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  • 1
    Electronic Resource
    Electronic Resource
    Effect of Substitution on the ESR Spectra and Electronic Ground State of ZnTPP Cation Radicals (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 447-454 
    Details
    ISSN: 1434-1948
    Keywords: Zinc ; Metalloporphyrins ; Porphyrins ; Cations ; Radicals ; ESR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Zinc(II) complexes of substituted tetraphenylporphyrins, Zn[T(X-P)P], where X = H, p-F, p-Cl, m-Cl, p-CH3O, and m-CH3O, have been synthesized and characterized. Peripheral substitution shows marked changes in the chemical shifts of the phenyl proton resonances and E1/2 values of the redox couples in the anodic region while the UV/Vis spectra are unaffected. The monocation radicals of these complexes are generated by chemical oxidation with bromine. The ESR spectra reveal the formation of two types of radical species, Zn[T(X-P)P]+·Br- (species I) and Zn[T(X-P)(Brn-P)]+·Br- (species II): Species I at 298 K shows a spectrum, with well-resolved bromine hyperfine features, characteristic of a 2A2u electronic ground state while species II, except for the complex with X = m-CH3O, shows a featureless, isotropic resonance attributable to a 2A1u state. Zn[T(m-CH3O-P)(Brn-P)]+·Br-, on the other hand, exhibits nine resolved nitrogen hyperfine features corresponding to a 2A2u state. Variable temperature ESR spectra (77-298 K) indicate reduction in the bromine and nitrogen hyperfine coupling constants and an increase in the g value of species I from 2.0049 to 2.0060 with lowering temperature and suggest a labile electronic ground state for species I. The p-CH3O substituted complex exhibits an electronic transformation from 2A2u to 2A1u while the remaining complexes, including m-CH3O, show a transformation from 2A2u to an admixed 2A1u/2A2u state. The effect of substitution on the variable temperature ESR spectra are discussed.
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  • 2
    Electronic Resource
    Electronic Resource
    New Syntheses of Flavones from Diels-Alder Reactions of 2-Styrylchromones with ortho-Benzoquinodimethanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 135-139 
    Details
    ISSN: 1434-193X
    Keywords: Flavones ; Chromones ; ortho-Benzoquinodimethanes ; Diels-Alder reactions ; NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The first reported cycloaddition reactions of 2-styrylchromones with ortho-benzoquinodimethane afforded 2-[2-(3-aryl-1,2,3,4-tetrahydronaphthyl)]chromones. These cycloadducts were converted into the corresponding 2-[2-(3-arylnaphthyl)]chromones (benzoflavone derivatives) by bromination/dehydrobromination processes. These benzoflavone derivatives were also obtained in one-pot cycloaddition reactions of 2-styrylchromones with ortho-benzoquinodibromomethane.
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  • 3
    Electronic Resource
    Electronic Resource
    The Structures of a Tetracarba-nido-octaborane(8) and a Novel Spiro Derivative of a 2,3,5-Tricarba-nido-hexaborane(7) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 533-537 
    Details
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Carboranes ; NMR ; X-ray analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydroboration of bis(diethylboryl)ethyne (1) with tetraethyldiborane(6) leads to a B-ethyl-substituted tetracarba-nido-octaborane 2, a spiro-carborane 3, which belongs to the 2,3,5-tricarba-nido-carborane family, and a hexacarba-arachno-dodecaborane(12) 4, along with polymeric material. The X-ray structure analysis of carborane 2, determined here, is fully consistent with the structure deduced earlier from NMR data. The structure of 3 in solution was established by theoretical analysis of its NMR data. Ab initio calculations of the structures of 2b and 3b (b denotes the B-metyhl-substituted derivatives) and the comparison of calculated with experimental NMR data support the suggested structures of 2 and 3 in solution. The calculated structure of the carborane cage of 2a also agrees with the experimental geometry of 2.
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis, Structure, and Stereodynamics of an N,N-Chiral “Proton Sponge” (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2501-2510 
    Details
    ISSN: 1434-193X
    Keywords: Proton Sponges ; N-Chirality ; Isotopic labelling ; Stereodynamics ; NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,8-Bis(N-benzyl-N-methylamino)naphthalene (2) and its hydrogen iodide salt [2H]+[I]- were synthesised from 1,8-diaminonaphthalene. The thermodynamic diastereomer ratios of (2) and [2H]+ in [D7]DMF are 73.4:26.6 and 89.7:10.3 respectively at 293 K. The solid state structures of the major dl-(RNRNSNSN) diastereomers were determined by single crystal X-ray diffraction. The minor diastereomers were shown to be the meso-(RNSN) forms by performing 1H-NMR NOE studies on isotopically desymmetrized 1-(N-benzyl-N-[13C]-methylamino)-8-(N′-benzyl-N′-methylamino)naphthalene [13C]-2 and the salt [13C]-[2H]+. In [D7]DMF at 298 K, the meso form of the free base 2 is 0.6 (± 0.07) kcal·mol-1 less stable than the dl form (ΔH° = -0.64 (±0.03) kcal·mol-1; ΔS° = -0.18 (±0.13) cal·K-1mol-1) and the activation barriers for interconversion are ca. 14.2 (±0.4) and 14.8 (±0.4) kcal·mol-1 respectively. The effect of solvent polarity on the entropy and enthalpy change on approach to the transition state was studied. An approximate correlation with the solvent dielectric constant was found for both ΔH# and ΔS# and this may be ascribed to the development of a net dipole in the transition state due to substantially different hybridisation and geometry at the two nitrogen centres.
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  • 5
    Electronic Resource
    Electronic Resource
    Structure analysis of a soluble polysiloxane-block-polyimide and kinetic analysis of the solution imidization of the relevant polyamic acid (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2237-2245 
    Details
    ISSN: 0887-624X
    Keywords: NMR ; polysiloxane, polysiloxane-block-polyimide ; solution imidization ; kinetic analysis ; structure analysis ; spin-lattice relaxation time ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of polysiloxane-block-polyimides were synthesized by solution imidization of the polyamic acids derived from the combination of 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), and diamino(polysiloxane) (PSX (Mw = 750)) in N-methyl-2-pyrrolidone (NMP). Their structures were analyzed by 1H-, 13C-, and 29Si-NMR spectra as well as by IR spectroscopy. The solid-state NMR spectrum was also measured to determine the spin-lattice relaxation time of the copolyimides. The observed relaxation times of both aromatic and polysiloxane segments were similar in the copolyimides having 10-30 wt % of PSX, while those in the copolyimide with 50 wt % of PSX was significantly different. This may be attributed to the morphology change due to the increase in PSX composition in the polymer backbone. The reduced viscosity of the copolyimides could be controlled by changing the monomer ratio in the feed or by adding an end-capping reagent such as phthalic anhydride into the polymerization system. The kinetic study of the solution imidization revealed that the imidization reaction obeyed second-order kinetics. The activation energy calculated for this imidization was 99.2 kJ/mol, being similar to that for the imidization of the DSDA-based aromatic polyimides. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2237-2245, 1998
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  • 6
    Electronic Resource
    Electronic Resource
    Investigation of the microstructure of metallocene-catalyzed norbornene-ethylene copolymers using NMR spectroscopy (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1633-1638 
    Details
    ISSN: 0887-624X
    Keywords: cyclic olefin copolymers ; norbornene ; metallocene catalysts ; NMR ; microstructure ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Norbornene-ethylene copolymers were prepared using the metallocene catalyst ethylene bis (indenyl) zirconium dichloride with MAO, and their microstructure was characterized with 1H-NMR and 13C-NMR methods. From a Cosy 1H-NMR spectrum it was found that all norbornene units are enchained in the exo-configuration. The sequence distribution of norbornene units was investigated using 13C-1H correlations, hmqc for one-bond correlations, and hmbc for two- or three-bond correlations. It was shown that norbornene diads were formed at a high norbornene content (45 mol %). When further increasing the norbornene incorporation (66 mol %) a number of new signals were obtained. A Cosy 1H-NMR spectrum revealed a new crosspeak which, according to the corresponding 13C-NMR shifts (hmqc), correlated well with a terminal unit of a trimer of norbornene. This means that at very high norbornene contents, norbornene triads can be formed. Because the formation of isotactic norbornene triads is very difficult to understand from a sterical point of view, an epimerization process causing stereoirregularities in the norbornene triad is proposed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1633-1638, 1998
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  • 7
    Electronic Resource
    Electronic Resource
    Unusually facil cis to trans isomerization of a polypropiolate bearing a long alkyl chain polymerized using a [Rh(norbornadiene)Cl]2 catalyst: An ESR study (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2457-2461 
    Details
    ISSN: 0887-624X
    Keywords: polyalkylpropiolate ; Rh complex catalyst ; isomerization ; ESR ; soliton ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkylpropiolate having n-hexadecyl moiety in the ester group was stereospecifically polymerized with a [Rh(norbornadiene)Cl]2 complex catalyst in alcohol to give rise to cis-transoid polyacetylenes in high yields. The unusually facile cis to trans isomerization for the polymer was found to be induced when the polymer was warmed to even less than ca. 57°C. Under these conditions ESR spectra bearing hyperfine structures due to the radicals generated by the rotational scission in the cis-π bond were observed. This isomerization induced a large g value shift in the ESR spectra together with an increase of the radical concentration during the isomerization, indicating formation of planar conjugated trans sequences that stabilize mobile unpaired electrons as solitons. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2457-2461, 1998
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  • 8
    Electronic Resource
    Electronic Resource
    Kinetic investigations on the photopolymerization of di- and tetrafunctional methacrylic monomers in polymeric matrices. ESR and calorimetric studies. II. Postpolymerization reactions (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2785-2791 
    Details
    ISSN: 0887-624X
    Keywords: postpolymerization reactions ; ESR ; polymeric matrices termination reactions ; H-transfer reactions ; kinetic constants ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction kinetics in the dark of photopolymerized mono- and dimethacrylates in a polymeric binder has been studied. Electron spin resonance spectroscopy (ESR) provided useful information regarding the nature of the radicals involved in postpolymerization reactions. Computer simulations were performed to study the decay of the propagating radicals by considering normal bimolecular termination and transfer reactions of the radicals to the binder. Differences were found in the termination reactions for mono- and difunctional monomers when they were photopolymerized in a solid medium. Absolute kinetic constants for H-transfer reaction with the binder, relative kinetic rate constants for radical-radical coupling, and average lifetimes for the radicals have been calculated. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2785-2791, 1998
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  • 9
    Electronic Resource
    Electronic Resource
    Stereochemical and compositional assignment of acrylonitrile/methyl methacrylate copolymers by DEPT and inverse HECTOR NMR spectroscopy (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1081-1092 
    Details
    ISSN: 0887-624X
