    ISSN: 1572-8854
    Keywords: cyclic dipeptides ; Tryptophan ; Proline ; x-rays ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The structure and conformation of the cyclic dipeptides [cyclo(L-Trp–L-Trp)·C2H6SO] and cyclo(L-Trp–L-Pro) have been investigated with X-ray crystallographic and spectroscopic methods. Cyclo(L-tryptophanyl-L-tryptophanyl)·DMSO solvate crystallized in the space group P2 12121 with cell dimensions a = 6.193(2), b = 11.545(3), c = 31.117(4) Å. The crystal structure is stabilized by four hydrogen bonds (three intermolecular hydrogen bonds and one intramolecular bond). The first intermolecular bond is between the oxygen of DMSO and the nitrogen of indole ring 2, in contrast to the second intramolecular hydrogen bond between the nitrogen of indole ring 1 and the oxygen of DMSO. The two remaining intermolecular hydrogen bonds are between the nitrogens of the DKP ring and the carbonyl oxygens of the DKP ring. The values of χ1A 1 (−45.764) and χ1A 2 (67.437) indicate an extended side chain conformation for Trp residue 1 (EN) and a folded conformation for Trp residue 2. The DKP ring is more planar than in other cyclic dipeptide compounds (ϕ1 = 11.414, Ψ1 = −7.516, ϕ2 = 12.471, and Ψ2 = −8.256). In cyclo(L-Trp–L-Trp) the Cβ resonance of L-tryptophan (29.88 ppm) is shifted upfield 0.82 ppm when compared with the same resonance in cyclo(L-Trp–L-Gly) (30.7 ppm) and cyclo(L-Leu–L-Trp) (30.7 ppm). Two conformations of cyclo(Trp–Pro) crystallized in the space group P1 with cell dimensions a = 5.422(1), b = 9.902(1), c = 13.443(2) Å, α = 80.42(1), β = 78.61(1), and γ = 89.13(1)°. The conformation of the backbone and the orientation of the aromatic side chains for these conformers are very similar. The DKP rings for both conformers adopt a typical boat conformation in contrast to the flattened chair conformation observed for cyclo(Tyr–Pro) and cyclo(Phe–F-Pro). The tryptophan side chains of these conformers are folded towards the diketopiperazine (DKP) ring. The pyrrolidine ring for conformer 1 can be described as an envelope (Cs–Cβ-endo) conformation in contrast to the pyrrolidine ring symmetry for conformer 2 which is an intermediate between Cs and C2 rather than pure Cs for the proline ring with Cβ-endo and Cγ-exo with respect to C′. The two prolyl rings are puckered at the β-carbon atoms which deviate from the best planes defined by the four remaining atoms. The crystal structures are stabilized by four intermolecular hydrogens bonds. An intermolecular bond between the nitrogen of the indole ring (conformer 1) and the carbonyl oxygen of the DKP ring (conformer 2) was observed. The second hydrogen bond is between the nitrogen of the indole ring (conformer 2) and the carbonyl oxygen of the DKP ring (conformer 1). The last two hydrogens involve the carbonyl oxygens of the DKP rings and the nitrogens of the DKP rings [carbonyl oxygen of DKP ring (conformer 1)––––nitrogen of DKP ring (conformer 2); nitrogen of DKP ring (conformer 1)––––––carbonyl oxygen of DKP ring (conformer 2)].
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    A Direct Carbon-13 and Nitrogen-15 NMR Study of Cerium(III)–Isothiocyanate Complexation in Aqueous Solvent Mixtures (1999)
    Springer
    Journal of solution chemistry 28 (1999), S. 193-210 
    Details
    ISSN: 1572-8927
    Keywords: carbon-13 ; nitrogen-15 ; chlorine-35 ; NMR ; cerium(III)–isothiocyanate complexes ; water–acetone–Freon ; water–methanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A study of lanthanide complexation with isothiocyanate is underway using a multinuclear magnetic resonance technique. For isothiocyanate solutions in water–acetone–Freon mixtures at low temperature, −85–−125°C, ligand exchange is slow enough to permit the observation of 13C and 15N NMR signals for coordinated and free anions. For the Ce3+–NCS− system, four coordinated anion signals, displaced from the free anion signal by about +450 to +550 ppm for 15N and +50 to +80 ppm for 13C, are observed. The 13C and 15N spectral data are complementary, showing a signal area concentration dependence and measured coordination numbers consistent with the formation of Ce(NCS)2+ through Ce(NCS)1- 4. In water–methanol, the extent of complexing is decreased, presumably because of the higher dielectric constant of this medium. In addition, the results of a competitive study of NCS− and Cl− ion binding, carried out using 35Cl NMR, is presented.
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    URL: http://dx.doi.org/10.1023/A:1021754214188
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    Molecular Modeling Study of the PtCl2 Complexes of Unsaturated S2On+1-Coronands: Dynamic Simulations and Investigation of the Ring Interconversion (1999)
    Springer
    Journal of molecular modeling 5 (1999), S. 72-77 
    Details
    ISSN: 0948-5023
    Keywords: Keywords Thiacrown ether ; NMR ; Pt(II) complexes ; Molecular dynamic simulations ; Ring interconversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract   Maleonitrile-dithiacrown ethers mn-12S2O2 - mn-21S2O5 (mn = maleonitrile) are preorganized S2On+1-coronands (n = 1–4) which force B, AB and A class metal ions into mixed S/O coordination spheres. Moreover, they form chelate complexes with MX2 salts (M = Pd, Pt; X = Cl, Br), which were studied in this paper. The structures of mn-S2On+1 and [PtCl2(mn-S2On+1)] (n = 2, 3) were investigated theoretically by empirical and semiempirical methods using SYBYL (TRIPOS force field) and MSI/DISCOVER97 (ESFF force field). mn-12S2O2 was investigated experimentally by X-ray analysis and 1D and 2D NMR spectroscopy in solution and the complex formation was studied by 1H, 13C and 195Pt NMR titration experiments, respectively. S-inversion was also investigated in order to determine the ring corresponding interconversional barriers. Different orientations of the macrocyclic ring system mn-18S2O4 and of its transition states are shown.
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    URL: http://dx.doi.org/10.1007/s008940050106
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    In situ MAS NMR investigations of molecular sieves and zeolite-catalyzed reactions (1999)
    Springer
    Catalysis letters 58 (1999), S. 1-19 
    Details
    ISSN: 1572-879X
    Keywords: zeolites ; chemicals ; NMR ; alkane activation ; reaction mechanism ; in situ investigation ; alkylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Solid-state MAS NMR is a powerful technique to study heterogeneous catalysts and the way by which they operate. In situ MAS NMR has been demonstrated to be a powerful method to understand reaction mechanisms, to study the nature, dynamics and reactivity of surface intermediates and active sites, and to characterize structural modifications in the catalyst itself, in particular when using 13C strategically labelled substrates. In this paper, three examples selected from our own work are used to illustrate the potential of in situ MAS NMR. They are the formation of cumene and its isomerization to n-propylbenzene on zeolite H-ZSM-11, the activation of propane at low temperature and the alkylation of benzene with propane on zeolite H-ZSM-5, and the characterization of the aluminophosphate molecular sieve VPI-5 structure with temperature. Studies of the alkylation of benzene with propene confirmed that cumene was the primary reaction product. The undesired n-propylbenzene by-product results from the intermolecular reaction between cumene and benzene, enhanced by molecular shape-selective effects in medium pore size zeolites (e.g., H-ZSM-11). It explains why large pore zeolites, e.g., zeolite Beta, are used commercially today for this process. Propane can be activated at low temperature (ca. 573 K) on bifunctional medium pore size zeolites possessing intimately related acidic Brønsted sites and a dehydrogenation function provided by Ga or Zn species. In Ga/H-ZSM-5 catalysts, at 573 K, the activation of propane was shown to occur via a protonated pseudocyclopropane (PPCP) intermediate (or transition state). The latter evolves in a manner that can be formally described by the formation of CH 3 + , C2H 2 + , and C3H 7 + carbenium ion intermediates. These species can react with olefins, alkanes, or other electron-rich molecules such as benzene. The primary reaction products of the reaction of propane with benzene are n-propylbenzene (in small amount), ethylbenzene and toluene. Their subsequent reactions lead eventually to toluene and xylenes as the final products. In the structural characterization of VPI-5, 27Al, 31P, and 27Al nutation MAS NMR spectra show that, at 294 K, fully hydrated VPI-5 contains three equally populated Al and P crystallographic sites and that one-third of Al is 6-coordinate. The VPI-5 structure then belongs to the P63 space group. Above 353 K, VPI-5, fully or partially hydrated, undergoes a structural transformation to a higher framework symmetry, i.e., the P63cm space group. The transformation occurs at nearly the same temperature in both cases, indicating that the breakdown of the hydrogen-bonded helical water structure inside the VPI-5 pores is not a factor in the process.
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    URL: http://dx.doi.org/10.1023/A:1019044926400
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    What do we know about the acidity of solid acids? (1999)
    Springer
    Catalysis letters 62 (1999), S. 1-13 
    Details
    ISSN: 1572-879X
    Keywords: acid catalysis ; zeolites ; temperature‐programmed desorption ; microcalorimetry ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract With a proper understanding of the nature of solid acidity, zeolites and other solid acids have great potential for replacing homogeneous acids in a wide range of catalytic applications. This paper describes results from our laboratory on the characterization and description of the acid sites in high‐silica zeolites, especially H‐MFI. A crucial observation from this work is the identification of stoichiometric adsorption complexes, one molecule per framework Al, for a wide range of adsorbates, including amines, alcohols, nitriles, ketones, and thiols. Examples are given in which temperature‐programmed desorption is used to identify these complexes and characterize their initial chemistries. Calorimetric measurements on the 1:1 complexes have been used to compare the enthalpies of protonation in the zeolite to enthalpies of protonation in the gas phase and in aqueous phase and to demonstrate that a gas‐phase basis provides better predictive capabilities. The issue of carbenium‐ion stabilities is discussed, as well as the unusual catalytic properties of acid sites formed by framework substitution of Fe. The effect of sorption and cavity size on reactions is described. Finally, the problems associated with trying to define or characterize solid acids by using ammonia TPD or 13C NMR isotropic shifts of ketones without proper consideration of the complicated nature of these techniques are discussed.
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    URL: http://dx.doi.org/10.1023/A:1019010013989
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    A 31P nuclear magnetic resonance study of phosphate levels in roots of ectomycorrhizal and nonmycorrhizal plants of Castanea sativa Mill. (1999)
    Springer
    Trees 13 (1999), S. 168-172 
    Details
    ISSN: 0931-1890
    Keywords: Key words Castanea sativa ; Pisolithus tinctorius ; Ectomycorrhiza ; Phosphate ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  31P-Nuclear Magnetic Resonance (NMR) was used to assess phosphate distribution in ectomycorrhizal and nonmycorrhizal roots of Castanea sativa Mill. as well as in the mycorrhizal fungus Pisolithus tinctorius in order to gain insight into phosphate trafficking in these systems. The fungus P. tinctorius accumulated high levels of polyphosphates during the rapid phase of growth. Mycorrhizal and nonmycorrhizal roots accumulate orthophosphate. Only mycorrhizal roots presented polyphosphates. The content in polyphosphates increased along the 3 months of mycorrhiza formation. In mycorrhizal roots of plants cultured under axenic conditions, the orthophosphate pool decreased along the culture time. In nonmycorrhizal roots the decrease in the orthophosphate content was less pronounced. The level of orthophosphate in mycorrhizal roots was significantly lower than in nonmycorrhizal ones, which indicates that this system relies upon the fungal polyphosphates as a major source of phosphate.
