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  • Articles  (28)
  • NMR  (28)
  • Springer  (28)
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  • 2000-2004  (28)
  • 1995-1999
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  • 2000  (28)
  • Chemistry and Pharmacology  (22)
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  • Articles  (28)
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  • Springer  (28)
  • American Chemical Society
  • American Geophysical Union
  • De Gruyter
  • EDP Sciences
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  • 2000-2004  (28)
  • 1995-1999
  • 1970-1974
  • 1930-1934
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  • 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
    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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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
    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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