    Keywords: NMR ; microstructure ; acrylonitrile/methyl methacrylate copolymer ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The acrylonitrile/methyl methacrylate copolymers of different monomer concentration were prepared by photo polymerization using uranyl ion as initiator. The carbon 13 and proton spectra of these copolymers are overlapping and complex. The complete spectral assignment of the 13C- and 1H-NMR spectra were done with the help of Distortionless Enhancement by Polarization Transfer (DEPT) and two dimensional 13C-1H Heteronuclear Single Quantum Correlation (HSQC) experiments. The methylene, methine and the methyl carbon resonances show both stereochemical (triad level) and compositional (dyad, triad, tetrad, pentad and hexad level) sensitivity. 2D Double Quantum Filtered Correlated Spectroscopy (DQFCOSY) experiment was used to ascertain the various geminal couplings between the methylene protons. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1081-1092, 1998
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  • 10
    Electronic Resource
    Electronic Resource
    Kinetic investigations on the photopolymerization of di- and tetrafunctional (meth)acrylic monomers in polymeric matrices. ESR and calorimetric studies. I. Reactions under irradiation (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2775-2783 
    Details
    ISSN: 0887-624X
    Keywords: photopolymerization kinetics ; ESR ; polymeric binders ; radical environment ; photocalorimetry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photopolymerization of several di- and tetrafunctional (meth)acrylic monomers in the presence of a styrene-butadiene-styrene polymeric matrix (SBS) has been studied. Electron spin resonance spectroscopy (ESR) and differential scanning photocalorimetry (photo-DSC) were used as monitoring techniques to identify the photogenerated radicals and analyze photopolymerization profiles, radical environments, and radical secondary reactions. The study of the photopolymerization and/or photocrosslinking reactions of these monomers in the solid media was carried out by taking into consideration different factors, such as the influence of both monomer and photoinitiator structures on the hydrogen abstraction in the binder with formation of benzylic and allylic radicals, the polymerization of the monomers itself and the hydrogen abstraction reaction in the polymerized acrylic chains. Finally, irradiation of the system SBS/photoinitiator in the absence of monomer was also accomplished. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2775-2783, 1998
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  • 11
    Electronic Resource
    Electronic Resource
    Synthesis of novel polyaryl(ether-ketones) with tert-butyl pendent groupsDedicated to Prof. F. J. Baltaá Calleja on the occasion of his 60th birthday. (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1251-1256 
    Details
    ISSN: 0887-624X
    Keywords: ether ketones ; synthesis ; NMR ; thermal properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Linear polyaryl(ether ketones) containing tert-butyl pendent groups were prepared from aromatic hydrocarbons and aromatic diacid chlorides, both classes of monomers containing tert-butyl pendent groups. The polymers were prepared in high yield and high molecular weight by low-temperature precipitation polycondensation in 1,2-dichloroethane. The presence of meta-oriented moieties and bulky pendent groups played a beneficial role with regard to solubility, while the thermal transitions and thermal resistance were not greatly impaired relative to conventional all para-oriented polyaryl(ether-ketones). The current polyaryl(ether-ketones) showed glass transition temperatures in the range 170-240°C and decomposition temperatures, as measured by TGA, of about 500°C. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1251-1256, 1998
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  • 12
    Electronic Resource
    Electronic Resource
    Kinetic and ESR studies on radical copolymerization of p-tert-butoxystyrene and di-n-butyl maleate in benzene (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1449-1455 
    Details
    ISSN: 0887-624X
    Keywords: radical copolymerization ; p-t-butoxystyrene ; dibutyl maleate ; penultimate effect ; ESR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The copolymerization of p-tert-butoxystyrene (TBOSt) (M1) and di-n-butyl maleate (DBM) (M2) with dimethyl 2,2′-azobisisobutyrate (MAIB) in benzene at 60°C was studied kinetically and by means of ESR spectroscopy. The monomer reactivity ratios were determined to be r1 = 2.3 and r2 = 0 by a curve-fitting method. The copolymerization system was found to involve ESR-observable propagating polymer radicals under practical copolymerization conditions. The apparent rate constants of propagation (kp) and termination (kt) at different feed compositions were determined by ESR. From the relationship of kp and f1 (f1 = [M1]/([M1] + [M2])) based on a penultimate model, the rate constants of five propagations of copolymerization were evaluated as follows; k111 = 140 L/mol s, k211 = 3.5 L/mol s, k112 = 61 L/mol s, k212 = 1.5 L/mol s, and k121 = 69 L/mol s. Thus, a pronounced penultimate effect was predicted in the copolymerization. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1449-1455, 1998
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  • 13
    Electronic Resource
    Electronic Resource
    NMR and semi-empirical study of the tautomerism of­2,2′-bisbenzimidazolyl (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 411-418 
    Details
    ISSN: 0894-3230
    Keywords: 2,2′-bisbenzimidazolyl ; tautomerism ; NMR ; semi-empirical calculations ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A dynamic NMR study of the tautomerism of 2,2′-bisbenzimidazolyl in DMSO-d6 and a mechanistic interpretation of the process, based on a stepwise, single-proton transfer and formation of a zwitterionic intermediate, are presented. This interpretation is substantiated by semi-empirical calculations of the postulated intermediate and transition state, that yield results which are compared with previous studies on related aliphatic systems. © 1998 John Wiley & Sons, Ltd.
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  • 14
    Electronic Resource
    Electronic Resource
    Enantioselective synthesis of α-aminophosphonic acid derivatives by hydrogenation (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 564-572 
    Details
    ISSN: 0899-0042
    Keywords: asymmetric hydrogenation ; aminophosphine phosphinites ; rhodium complexes ; dehydro aminophosphonic acids ; NMR ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral α-aminophosphonic acid derivatives are efficiently synthesized by asymmetric hydrogenation of the prochiral N-acyl-α,β-dehydroaminophosphonates. PROPRAPHOS-Rh-catalysts from readily available (S)- and (R)-Propranolol proved to be suitable in the homogenous reaction affording an enantiomeric excess of 87-92% with high rate. The aminophosphonic acid derivatives and precursors were fully characterized by 1H, 13C, and 31P NMR spectroscopy. Chirality 10:564-572, 1998. © 1998 Wiley-Liss, Inc.
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  • 15
    Electronic Resource
    Electronic Resource
    Stereochemistry of polycyclohexyl systems (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 159-168 
    Details
    ISSN: 0899-0042
    Keywords: symmetry ; conformation ; chirality ; stereochemistry ; NMR ; rotational barrier ; interconversion graph ; gear meshing ; molecular propellers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The static and dynamic stereochemistries of tricyclohexylmethane, tetracyclohexylmethane, and tetracyclohexylethene are reviewed. Chirality 10:159-168, 1998. © 1998 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/chir.25
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  • 16
    Electronic Resource
    Electronic Resource
    A New Class of Oligonuclear Platinum-Thallium Compounds with a Direct Metal-Metal Bond - 3. Unusual Equilibria in Aqueous Solution (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 565-570 
    Details
    ISSN: 1434-1948
    Keywords: Equilibrium ; Metal-metal bond ; Stability constants ; Platinum ; Thallium ; NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new series of four binuclear platinum-thallium cyano compounds containing a direct and unsupported by ligands metal-metal bond has been prepared in aqueous solution. These compounds are represented by the formula[(NC)5Pt-Tl(CN)n-1](n-1)- (n = 1-4 for compounds I, II, III IV, respectively) and [(NC)5Pt-Tl-Pt(CN)5]3- (for compound V). The oligonuclear complexes are synthesised according to the reaction mPt(CN)42- + Tl3+ + nCN- █[PtmTl(CN)4m+n]3-2-n. Thus, there occurs a change of the coordination number of the Pt center from four (square planar) to six (octahedral). Consequently, the formation of binuclear platinum-thallium cyano compounds involves at least two steps: (i) formation of metal-metal bond and (ii) formation of (NC)5Pt- unit by a cyanide transfer process. - The complexes exist in an equilibrium, which also includes the parent complexes Pt(CN)42- and Tl(CN)n3-n (n = 0-4), and can be controlled by varying the cyanide concentration and/or pH of the solution. The stability constants of the compounds βN =[PtmTl(CN)4m+n3-2m-n{[Pt(CN)42-]m · [Tl3+] · [CN-]n} have been determined by means of multinuclear NMR (195Pt, 205Tl): logβN = 19.9±0.4, 30.7±0.3, 38.6±0.3, and 44.8±0.2 for I, II, III and IV(m = 1, n = 1-4), and 32.1±0.3 for V(m = 2, n = 2), respectively, (in 1 M NaClO4 as ionic medium, at 25 oC). To our knowledge, the present work constitutes the first detailed equilibrium study of metal-metal bonded compounds; it indicates that also other cluster formation reactions described in the literature may represent real equilibria.
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  • 17
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    VTF to arrhenius crossover in temperature dependence of conductivity in (PEG)xNH4ClO4 polymer electrolyte (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1201-1209 
    Details
    ISSN: 0887-6266
    Keywords: polymer electrolytes ; NMR ; conductivity ; glasses ; Arrhenius and VTF dependences ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We have studied the temperature variation of conductivity and 1H NMR linewidth of (PEG)xNH4ClO4 (x = 20, 30, 46, 100, 200, & 1000) polymer electrolyte systems. The temperature dependence of the conductivity shows two distinct behaviors, the low temperature VTF dependence crossing over to Arrhenius dependence at higher temperatures. The departure from the VTF behavior is found to be composition dependent. NMR spectra indicate the presence of large fractions of crystalline regions that start to melt around the crossover temperature. We understand the deviation from the VTF behavior as a consequence of this crystalline to elastomer transition. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1201-1209, 1998
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  • 18
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    Conformation and membrane activity of an analogue of the peptaibol antibiotic trichogin GA IV with a lipophilic amino acid at the N-terminus (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 4 (1998), S. 389-399 
    Details
    ISSN: 1075-2617
    Keywords: conformational analysis ; lipo-amino acid ; membrane activity ; NMR ; peptide antibiotic ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have synthesized by solution-phase methods two analogues of the 11-residue lipopeptaibol antibiotic trichogin GA IV in which the N-terminal n-octanoyl group is replaced either by an N-acetylated 2-amino-2-methyl-l-undecanoic acid or by an N-acetylated α-aminoisobutyric acid. CD, FTIR absorption, and NMR analyses unequivocally show that the main structural features of trichogin GA IV are preserved in these analogues. Since only the peptide containing the lipophilic chain exhibits membrane-modifying properties, these results strongly support the view that moving the long acyl moiety from the Nα-blocking group to the side chain of the N-terminal extra-residue does not affect the conformational properties or the membrane activity of trichogin GA IV. © 1998 European Peptide Society and John Wiley & Sons, Ltd.