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    URL: http://dx.doi.org/10.1007/PL00009748
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    Solution structure of reduced horse heart cytochrome c (1999)
    Springer
    JBIC 4 (1999), S. 21-31 
    Details
    ISSN: 1432-1327
    Keywords: Key words Reduced cytochrome c ; Solution structure ; NMR ; Heme proteins ; Electron transfer proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  In the frame of a broad study on the structural differences between the two redox forms of cytochromes to be related to the electron transfer process, the NMR solution structure of horse heart cytochrome c in the reduced form has been determined. The structural data obtained in the present work are compared to those already available in the literature on the same protein and the presence of conformational differences is discussed in the light of the experimental method employed for the structure determination. Redox-state dependent changes are analyzed and in particular they are related to the role of propionate-7 of the heme. Also some hydrogen bonds are changed upon reduction of the heme iron. A substantial similarity is observed for the backbone fold, independently of the oxidation state. At variance, some meaningful differences are observed in the orientation of a few side chains. These changes are related to those found in the case of the highly homologous cytochrome c from Saccharomyces cerevisiae. The exchangeability of the NH protons has been investigated and found to be smaller than in the case of the oxidized protein. We think that this is a characteristic of reduced cytochromes and that mobility is a medium for molecular recognition in vivo.
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    Interaction of cis- and trans-RuCl2(DMSO)4 with the nucleotides GpA, d(GpA), ApG, d(ApG) and d(CCTGGTCC): high-field NMR characterization of the reaction products (1999)
    Springer
    JBIC 4 (1999), S. 199-208 
    Details
    ISSN: 1432-1327
    Keywords: Key words Ruthenium ; Nucleotides ; Dimethyl sulfoxide ; Anticancer ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  Both cis- and trans-RuCl2(DMSO)4 (cis-Ru and trans-Ru) react with ApG, GpA, d(ApG) and d(GpA) to yield products with bifunctional metal coordination of the bases. For each dinucleotide one major product and several minor species are formed. This is in contrast to previous results on analogous reactions between trans-Ru and d(GpG) where a substantial amount of an intermediate species was found. The rates of reaction between dinucleotides and cis-Ru are approximately 20-fold slower than for trans-Ru. The compounds formed with the two isomers exhibit identical proton NMR spectra, suggesting the same coordination mode for ruthenium in the final product. The two purine bases are coordinated to ruthenium through N7 in a head-to-head conformation with the glycosidic angles being in the anti range. Coupling constants indicate a relatively pure 3′-endo conformation for the 5′-sugar and mainly 2′-endo for the 3′-sugar. The similar bifunctional binding mode of cis- and trans-Ru(II) with dinucleotides as evident from the NMR spectra are in contrast to the different mode of interaction suggested earlier for cis- and trans-Ru complexes with DNA. trans-Ru interacts with the deoxyoctanucleotide d(CCTGGTCC), giving two main products during the first 2 h of incubation time. Four H8 guanine resonances are shifted downfield, characteristic of N7 metal coordination. The products are not analyzed in detail, but it is suggested that the structures may be described as two chiral G(N7/N7) chelates.
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    Magnetic properties of human liver and brain ferritin (1999)
    Springer
    European biophysics journal 28 (1999), S. 263-267 
    Details
    ISSN: 1432-1017
    Keywords: Key words Human liver ; Human brain ; Ferritin ; Electron microscopy ; Mössbauer spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Human brain (globus pallidus) and liver tissues were investigated by means of electron microscopy (EM), Mössbauer spectroscopy (MS) and SQUID magnetometry techniques. Based on MS measurements, the iron present was identified to be in the ferritin-like form (61–88%) and in the form of a low-spin iron species (the balance). Its overall concentration was estimated as 1.5(3) mg in the brain and 2.4(5) mg in the liver, per gram of lyophilized tissue. The average core diameter was determined by EM measurements to be equal to 7.5(1.3) nm for the liver and 3.3(5) nm for the brain. Magnetization measurements carried out between 5 and 300 K yielded an estimation of an average blocking temperature, KT BL, as equal to 6.7 K and 8.5 K for the liver and the brain, respectively. From the dependence of KT BL on the external magnetic field it was concluded that the ferritin-like cores in the studied samples can be regarded as non-interacting particles. Finally, the uniaxial magnetic anisotropy constant was determined to be 6×103 J/m3 for the liver and 4×104 J/m3 for the brain.
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    The interactions of the N-terminal fusogenic peptide of HIV-1 gp41 with neutral phospholipids (1999)
    Springer
    European biophysics journal 28 (1999), S. 427-436 
    Details
    ISSN: 1432-1017
    Keywords: Key words HIV-1 fusion peptide ; EPR ; NMR ; Solid state NMR ; Circular dichroism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract We have studied the interactions with neutral phospholipid bilayers of FPI, the 23-residue fusogenic N-terminal peptide of the HIV-1LAI transmembrane glycoprotein gp41, by CD, EPR, NMR, and solid state NMR (SSNMR) with the objective of understanding how it lyses and fuses cells. Using small unilamellar vesicles made from egg yolk phoshatidylcholine which were not fused or permeabilised by the peptide we obtained results suggesting that it was capable of inserting as an α-helix into neutral phospholipid bilayers but was only completely monomeric at peptide/lipid (P/L) ratios of 1/2000 or lower. Above this value, mixed populations of monomeric and multimeric forms were found with the proportion of multimer increasing proportionally to P/L, as calculated from studies on the interaction between the peptide and spin-labelled phospholipid. The CD data indicated that, at P/L between 1/200 and 1/100, approximately 68% of the peptide appeared to be in α-helical form. When P/L=1/25 the α-helical content had decreased to 41%. Measurement at a P/L of 1/100 of the spin lattice relaxation effect on the 13C nuclei of the phospholipid acyl chains of an N-terminal spin label attached to the peptide showed that most of the peptide N-termini were located in the interior hydrocarbon region of the membrane. SSNMR on multilayers of ditetradecylphosphatidyl choline at P/Ls of 1/10, 1/20 and 1/30 showed that the peptide formed multimers that affected the motion of the lipid chains and disrupted the lipid alignment. We suggest that these aggregates may be relevant to the membrane-fusing and lytic activities of FPI and that they are worthy of further study.
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    The solution structure of a monomeric, reduced form of human copper,zinc superoxide dismutase bearing the same charge as the native protein (1999)
    Springer
    JBIC 4 (1999), S. 795-803 
    Details
    ISSN: 1432-1327
    Keywords: NMR ; Superoxide dismutase ; Solution structure ; Monomeric mutants ; Structure-function relationship
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: 2 , has RMSD values with respect to the average structure of 0.94 ± 0.14 Å2 and 1.50 ± 0.14 Å2 for the backbone and the heavy atoms, respectively. The overall folding, which includes the classical eight-stranded Greek-key β-barrel and a short α-helix, is very close to that of the previously characterized monomeric mutant E133QM2SOD and to that of wild-type SOD. The region involved in the subunit-subunit interactions in the dimeric protein is confirmed to be disordered in the monomeric species. It is also observed that a sizable rearrangement of the charged groups of the electrostatic loop and of Arg143 takes place in the monomeric species. The width of the active site channel, both at its entrance and at the bottleneck of the active site, is discussed in the light of the influence on the enzymatic activity and the latter with respect to the overall charge. It is also confirmed that the NH proton of His63 shields the Cu(I) from the bulk solvent, thus supporting the suggestion that superoxide may interact with the reduced metal ion in an outer-sphere fashion.
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    Thermal Dehydration and Miscibility of PHEMA/PMAA Blends (1999)
    Springer
    Journal of thermal analysis and calorimetry 56 (1999), S. 1059-1063 
    Details
    ISSN: 1572-8943
    Keywords: dehydration ; miscibility ; NMR ; polymer blend ; poly(2-hydroxyethyl methacrylate) (PHEMA) ; poly(methacrylic acid) (PMAA) ; TG ; TMDSC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Miscibility and dehydration of poly(2-hydroxyethyl methacrylate) and poly(methacrylic acid) (PHEMA/PMAA) blends were investigated by temperature modulated DSC (TMDSC), TG and solid-state 13C NMR methods. TMDSC spectra and 1H spin-relaxation times showed that the blends are homogeneous on a scale of 5-10 nm for all compositions. From TG and 13C NMR, we elucidated that the mass loss of the blends at 300°C is ascribed to the dehydration between the hydroxyl group of PHEMA and the carboxyl group of PMAA.
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    An Improved Model for Predicting Proton NMR Shielding by Alkenes Based on Ab Initio GIAO Calculations (1999)
    Springer
    Structural chemistry 10 (1999), S. 375-380 
    Details
    ISSN: 1572-9001
    Keywords: Magnetic anisotropy ; NMR ; shielding cone ; isotropic shielding ; GIAO ; (de)shielding surface ; alkenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In a strong magnetic field, nuclei located over a carbon-carbon double bond experience NMR shielding effects that are the net result of the magnetic anisotropy of the nearby double bond and various other intramolecular shielding effects. We have used GIAO, a subroutine in Gaussian 4, to calculate isotropic shielding values and to predict the proton NMR shielding increment for a simple model system: methane held in various orientations and positions over ethene. The average proton NMR shielding increments of several orientations of methane have been plotted versus the Cartesian coordinates of the methane protons relative to the center of ethene. A single empirical equation for predicting the NMR shielding experienced by protons over a carbon-carbon double bond has been developed from these data. The predictive capability of this equation has been validated by comparing the shielding increments for several alkenes calculated using our equation to the experimentally observed shielding increments. This equation predicts the NMR shielding effects more accurately than a previous model that was based on only one orientation of methane over ethene. Deshielding is predicted by this equation for protons over the center and within about 3 Å of a carbon-carbon double bond. This result is in contrast to predictions made by the long-held “shielding cone” model based on the McConnell equation found in nearly every textbook on NMR, but is consistent with experimental observations.
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    In situ NMR of heterogeneous catalysis: new methods and opportunities (1999)
    Springer
    Topics in catalysis 8 (1999), S. 81-86 
    Details
    ISSN: 1572-9028
    Keywords: NMR ; zeolite ; mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In situ NMR has been extensively applied in the past decade to obtain basic mechanistic information about reactions in heterogeneous catalysis. Most studies in the literature have employed either sealed glass ampoules of catalyst and adsorbate that are heated outside of the NMR probe or variable temperature studies of samples sealed in magic‐angle spinning (MAS) rotors. In situ NMR studies of sealed samples fail to duplicate the conditions of temperature, reagent introduction and product removal found in bench‐top microreactor studies of catalysis. Previous attempts to more closely duplicate the conditions in flow reactors have motivated NMR studies using temperature jumps and the development of MAS probes with reagent flow. These methods have not yet achieved the time scales of several seconds or tenths of seconds that are typical of catalytic reactions. The pulse‐quench catalytic reactor has been developed to permit NMR studies of catalyst samples that have been prepared under actual reaction conditions. Pulse‐quench studies have provided evidence in support of a carbon‐pool mechanism for methanol‐to‐gasoline chemistry on HZSM‐5 and led to the identification of a pentamethylbenzenium cation formed in a zeolite by the alkylation of benzene with excess methanol.
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    Synthesis of CIT-6, a zincosilicate with the *BEA topology (1999)
    Springer
    Topics in catalysis 9 (1999), S. 35-42 
    Details
    ISSN: 1572-9028
    Keywords: CIT-6 ; zincosilicate ; zinc beta ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new, large pore zincosilicate denoted CIT-6 with the framework topology of zeolite beta has been synthesized from reaction mixtures containing Li+, Zn2+ and tetraethylammonium hydroxide (TEAOH) as a structure-directing agent (SDA). The effects of the concentrations of Li+, Zn2+ and TEAOH on the preparation of CIT-6 are investigated and it is shown that there are critical ranges in concentration for all three components for the crystallization of pure CIT-6. The incorporation of Zn2+ into the CIT-6 framework is confirmed by 29Si MAS-NMR and ion exchange results. CIT-6 is the first molecular sieve to contain framework zinc sites accessible to organic molecules.