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  • 19
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    Conformational sampling of bioactive conformers: a low-temperature NMR study of 15N-Leu-enkephalin (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 4 (1998), S. 253-265 
    Details
    ISSN: 1075-2617
    Keywords: Opioids ; enkephalin ; selectivity ; conformation ; NMR ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational studies of enkephalins are hampered by their high flexibility which leads to mixtures of quasi-isoenergetic conformers in solution and makes NOEs very difficult to detect in NMR spectra. In order to improve the quality of the NMR data, Leu-enkephalin was synthesized with 15N-labelled uniformly on all amide nitrogens and examined in a viscous solvent medium at low temperature. HMQC NOESY spectra of the labelled Leu-enkephalin in a DMSOd6/H2O mixture at 275 K do show numerous NOEs, but these are not consistent with a single conformer and are only sufficient to describe the conformational state as a mixture of several conformers. Here a different approach to the structure-activity relationships of enkephalins is presented: it is possible to analyse the NMR data in terms of limiting canonical structures (i.e. β- and γ-turns) and finally to select only those consistent with the requirements of δ selective agonists and antagonists. This strategy results in the prediction of a family of conformers that may be useful in the design of new δ selective opioid peptides. © 1998 European Peptide Society and John Wiley & Sons, Ltd.
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    Effect of extracellular glutamine concentration on primary and secondary metabolism of a murine hybridoma: An in vivo 13C nuclear magnetic resonance study (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 172-186 
    Details
    ISSN: 0006-3592
    Keywords: hybridoma ; futile cycling ; hollow fiber bioreactor ; glutamine ; NMR ; C-13 ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effect of changes in extracellular glutamine level on metabolism of a murine hybridoma was examined with in vivo nuclear magnetic resonance (NMR) spectroscopy. Cells were cultured in a hollow-fiber bioreactor at high cell density to allow intracellular metabolite levels to be determined on a metabolically relevant time scale. Steady infusions of [1-13C] glucose were used to label glycolytic and tricarboxylic acid cycle intermediates, which permitted continuous monitoring with NMR spectroscopy during changes in environmental glutamine level. Samples of the extracellular medium were also analyzed to determine the effect of glutamine on other metabolites associated with primary and secondary metabolism. The changes in glutamine concentration had several effects on primary and secondary metabolism, depending on the rate the changes were made. For a brief reduction in feed glutamine concentration from 4 to 0 mM (which produced a rapid change from 0.67 to ∼0 mM in residual glutamine), large changes were observed in the rate of consumption of metabolites normally associated with energy production. Antibody synthesis was strongly stimulated and nitrogen metabolism was significantly altered. For a more prolonged reduction from 2.4 to 1.2 mM (which produced a slower reduction from 0.30 to 0.08 mM in residual glutamine), much smaller changes were observed even though the concentration of glutamine at the reduced feed level was very low. Energy metabolism did not appear to be limited by glutamine at 0.08 mM, which suggests that significant futile cycling may occur in energy producing pathways when excess glucose and glutamine are available. However, this concentration of extracellular glutamine appeared to affect some anabolic pathways, which require amino groups from glutamine. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 172-186, 1998.
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    Molecular motion of ends of isolated poly(isobutylene) chains tethered on the poly(tetrafluoroethylene) surface in vacuo (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2095-2102 
    Details
    ISSN: 0887-6266
    Keywords: molecular motion ; polyisobutylene ; isolated chain ; ESR ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly(isobutylene) (PIB) chains with a radical at the chain end were graft-copolymerized on the poly(tetrafluoroethylene) (PTFE) surface in vacuo at 77 K. The PIB chains tethered on the PTFE surface in vacuo were regarded as isolated chains from neighboring tethered PIB chains. The molecular motion of the ends of the isolated PIB chains was observed by an electron spin resonance (ESR) spectrometer in the temperature range from 3 to 125 K, which was lower than Tg of PIB, 200 K,1 and two motion modes were found: One is a quantum tunneling of the methyl group located at the chain end at 3 K, and the other is an interconformation transition with freely rotating methyl group at the end at 77 K, where the transition rate was estimated to be 15 MHz at that temperature. The transition rate increased with an increase in temperature. The activation energy of the transition was estimated to be 370 J/mol. The high mobility and low activation energy was attributed to the isolation of PIB chains in vacuo. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2095-2102, 1998
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    Characterization of the diffusive properties of biofilms using pulsed field gradient-nuclear magnetic resonance (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 60 (1998), S. 283-291 
    Details
    ISSN: 0006-3592
    Keywords: diffusion ; biofilms ; gels ; NMR ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The mobility of water in intact biofilms was measured with pulsed field gradient nuclear magnetic resonance (PFG-NMR) and used to characterise their diffusive properties. The results obtained with several well-defined systems, viz. pure water, agar, and agar containing inert particles or active bacteria were compared to glucose diffusion coefficients measured with micro-electrodes and those calculated utilising theoretical diffusion models. A good correspondence was observed indicating that PFG-NMR should also enable the measurement of diffusion coefficients in heterogeneous biological systems. Diffusion coefficients of several types of natural biofilms were measured as well and these results were related to the physical biofilm characteristics. The values had a high accuracy and reflected the properties of a sample of ca. 100 biofilms, while non-uniformity or non-geometrical shapes did not negatively influence the results. The monitored PFG-NMR signal contains supplementary information on e.g. cell fraction or spatial organisation but quantitative analysis was not yet possible. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 60: 283-291, 1998.
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    7Li and 23Na NMR studies of transmembrane cation transport mediated by ionophore lasalocid A (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 4 (1998), S. 15-20 
    Details
    ISSN: 1075-2617
    Keywords: ion transport ; kinetics ; lithium ; NMR ; shift reagent ; vesicles ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ion transport across phospholipid vesicles was studied by 7Li and 23Na-NMR using an aqueous anionic paramagnetic shift reagent, dysprosium nitrilotriacetate [Dy(NTA)2]3-, mediated by ionophores, lasalocid A and A23187. The intra- and extracellular 7Li and 23Na-NMR signals were well separated (20 Hz) at mM concentration of the shift reagent. The observed data on the rate constant for lithium transport across DPPC vesicles at various concentrations of the ionophores indicated that lasalocid A is a more efficient carrier for lithium ion compared with the sodium ion transport by this ionophore, while A23187 was not specific to either of the ions (Li or Na). ©1998 European Peptide Society and John Wiley & Sons, Ltd.
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    Solution conformation of an immunogenic peptide from HRV2: comparison with the conformation found in a complex with a Fab fragment of an anti-HRV2 neutralizing antibody (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 4 (1998), S. 101-110 
    Details
    ISSN: 1075-2617
    Keywords: NMR ; random coil ; rhinovirus ; synthetic vaccine ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformation of a [15]-peptide (H-VKAETRLNPDLQPTE-NH2) from VP2 of rhinovirus HRV2 complexed with a Fab fragment was previously shown by X-ray crystallographic studies to be similar to the one found in the corresponding region of HRV1A. Antibodies raised against this peptide bind to and neutralize HRV2. In order to identify structural features preserved in solution that may explain the ability of this short peptide to mimic the structure of the protein surface, the peptide has been studied by NMR in aqueous solution as well as under denaturing conditions.The peptide is shown to be a random coil in solution. However, the sequence forming a 310 helix in the complex is biased into a helical conformation according to NOE intensity data as well as from urea and pH titrations. This sequence adopts the same conformation in an unrelated protein. NOE data suggest that a β-turn found in the complex may be sampled in solution. Also, Glu4, interacting with Arg6 in the crystal, has a reduced pKa value in solution. It is concluded that the local structure present in the random coil state of VP2(156-170) contains enough information to direct the production of antibodies that bind to and neutralize HRV2. © 1998 European Peptide Society and John Wiley & Sons, Ltd.
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    A conformational study in solution of pro-somatostatin fragments by NMR and computational methods (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 4 (1998), S. 305-318 
    Details
    ISSN: 1075-2617
    Keywords: pro-somatostatin ; β-turn ; NMR ; computational methods ; conformational analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The results of a conformational study by nuclear magnetic spectroscopy and computational methods on a series of point-mutated synthetic peptides, containing 14 amino acid residues and mimicking the region containing the Arg-Lys dibasic cleavage site of pro-somatostatin, have confirmed the possible role of a well defined secondary structure in the recognition phenomenon by processing enzymes.The importance of the residues located near the Arg-Lys dibasic site in the C-terminal region of the pro-hormone for the cleavage of the precursor into somatostatin-14 has been confirmed. The present structural analysis indicates the occurrence of two β-turns in the 4-7 and 11-14 regions, flanking the cleavage site, for all the peptides recognized as substrates by the processing enzyme.Interestingly, in the point-mutated analogue not processed by the enzyme and containing the replacement of proline by alanine in position 5 the first β-turn is displaced by one residue and involves the Ala5-Arg8 segment. This observation may explain the lack of recognition by the maturation enzyme. © 1998 European Peptide Society and John Wiley & Sons, Ltd.
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    Identification of Mo(V) commonly observed in passive films formed on stainless steels (1998)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 26 (1998), S. 155-159 
    Details
    ISSN: 0142-2421
    Keywords: XPS ; x-ray photoelectron spectroscopy ; ESR ; electron spin resonance ; Mo 3d ; Mo 3p ; O 1s ; binding energies ; Mo(IV) ; Mo(V) ; Mo(VI) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: There has been a longstanding debate and controversy in the literature with regard to the determination by XPS of the exact oxidation state of a molybdenum species commonly observed in the passive films of stainless steel. In this paper we have compared both the XPS and ESR analyses of molybdenum oxyhydroxides previously postulated to contain Mo(V) as well as Mo(IV) and Mo(VI). The compositions of these compounds closely resemble those found in the passive films of Mo-bearing stainless steel. It has been shown that the same Mo species exhibiting an XPS Mo 3d5/2 spectrum binding energy value of 230.8 eV is observed to exhibit an ESR spectra having a g factor of 1.921, which corresponds to Mo(V). © 1998 John Wiley & Sons, Ltd.
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    Synthesis and characterization of arsenobetaine and arsenocholine derivatives (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 12 (1998), S. 635-641 
    Details
    ISSN: 0268-2605
    Keywords: arsenobetaine ; arsenocholine ; non-hygroscopic ; NMR ; FAB MS ; ICP MS ; synthesis ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multigram quantities of arsenobetaine bromide and arsenocholine iodide were synthesized from trimethylarsine using uncomplicated techniques. Arsenobetaine bromide and arsenocholine iodide are both non-hygroscopic. Arsenocholine iodide is, however, light-sensitive and should be used with actinic glassware. Both compounds were characterized by elemental and spectroscopic techniques and found to be suitable for use as primary analytical standards. © 1998 John Wiley & Sons, Ltd.