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    Structural Investigation of the First Stages of Pyrolysis of Si-C-O Preceramic Polymers Containing Si–H Bonds (1999)
    Springer
    Journal of sol gel science and technology 14 (1999), S. 39-48 
    Details
    ISSN: 1573-4846
    Keywords: polysiloxanes ; oxycarbide glasses ; NMR ; mass spectrometry ; pyrolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The polymer-to-glass transformation in the Si-C-O system usually involves cross-linking reactions at the C sites, which transform for example ≡Si– $$\underline {\text{C}} $$ H3 sites into $$\underline {\text{C}} $$ (Si)4 sites, leading to the formation of a silicon oxycarbide network. Identification of the various C sites that form during pyrolysis under inert atmosphere is rather difficult from 13C MAS-NMR spectra, due to strong overlap of resonance lines, which prevents an accurate determination of the chemical shift values. This paper reports on the use of a spectral editing technique called Inversion Recovery Cross Polarization (IRCP), which, when combined with Cross Polarization (CP) technique, allows us to identify and quantify the formation of Si- $$\underline {\text{C}} $$ H2-Si bridges during the early stages of the pyrolytic transformation of a polysiloxane containing Si–CH3 and Si–H groups. Several Si-C-O systems characterized by the same initial number of Si–CH3 bonds but with increasing number of Si–H bonds, have been investigated by MAS-NMR as well as thermogravimetric analysis coupled with mass spectrometry (TG/MS). The Si—H bonds play clearly an active role in the insertion of C atoms within the silica network.
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    Silicon Oxycarbide Glasses (1999)
    Springer
    Journal of sol gel science and technology 14 (1999), S. 7-25 
    Details
    ISSN: 1573-4846
    Keywords: black glass ; silicon oxycarbide ; Nicalon ; NMR ; Raman ; TEM ; high temperature stability ; surface chemistry ; network carbon ; elemental carbon ; structure ; free carbon ; FTIR ; nanocomposite ; silicon carbide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The first attempts to introduce carbon into glass date back to 1951. But up until recently, the use of carbon or carbide raw materials, and the oxidation, volatilization and decomposition that accompany high temperature melting, have limited the synthesis of true silicon oxycarbide glasses. Here, the term silicon-oxycarbide refers specifically to a carbon-containing silicate glass wherein oxygen and carbon atoms share bonds with silicon in the amorphous, network structure. Thus, there is a distinction between black glass, which contains only a second-phase dispersion of elemental carbon, and oxycarbide glasses which usually contain both network carbon and elemental carbon. In addition to exploring the unique properties and applications of these glasses, per se, they are also of interest for developing models of the residual amorphous phases in polymer-derived silicon-carbide and silicon-nitride ceramics. The application of sol/gel techniques to glass synthesis has significantly advanced the development and characterization of silicon oxycarbide glasses. In this approach, alkyl-substituted silicon alkoxides, which are molecular precursors containing oxygen and carbon functionalities on the silicon, can be hydrolyzed and condensed without decomposition or loss of the carbon functional group. A low-temperature (〈1000°C) heat-treatment of the gel creates a glassy silicate material whose molecular structure consists of an oxygen/carbon anionic network. In addition, there is always a blackening of the material due to elemental carbon, which forms during pyrolysis and densification of the gel. The nature of the network carbon, and especially the distribution and form of the elemental carbon, are fundamental to the structure and properties of these novel materials. Their chemical and physical characteristics as revealed by NMR, Raman and TEM are discussed in the overview. In addition, the high temperature stability of these glasses (up to 1750°C), and the effect of hot-pressing, are described. It will be shown that the silicon oxycarbide network is stable up to 1000–1200°C. The network carbon is terminated with hydrogen (i.e., CH, =CH2 and –CH3), and with polyaromatic carbon (i.e., nC6Hx) wherein most of the elemental carbon resides. These glasses can be described as molecular composites of polyaromatic graphene-rings dispersed in a silicon oxycarbide network. After heating to temperatures in excess of 1000–1200°C, the oxycarbide network decomposes through the loss of hydrogen, and a two- or three-phase glass-ceramic consisting of nanocrystalline graphite, silicon carbide, and amorphous silica or cristobalite, is created. Some of the properties and applications of these glasses/glass-ceramics for coatings, composites and porous solids are summarized.
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    Topological structures of tetrahedral (Td and T) fullerenes with hexagonal and triangular faces and their vibration and NMR spectra (1999)
    Springer
    Theoretical chemistry accounts 102 (1999), S. 72-77 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Fullerenes ; Tetrahedral symmetry ; IR active ; Raman active ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. On analyzing the topological structures of the three types of tetrahedral fullerenes (which consist only of triangles and hexagons), (1) C n (T d ,n=12h 2; h=1,2,…), (2) C n (T d ,n=4h 2;h=1,2,…), and (3) C n (T,n=4(h 2+hk+k 2);h〉k,h,k=1,2,…), we have obtained theoretically the Infrared and Raman active modes by means of the derived formulas for the decomposition of their nuclear motions into irreducible representations, and the 13C NMR spectra with natural abundance for 13C by using the distribution functions for all of the tetrahedral (T d and T) fullerenes, respectively.
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    Types, numbers and distribution of synapses on the dendritic tree of an identified visual interneuron in the brain of the locust (1999)
    Springer
    Cell & tissue research 296 (1999), S. 645-665 
    Details
    ISSN: 1432-0878
    Keywords: Key words Descending contralateral movement detector (DCMD) ; Identified neuron ; Vesicles ; Electron microscopy ; 3-D reconstruction ; Locust ; Schistocercagregaria (Insecta)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  The descending contralateral movement detector (DCMD), an identified descending interneuron in the brain of the locust Schistocerca gregaria has been investigated by using light and electron microscopy. We describe the fine structure, distribution and numbers of synapes that it receives from another identified brain neuron, the lobular giant movement detector (LGMD), and from unidentified neurons. The DCMD dendrites emerging from the integrative segment vary in form and number between individuals and sexes but always form a flattened dendritic domain. The arborizations and the integrative segment appear to be exclusively postsynaptic. Two types of synaptic contacts (Type 1 and 2) onto the DCMD can be discerned as having either round (Type 1) or pleiomorphic synaptic vesicles (Type 2) and by large (Type 1) or small (Type 2) subsynaptic appositions. Contact zones of Type 1 synapses are smaller than those of Type 2. LGMD-synapses are of Type 1 and occur intermingled with presynaptic sites of unidentified units. Some branches of the DCMD receiving input from unidentified units are devoid of contacting LGMD processes. Synapses of both types are randomly distributed over the DCMD integrative segment and at fibres with similar sizes.Type 1 synapses are much more frequent than Type 2 synapses and their number is negatively correlated with fibre diameter. For a whole DCMD dendritic arborization, a total of 8500 active zones of chemical synapses has been calculated, including a mininum of 2250 LGMD-synapses and about 1000 Type 2 synapses. The DCMD may thus receive a considerable amount of input from as yet unidentified neurons.
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    URL: http://dx.doi.org/10.1007/s004410051325
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    Metaphase-specific cell death in meiotic spermatocytes in mice (1999)
    Springer
    Cell & tissue research 296 (1999), S. 359-369 
    Details
    ISSN: 1432-0878
    Keywords: Key words Apoptosis ; Electron microscopy ; Meiosis ; Spermatocytes ; Spermatogenesis ; Testis ; TUNEL ; Mouse (10 strains)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  Apoptosis of male germ cells is a widespread but little-understood phenomenon in many animal species. The elucidation of its mechanisms could be useful in the understanding of male infertility. We have examined the distribution of dying cells with the terminal transferase-mediated nick-end labeling (TUNEL) method and by an electron-microscopic procedure in the testes of 10 mouse strains, viz., C57BL/10 (B10), SL/NiA (SL), C57BL/6 (B6), C3H/He (C3H), BALB/c (BALB), DBA2 (DBA), CBA/J (CBA), MRL/MpJ-+/+ (M+), MRL/MpJ-lpr/lpr (lpr), and wild-type NJL mice (Mus musculus musculus). In the testes of the B10, NJL, SL, B6, C3H, BALB, DBA, and CBA mice, very few TUNEL-positive cells are distributed in the seminiferous tubules, whereas in the testes of the M+ and lpr mice, many TUNEL-positive cells, which are restricted to stage XII seminiferous tubules, have been identified. The most important finding is that many metaphases of meiotic spermatocytes show a marked TUNEL-positive reaction. Some metaphases show apoptotic morphology electron-microscopically. These results suggest that the testes of MRL strains will provide a useful model for the study of the mechanism of metaphase-specific apoptosis in meiotic spermatocytes.
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    URL: http://dx.doi.org/10.1007/s004410051296
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    Effect of high-level oxygen exposure on the peroxidase activity and the neuromelanin-like pigment content of the nerve net in the earthworm, Lumbricus terrestris (1999)
    Springer
    Cell & tissue research 295 (1999), S. 349-354 
    Details
    ISSN: 1432-0878
    Keywords: Key words Neuromelanin ; Neuron ; Peroxidase ; Oxygen metabolism ; High-definition light microscopy ; Electron microscopy ; Ultrastructure ; Cytochemistry ; Substantia nigra ; Lumbricusterrestris (Annelida)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Histochemical examination of 1-μm tissue sections from the dorsal nerve plexus of the earthworm, Lumbricus terrestris, reveals multiple brown intraneuronal granules. These granules contain material morphologically and histochemically consistent with neuromelanin. When viewed with transmission electron microscopy, these were seen as single membrane-enclosed biphasic granules with diameters of 370–730 nm. Exposure of L. terrestris to high-level environmental oxygen resulted in an increase in the number of neuromelanin-like pigment granules within the neurons of the circular muscle layer. As measured by ortho-phenylenediamine hydrochloride, the endogenous peroxidase activity of extracts from worms incubated in high-level environmental oxygen was 51% more than controls. The endogenous peroxidase activity was localized in situ with 3,3-diaminobenzidine (DAB) and was found to increase in and around the neuromelanin-like pigment-containing neurons within the circular muscle layer. These studies suggest that the nerve net of L. terrestris may serve as a model to study the role of neuromelanin production in oxidative stress and its relationship to endogenous peroxidases.
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    Op/op mice defective in production of functional colony-stimulating factor-1 lack macrophages in muscularis externa of the small intestine (1999)
    Springer
    Cell & tissue research 295 (1999), S. 485-493 
    Details
    ISSN: 1432-0878
    Keywords: Key words Immunohistochemistry ; Electron microscopy ; Interstitial cells of Cajal ; F4/80 ; CSF-1 ; Kit-receptor ; Mouse (op/op)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The osteopetrotic (op/op) mutant mouse possesses an inactivating mutation in the colony-stimulating factor-1 (CSF-1) gene, which results in the absence of certain macrophages and in osteopetrosis, following a lack of osteoclasts. Studies of the op/op mouse indicate that CSF-1-dependent tissue macrophages may belong to a trophic and/or scavenger subpopulation, which through their effect on other cell types can significantly affect tissue functions, and that cells which are CSF-1 independent have antigen presentation and immunological functions.We have previously identified a cell system of regularly distributed macrophages in the muscularis externa of the small intestine and wanted to extend these studies to the op/op mouse.The present investigations with light- and electron-microscopic methods using fluorescent dextran, methylene blue and immunohistochemistry (F4/80, anti-kit receptor, anti-CD3, anti-CD45R/B220) show that macrophages are absent from the muscle layers, with only an occasional macrophage present in the subserosa. In the lamina propria and submucosa, macrophage numbers are reduced. In all other respects the muscularis externa appears normal, including normal organization and number of interstitial cells of Cajal. Control and op/op mice both lack cells expressing CD3 (T lymphocytes), CD45R/B220 (B lymphocytes) and mast cells in the muscularis externa. This leaves the muscularis externa macrophages as the most likely source of local cytokine production under such conditions as postoperative ileus and intussusception in infants, where the muscularis externa appears to be one target of cytokines. We conclude that the lack of macrophages, combined with the preservation of otherwise normal structure, will make the op/op mouse a valuable model by which to assess the functions and relative importance of the muscularis externa macrophages in relation to intestinal motility under normal and pathological conditions.