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    Synthesis and characterization of diorganotin(IV) complexes of N-(2-pyridylmethylene)arylamines and mutagenicity testing in vivo of Et2SnCl2·[L4=N-(2-pyridylmethylene)-4-toluidine] (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 12 (1998), S. 503-513 
    Details
    ISSN: 0268-2605
    Keywords: organotin ; N-(2-pyridylmethylene)arylamines ; IR ; NMR ; Mössbauer ; mutagenicity ; sister chromatid exchange ; cell cycle delay ; bone-marrow cells ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Diorganotin(IV) dichloride complexes of the type R2SnCl2·L (R = methyl, ethyl, vinyl, t-butyl, n-butyl or phenyl; L = N-(2-pyridylmethylene)arylamine) have been synthesized and characterized on the basis of IR, NMR and 119Sn Mössbauer studies. Investigation of the complexes indicated that N-(2-pyridylmethylene)arylamines form distorted trans-octahedral complexes with R2SnCl2 similar to the well-known R2SnCl2·L. Cytogenetic toxicology testing has been performed for Et2SnCl2·L4 [L4 = N-(2-pyridylmethylene)-4-toluidine] in mouse bone-marrow cells in vivo since such testing is a regulatory requirement before new drugs are released. This tin compound induced delay in cell-cycle kinetics and sister chromatid exchanges (SCEs) significantly. The effect of Et2SnCl2·L4 was greater when endogenous glutathione (GSH) was depleted by buthionine sulphoximine (BSO). It seems that Et2SnCl2·L4 induces SCEs due to formation of adduct by binding on DNA which could interfere in DNA synthesis and cause delay in cell proliferation. Depletion of GSH could reduce the shielding effect of GSH on chromatin and allows more Et2SnCl2·L4 to bind on DNA. © 1998 John Wiley & Sons, Ltd.
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    Diorganotin(IV)-2-mercaptopyrimidine complexes (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 12 (1998), S. 861-871 
    Details
    ISSN: 0268-2605
    Keywords: diorganotin ; Pyrimidine ; complex ; Mössbauer ; IR ; NMR ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexes formed between the diorganotin(IV) moieties, R2Sn(IV), and the ligand 2-mercaptopyrimidine, (H)SPym, were investigated. Complexes R2SnHal(SPym) and R2Sn(SPym)2 [R = Me, iPr, nBu, iBu, tBu, cyclohexyl(Cy), Ph] were synthesized, and characterized by elemental analysis. In the solid state, chelation of SPym through S and N donors was established by IR spectroscopy, and the nature of the environment of tin centers was investigated by 119Sn Mössbauer spectroscopy. From the dynamics of 119Sn nuclei determined by variable-temperature measurements on representative compounds [Me2SnCl(SPym) and Cy2SnBr(SPym)], as well as by point-charge model treatment of nuclear quadrupole splitting parameters, it was inferred that Me2SnCl-­(SPym) may assume a trans-Me2 octahedral coordination geometry around tin in a monodimensional polymer, or a monomeric trigonal-bipyramidal structure (distorted). The latter type of structure was assigned to the other R2SnHal(SPym) species, while R2Sn(SPym)2 complexes assume a trans-octahedral, or skew trapezoidal, tin environment. In CHCl3-CDCl3 solutions, monomeric species occur (according to vapor-pressure osmometry), where 1H and 13C NMR spectroscopic parameters of SPym indicate the persistence of Sn chelation by S and N donor atoms. The Me2SnCl(SPym) species assume trigonal-bipyramidal structures with a chelating SPym ligand, in CDCl3 and C2H5OH solutions, according to the coupling constants 1J(119Sn,13C), as well as IR and 119Sn Mössbauer spectroscopic data. 119Sn NMR parameters fully correspond with data for the homologous complexes with 2-mercaptopyridine. Copyright © 1998 John Wiley & Sons, Ltd.
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    Antiferromagnetism of colloidal [Mn0·0.3THF]x (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 12 (1998), S. 387-391 
    Details
    ISSN: 0268-2605
    Keywords: colloidal manganese ; ESR ; susceptibility ; antiferromagnetism ; superparamagnetism ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reduction of MnBr2·2THF (THF = tetrahydrofuran) using K[BEt3H] yields the organosol [Mn·0.3THF]x. According to the UV/Vis, ESR (electron spin resonance spectroscopy), HRTEM (high-resolution transmission electron microscopy), XPS (X-ray photoelectron spectroscopy) and XAS (X-ray absorption spectroscopy) data, this nanosized metal colloid consists of small THF-stabilized Mn0 particles which show, in susceptibility investigations, a diminished magnetic coupling as deduced from the Weiss temperature, Θ = 96 K. The Neél temperature TN is likewise strongly reduced in comparison with the bulk value (95 K). The THF-stabilized Mn0 particles exhibit superparamagnetism below 20 K, with a partial blocking at 10 K, and to our knowledge represent the first colloid consisting of particles of an elemental antiferromagnetic metal. © 1998 John Wiley & Sons, Ltd.
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    Ab initio prediction of 15N-NMR chemical shift in α-boron nitride based on an analysis of connectivities (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 716-725 
    Details
    ISSN: 0192-8651
    Keywords: NMR ; boron nitride ; solid state ; theoretical chemistry ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Hydrogen-saturated cut-outs of hexagonal boron nitride have been used to model the solid state. Model compounds have been geometry optimized by means of density functional theory, whereas chemical shift calculations have been carried out at the coupled-perturbed Hartree-Fock level of theory employing gauge-including atomic orbital (GIAO) basis sets. The reliability of results has been tested against experimental values for chemical shifts in stable molecules with similar structural elements. With increasing cluster size, viz. a vanishing influence of the saturating hydrogens on the innermost nitrogen atoms, we find a convergence of 15N chemical shifts. A classification scheme for the chemical environment of a nitrogen atom has been set up according to its bonding graph including the second coordination sphere. For a given connectivity, chemical shifts vary within a few parts per million, thus enabling us to predict a 15N-NMR chemical shift of -285 ± 5 ppm for solid α-boron nitride.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 716-725, 1998
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    Determination of molecular weight distributions of novolac resins by gel permeation chromatography (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 1399-1407 
    Details
    ISSN: 0887-624X
    Keywords: phenol-formaldehyde resin; ; novolac ; GPC ; molecular weight averages ; NMR ; hydrodynamic volume ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The number- and weight-average molecular weights of several statistical and high ortho novolac resins were determined using gel permeation chromatography (GPC). The standards used were pure compounds having between 2 and 12 phenol units bridged via methylene linkages. Three series of compounds were studied: (i) those with methylene linkages substituted in only the ortho positions relative to the phenolic hydroxyl group; (ii) those in which all para positions, together with sufficient ortho positions, were used to synthesize the compounds; and (iii) those in which the methylene linkages were substituted at a mixture of ortho and para positions. Such compounds, having known molecular architecture and units similar to the segments of industrial novolac resins, provide for a more exact measurement of the molecular weight than do the commonly used poly(styrene) standards. Using these new standards the number average molecular weights of the resins determined by GPC were in good agreement with the average molecular weight obtained by 1H-NMR spectra of the resins, particularly for low molecular weight resins. GPC analysis of higher molecular weight resins tends to underestimate the molecular weights because of complications introduced by hydrogen bonding. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1399-1407, 1997
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    ESR study on chemical crosslinking reaction mechanisms of polyethylene using a chemical agent (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 279-284 
    Details
    ISSN: 0887-624X
    Keywords: polyethylene ; dicumyl-peroxide ; crosslinking ; free radical ; ESR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction mechanisms of thermal crosslinking of polyethylene with dicumyl peroxide (DCP) at high temperatures were investigated by electron spin resonance (ESR). The crosslinking reactions were induced by the alkyl radicals formed by the thermal decomposition of DCP above 120°C. The kinetics of the free radical reaction were followed during crosslinking reactions at temperatures between 145 and 180°C. © 1997 John Wiley & Sons, Inc.
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    Chemistry of novolac resins. II. Reaction of model phenols with hexamethylenetetramine (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 1389-1398 
    Details
    ISSN: 0887-624X
    Keywords: benzylamines ; benzoxazines ; curving ; HMTA ; NMR ; novolac resins ; xylenols ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is proposed that the reactions of hexamethylenetetramine (HMTA) with 2,4-xylenol and with 2,6-xylenol occur by different pathways. The rate of reaction and the final product distribution depend on the initial xylenol : HMTA ratio and are different in the two systems. Measured by HMTA consumption, with 2,4-xylenol the reaction rate increased with increasing xylenol : HMTA ratios, whereas with 2,6-xylenol the rate of reaction decreased with increasing 2,6-xylenol : HMTA ratio. In systems which contain both 2,4- and 2,6-xylenol, a strong preference for reaction of the HMTA with the ortho site of 2,4-xylenol was noted. This preference was apparent even in mixtures in which 2,6-xylenol was present in greater amounts than 2,4-xylenol. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1389-1398, 1997
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    Influence of the stoichiometry of epoxy-cyanate systems (non-catalyzed and catalyzed) on molten state reactivity (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 3101-3115 
    Details
    ISSN: 0887-624X
    Keywords: molten state reactivity cyanate esters ; epoxy resins ; NMR ; 13C (liquid and solid) ; FTIR ; DSC ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Based on an FT-IR and 13C-NMR spectroscopic study using model compounds, we previously proposed an epoxy-cyanate coreaction path in the molten state, by identifying all chemical species and their role in the reaction mixture. These data were then applied to difunctional systems involving diglycidyl ether of bisphenol A (DGEBA) and bisphenol A dicyanate (BADCy), with mixtures prepared in different epoxy/cyanate ratios. Using FT-IR and solid state 13C-NMR spectroscopic analyses, we show the effect of epoxy group concentration on the final structure of the system. We were able to show that epoxy functions react on the triazine rings formed in the first step of homopolymerization of cyanates, and that the structure of the final system depends on their initial concentration. In addition, a study of difunctional systems for identical cyanate-epoxy stoichiometry was undertaken in the presence of anionic (imidazole) and metallic (AcAcCu and AcAcCr) catalysts in order to determine their effect on the reactivity of the two monomers and on the structure of the final system. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3101-3115, 1997
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    NMR study of the structure and properties of poly(MMA-co-VP) crosslinked hydrogels (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 3619-3625 
    Details
    ISSN: 0887-624X
    Keywords: NMR ; structure ; porperties ; poly(MMA-co-VP) ; hydrogels ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H- and 13C-NMR techniques were used to study the microscopic structure of NMA/VP copolymer hydrogels. Evidence was obtained for a plasticization effect of MMA chains by VP. An original 1H-NMR approach revealed the existence of several types of water with various degree of bounding to the polymer network, a conclusion that is corroborated by a complementary 13C-NMR study. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3619-3625, 1997
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    Novel emulsion graft copolymerization onto the silylmethyl group of poly(dimethylsiloxane) (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 2607-2617 
    Details
    ISSN: 0887-624X
    Keywords: poly(dimethylsiloxane) ; emulsion graft copolymerization ; hydrogen abstraction reaction ; peroxide ; NMR ; lubricity ; MOPAC ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of radical initiators upon the emulsion graft copolymerization of styrene and acrylonitrile onto poly(dimethylsiloxane) (PDMS) was studied. As initiators, a series of peroxides and hydroperoxides were coupled with ferrous sulfate, among which the tert-butyl peroxylaurate system gave the highest grafting efficiency (30%). The tert-butyl peroxylaurate initiator fulfills the criteria for efficient radical grafting by generating only the tert-butoxy radical, which is reluctant to form a carbon radical via β-scission, being highly hydrophobic, and not carrying a tertiary hydrogen that may be abstracted by a radical. 13C-NMR analysis of the products showed that the grafting occurred on the silylmethyl groups of PDMS to give 10-25 grafts per polymer and graft ratio in the range 44-140%. The PDMS graft copolymers thus obtained could be used as surface-modifying agents to improve the lubricity and water-repellency of ABS [poly(styrene-co-acrylonitrile)-graft-polybutadiene]. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2607-2617, 1997
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    Aggregation kinetics and precipitation phenomena in poly(phenylisocyanide) (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 439-446 
    Details
    ISSN: 0887-624X
    Keywords: poly(phenylisocyanide) ; NMR ; GPC ; light-scattering techniques ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of N-phenyl-substituted poly(isocyanide) (N-φ-PIM) utilizing a Ni(II) catalyst in methanol yields a brown material having a number average molecular weight of about 2000. Analysis of this “as prepared” polymer indicates that a rigid rod structure is present in the derived solid. Dissolution of this “as prepared” N-φ-PIM in halocarbon solvents or THF apparently leads to unraveling of the helical polymer with subsequent aggregation and precipitation of materials that have different properties from the original. These processes have been investigated by NMR, GPC, and light-scattering techniques in THF and other solvents. UV spectroscopy has been utilized to follow the kinetics of the aggregation process in solution. X-ray diffraction (XRD) measurements have been employed to investigate the changes attendant with precipitation. An explanation of these observations is offered that implicates the uncoiling of the rigid rod helix as the most important step in defining subsequent physical and chemical properties of the ultimate amorphous polymer. © 1997 John Wiley & Sons, Inc.