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    Caveolin and its cellular and subcellular immunolocalisation in lung alveolar epithelium: implications for alveolar epithelial type I cell function (1999)
    Springer
    Cell & tissue research 295 (1999), S. 111-120 
    Details
    ISSN: 1432-0878
    Keywords: Key words Caveolin ; Caveolae ; Lung ; Alveolar epithelial type I cell ; Immunocytochemistry ; Electron microscopy ; Confocal laser scanning microscopy ; Rat (CD)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Caveolae are flask-shaped invaginations of the plasmalemma which pinch off to form discrete vesicles within the cell cytoplasm. Biochemically, caveolae may be distinguished by the presence of a protein, caveolin, that is the principal component of filaments constituting their striated cytoplasmic coat. Squamous alveolar epithelial type I (ATI) cells, comprising approximately 95% of the surface area of lung alveolar epithelium, possess numerous plasmalemmal invaginations and cytoplasmic vesicles ultrastructurally indicative of caveolae. However, an ultrastructural appearance does not universally imply the biochemical presence of caveolin. This immunocytochemical study has utilised a novel application of confocal laser scanning and electron microscopy unequivocally to localise caveolin-1 to ATI cells. Further, cytoplasmic vesicles and flask-shaped membrane invaginations in the ATI cell were morphologically identified whose membranes were decorated with anti-caveolin-1 immunogold label. Coexistent with this, however, in both ATI and capillary endothelial cells could be seen membrane invaginations morphologically characteristic of caveolae, but which lacked associated caveolin immunogold label. This could reflect a true biochemical heterogeneity in populations of morphologically similar plasmalemmal invaginations or an antigen threshold requirement for labelling. The cuboidal alveolar epithelial type II cell (ATII) also displayed specific label for caveolin-1 but with no ultrastructural evidence for the formation of caveolae. The biochemical association of caveolin with ATI cell vesicles has broad implications for the assignment and further study of ATI cell function.
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    A novel cytokine-inducing glycolipid isolated from the lipoteichoic acid fraction of Enterococcus hirae ATCC 9790: A fundamental structure of the hydrophilic part (1999)
    Springer
    Glycoconjugate journal 16 (1999), S. 213-221 
    Details
    ISSN: 1573-4986
    Keywords: acetolysis ; IL-6 ; MALDI-TOF-MS ; mannan ; NMR ; poly(glycerophosphate) structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Previously, we showed that quantitatively minor several glycolipids only less than 5% of the lipoteichoic acid (LTA) fraction from Enterococcus hirae ATCC 9790 possessed cytokine-inducing activity, whereas the major component (over 90%) did not [Suda et al. (1995) FEMS Immun Med Microbiol 12:97–112]. The major inactive component was shown to have the chemical structure as was proposed for the LTA by Fischer [Hashimoto et al. (1997) J Biochem 121:779–86], suggesting that so-called LTA is not a cytokine-inducing component in the Gram-positive bacteria. In the present paper, the structure of the hydrophilic part of one of the cytokine-inducing glycolipid tentatively named GL4 is elucidated. GL4 was first subjected to hydrolysis with aqueous HF to give a polysaccharide and a mixture of low molecular weight products. The polysaccharide was composed mainly of highly branching mannan as concluded from NMR and MS analyses of its acetolysis products. The low molecular weight products consisted of phosphate and glycerol, suggesting the presence of a poly(glycerophosphate) structure in the original GL4. From these observations, the hydrophilic part of GL4 was shown to consist of mannose-rich polysaccharide and poly(glycerophosphate), the latter being bound to the former by a phosphodiester linkage.
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    URL: http://dx.doi.org/10.1023/A:1007076304254
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    Three-dimensional structure of scorpion toxins: Towards a new model of interaction with potassium channels (1999)
    Springer
    Perspectives in drug discovery and design 15-16 (1999), S. 41-60 
    Details
    ISSN: 1573-9023
    Keywords: dipole moment ; neurotoxin ; NMR ; potassium channel ; scorpion ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Scorpion venom contains various toxins which block ion-channels, responsible for either sodium, potassium, calcium or chloride membrane permeation. This review focuses on the three-dimensional structure of scorpion toxins specific for potassium channels, and on their structure–activity relationships. The overall fold of all these toxins is similar, despite their various specificities towards different types of potassium channels. Fine studies of the influence of punctual mutations of both toxins and channels have converged on a precise description of the scorpion toxins functional maps. From this knowledge, it now becomes possible to predict the specificity of a newly described scorpion toxin. The way is thus now open that leads to the design of new potent synthetic potassium channel blockers which in turn could be used as therapeutic drugs.
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    URL: http://dx.doi.org/10.1023/A:1017070801207
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    NMR Studies of Retinoid-Protein Interactions: The Conformation of [13C]-β-Ionones Bound to β-Lactoglobulin B (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 651-659 
    Details
    ISSN: 1573-904X
    Keywords: 13C-edited ; NMR ; retinol ; retinoic acid ; β-lactoglobulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Vitamin A (retinol) and its metabolites comprise the natural retinoids. While the biological action of these molecules are thought to be primarily mediated by ca. 55 kDa nuclear retinoic acid receptors, a number of structurally similar 15-20 kDa proteins are involved in the transport, and possibly metabolism, of these compounds. The milk protein β-lactoglobulin B (β-LG) is an 18 kDa protein which binds retinol and may be involved in oral delivery of retinol to neonates. β-LG also binds drugs and other natural products and is of potential interest as a protective delivery vehicle. Methods. To examine the conformation of the model retinoid β-ionone both in solution and when bound to β-LG, NMR and computational methods have been employed. Results. Taken together, NMR studies of β-ionone in solution measuring scalar and dipolar coupling, as well as CHARMm calculations, suggest β-ionone prefers a slightly twisted 6-s-cis conformation. Isotope-edited NMR studies of l3C-labeled β-ionones bound to β-LG, primarily employing the HMQC-NOE experiment, suggest β-ionone also binds to β-LG in its 6-s-cis conformation. Conclusions. The methods employed here allow estimates of protein-bound ligand conformation. However, additional sites of ligand labeling will be necessary to aid in binding site localization.
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    Phase and aggregation behaviour of double-chain cationic surfactants from the class of N-alkyl-N-alkyl′-N, N-dimethylammonium bromide surfactants (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 856-867 
    Details
    ISSN: 1435-1536
    Keywords: Key words Double chain surfactants ; Aggregates ; Phase diagrams ; Lamellar phases ; Electron microscopy ; SANS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We present the phase diagrams and the properties of newly synthesised double-chain cationic N-alkyl-N-alkyl′-N,N-dimethylammonium bromide surfactants [C x C y DMABr (x = 12, 14 and 16; y = 10, 11, 12, 14 and 16)]. All the systems studied form liquid-crystalline lamellar phases but with different morphologies: unilamellar vesicles at low surfactant concentrations, multilamellar vesicles and tubular aggregates for surfactant concentrations between 2 and 10 wt% and at even higher concentrations planar bilayers of surfactant molecules in the classical Lα phase. The phase diagrams were determined with macroscopic and microscopic methods (polarisation microscopy, freeze-fracture transmission electron microscopy, scanning electron microscopy and differential interference contrast microscopy). The properties of the surfactant solutions were determined with differential scanning calorimetry measurements for Krafft point determination and small-angle neutron scattering measurements for interlamellar spacing and bilayer thickness. Finally, conductivity and viscosity measurements for phase characterisation were carried out.
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    NMR Investigations of the Inclusion of Thyroxine and Derivatives in Natural Cyclodextrins (1999)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 33 (1999), S. 307-319 
    Details
    ISSN: 1573-1111
    Keywords: cyclodextrins β and γ ; thyroxine ; thyroid hormones ; inclusion complex ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Thyroxine T4 and its derivatives (T3, T2) are very sparingly soluble in aqueous solutions even in the form of salts. In the presence of β or γ-cyclodextrins and in buffered basic solution, their solubilities are increased by inclusion in the cavity. The inclusion of these hormones in cyclodextrins was investigated by 1H-NMR in order to derive the influence of the number and position of the iodine atoms, and of the ionization state of the phenol group on the inclusion geometries.
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    Synthesis of colloids and films of Pr, Er and Yb with nonaqueous solvents (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 164-173 
    Details
    ISSN: 1435-1536
    Keywords: Keywords Nanostructures ; Thin films ; Vapor deposition ; Electron microscopy ; Optical properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Colloidal dispersions of Yb, Er and Pr have been prepared by chemical liquid deposition. The metals were cocondensed at 77 K with 2-methoxyethanol and ethanol to produce solvated metal atoms. The particle size of the dispersions was determined by transmission electron microscopy to range from 52 to 1080 Å; the particles had spherical shapes. After solvent evaporation under vacuum, active solids and amorphous powder were deposited over Cu and Al metal. Dispersion stability, particle size, UV/Vis absorption and zeta potential were studied. The solids prepared by solvent evaporation were characterized by Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The films prepared on Al were studied by scanning electron microscopy. The most stable colloid was obtained using 2-methoxyethanol: several concentrations were stable for several months and the zeta potential indicated that this colloid stability is mainly due to solvation effects. FTIR spectroscopy of the solids indicated solvent incorporation in the film. This observation was corroborated by thermal analysis. Information on the thermal stability of the films was obtained by TGA. The UV/Vis absorption spectrum was measured at several concentrations under different conditions.
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    A Quantum Chemical and Electrostatic Study of Alkyl and Substituted Benzenonium Cations and Related Molecules: The Effect of Atomic Charge Distribution on Carbocation Energy and Geometry (1999)
    Springer
    Structural chemistry 10 (1999), S. 121-127 
    Details
    ISSN: 1572-9001
    Keywords: NPA ; CHELPG ; MK ; AIM ; atomic charge ; NMR ; carbocation ; benzenonium ; electrostatic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Geometries, NMR chemical shifts, atomic charges, and bond orders were calculated at the MP2/6-31G* level of theory for the isopropyl, sec-butyl, tert-butyl, benzenonium, and six methyl- and trifluoromethyl-substituted benzenonium ions. The NPA charges correlate better than the CHELPG, MK, and AIM charges with the experimental and calculated carbon chemical shifts. The electrostatic energies of isomeric ions, calculated by treatment of the NPA charges as point charges, are comparable to their MP2 energy differences. The electrostatic calculations, although classical approximations, provide a qualitative understanding of the coulombic basis of the methyl and trifluoromethyl substituent effects. It is apparent that these species are stabilized by having adjacent, oppositely charged atoms (for example, having the negatively charged carbon of a methyl group bonded to a positive carbon). It is proposed that a methyl group be termed a nucleophilic (rather than electron-donating) substituent and that a trifluoromethyl group be termed an electrophilic substituent. In the benzenonium ions and in toluene, fluoromethylbenzene, difluoromethylbenzene, and benzotrifluoride, the endocyclic angle at the substituent increases with increasing electrophilicity of the substituent. An electrostatic calculation again provides some insight into the coulombic basis of these changes.
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    NMR studies of interfaces, strain and anisotropy in Co/Cu multilayers (1999)
    Springer
    Hyperfine interactions 120-121 (1999), S. 23-30 
    Details
    ISSN: 1572-9540
    Keywords: NMR ; Co/Cu ; multilayers ; anisotropy ; 59Co
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 59Co NMR studies of multilayers are able to give three direct pieces of information: (i) the crystal phase of Co, fcc (217.4 MHz), hcp (220–228 MHz) and in exotic cases bcc (198 MHz) for films measured at T= 4.2 K, (ii) the nature of the interfaces from low frequency satellite lines, and (iii) the strain state deduced from small changes in the line positions. Extensive studies of Co/Cu multilayer interfacial structures as a function of deposition technique, layer thickness, substrate/buffer layer structure and annealing temperature have been undertaken. This work has shed new light on the relationship between interfacial structure and magnetoresistance and in particular has demonstrated that flat, atomic scale, interfaces lead to greater magnetoresistance. The difference between the Co and Cu lattice constant results in an extensive, tensile in-plane strain developing in Co layers provided that some epitaxial registry is present. Information on strain effects can be obtained from the position and width of the NMR lines. The magnetic anisotropy field can be determined by measuring the field dependence of the enhancement effect due to electronic magnetisation. This provides unique insight into the distribution of magnetic anisotropy within the Co layers, as the enhancement can be investigated independently for each NMR line and, hence, provides environment specific information on magnetic anisotropy at the interfaces and in the interior of the layers.