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    Allyl endcapped polyethylene oxide crosslinkers and their use in superabsorbents (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 799-806 
    Details
    ISSN: 0887-624X
    Keywords: allyl crosslinkers ; poly(acrylic acid) ; NMR ; superabsorbent ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several new crosslinkers have been synthesized for evaluation in superabsorbent polymers. These crosslinkers are allyl endcapped polyethylene glycols (PEG) of 200, 600, and 3400 molecular weight. A branched polyethylene oxide of 600 molecular weight, initiated with glycerin, was also synthesized as a trifunctional crosslinker. The allyl functionality was chosen because it is less reactive during radical polymerization than acrylate crosslinkers, an attribute that was necessary to achieve a more uniform gel network. A synthesis route was devised to make the crosslinkers in high purity and yield. The purity of the crosslinkers was determined by 13C NMR, liquid chromatography, and size exclusion chromatography. Gels that were produced with the allyl crosslinkers gave excellent soluble polymer levels and swelling characteristics. The mechanism of incorporation of the allyl functionality was determined to be exclusively vinyl polymerization rather than through hydrogen abstraction. This was determined using NMR spectroscopy, monitoring the polymerization of a model system consisting of acrylic acid and allylacetate. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 799-806, 1997
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    ESR study on chemical crosslinking reaction mechanisms of polyethylene using a chemical agent - II. The effect of phenolic antioxidants (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 2431-2439 
    Details
    ISSN: 0887-624X
    Keywords: polyethylene ; dicumyl-peroxide ; crosslinking ; free radical ; ESR ; antioxidant ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of antioxidant on the reaction mechanism of chemical crosslinking of polyethylene (PE) with dicumyl peroxide (DCP) at high temperatures was investigated by electron spin resonance (ESR). The antioxidant reacts with the alkyl radicals in PE formed by the thermal decomposition of DCP above 120°C, and disturbs the crosslinking. A phenolic type antioxidant produced the phenoxy radical by the reaction with alkyl radicals formed in PE. It is suggested that the selection of a suitable antioxidant for PE crosslinking can be made by ESR analysis. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2431-2439, 1997
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    Identifying crosslinks in polyethylene following gamma-irradiation in acetylene: A model compound study (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 1549-1562 
    Details
    ISSN: 0887-624X
    Keywords: polyethylene ; γ-irradiation ; crosslinking ; NMR ; alkanes ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Long-chain linear alkanes have been used as model compounds for polyethylene in an attempt to identify the chemical nature of crosslinks formed in polyethylene when it undergoes γ-irradiation in the presence of acetylene. IR and UV spectral analysis of alkanes and polyethylene following acetylene-sensitized irradiation shows the formation of vinyl, trans-vinylene, and diene groups. A correlation of the conditions of formation suggests that in polyethylene the vinyl groups are restricted to amorphous regions, diene groups are restricted to the crystalline regions, and trans-vinylene groups are formed in both regions. There is no information on the nature of crosslinks. 13C-NMR analysis of alkanes following irradiation of molten alkanes in the presence of 13C-enriched acetylene has shown that a range of saturated alphatic structures are formed by inclusion of acetylene molecules in the alkane structure. They include ethyl branches, γ-branches,—CH(CH3)—, and —CH2—CH2— branches as the major species; the latter two are potential crosslink sites in the irradiation of polyethylene. In addition, the NMR analysis confirmed that the C atoms of the vinyl groups come from acetylene molecules and those of the trans-vinylene groups come from alkane molecules. Data on irradiation of the alkanes in the crystalline state showed that acetylene inclusion in the alkane structure is minimal under these conditions. The principal finding of this work is that acetylene can be incorporated as saturated aliphatic crosslinks in the amorphous regions of polyethylene during high-energy irradiation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1549-1561, 1997
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    O-nitromandelic acid: A chiral solvating agent for the NMR determination of chiral diamine enantiomeric purity (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 556-562 
    Details
    ISSN: 0899-0042
    Keywords: O-nitromandelic acid ; chiral solvating agent ; NMR ; enantiomeric purity ; mandelic acid ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: O-Nitromandelic acid, easily prepared from either enantiomer of mandelic acid, has been used as a chiral solvating agent for the determination of enantiomeric purity of several diamine derivatives and other compounds using 1H NMR spectroscopy. Chirality 9:556-562, 1997. © 1997 Wiley-Liss, Inc.
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    Application of phenylglycine methyl ester (PGME) to determination of the absolute configuration of carboxylic acids having phenylalkyl group (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 550-555 
    Details
    ISSN: 0899-0042
    Keywords: NMR ; chiral anisotropic reagent ; long-chain carboxylic acid ; Mosher's method ; absolute configuration ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (R)- and (S)-phenylglycine methyl ester (PGME) was applied to elucidate the absolute configuration of a series of aliphatic carboxylic acids, 2a and 2b (n = 1-6), which possess a phenyl group on the chain, by the process similar to the modified Mosher's method. (S)-PGME was condensed with rac-2a and 2b, and the resulting diastereomeric pair was separated for each of 2a and 2b. Δδ values were calculated from the 1H-NMR chemical shifts of (R)-2a-(or 2b)-(S)-PGME and (R)-2a-(or 2b)-PGME amides. By analyzing the positive and negative distribution patterns for each compound, it was concluded that this new method was successful to predict the absolute configuration of such type of acids, and that no significant interaction between the two phenyl groups, one in the chain and the other in the PGME, was present. Chirality 9:550-555, 1997. © 1997 Wiley-Liss, Inc.
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    Computer-simulation analysis of the ESR spectra of mechanoradicals in PMMA (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 2195-2200 
    Details
    ISSN: 0887-6266
    Keywords: ESR ; mechanoradicals ; PMMA ; drilling apparatus ; computer simulation ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In this study, initially, we tried to obtain the mechanoradicals of PMMA (poly(methyl methacrylate)). For this purpose, we designed a simple drilling apparatus. Using this apparatus, we prepared some PMMA samples at 77 K in vacuum. Later, by using an ESR (electron spin resonance spectrometer), we observed ESR signals for these samples at 77 K. This means that mechanoradicals have been successfully produced by mechanical fracture in PMMA using our drilling apparatus. Secondly, we tried to identify the radicals from these spectra through using theoretical analyses and, some computer simulations have been done by suggesting two different theoretical models for these ESR signals. Finally, by using experimental and theoretical data, we showed that our simple apparatus could be used to obtain mechanoradicals from polymers. Results were seen to be in very good agreement with the literature. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2195-2200, 1997
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    Bidirectional reaction steps in metabolic networks: I. Modeling and simulation of carbon isotope labeling experiments (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 101-117 
    Details
    ISSN: 0006-3592
    Keywords: stationary flux analysis ; metabolite flux balancing ; 13C isotope labeling experiments ; NMR ; metabolic engineering ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The extension of metabolite balancing with carbon labeling experiments, as described by Marx et al. (Biotechnol. Bioeng. 49: 11-29), results in a much more detailed stationary metabolic flux analysis. As opposed to basic metabolite flux balancing alone, this method enables both flux directions of bidirectional reaction steps to be quantitated. However, the mathematical treatment of carbon labeling systems is much more complicated, because it requires the solution of numerous balance equations that are bilinear with respect to fluxes and fractional labeling. In this study, a universal modeling framework is presented for describing the metabolite and carbon atom flux in a metabolic network. Bidirectional reaction steps are extensively treated and their impact on the system's labeling state is investigated. Various kinds of modeling assumptions, as usually made for metabolic fluxes, are expressed by linear constraint equations. A numerical algorithm for the solution of the resulting linear constrained set of nonlinear equations is developed. The numerical stability problems caused by large bidirectional fluxes are solved by a specially developed transformation method. Finally, the simulation of carbon labeling experiments is facilitated by a flexible software tool for network synthesis. An illustrative simulation study on flux identifiability from available flux and labeling measurements in the cyclic pentose phosphate pathway of a recombinant strain of Zymomonas mobilis concludes this contribution. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 101-117, 1997.