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    Mammalian Exocrine Secretions. XII: Constituents of Interdigital Secretions of Bontebok, Damaliscus dorcas dorcas, and Blesbok, D. d. phillipsi (1999)
    Springer
    Journal of chemical ecology 25 (1999), S. 2057-2084 
    Details
    ISSN: 1573-1561
    Keywords: Damaliscus dorcas ; mammalian semiochemicals ; mammalian pheromones ; exocrine secretions ; interdigital secretions ; chemical communication ; mass spectrometry ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract In addition to the nine compounds identified in the interdigital secretion of the bontebok, Damaliscus dorcas dorcas, in a previous study, 76 compounds belonging to different compound types, were identified in the interdigital secretions of the bontebok and the blesbok, D. d. phillipsi. These compounds include alkanes, alcohols, aldehydes, ketones, fatty acids, terpenoids, γ-lactones, an isopropyl ester, long-chain hydroxyesters, 2-substituted pyridines, phenols, steroids, and dimethylsulfone. No qualitative differences were found between secretions from the two sexes or from animals from different habitats. Although no attempt was made to correlate territorial behavior or other behavioral phenomena with the qualitative composition of interdigital secretions from individual animals, available information seems to indicate that quantitative differences probably do not have a major semiochemical function. Only two species of bacteria, Bacillus brevis and Planococcus citreus, were found in the interdigital pouches of male and female members of the two subspecies, regardless of the habitat of the animals. B. brevis synthesized, among other unidentified constituents, (Z)-3-penten-2-ol, 2-hexanone, 2-octanone, 2-nonanone, tetradecanoic acid, pentadecanoic acid, heptadecanoic acid, octadecanoic acid, (Z)-9-hexadecenoic acid, and isopropyl hexadecanoate in vitro, while P. citreus produced, among others, the γ-lactones dodecan-4-olide and (Z)-6-dodecen-4-olide, which is one of the major constituents of the interdigital secretions of both subspecies. Some components of the interdigital secretions are not present in the interdigital glandular tissue, and the possibility is discused that these compounds could be produced by microbiological activity in the interdigital pouch.
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    Molecular Complex Formation between Some Azacrown Ethers and 2,4,6-Trinitrophenol (1999)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 34 (1999), S. 431-443 
    Details
    ISSN: 1573-1111
    Keywords: 2,4,6-trinitrophenol ; aza-crown ethers ; molecular complexes ; spectrophotometry ; IR ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The formation of molecular complexes with 1 : 1 stoichiometry between 2,4,6-trinitrophenol and aza-12-crown-4, aza-15-crown-5 and aza-18-crown-6 in chloroform solution was investigated spectrophotometrically. The resulting complexes were isolated and characterized by microchemical analysis, IR and NMR spectroscopy. The equilibrium constants of the 1 : 1 adducts were evaluated from the non-linear least-squares fitting of the absorbance-mole ratio data. The overall stability of the 2,4,6-trinitrophenol complexes was found to vary in the order aza-15-crown-5 〉 aza-18-crown-6 ≈ aza-12-crown-4. The kinetics of complex formation between 2,4,6-trinitrophenol and the aza-substituted crown ethers used were investigated and in all cases the results showed the occurrence of an oscillating chemical reaction in solution.
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    Structure of 2-acetoxy-3-(3-methoxy-4-acetoxy-5-chlorophenyl)-propenoic acid (1998)
    Springer
    Journal of chemical crystallography 28 (1998), S. 139-143 
    Details
    ISSN: 1572-8854
    Keywords: X-ray ; NMR ; enol acetate ; phenylpropenoic acid ; azlactone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 2-Acetoxy-3-(3-methoxy-4-acetoxy-5-chlorophenyl)-propenoic acid 2 was synthesized from the azlactone of 5-chlorovanillin and its structure confirmed by X-ray crystallography and nuclear magnetic resonance methods. Compound 2 crystallized with a molecule of acetic acid in the P-1(#2) space group (Z = 2) and with cell dimensions a = 6.303(2), b = 9.779(1), c = 15.528(3) Å, α = 101.46(2), β = 100.71(2) and γ = 90.21(2)°. This study reveals the formation of an α-acetoxy propenoic acid with a trans extended side acid side chain conformation. The 1H and 13C NMR spectral values of 2 also show the existence of the enolic ester in solution.
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    Enol tautomer of the acetate ester of 3-methoxy-4-hydroxyphenylpyruvic acid: Crystallographic and NMR spectroscopic evidence (1998)
    Springer
    Journal of chemical crystallography 28 (1998), S. 193-196 
    Details
    ISSN: 1572-8854
    Keywords: x-ray ; NMR ; tautomerism ; enolate ; phenylpyruvic acid ; vanillin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The para acetate ester azlactone of vanillin 2 was synthesized from vanillin 1 and hydrolyzed with sodium hydroxide. The yielded product 3 was investigated with X-ray Crystallographic and nuclear magnetic resonance techniques. Compound 3 crystallized in the orthorhombic Pbca space group (Z = 8) and with cell dimensions a = 14.732(2), b = 12.756(3), c = 12.747(6)Å revealing the enolate tautomer and not the keto form of 3-methoxy-4-hydroxyphenylpyruvic acid as the acetate ester. The structure exhibited the pyruvic acid side chain in the trans extended conformation. A single proton on the benzylic carbon atom further suggested the existence of the enolate tautomer form of 3 in solution. The chemical shift values and peak integration in the NMR spectra add additional support to this finding.
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    Structure of 4-(2-chloro-4,5-dimethoxybenzylidene)-2-methyl-5-oxazolone. X-ray and NMR study (1998)
    Springer
    Journal of chemical crystallography 28 (1998), S. 811-814 
    Details
    ISSN: 1572-8854
    Keywords: X-ray ; NMR ; Z-isomer ; azlactone ; veratraldehyde
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The azlactone of 6-chloroveratraldehyde 3 (4-(2-chloro-4,5-dimethoxybenzylidene)-2-methyl-5-oxazolone) was synthesized from 6-chloroveratraldehyde 2 and its structure investigated using X-ray crystallographic and nuclear magnetic resonance methods. Compound 3 crystallized in the P21/c (#14) space group (Z = 4) with cell dimensions a = 9.148(2), b = 22.938(2), c = 6.707(1) Å, and β = 111.50(2)°. The X-ray study shows that azlactone 3 exists as the Z-isomer and crystallizes as a planar structure, i.e., both the phenyl and azlactone ring systems, as well as the functional groups attached to them, lie in the same plane. The 1H and 13C NMR spectral values also support the formation of the Z-isomer only, during the synthesis of 4-(2-chloro-4,5-dimethoxybenzylidene)-2-methyl-5-oxazolone.
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    Formation of Platinum–Tin Bond by Tin(II)Chloride Insertion (1998)
    Springer
    Journal of cluster science 9 (1998), S. 321-328 
    Details
    ISSN: 1572-8862
    Keywords: NMR ; tin(II)chloride ; insertion ; platinum ; platinum–tin bond
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The first 119Sn NMR evidence for the presence of direct platinum–tin bond in solution has been obtained for PtCl(SnCl3)(bdpp) complex (bdpp = (2S,4S)-2,4-bis(diphenylphosphino)pentane). Various PtCl2(L2) complexes (L2 = heterobidentate P−P, P−O, P−N, P−S chelating ligands) have been reacted with tin(II)chloride resulting in the formation of the corresponding PtCl(SnCl3)(L2) derivatives. Tin(II)chloride has been inserted into the Pt−Cl bond transto the harder donor atom of the L2 ligand.
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    Interaction of Cu(II) 3,5-diisopropylsalicylate with human serum albumin - an evaluation of spectroscopic data (1998)
    Springer
    BioMetals 11 (1998), S. 21-26 
    Details
    ISSN: 1572-8773
    Keywords: copper(II) 3,5-diisopropylsalicylate ; EPR ; human serum albumin ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The copper(II) complex of 3,5-diisopropylsalicylate is a lipophilic water-insoluble binuclear complex, Cu(II) (3,5-DIPS) , that has attracted interest because of a wide range of pharmacological activities. This study was undertaken to examine bonding interactions between the complex and human serum albumin (HSA) to help elucidate the mode of transport of the complex in vivo. Electron paramagnetic resonance, numerical magnetic resonance and UV-visible absorption spectroscopic studies were performed using 200 μM aqueous solutions (pH 7.5) of HSA to which had been added up to three molar equivalents of CuCl , CuSO , or Cu(II) (3,5-DIPS). Both EPR and UV-visible spectra demonstrated the presence of more than one copper bonding site on HSA, and proton NMR spectra showed that the 3,5-DIPS ligand is also bonded to HSA. These results indicate that there is no observable direct coordination of the ligand to copper in the presence of HSA, and that the majority of the copper and 3,5-DIPS bond to HSA at separate sites. Addition of solid Cu(II) (3,5-DIPS) to HSA at pH 7.5 similarly resulted in spectra that suggest that there are no ternary Cu(II)(3,5-DIPS), Cu(II)(3,5-DIPS) , or Cu(II) (3,5-DIPS) complexes formed with HSA. It is concluded that any ternary complexes formed in the presence of HSA are below the spectroscopic detection limits and represent less than 5% of the total copper. © Rapid Science 1998.
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    Interaction of aluminum ion with ATP. Mechanism of the aluminum inhibition of glycerol kinase and its reversal by spermine (1998)
    Springer
    BioMetals 11 (1998), S. 63-67 
    Details
    ISSN: 1572-8773
    Keywords: aluminum ion ; glycerol kinase ; NMR ; spermine ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Aluminum ion inhibited yeast glycerol kinase competitively with respect to the substrate MgATP. The K value of the enzyme for aluminum ion was about 3 μM. Spermine at physiological concentrations prevented glycerol kinase from the inhibition by aluminum ion. Nuclear magnetic resonance spectroscopy showed the specific elimination by spermine of aluminum from the metal-ATP complex, but no dissociation of MgATP complex by spermine. Inhibition by aluminum ion of glycerol kinase as well as hexokinase can reduce the utilization of energy fuel in yeast. Change in polyamine concentration may control energy production in vivo, and is responsible for the development of age-related aluminum toxicity. © Rapid Science 1998.
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    1H-NMR Relaxation of Water Molecules in the Aqueous Microcrystalline Cellulose Suspension Systems and Their Viscosity (1998)
    Springer
    Cellulose 5 (1998), S. 231-247 
    Details
    ISSN: 1572-882X
    Keywords: microcrystalline cellulose ; water ; bound water ; particle ; suspension ; spin-spin relaxation time ; NMR ; viscosity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract An intensive study for aqueous microcrystalline cellulose (MCC) suspensions was carried out in view of the relationship between a viscosity and a 1H spin-spin relaxation time (T2) of water. An investigation was carried out for four suspension systems with the different particle size distributions. The proton mole ratio (α) of bound water against MCC particles and T2 of bound water (T2,b) were evaluated from the T2 values obtained by Carr-Purcell- Meiboom-Gill (C.P.M.G) method and those by solid echo method, respectively. As a result of these analyses, the T2,b value for the aqueous MCC suspension was evaluated as 5 × 10−3 s and it was found that the system having a larger α tended to show a higher viscosity. By relating the above results to the observation of the suspensions by an optical microscope, it was concluded that a network formed by MCC particles plays an important role in generating a high viscosity of MCC suspension, and that an averaged mobility of water molecules is sensitively affected by the network structure.
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    Multinuclear Magnetic Resonance Study of Zinc(II) and Cadmium(II) Complexing with Isothiocyanate (1998)
    Springer
    Journal of solution chemistry 27 (1998), S. 331-359 
    Details
    ISSN: 1572-8927
    Keywords: Hydrogen-1 ; carbon-13 ; nitrogen-15 ; cadmium-113 ; NMR ; infrared ; zinc(II) ; cadmium(II) ; isothiocyanate ; complexation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A study of zinc(II) and cadmium(II) complexes with isothiocyanate ion has been completed, using a low-temperature, multinuclear magnetic resonance technique that permits the observation of separate resonance signals for bound and free ligand, and Cd(II) metal ion. The Zn2+–NCS− complexes were studied by 1H, 13C, and 15N NMR spectroscopy. In the 1H spectra, the intensity of the coordinated water signal, corresponding to a Zn(II) hydration number of six in the absence of NCS−, decreases dramatically as this anion is added, indicating the complexing process involves more than a simple 1:1 ligand replacement. The 13C and 15N NMR spectra reveal signals for four species, most reasonably assigned to a series of tetrahedrally coordinated Zn2+–NCS− complexes. In the Cd2+–NCS− solution spectra, the 13C and 15N signals for four complexes also are observed and they are three line patterns, corresponding to a doublet from 113Cd J-coupling, and a dominant central peak, resulting from bonding to magnetically inactive Cd isotopes. The 113Cd spectra, showing signals for four complexes, correlate well in all respects with the 13C and 15N results, including coupling in specific cases. The spectral results for both metal ions reflect binding at the nitrogen atom of NCS−, with the complexes changing from an octahedral to a tetrahedral configuration when doing so. Confirming evidence for these conclusions also was provided by several infrared measurements of these metal–ion systems.
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    URL: http://dx.doi.org/10.1023/A:1022675615486
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    A Direct Carbon-13 and Nitrogen-15 NMR Study of Samarium(III)–Isothiocyanate Complexation in Aqueous Solvent Mixtures (1998)
    Springer
    Journal of solution chemistry 27 (1998), S. 581-600 
    Details
    ISSN: 1572-8927
    Keywords: Carbon-13 ; nitrogen-15 ; chlorine-35 ; NMR ; samarium(III) ; isothiocyanate ; Sm3+ − NCS− complexes ; water–acetone–Freon ; water–methanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Multinuclear magnetic resonance studies of trivalent lanthanide inner-shell ion-pairing with nitrate and isothiocyanate are continuing. For NCS− solutions in water–acetone–Freon mixtures at low temperature, generally −100 to −125°C, ligand exchange is slow enough to permit the observation of 13C and 15N NMR signals for coordinated and free anions. For samariuni(III) solutions, four coordinated NCS−signals, displaced about +35 ppm and +250 ppm from free anion, are observed in the 13C and 15N NMR spectra, respectively. The 13C and 15N NMR data are complementary, showing a signal area concentration dependence and measured coordination numbers consistent with the formation of Sm(NCS)2+ through Sm(NCS) 4 1 . The coordination numbers reach a maximum of about three moles of NCS− per mole of Sm(III) with both nuclides, a result confirmed by spectral appearance showing the dominance of Sm(NCS)3 at the highest concentration studied. An analysis of the chemical shifts indicates that binding occurs at the nitrogen atom of NCS−. In water–methanol, due to the higher dielectric constant of such mixtures, coordination was less extensive. A competitive binding study with Ci− by 35Ci NMR demonstrated conclusively the superior coordinating ability of NCS−.
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    High resolution NMR techniques in catalysis (1998)
    Springer
    Topics in catalysis 5 (1998), S. 133-147 
    Details
    ISSN: 1572-9028
    Keywords: NMR ; catalysis ; high pressure ; dynamic equilibria ; magnetization transfer ; sapphire tube ; gas phase ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract High resolution NMR techniques are applicable to a variety of aspects of catalysis. Methods for studying homogeneously-catalyzed systems under high gas pressure are described along with approaches for obtaining mechanistic and dynamic information. Many of the same techniques may be applied to heterogeneous catalysis by following the reaction chemistry by gas phase NMR.
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    Metal ion binding to calmodulin: NMR and fluorescence studies (1998)
    Springer
    BioMetals 11 (1998), S. 213-222 
    Details
    ISSN: 1572-8773
    Keywords: calmodulin ; fluorescence spectroscopy ; metal ions ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Calmodulin is an important second messenger protein which is involved in a large variety of cellular path-ways.Calmodulin is sensitive to fluctuations in the intracellular Ca levels and is activated by the bindingof four Ca ions. In spite of the important role it plays in signal transduction pathways, it shows a surpris-inglybroad specificity for binding metal ions. Using 15N-Gly biosynthetically-labelled calmodulin, we havestudied the binding of different metal ions to calmodulin, including K+, Na+, Ca, Mg, Zn, Cd, Pb, Hg, Sr, La and Lu, by 1H, 15N HMQC NMR experiments. The effects of these ions on the substrate-bindingability of calmodulin have also been studied by fluorescence spectroscopy of the single tryptophan residue in a 22-residue synthetic peptide encompassing the skeletal muscle myosin light chain kinase calmod-ulin-binding domain. Most of these metal ions can activate a calmodulin target enzyme to some extent,though they bind to calmodulin in a different manner. Mg, which is of direct physiological interest, has adistinct site-preference for calmodulin, as it shows the highest affinity for site I in the N-terminal domain,while the C-terminal sites III and IV are the high affinity binding sites for Ca (as well as for Cd ). At ahigh concentration of Mg and a low concentration of Ca, calmodulin can bind Mg in its N-terminallobe while the C-terminal domain is occupied by Ca; this species could exist in resting cells in which the Mg level significantly exceeds that of Ca. Moreover, our data suggest that the toxicity of Pb-which,like Sr, binds with an equal and high affinity to all four sites-may be related to its capacity to tightlybind and improperly activate calmodulin.
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    Room-temperature formation of thermally stable aluminium-rich mesoporous MCM-41 (1998)
    Springer
    Catalysis letters 52 (1998), S. 21-23 
    Details
    ISSN: 1572-879X
    Keywords: RT synthesis ; thermal analysis ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The room-temperature (RT) synthesis of MCM-41 mesoporous compounds with high substitution levels of aluminium (Si / Al = 1.5) is achieved in a minimum time of synthesis. The compound shows similar characteristics to hydrothermally synthesized materials. 27Al NMR study confirms the presence of tetrahedral aluminium in as-synthesized material as well as in the calcined material without observing the presence of octahedral aluminium after calcination.
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    Biological, thermal and photochemical transformation of 2-trifluoromethylphenol (1998)
    Springer
    Biodegradation 9 (1998), S. 487-499 
    Details
    ISSN: 1572-9729
    Keywords: Bacillus ; biotransformation ; NMR ; thermophilic ; trifluoromethylphenol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract This is the first report on the metabolism of trifluoromethyl aromatics in a thermophilic bacterium, Bacillus thermoleovorans A2. Enzymes of the phenol degradation pathway are induced when cultivating Bacillus thermoleovorans A2 on complex medium. Direct measurements of fluorinated xenobiotics in cell suspensions using 19F-NMR made it possible to follow quantitatively the biotransformation routes. During the biotransformation of 2-CF3-phenol by B. thermoleovorans A2, a fluorinated metabolite, 2-hydroxy-6-oxo-7,7,7,-trifluorohepta-2,4-dienoate (7-TFHOD), accumulated. This metabolite is transformed non-enzymatically when exposed to sunlight. The accumulation of 7-TFHOD as an intermediate in the 2-CF3-phenol pathway was rationalized by calculating molecular properties of a series of meta-cleavage products.
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    On the detection of environmental effects on complex matrices combining off-line liquid chromatography and 1H-NMR (1998)
    Springer
    Biodegradation 9 (1998), S. 513-525 
    Details
    ISSN: 1572-9729
    Keywords: automation ; environment ; fingerprinting ; GLP ; LC ; NMR ; statistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract An off-line combination of 400 MHz proton (1H)-NMR spectroscopy and liquid chromatography (LC) has been used for the multi-component comparison of low-molecular weight compounds (i.e., chemical fingerprinting) in model fluid broths and (processed) tomato. The focus of the research described is on (i) devising GLP-like methods for sample handling and NMR measurements that will ensure reproducibility, (ii) an automated handling of data, (iii) validity of the designed methodology and (iv) the interpretation of large amounts of data.
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    Modulation of Bacillus pasteurii cytochrome c 553 reduction potential by structural and solution parameters (1998)
    Springer
    JBIC 3 (1998), S. 371-382 
    Details
    ISSN: 1432-1327
    Keywords: Key words Bacillus pasteurii ; cytochrome c553 ; electrochemistry ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  Direct cyclic voltammetry and 1H NMR spectroscopy have been combined to investigate the electrochemical and spectroscopic properties of cytochrome c 553 isolated from the alkaliphilic soil bacterium Bacillus pasteurii. A quasi-reversible diffusion-controlled redox process is exhibited by cytochrome c 553 at a pyrolitic graphite edge microelectrode. The temperature dependence of the reduction potential, measured using a non-isothermal electrochemical cell, revealed a discontinuity at 308 K. The thermodynamic parameters determined in the low-temperature range (275–308 K;ΔS°′=–162.7±1.2 J mol–1 K–1, ΔH°′=–53.0±0.5 kJ mol–1, ΔG°′=–4.5±0.1 kJ mol–1, E°′=+47.0±0.6 mV) indicate the presence of large enthalpic and entropic effects, leading, respectively, to stabilization and destabilization of the reduced form of cytochrome c 553. Both effects are more accentuated in the high-temperature range (308–323 K;ΔS°′=–294.1±8.4 J mol–1 K–1, ΔH°′=–93.4±3.1 kJ mol–1, ΔG°′=–5.8±0.6 kJ mol–1, E°′=+60.3±5.8 mV), with the net result being a slight increase of the standard reduction potential. These thermodynamic parameters are interpreted using the compensation theory of hydration of biopolymers as indicating the extrusion, upon reduction, of water molecules from the hydration sphere of the cytochrome. The low-T and high-T conformers differ by the number of water molecules in the solvation sphere: in the high-T conformer, the number of water molecules extruded upon reduction increases, as compared to the low-T conformer. The ionic strength dependence of the reduction potential at 298 K, treated within the frame of extended Debye-Hückel theory, yields values of E °′ (I=0) =–25.4±1.4 mV, z red=–11.3, and z ox=–10.3. The pH dependence of the reduction potential at 298 K shows a plateau in the pH range 7–10 and an increase at more acidic pH, allowing the calculation of pK O=5.5 and pK R=5.7, together with the estimate of the reduction potentials of completely protonated (+71 mV) and deprotonated (+58 mV) forms of cytochrome c 553. 1H NMR spectra of the oxidized paramagnetic cytochrome c 553 indicate the presence of a His-Met axial coordination of the low-spin (S=1/2) heme iron, which is maintained in the temperature interval 288–340 K at pH 7 and in the pH range 4.8–10.0 at 298 K. The temperature dependence of the hyperfine-shifted signals shows both Curie-type and anti-Curie-type behavior, with marked deviations from linearity, interpreted as indicating the presence of a fast equilibrium between the low-T and high-T conformers, having slightly different heme electronic structures resulting from the T-induced conformational change. Increasing the NaCl concentration in the range 0–0.2 M causes a slight change of the 1H NMR chemical shifts of the hyperfine-shifted signals, with no influence on their linewidth. The calculated lower limit value of the apparent affinity constant for specific ion binding is estimated as 5.2±1.1 M–1. The pH dependence of the isotropically shifted 1H NMR signals of the oxidized cytochrome displays at least one ionization step with pK O=5.7. The thermodynamic and spectroscopic data indicate a large solvent-derived entropic effect as the main cause for the observed low reduction potential of B. pasteurii cytochrome c 553.