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    Lipopeptides with Improved Properties: Structure by NMR, Purification by HPLC and Structure-Activity Relationships of New Isoleucyl-rich Surfactins (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 145-154 
    Details
    ISSN: 1075-2617
    Keywords: biosurfactant ; lipopeptide ; surfactins ; Bacillus subtilis ; NMR ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The biosynthesis of bacterial isoleucyl-rich surfactins was controlled by supplementation of L-isoleucine to the culture medium. Two new variants, the [Ile4,7]- and [Ile2,4,7]surfactins, were thus produced by Bacillus subtilis and their separation was achieved by reverse-phase HPLC. Amino acids of the heptapeptide moiety were analysed by chemical methods, and the lipid moiety was identified to β-hydroxy anteiso pentadecanoic acid by combined GC/MS. Sequences were established on the basis of two-dimensional NMR data. Because conformational parameters issuing from NMR spectra suggested that the cyclic backbone fold was globally conserved in the new variants, structure-activity relationships were discussed in details on the basis of the three-dimensional model of surfactin in solution. Indeed, both variants have increased surface properties compared with that of surfactin, and this improvement is assigned to an increase of the hydrophobicity of the apolar domain favouring micellization. Furthermore, the additional Leu-to-Ile substitution at position 2 in the [Ile2,4,7]surfactin leads to a substantial increase of its affinity for calcium, when compared with that of [Ile4,7]surfactin or surfactin. This effect is assigned, from the model, to an increase in the accessibility of the acidic side chains constituting the calcium binding site. Thus, the propensities of such active lipopeptides for both hydrophobic and electrostatic interactions were improved, further substantiating that they can be rationally designed. © 1997 European Peptide Society and John Wiley & Sons, Ltd
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    3D structure of kaliotoxin: is residue 34 a key for channel selectivity? (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 314-319 
    Details
    ISSN: 1075-2617
    Keywords: kaliotoxin ; NMR ; K+ channel blockers ; scorpion toxin ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kaliotoxin (KTX) is a natural peptide blocker of voltage-dependent K+ channels. The 3D structure of a truncated analogue of KTX (Fernández et al. (1994) Biochemistry 33, 14256-14263) was determined by NMR spectroscopy and showed significant differences from structures established for other related scorpion toxins. A recent publication with the structure of the complete toxin (Aiyar et al. (1995) Neuron 15, 1169-1181) did not confirm these differences. In this communication we report NMR data for KTX at pH 3.0, 5.5 and 7.2 and the 3D structure obtained from data at pH=5.5. Complete KTX displays a folding similar to that of other toxins with an α-helix and a β-sheet linked by two disulphide bonds. The pKa of His 34 is anomalously low (4.7-5.2 depending on the buffer) owing to its interaction with two Lys residues (including the essential Lys 27), the charged N-terminus and the side chain of Met 29. Charged residues are placed symmetrically with respect to an axis that approximately coincides with one of the principal components of the moment of inertia of the toxin. His 34, which occupies a well-defined position between two conserved Cys, is located on the centre of a layer of charged groups. Positively and negatively charged residues are found at the same position in related toxins. It is suggested that electrostatic effects modulate the distances between positive charges in flexible side chains, contributing to the fine tuning of the selectivity toward different channel subclasses and that the approximate coincidence between the moment of inertia and the charge axis facilitate the approach of the toxin to the channel. The very low pKa of His 34 implies that it will be completely unprotonated at physiological pH. © 1997 European Peptide Society and John Wiley & Sons, Ltd.
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    Proton NMR investigation of the local dynamics of PEO in PEO/PMMA blends (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 1095-1105 
    Details
    ISSN: 0887-6266
    Keywords: NMR ; dynamics ; polyethylene oxide (PEO) ; polymethyl methacrylate (PMMA) ; polymer blend ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Longitudinal relaxation of proton magnetisation was used to characterize the molecular motions of PEO chains in compatible PEO (hydrogenated)/PMMA (deuterated) blends. Both the temperature and the PEO concentration, Φ, were varied. A maximum in the spin-lattice relaxation rate was observed and its properties were analyzed as a function of Φ. For Φ ≤ 0.50, the maximum is observed below the glass transition temperature of the blend; this shows that PEO chains dispersed in a matrix of PMMA remain highly mobile on a local scale even below Tg(Φ). A frequency-temperature correspondence procedure, applied to the measurements performed at two Larmor frequencies, 32 and 60 MHz, leads to a characteristic correlation time for PEO molecular motions. Its temperature dependence obeys a WLF free volume relation above the glass transition of the blends. The PEO free volume fraction and its thermal expansion are strongly reduced by the presence of the PMMA chains. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1095-1105, 1997
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    Characterization of mechanically sheared ethylene-propylene copolymers by high resolution NMR (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 1955-1961 
    Details
    ISSN: 0887-6266
    Keywords: NMR ; EPM ; EPDM ; polyolefin ; mechanochemistry ; chain ends ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We report high-resolution solution-state NMR experiments on chain ends generated in ethylene-propylene copolymers by mechanical shearing in an extruder. The use of the higher resolution of the 13C-NMR spectrum, in a two-dimensional 1H-13C chemical shift correlation experiment, has allowed the complete resolution and assignment of the olefinic chain-end region of the 1H-NMR spectrum. Simultaneously, the assignments of the 13C olefinic resonances, previously identified [A. C. Kolbert, J. G. Didier, and L. Xu, Macromolecules, 29, 8591 (1996)] are confirmed. An iterative method for calculating the average molecular weight, based on quantitative measurements of the olefinic 1H-NMR peak intensities is introduced and these results are compared with measurements from 13C-NMR and size exclusion chromatography and correlated to reduced viscosities. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1955-1961, 1997
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    Nanoheterogeneity in PEO/PMMA blends probed by 129Xe-NMR (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 2681-2688 
    Details
    ISSN: 0887-6266
    Keywords: NMR ; 129Xe ; blends ; PEO ; PMMA ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Xenon has been used as a structural probe of solid poly(ethylene oxide)/atactic poly(methyl methacrylate) (PEO/PMMA) blends of concentrations 10/90 to 75/25. 129Xe-NMR spectra at 293 K show significant changes in line width and chemical shift as the blend composition is varied. The 129Xe spectra are interpreted in terms of exchange between amorphous single-phase PEO and PMMA domains. It is shown that a simple two-site exchange model can be used to calculate spectra which fit the experimental data over the whole concentration range. Xe exchange between blend subregions is demonstrated also by a two-dimensional NMR experiment. The PEO/PMMA results are compared to previously published poly(vinylidene fluoride)/PMMA 129Xe spectra. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2681-2688, 1997
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    Polyaniline Microrods (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 7 (1997), S. 149-156 
    Details
    ISSN: 1057-9257
    Keywords: polyaniline ; synthesis ; surface tension effect ; morphology ; SEM ; ESR ; electrical conductivity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Polyaniline (PANI) prepared in water or a water-methanol (1:1) mixed solvent by anodic oxidation of aniline hydrochloride at a potential of 0.8 V (and higher) vs. Ag/AgCl appears to form microrods of almost uniform shape and dimensions: a diameter of 0.7 μm and a length of 2-3 μm or more. A surface point contact Pt or Ir electrode has been used as the working electrode to get a better ordering in the product due to the surface tension effect. The structure observed with a scanning electron microscope (SEM) is complex: the sample is highly porous and looks like a coral reef; the average channel diameter is 1.5 and 2.5 μm for narrow and wide channels respectively. The rods appearing in great number in the sample are surprisingly uniform, particularly with respect to the diameter. The electrical conductivity is of the order of 10-1 S cm-1 for most samples examined. The electron spin resonance (ESR) spectra consist of a strong singlet line (g = 2.0030-2.0039, ΔH =;0.12-0.50 mT); similarly, the infrared (IR) spectra show a strong and broad absorption due to electron excitations and electron-lattice interactions, which we have observed previously for many PANI samples examined in our laboratory. © 1997 John Wiley & Sons, Ltd.
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    An NMR and vibrational study of 5-bromouridine and its base pairing with guanosine and adenosine (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biospectroscopy 3 (1997), S. 241-249 
    Details
    ISSN: 1075-4261
    Keywords: NMR ; vibrational spectroscopy ; 5-bromouridine ; base pairing ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: A multinuclear magnetic resonance and vibrational study on 5-bromouridine and its base pairing with guanosine and adenosine in deuterated dimethyl sulfoxide at different concentrations is reported. A dicarbonylic non-self-associated form is suggested for 5-bromouridine on the basis of the 1H-, 15N-NMR, and Raman data. When guanosine is added in equimolar amounts, a downfield shift of the (N3)H proton of 5-bromouridine and of the (N1)H and NH2 protons of guanosine is observed; these results can be interpreted, according to the Raman ones, considering that only a fraction of guanosine is “wobble base paired” with 5-bromouridine, whereas the remaining part is self-associated. When 5-bromouridine is mixed with adenosine, the proton chemical shift of the aminic NH2 of adenosine increases and the (N3)H iminic of 5-bromouridine moves downfield at a value higher than that observed for the 5-bromouridine-guanosine mixture. This behavior supports the hypothesis that 5-bromouridine interacts more with adenosine than with guanosine, but the results obtained are not able to establish which type of pairing (Watson-Crick or Hoogsteen) is present. Finally, the infrared spectrum of the solid 5-bromouridine: adenosine adduct, for which X-ray measurements of other authors suggested a Hoogsteen pairing, is reported and the observed bands are discussed. © 1997 John Wiley & Sons, Inc. Biospect 3: 241-249, 1997
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    Constrained Refinement Based on NOE and Chemical Shift Information: The Monomer Form of Arginine-Vasopressin-like Insect Factor (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 133-140 
    Details
    ISSN: 1075-2617
    Keywords: NMR ; chemical shift estimation ; restrained refinement ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Via the refinement process of the monomer form of an arginine-vasopressin-like insect factor, the paper analyses the most relevant NMR information to define the solution structure of a flexible peptide. The relative importance of the different NOE constraints is discussed. © 1997 European Peptide Society and John Wiley & Sons, Ltd.
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    The design of a specific ligand of HIV gp120 (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 383-390 
    Details
    ISSN: 1075-2617
    Keywords: CD4 ; gp120 ; NMR ; structure ; peptides ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of CD4 suggested that the C/G38 and C/L44 replacements with the consequent cystine bridge formation are compatible with the native structure of that molecular moiety. As the NQGSF sequence, corresponding to the 39-43 fragment of human CD4 protein, was found to be involved in the HIV gp120 interaction, it has been synthesized in a cyclic form by adding two cysteine residues at the amino and carboxy termini. 1H-NMR studies show that the predominant solution conformation of cyclo-[CNQGSFC] is a type II β-turn centred on the NQGS segment. Structural and dynamic properties of the peptide are also analysed in relation to the in vitro activity. © 1997 European Peptide Society and John Wiley & Sons, Ltd.J. Pep. Sci. 3: 383-390No. of Figures: 7. No. of Tables: 1. No. of References: 33.