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    The effect of axial ligand plane orientation on the contact and pseudocontact shifts of low-spin ferriheme proteins (1998)
    Springer
    JBIC 3 (1998), S. 581-594 
    Details
    ISSN: 1432-1327
    Keywords: Key words Heme protein ; NMR ; paramagetic ; contact ; pseudocontact ; axial ligand
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The effect of axial ligand nodal plane orientation on the contact and pseudocontact shifts of a symmetrical low-spin octamethylferriheme center has been calculated as a function of the angle of the axial ligand. Simple Hückel techniques have been used to estimate the contact contribution, and values obtained from model hemes, together with counter-rotation of the g-tensor, have been used to estimate the pseudocontact contribution, for the eight β-pyrrole methyl and four meso-H positions. It is found that the maximum and minimum contact shifts occur when the axial ligand is aligned at an angle of ±15° to the meso-H axes of the heme, rather than when the axial ligand plane lies along the porphyrin nitrogens, as assumed previously by some investigators. For systems having one planar axial ligand or two ligands in parallel planes, the contact and pseudocontact contributions at the meso-H positions are comparable in size (at least on the basis of simple Hückel estimates), while the contact contribution clearly dominates the isotropic shifts of the heme methyls. Allowing for the substituent effect of the 2,4-vinyls of protohemin, or the 2,4-thioethers of hemin c, as well as the average diamagnetic shifts of the heme methyls and meso-H, plots of the predicted shifts as a function of axial ligand nodal plane orientation have been constructed for hemin b- and c-containing proteins. Excellent agreement in the order of shifts, and reasonable agreement in the sizes of the observed shifts, is observed in the majority of the ferriheme proteins for which the methyl and meso-H resonances have been assigned and proton shifts reported. Plots have also been constructed for hemin c-containing proteins having the two axial ligand nodal planes oriented at relative angles of 40°, 70°, and 80°. Excellent agreement in the order of shifts, and reasonable agreement in the magnitudes of the observed shifts, is observed in all cases of bacterial cytochromes which do not fit the plots that assume the ligands are in parallel planes, except one – the cytochrome c-552 of Nitrosomonas europae. Except for this case, where the order of the predicted methyl shifts at any angle of the axial ligands disagrees with the observed, the reasons can usually be attributed to a large dihedral angle between two axial ligand nodal planes, to strong H-bonding interactions involving His and/or CN– ligands, or to off-axis binding of one (or both) axial ligand(s). Ruffling of the porphyrin ring may also contribute to the contact shift in as yet undefined ways. Hence, despite the simplicity of the calculations, the agreement with observed data is highly satisfying and the concept of the importance of axial ligand plane orientation on the observed proton shifts of heme proteins is fully confirmed.
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    Dodecylphosphocholine micelles as a membrane-like environment: new results from NMR relaxation and paramagnetic relaxation enhancement analysis (1998)
    Springer
    European biophysics journal 28 (1998), S. 48-58 
    Details
    ISSN: 1432-1017
    Keywords: Key words Dodecylphosphocholine ; Peptide-lipid interaction ; Paramagnetic probe ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract To further examine to what extent a dodecylphosphocholine (DPC) micelle mimics a phosphatidylcholine bilayer environment, we performed 13C, 2H, and 31P NMR relaxation measurements. Our data show that the dynamic behavior of DPC phosphocholine groups at low temperature (12 °C) corresponds to that of a phosphatidylcholine interface at high temperature (51 °C). In the presence of helical peptides, a PMP1 fragment, or an annexin fragment, the DPC local dynamics are not affected whereas the DPC aggregation number is increased to match an appropriate area/volume ratio for accommodating the bound peptides. We also show that quantitative measurements of paramagnetic relaxation enhancements induced by small amounts of spin-labeled phospholipids on peptide proton signals provide a meaningful insight on the location of both PMP1 and annexin fragments in DPC micelles. The paramagnetic contributions to the relaxation were extracted from intra-residue cross-peaks of NOESY spectra for both peptides. The location of each peptide in the micelles was found consistent with the corresponding relaxation data. As illustrated by the study of the PMP1 fragment, paramagnetic relaxation data also allow us to supply the missing medium-range NOEs and therefore to complete a standard conformational analysis of peptides in micelles.
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    Structure of the inactivating gate from the Shaker voltage gated K+ channel analyzed by NMR spectroscopy (1998)
    Springer
    European biophysics journal 27 (1998), S. 99-104 
    Details
    ISSN: 1432-1017
    Keywords: Key wordsShaker ; Potassium-channel ; NMR ; Structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Rapid inactivation of voltage-gated K+ (KV) channels is mediated by an N-terminal domain (inactivating ball domain) which blocks the open channel from the cytoplasmic side. Inactivating ball domains of various KV channels are also biologically active when synthesized separately and added as a peptide to the solution. Synthetic inactivating ball domains from different KV channels with hardly any sequence homology mediate quite similar effects even on unrelated KV channel subtypes whose inactivation domain has been deleted. The solution structure of the inactivating ball peptide from Shaker (Sh-P22) was analyzed with NMR spectroscopy. The NMR data indicate a non-random structure in an aqueous environment. However, while other inactivating ball peptides showed well-defined three-dimensional structures under these conditions, Sh-P22 does not have a unique, compactly folded structure in solution.
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    URL: http://dx.doi.org/10.1007/s002490050115
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    Determination of solution structures of paramagnetic proteins by NMR (1998)
    Springer
    European biophysics journal 27 (1998), S. 367-375 
    Details
    ISSN: 1432-1017
    Keywords: Key words Paramagnetic proteins ; Cytochromes ; Solution structure ; NMR ; Dipolar interactions ; Magnetic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Standard procedures for using nuclear Overhauser enhancements (NOE) between protons to generate structures for diamagnetic proteins in solution from NMR data may be supplemented by using dipolar shifts if the protein is paramagnetic. This is advantageous since the electron-nuclear dipolar coupling provides relatively long-range geometric information with respect to the paramagnetic centre which complements the short-range distance constraints from NOEs. Several different strategies have been developed to date, but none of these attempts to combine data from NOEs and dipolar shifts in the initial stages of structure calculation or to determine three dimensional protein structures together with their magnetic properties. This work shows that the magnetic and atomic structures are highly correlated and that it is important to have additional constraints both to provide starting parameters for the magnetic properties and to improve the definition of the best fit. Useful parameters can be obtained for haem proteins from Fermi contact shifts; this approach is compared with a new method based on the analysis of dipolar shifts in haem methyl groups with respect to data from horse and tuna ferricytochromes c. The methods developed for using data from NOEs and dipolar shifts have been incorporated in a new computer program, PARADYANA, which is demonstrated in application to a model data set for the sequence of the haem octapeptide known as microperoxidase-8.
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    URL: http://dx.doi.org/10.1007/s002490050144
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    Morphological and physical characterization of the capsular layer of Vibrio cholerae O139 (1998)
    Springer
    Archives of microbiology 170 (1998), S. 339-344 
    Details
    ISSN: 1432-072X
    Keywords: Key wordsV. cholerae O139 ; Lipopolysaccharide ; Electron microscopy ; Freeze-substitution technique ; Capsule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The morphological and physical characteristics of the capsule of Vibrio cholerae O139 were examined. An electron microscopic study using the freeze-substitution technique showed that all of the V. cholerae strains of the O139 serogroup examined have a very thin fibrous layer on the outside of the outer membrane. In contrast, the mutants of strain O139, strain MO10T4 (which lacks capsule synthesis), and strain Bengal-2R1 (which fails to synthesize both the capsule and the O-antigen of lipopolysaccharide) were all found to have lost the surface layer. In addition, the capsule layer could also not be observed on the surface of V. cholerae strain O1. To determine the biological characteristics of the capsule of strains of the O139 serogroup, we investigated the serum killing activity and bacterial phagocytosis by polymorphonuclear leukocytes. The O139 strains were more resistant to the serum killing activity than were the V. cholerae O1 strain and the O139 mutant strains, thus suggesting that the existence of the capsule gave a serum-resistant character to the O139 strains. The surface character of the O139 strains had the same hydrophobic character as did that of the O139 mutant strains and the O1 strain. In addition, all the V. cholerae O1 and O139 strains examined, including the mutant strains, were effectively ingested by the human polymorphonuclear leukocytes. The number of ingested bacteria was not significantly different among the strains, and the ingestion of the acapsular O139 mutants thus showed that the capsule does not play an antiphagocytic role. These data suggest that the capsule of V. cholerae O139 has a physiological function different from that of the ordinal hydrophilic capsule that is found in invasive bacteria such as Klebsiella pneumoniae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002030050651
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    Phylogenetic affiliation and ultrastructure of uncultured magnetic bacteria with unusually large magnetosomes (1998)
    Springer
    Archives of microbiology 169 (1998), S. 136-147 
    Details
    ISSN: 1432-072X
    Keywords: Key words Magnetic bacteria ; Biomineralization ; Magnetite ; 16S rRNA ; In situ hybridization ; Ultrastructure ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Natural enrichments of magnetic bacteria from the Itaipu lagoon near Rio de Janeiro were dominated by coccoid-to-ovoid morphotypes that produced unusually large magnetosomes. To determine the phylogenetic position of these unusual microorganisms, 16S rRNA genes were retrieved from bacteria magnetically separated from sediment of the Itaipu lagoon by in vitro amplification and cloning of PCR products into a plasmid vector. Partial sequencing of the obtained clones revealed two clusters of closely related sequences affiliated to a distinct lineage consisting exclusively of magnetic bacteria within the α-subclass of Proteobacteria. For a detailed phylogenetic analysis, several almost complete sequences of the 16S rRNA genes were determined. One representative clone of each cluster provided a PCR template for the in vitro transcription of group-specific polynucleotide probes complementary to a variable region of the 16S rRNA molecule. At least three different morphotypes of magnetic bacteria were reliably identified by post-embedding hybridization of ultra-thin sections. Electron microscopic analyses of hybridized cells enabled for the first time a detailed description of the morphological variety and ultrastructure of phylogenetically identified, uncultured magnetic bacteria. Two distinct coccoid bacteria were identified by the transcript probe complementary to the 16S rRNA sequence mabrj12, whereas the probe complementary to the sequence mabrj58 allowed the identification of an ovoid morphotype that displayed magnetosomes with the largest volumes observed to date.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002030050553
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  • 91
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    X-ray diffractometry and electron microscopy of DNA from Bacillus subtilis bound on clay minerals (1998)
    Springer
    Sciences of soils 3 (1998), S. 1-10 
    Details
    ISSN: 1432-9492
    Keywords: Transformation ; Clay-DNA complexes ; Nucleases ; X-ray diffraction ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract DNA bound on clay minerals, sand, and humic acids has been shown, both in vitro and in situ, to be capable of transforming bacteria and to resist degradation by nucleases, which could result in the crypticity of genes in soil and other natural habitats. To determine where DNA is bound on clay minerals, which may help to explain how bound DNA becomes resistant to degradation by nucleases but retains the ability to transform competent cells, chromosomal DNA from Bacillus subtilis bound on montmorillonite (M) and kaolinite (K) was examined by X-ray diffractometry and transmission and scanning electron microscopy. X-ray diffraction analysis showed that the basal spacings of M and K were not altered, indicating that this DNA did not significantly intercalate the clays. Scanning and transmission electron microscopy showed that the binding of this DNA was primarily on the edges of M and K, although some binding was also apparent on the planar surfaces. Based on the results of these studies, it is postulated that: 1.extension from the edges of the clays enables the unbound end of DNA to interact with receptor sites on competent cells and result in their transformation; and 2.binding on clays alters the electron distribution and/or conformation of DNA, which reduces its hydrolysis by nucleases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s10112-998-0001-3
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  • 92
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    An Empirical Proton NMR Shielding Equation for Alkenes Based on Ab Initio Calculations (1998)
    Springer
    Structural chemistry 9 (1998), S. 403-410 
    Details
    ISSN: 1572-9001