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    Structural comparison in solution of a native and retro peptide derived from the third helix of Staphylococcus aureus protein A, domain B: retro peptides, a useful tool for the discrimination of helix stabilization factors dependent on the peptide chain orientation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 299-313 
    Details
    ISSN: 1075-2617
    Keywords: NMR ; retro-enantio ; helix ; macrodipole ; protein A ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A peptide fragment corresponding to the third helix of Staphylococcus Aureus protein A, domain B, was chosen to study the effect of the main-chain direction upon secondary structure formation and stability, applying the retro-enantio concept. For this purpose, two peptides consisting of the native (Ln) and reversed (Lr) sequences were synthesized and their conformational preferences analysed by CD and NMR spectroscopy. A combination of CD and NMR data, such as molar ellipcitity, NOE connectivities, Hα and NH chemical shifts, 3JαN coupling constants and amide temperature coefficients indicated the presence of nascent helices for both Ln and Lr in water, stabilized upon addition of the fluorinated solvents TFE and HFIP. Helix formation and stabilization appeared to be very similar in both normal and retro peptides, despite the unfavourable charge-macrodipole interactions and bad N-capping in the retro peptide. Thus, these helix stabilization factors are not a secondary structure as determined for this specific peptide. In general, the synthesis and confirmational analysis of peptide pairs with opposite main-chain directions, normal and retro peptides, could be useful in the determination of secondary structure stabilization factors dependent on the direction. © 1997 European Peptide Society and John Wiley & Sons, Ltd.
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    Characterization of silane-modified ZrO2 powder surfaces (1997)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 25 (1997), S. 917-923 
    Details
    ISSN: 0142-2421
    Keywords: x-ray photoelectron spectroscopy ; infrared spectroscopy ; NMR ; silane, γ-MPS ; zirconia ; zircon ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Polymerizable organic silane molecules such as 3-(trimethoxysilyl)propylmethacrylate (γ-MPS) have been grafted onto the surface of ZrO2 powders, via hydroxyl groups, to obtain hybrid ‘macromonomers’. A combination of x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and 29Si nuclear magnetic resonance (NMR) spectroscopy have been employed to study the interaction between organic silane molecules and the surface of the ZrO2 powders. The core-level XPS regions, Zr3d, O1s, C1s and Si2p, have been studied to determine the nature of chemical bonding between the organic grafted monomer and inorganic phase and correlated with NMR results. Based upon the results obtained, it is proposed that grafting results in γ-MPS bonded to the ZrO2 powder surface via Zr—O—Si bonds accompanied by interlinkage of γ-MPS molecules through Si—O—Si bonding. © 1997 John Wiley & Sons, Ltd.
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    TPD, XPS and ESR Studies of the Surface Processes Involved in the Oxidation of n-Pentane on a (VO)2P2O7 System (1997)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 25 (1997), S. 667-676 
    Details
    ISSN: 0142-2421
    Keywords: XPS ; ESR ; temperature-programmed desorption ; vanadium phosphate ; selective oxidation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Surface-sensitive techniques such as XPS, temperature-programmed desorption-mass spectrometry (TPD-MS) and electron spin resonance (ESR) have been used to study the effect of O2 treatment on the interaction of n-pentane with the surface of an ‘equilibrated’ (VO)2P2O7 catalyst. The study was carried out by means of TPD studies after the catalyst had been in contact with n-pentane at 613 K in the presence and in the absence of O2 and by comparing the results, depending on whether the sample was subjected or not to O2 pretreatment at 613 K previously, to n-pentane adsorption. The valence state of vanadium and the changes in the short-range order around vanadium at the surface after former pretreatments were studied by XPS and ESR techniques, respectively. It was concluded that no oxygen radicals can be created on this catalyst, thus excluding the possibility that these kinds of radicals are involved in the oxidation process. On the other hand, despite the fact that the valence state of vanadium at the surface is an important variable, surface topology around vanadium centres at the surface of the ‘equilibrated’ (VO)2P2O7 sample clearly influences the interaction of n-pentane with the surface. The short-range order around the vanadium sites does not seem to have much effect on the first steps of interaction of n-pentane on the catalyst, but instead alters the further oxidation processes acting on the molecules resulting from the first steps.© 1997 by John Wiley & Sons, Ltd.
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    Synthesen und Eigenschaften von Tris(perfluoralkyl)arsen- und -antimon(III, V)-VerbindungenProfessor Hans Bürger zum 60. Geburtstag gewidmet (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 623 (1997), S. 1183-1189 
    Details
    ISSN: 0044-2313
    Keywords: Tris(perfluoroalkyl) arsenic and antimony ; tris(pentafluoroethyl) arsenic and antimony(V) halides ; synthesis ; NMR ; mass spectra ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Preparations and Properties of Tris(perfluoroalkyl) Arsenic and Antimony(III, V) CompoundsAs(Rf)3 and Sb(Rf)3 (Rf=C2F5, C4F9, C6F13) are prepared in good yields by the polar reactions of AsCl3 and SbCl3 with bis(perfluoroalkyl) cadmium compounds as colourless liquids or solids. The oxidation of As(C2F5)3 and Sb(C2F5)3 with XeF2 gives the difluorides M(C2F5)3F2 (M=As, Sb). As(C2F5)3Cl2 is prepared by chlorination of As(C2F5)3 in the presence of AlCl3, while Sb(C2F5)3Cl2 is formed in the reaction of Sb(C2F5)3F2 with (CH3)3SiCl. During the reaction of M(C2F5)3F2 with (CH3)3SiBr 19F-NMR spectroscopic evidence is found for M(C2F5)3 Br2. The thermal decompositions of M(C2F5)3F2 mainly yield C4F10 and M(C2F5)F2, while the thermal decompositions of M(C2F5)3Cl2 yield M(C2F5)2Cl and C2F5Cl. The properties and spectroscopic data of the new compounds are described.
    Notes: As(Rf)3 und Sb(Rf)3 (Rf=C2F5, C4F9, C6F13) werden durch Umsetzungen von AsCl3 und SbCl3 mit Bis(perfluoralkyl)cadmium-Verbindungen unter polaren Bedingungen in guten Ausbeuten als farblose Flüssigkeiten bzw. Festkörper dargestellt. Durch Oxidation von As(C2F5)3 und Sb(C2F5)3 mit XeF2 entstehen die Difluoride M(C2F5)3F2 (M=As, Sb). Die Darstellung von As(C2F5)3Cl2 gelingt durch Chlorierung von As(C2F5)3 in Gegenwart von AlCl3; die Darstellung von Sb(C2F5)3Cl2 durch Reaktion von Sb(C2F5)3F2 mit (CH3)3SiCl. Die Dibromide M(C2F5)3Br2 sind nur 19F-NMR-spektroskopisch bei der Reaktion von M(C2F5)3F2 mit (CH3)3SiBr nachweisbar. Bei der thermischen Zersetzung von M(C2F5)3F2 entstehen hauptsächlich C4F10 und M(C2F5)F2, während die thermische Zersetzung von M(C2F5)3Cl2 unter Bildung von M(C2F5)2Cl und C2F5Cl verläuft. Eigenschaften und spektroskopische Daten der neuen Verbindungen werden beschrieben.
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    Synthese, NMR-spektroskopische Charakterisierung und Struktur von Bis(1,2-dimethoxyethan-O,O′)barium-bis[1,3-bis(trimethylsilyl)-2-phenyl-1-aza-3-phosphapropenid] (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 623 (1997), S. 1237-1242 
    Details
    ISSN: 0044-2313
    Keywords: Barium 1-Aza-3-phosphapropenide ; 1,3-Azaphosphaallyl Anion ; NMR ; X-ray Structure Determination ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis, NMR Spectroscopic Characterization and Structure of Bis(1,2-dimethoxyethane-O,O′)barium Bis[1,3-bis(trimethylsilyl)-2-phenyl-1-aza-3-phosphapropenide]Barium-bis[bis(trimethylsilyl)phosphanide] 1 reacts with two equivalents of benzonitrile to give barium bis[1,3-bis(trimethylsilyl)-2-phenyl-1-aza-3-phosphapropenide]; the choice of the solvent determines whether a tris-(tetrahydrofuran)- or a bis(1,2-dimethoxyethane)-complex 2 can be isolated. 2 crystallizes from DME as red cuboids (monoclinic, C2/c, a = 1627.0(3), b = 1836.6(3), c = 1602.5(2) pm; β = 96.071(12)°; V = 4761.7(12); Z = 4; wR2 = 0.0851). The phosphorus atom displays a pyramidal surrounding in contrast to the planar coordination sphere of the nitrogen atom. In addition a twist within the P—C—N skeleton of the heteroallyl anion is observed.
    Notes: Barium-bis[bis(trimethylsilyl)phosphanid] 1 reagiert mit zwei Äquivalenten Benzonitril zu Barium-bis[1,3-bis(trimethylsilyl)-2-phenyl-1-aza-3-phosphapropenid]; durch die Wahl des Lösungsmittels läßt sich entweder der Tris(tetrahydrofuran)- oder der Bis(1,2-dimethoxyethan)-Komplex 2 isolieren. Verbindung 2 kristallisiert aus DME in Form roter Würfel aus (monoklin. C2/c, a = 1627,0(3), b = 1836,6(3), c = 1602,5(2) pm; β = 96,071(12)°; V = 4761,7(12); Z = 4; wR2 = 0,0851). Während die Koordinationssphäre des Stickstoffatoms planar ist, befindet sich das Phosphoratom in einer pyramidalen Umgebung. Zusätzlich beobachtet man im 1-Aza-3-phosphapropenid-Anion eine leichte Verdrillung.
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    Eigenschaften und Reaktionen von Tris(2,6-difluorphenyl)bismut(III)- und Tris(2,6-difluorphenyl)bismut(V)-Verbindungen (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 623 (1997), S. 122-128 
    Details
    ISSN: 0044-2313
    Keywords: tris(2,6-difluorophenyl)bismuth dihalides ; tris(2,6-difluorophenyl)bismuth bis(trifluoromethanesulfonate) ; tris(2,6-difluorophenyl)bismuth bis(trifluoroacetate) ; 2,6-difluorophenyliodine tetrafluoride ; synthesis ; NMR ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Properties and Reactions of Tris(2,6-difluorophenyl)bismuth(III) and Tris(2,6-difluorophenyl)bismuth(V) Derivatives(2,6-F2C6H3)3BiF2 and (2,6-F2C6H3)3BiCl2 are prepared oxidizing (2,6-F2C6H3)3Bi with XeF2 or Cl2 respectively, while direct fluorination effect the oxidation of the aromatic system. The reaction of (2,6-F2C6H3)3BiCl2 With (CH3)3SiCl yields (2,6-F2C6H3)3BiCl2. Attempts to oxidize (2,6-F2C6H3)3Bi with Br2, I2 and ICl give (2,6-F2C6H3)X and BiX′3 (X = Br, I; X′ = Cl, Br, I). The rection of (2,6-F2C6H3)3Bi with IF5 gives BiF3 and (2,6-F2C6H3)IF4. (2,6-F2C6H3)3Bi(OCOCF3)2 and (2,6-F2C6H3)3Bi(OSO2CF3)2 are formed via ligand exchange rection of (2,6-F2C6H3)3BiF2 with (CH3)3SiOR or of (2,6-F2C6H3)3BiCl2 with AgOR (R = COCF3, SO2CF3). The preparations and properties of the new compounds are described. (2,6-F2C6H3)3Sb and (2,6-F2C6H3)2Te are prepared by the transmetalation reactions of (2,6-F2C6H3)3Bi with Sb and Te.