    Keywords: Magnetic anisotropy ; NMR ; shielding cone ; shielding value ; GIAO ; ethene ; alkenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nuclei of hydrogen atoms located over a carbon-carbon double bond in the presence of a strong magnetic field experience a perturbed magnetic field caused primarily by the magnetic anisotropy of the π bond. However, the commonly used theoretical model for predicting the shielding effect of an alkene double bond on hydrogen nuclei is sometimes inconsistent with the observed proton NMR chemical shifts in structures that have covalently bonded hydrogens located over a carbon-carbon double bond. We have used the ab initio gauge including atomic orbital (GIAO) method to calculate isotropic shielding values and to determine the proton NMR shielding increments for a simple model system: methane held at various positions over ethene. These shielding increments calculated for one proton of methane have been mapped as a function of their position in Cartesian coordinates relative to the center of ethene. A mathematical function has been fit to this three-dimensional shielding increment surface at each of four distances from the face of the ethene molecule. Additionally, a single mathematical equation has been developed for predicting the shielding caused by the carbon-carbon double bond in ethene. In contrast to the traditionally employed shielding model, our results predict deshielding for protons within 3 Å above the center of a carbon-carbon double bond, consistent with experimental observations in several molecular systems. The NMR shielding increments predicted by this equation are compared to observed shielding increments in some test alkenes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022463914156
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    Structures and NMR Parameters of 1,2-Diphenylcyclobutanes (1998)
    Springer
    Structural chemistry 9 (1998), S. 419-427 
    Details
    ISSN: 1572-9001
    Keywords: NMR ; coupling constants ; cis and trans 1,2-diphenylcyclobutane ; angular dependence ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new reaction scheme for obtaining cis and trans 1,2-diphenylcyclobutane is described. Using 1H-NMR at 600 MHz, full spectral assignment was made for both isomers, obtaining all J coupling constants and chemical shifts. NMR results on cis and trans 1,2-diphenylcyclobutane are compared with the vicinal coupling constants obtained by the Barfield–Smith equations from the literature internal and dihedral angles of cyclobutane. In the trans isomer, in agreement with previous results on halo-cyclobutanes, the conformation with the phenyls in the pseudo-di-equatorial position is strongly preferred. On the contrary, the cis isomer fluctuates between the two equivalent conformations: phenyl pseudo-axial and pseudo-equatorial.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022468015064
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    Sulfide Gels and Films: Products of Non-Oxide Gelation (1998)
    Springer
    Journal of sol gel science and technology 13 (1998), S. 61-64 
    Details
    ISSN: 1573-4846
    Keywords: cadmium sulfide nanocrystals ; sol-gel transition ; aggregation ; NMR ; small angle X-ray scattering (SAXS) ; thin films
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The preparation of concentrated sols and transparent stiff gels of II-VI semiconductors nanocrystals is reported. A two-step process for the production of cadmium sulfide is reported. Sol stabilization and gelation control are achieved through successive passivation and depassivation of the surface of the nanocrystals which are complexed with thiols. The mechanisms driving the aggregation and the gelation are explained on the basis of NMR and SAXS experiments. Thin films as well as monoliths can be produced. The general principles of the method presented are not restricted to chalcogenide systems and thus enlarge the domain of application of the inorganic sol-gel process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008695003946
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    Hybrid Xerogel Structure and Molecular Guest Dynamics (1998)
    Springer
    Journal of sol gel science and technology 13 (1998), S. 457-460 
    Details
    ISSN: 1573-4846
    Keywords: hybrid organic-inorganic materials ; gel drying ; molecular dynamics ; NMR ; sol-gel transition ; confinement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new experimental approach to study the porosity of hybrid organic-inorganic glasses is reported. It relies upon nuclear magnetic resonance observation of molecular guest dynamics. It is shown that in MTEOS xerogels, there exists an interconnected organic-rich network in which organic guests are trapped and can eventually diffuse. The interpore translational diffusion is strongly activated and its spatial extension gives information on the pore connectivity, whose decay is characterized by the interpore jump probability given by the theoretical model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008633630489
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  • 96
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    Correlations between 29Si, 17O and 1H NMR properties and local structures in silicates: an ab initio calculation (1998)
    Springer
    Physics and chemistry of minerals 26 (1998), S. 14-30 
    Details
    ISSN: 1432-2021
    Keywords: Key words ab initio ; NMR ; silicates ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  In order to gain insight into the correlations between 29Si, 17O and 1H NMR properties (chemical shift and quadrupolar coupling parameters) and local structures in silicates, ab initio self-consistent field Hartree-Fock molecular orbital calculations have been carried out on silicate clusters of various polymerizations and intertetrahedral (Si-O-Si) angles. These include Si(OH)4 monomers (isolated as well as interacting), Si2O(OH)6 dimers (C2 symmetry) with the Si-O-Si angle fixed at 5° intervals from 120° to 180°, Si3O2(OH)8 linear trimers (C2 symmetry) with varying Si-O-Si angles, Si3O3(OH)6 three-membered rings (D3 and C1 symmetries), Si4O4(OH)8 four-membered ring (C4 symmetry) and Si8O12(OH)8 octamer (D4 symmetry). The calculated 29Si, 17O and 1H isotropic chemical shifts (δi Si, δi O and δi H) for these clusters are all close to experimental NMR data for similar local structures in crystalline silicates. The calculated 17O quadrupolar coupling constants (QCC) of the bridging oxygens (Si-O-Si) are also in good agreement with experimental data. The calculated 17O QCC of silanols (Si-O-H) are much larger than those of the bridging oxygens, but unfortunately there are no experimental data for similar groups in well-characterized crystalline phases for comparison. There is a good correlation between δi Si and the mean Si-O-Si angle for both Q 1 and Q 2, where Q n denotes Si with n other tetrahedral Si next-nearest neighbors. Both the δ i O and the 17O electric field gradient asymmetry parameter, η of the bridging oxygens have been found to depend strongly on the O site symmetry, in addition to the Si-O-Si angle. On the other hand, the 17O QCC seems to be influenced little by structural parameters other than the Si-O-Si angle, and is thus expected to be the most reliable 17O NMR parameter that can be used to decipher Si-O-Si angle distribution information. Both the 17O QCC and the 2H QCC of silanols decrease with decreasing length of hydrogen bond to a second O atom (Si-O-H···O), and the δ i H increase with the same parameter.
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    URL: http://dx.doi.org/10.1007/s002690050157
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    Distribution and submicroscopic immunogold localization of cellular prion protein (PrPc) in extracerebral tissues (1998)
    Springer
    Cell & tissue research 292 (1998), S. 77-84 
    Details
    ISSN: 1432-0878
    Keywords: Key words Prion protein (PrPc) ; Electron microscopy ; Secretory granules ; Membrane ; Extracerebral tissues ; Hamster ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  In transmissible spongiform encephalopathies (TSE), such as scrapie in animals and Creutzfeldt-Jakob disease in humans, the central event is the conversion of a host-encoded amyloidogenic protein (PrPc) into an abnormal isoform (PrPsc) that accumulates as amyloid in TSE brain. PrPc is a membrane sialoglycoprotein synthesized in the central nervous system and elsewhere. We have examined the ultrastructural localization of PrPc in numerous hamster and some human extracerebral tissues, by means of a post-embedding electron-microscopic method combined with immunogold labeling. In stomach, intestine, lung, and kidney from hamsters, and in stomach, kidney, and spleen from humans, immunogold labeling specific for PrPc is observed on various cellular substructures related to secretory pathways: Golgi apparatus, secretory globules, and plasma membrane. In mucous epithelial cells of stomach and intestine, PrPc appears to be concentrated in secretory globules, suggesting a role for PrPc in the secretory function of the digestive tract. The secretory aspect of PrPc may be a key to understanding the physiopathological mechanisms underlying TSE.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410051036
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    A role for vesicles in human basophil secretion (1998)
    Springer
    Cell & tissue research 293 (1998), S. 1-22 
    Details
    ISSN: 1432-0878
    Keywords: Key words Piecemeal degranulation ; Histamine ; Charcot-Leyden crystal protein ; Anaphylactic degranulation ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  The evidence for vesicular transport as a mechanism for secretion by human basophils is reviewed. Initially, direct electron-microscopic inspection of experimentally produced and sequentially biopsied contact allergy skin lesions revealed a unique form of secretion termed piecemeal degranulation, characterized by the slow emptying of secretory granule contents (with retention of empty containers) in the absence of extrusion of entire granules. Budding of small vesicles to/from secretory granules was observed, and cytoplasmic vesicles were abundant. A generalized degranulation model was proposed to unify classical regulated secretion and this new form of secretion. Investigation of the mechanism(s) of secretion from human basophils required the development of numerous tools and resources. Chief among these were: (a) isolation and purification of circulating basophils; (b) identification of specific growth factors to increase the supply of this rare granulocyte; (c) understanding of secretogogue mechanisms and reliable analyses of secreted basophil products; and (d) development of ultrastructural preparations allowing imaging of small vesicles and quantifiable small electron-dense tags for granule materials in small vesicles. Applications of these tools to well-defined models of basophil secretion have established a role for vesicles as a mechanism for effecting secretion of histamine and the Charcot-Leyden crystal protein from activated human basophils.
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    URL: http://dx.doi.org/10.1007/s004410051093
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    Maturation of rat dendritic cells during intrahepatic translocation evaluated using monoclonal antibodies and electron microscopy (1998)
    Springer
    Cell & tissue research 294 (1998), S. 503-514 
    Details
    ISSN: 1432-0878
    Keywords: Key words Dendritic cells ; Maturation ; Intrahepatic translocation ; Immunohistochemistry ; Electron microscopy ; Rat (Wistar)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Specific populations of hepatic sinusoidal cells were stained with monoclonal antibodies that recognize monocytes/macrophages (ED1), tissue macrophages (Kupffer cells) (ED2), MHC class II (Ia) antigen (MRC OX6), and dendritic cells/γ,δ T-cells (MRC OX62) and analyzed by light and electron microscopy. The majority of ED1+ and/or ED2+ cells were localized to the hepatic parenchyma, whereas OX6+ and/or OX62+ cells were more densely distributed within Glisson’s sheath than in the hepatic parenchyma. Double-immunoperoxidase staining of normal liver for ED1, ED2, and OX6 identified dendritic cells (DC) of two different phenotypes, ED1+ED2–OX6+ and ED1–ED2–OX6+. DC can be classified into three different types based on ultrastructural characteristics. The first type (type I) is characterized by one or more long cytoplasmic processes and a well-developed lysosomal system. The second type (type II) has an inconspicuous lysosomal system, abundant hyaloplasm, and characteristic short cytoplasmic processes. The third type (type I–II) has cytologic features intermediate between those of type I and type II DC. At the electron-microscopic level, these three cell types are found in the sinusoidal lumen, whereas the majority of type II DC are located in the space of Disse and Glisson’s sheath. Furthermore, some OX6-labeled elongated DC appeared to traverse the lumen of sinusoids through endothelial pores to enter the space of Disse. One hour after intravenous injection of latex particles (0.81 μm in diameter), numerous latex-laden dendritic cells (ED1+OX6+, type I and type I–II) were detected in the lumen of hepatic sinusoids, but not in the space of Disse or Glisson’s sheath. These findings suggest that normal rat liver contains resident dendritic cells which downregulate phagocytic activity and mature into potent accessory cells during migration from the portal vein toward the central vein. These DC then traverse the sinusoidal lumen to the hepatic lymph system via the space of Disse.
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    URL: http://dx.doi.org/10.1007/s004410051201
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  • 100
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    Interaction of the Escherichia coli DnaA protein with bacteriophage k DNA (1998)
    Springer
    Molecular genetics and genomics 259 (1998), S. 679-688 
    Details
    ISSN: 1617-4623
    Keywords: Key words Bacteriophage λ ; DnaA-DNA interactions ; Electron microscopy ; DNA-protein complexes ; Escherichia coli
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Interaction of the Escherichia coli DnaA (replication initiator) protein with restriction fragments of phage λ DNA demonstrated differential binding of DnaA along the whole λ DNA. Interaction of DnaA with the λ replication region (from the promoter p R to the origin of replication, oriλ) demonstrated a strong binding of DnaA to the region around the p o promoter where synthesis of a short antisense oop RNA is initiated. The four sequences protected by DnaA (two 9mers and two 5mers) are not related even to a relaxed DnaA box. The pattern of protection of these four sequences and the location of three DNase I hypersensitive sites in the λ DNA r strand, together with results of mobility shift assays and electron microscopy studies, may indicate an interaction involving DnaA monomers bound to different DNA positions on one side of the helix and the formation of higher-order nucleoprotein structures. Therefore, it is tempting to suggest that DnaA, in addition to its activity in regulation of replication and transcription, could be considered as a factor which structures certain chromosomal regions.
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    URL: http://dx.doi.org/10.1007/s004380050863
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