    Notes: (2,6-F2C6H3)3 BiF2und(2,6-F2C6H3)3BiCl2 werden durch Oxidation von (2,6-F2C6H3)3 Bi mit XeF2 bzw. Cl2 dargestellt, während die Direktfluorierung zu einer Oxidation des aromatischen Systems führt, (2,6-F2C6H3)3BiCl2 wird auch durch die Umsetzung von (2,6-F2C6H3)3 BiF2 mit (CH3)3SiCl erhalten. Oxidationsversuche von (2,6-F2C6H3)3Bi mit Br2, I2 und ICl ergeben (2,6-F2C6H3)X und BiX′3 (X = Br, I; X′ = Cl, Br, I). Die Umsetzung von (2,6-F2C6H3)3Bi mit IF5 führt zur Bildung von BiF3 und (2,6-F2C6H3)IF4. (2,6-F2C6H3)3Bi(OCOCF3)2 bzw. (2,6-F2C6H3)3Bi(OSO2CF3)2 werden durch Ligandenaustauschreaktionen von (2,6-F2C6H3)3BiF2 mit (CH3)3SiOR oder von (2,6-F2C6H3)3BiCl2 mit AgOR gebildet (R COCF3, SO2CF3). Die Syntheseverfahren und Eigenschaften der neuen Verbindungen werden beschrieben. Durch Transmetallierungsreaktionen von (2,6-F2C6H3)3Bi mit Te und Sb werden (2,6-F2C6H3)3Sb und (2,6-F2C6H3)2Te dargestellt.
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    Organometallic Complexes with Biological Molecules: VII. Dialkyl- and Trialkyl-tin (IV)[meso-tetra(4-carboxyphenyl)porphinate] Derivatives: Solid-state, Solution-phase Structural Aspects and In Vivo Effects (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 11 (1997), S. 499-511 
    Details
    ISSN: 0268-2605
    Keywords: organotin ; porphyrin ; structures ; Mössbauer ; infrared ; NMR ; biologial activity ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, the structural features and the in vivo biological activity of diorganotin(IV) and triorganotin(IV) derivatives of [meso-tetra(4-carboxyphenyl)porphine] (H4TPPC) are reported. Derivatives with general formula (R2Sn)2TPPC and (R3Sn)4TPPC (R=Me, Bu, and Ph) were obtained, and the main information extracted from the infrared and Mössbauer spectral data, in the solid state, was in favor of the occurrence of five-coordinated tin(IV) atoms, in a polymeric trigonal-bipyramidal configuration, attained through two differently coordinated, ester-type and chelating respectively, carboxylate anions in [R2Sn]2TPPC, while in [Alk3Sn]4TPPC five-coordination of the tin(IV) atom is reached through bridging carboxylate groups.1H and 13C NMR spectra, in DMSO-d6 or CDCl3 suggested that the soluble derivatives, at room temperature or at 342 K, were present in solution as simple monomers.The interactions of (trimethyltin)4[meso-tetra(4-carboxyphenyl)porphinate] (TMTPPC) and (tributyltin)4[meso-tetra(4-carboxyphenyl)porphinate] (TBTPPC) with Bluescript KS(+) plasmid and cultured 3T3 fibroblasts were studied.Both compounds have a clear inhibitory effect on the growth of cultured mouse embryonal fibroblasts (NIH-3T3), TBTPPC being much more active. No evidence was found, however, for DNA cleavage by the compounds at molar ratios as high as 1:10 (TMTPPC, TBTPPC/DNA base pairs).According to our observations, the cytotoxicity of TBTPPC and TMTPPC does not seem to be based on direct interaction with DNA. © 1997 John Wiley & Sons, Ltd.
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    Organometallic Complexes with Biological Molecules: VIII. Synthesis, Solid State and in vivo Investigation of Triorganotin(IV) Derivatives of L-Homocysteic Acid (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 11 (1997), S. 601-616 
    Details
    ISSN: 0268-2605
    Keywords: triorganotin(IV) ; L-homocysteic acid ; infrared ; Mössbauer ; NMR ; sea urchin ; Paracentrotus lividus (Echinodermata) ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several new triorganotin(IV) derivatives of L-homocysteic acid (L-HCAH) with formula R3Sn(L-HCA) (R=Me, nBu, Ph) have been synthesized. Their solid-state configurations were determined by IR and Mössbauer spectroscopy. The tin(IV) atom is five-coordinated in all the complexes, with the L-homocysteic acid behaving as a monoanionic bidentate ligand coordinating the tin(IV) atom through a chelating or bridging carboxylate group. The sulfonate (SO3-) and NH3+ groups of L-homocysteic acid maintain their free acid configuration and hence do not participate to the coordination of the tin(IV) atom. Coordination hypotheses have been checked through the correlation between the Mössbauer parameter isomer shift, δ, and partial atomic charge on the tin atoms, QSn, performed, for all the new organotin(IV) compounds, on the basis of an equalization procedure applied to idealized trigonal-bipyramidal structures for R3Sn(L-HCA).1H and 13C NMR spectra of the complexes show that pentacoordination of the tin atom, with R groups in the equatorial plane of a trigonal bipyramid, is retained in DMSO solution. The NMR data confirm also that the uncoordinated NH3+ group of the ligand is still present in solution.Results gathered after exposure of two- to four-cell embryos of the sea urchin Paracentrotus lividus (Echinodermata) to the triorganotin(IV) L-homocysteate derivatives as well as to the parent triorganotin(IV) chlorides document cytotoxicity of the complexes, while free L-homocysteic acid exerts no significant toxic activity. The trimethyltin(IV) L-homocysteate derivative seems to exert a lower cytotoxicity than the tributyl- and triphenyl-tin(IV) ones. Different structural lesions have been identified by comparative analysis of mitotic chromosomes from untreated embryos (negative controls) and embryos treated with triorganotin(IV) L-homocysteate derivatives, such as (1) suppression of the stretch among sister chromatids at the beginning of anaphase stage; (2) deeply stained zones mainly located at the telomeric regions of chromosomes; (3) arm breakages; and (4) chromosome bridges among daughter chromosomes at anaphase stage. A colchicine-like effect of triorganotin(IV) L-homocysteate derivatives was observed. © 1997 John Wiley & Sons, Ltd.
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    The Effect of Organotin Compounds on the Permeability of Model Biological Membranes (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 11 (1997), S. 369-379 
    Details
    ISSN: 0268-2605
    Keywords: efflux ; liposomes ; dimethylarsinic acid ; membrane modification ; egg phosphatidylcholine ; bilayer ; tributyltin chloride ; monobutyltin trichloride ; facilitated diffusion ; NMR ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The efflux of dimethylarsinic acid (DMA) from liposomes formed from egg phosphatidylcholine (EPC) is increased when tributyltin chloride (TBT) is added to the extraliposomal compartment; however the addition of monobutyltin trichloride (MBT) slows down the efflux. When the liposomes are prepared from EPC and organotin compounds, different mechanisms for DMA efflux seem to operate: TBT-EPC liposomes show a mixture of facilitated and passive diffusion; MBT-EPC liposomes show only passive diffusion. The facilitated diffusion of DMA- seems to be stopped by the addition of TBT to the extraliposomal compartment. © 1997 by John Wiley & Sons, Ltd.
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    Organometallic complexes with biological molecules. IX. Diorgano- and triorgano-tin(IV)[meso-tetra (4-sulfonatophenyl)porphinate] derivatives: solid-state and solution-phase structural aspects and in vivo effects (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 11 (1997), S. 707-719 
    Details
    ISSN: 0268-2605
    Keywords: organotin(IV) ; porphine ; Mössbauer ; NMR ; development ; Ascidiaceae ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Diorgano- and triorgano-tin(IV) derivatives of meso-tetra(4-sulfonatophenyl)porphine (H4TPPS) with general formula (R2Sn)2TPPS and (R3Sn)4TPPS (TPPS4-=[meso-tetra(4-sulfonatophenyl)porphinate]4-, R=Me, Bu, Ph) have been obtained and their solid-state configuration inferred on the basis of IR and Mössbauer spectroscopy, while solution-phase studies have been carried out by 1H and 13C NMR in DMSO-d6, together with determination of the in vivo cytotoxicity of the new derivatives towards embryonic development of Ciona intestinalis. In particular, octahedral and trigonal-bipyramidal eq-R3Sn polymeric configurations are proposed, in the solid state, respectively for (R2Sn)2TPPS and (R3Sn)4TPPS complexes, with the arylsulfonate groups behaving as monoanionic bidentate bridging ligands.The 1H and 13C NMR data lead to the conclusion that the metal-to-ligand ratio (2:1 or 4:1), binding site (the sulfonato-group oxygens), and the coordination polyhedron around the metal (trans-octahedral or trigonal-bipyramidal) found in the solid state are preserved in solution. © 1997 John Wiley & Sons, Ltd.
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    Synthesis, characterization and cytotoxic activity of complexes of diorganotin(IV) halides with N-methyl-2,2′-bisimidazole (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 11 (1997), S. 963-968 
    Details
    ISSN: 0268-2605
    Keywords: diorganotin(IV) halides ; N-methyl-2,2′-bisimidazole ; Mössbauer ; IR ; NMR ; cytostatic activity ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The compounds [SnR2X2(MBIm)] (MBIm=N-methyl-2,2′-bisimidazole; R=Me, Et, Bu, Ph; X=Cl or Br) have been synthesized and characterized by IR, Raman, Mössbauer and NMR spectroscopy, and their capacity to inhibit tumour cell division has been assayed. Measurements of conductivity in acetonitrile show the adducts to behave as non-ionogens in this solvent. The IR, Raman and Mössbauer data suggest that all the complexes have analogous pseudo-octahedral coordination geometries, with the R groups trans and MBIm bidentate. The 1H NMR spectra show the MBIm ligand to be partially dissociated in CDCl3. The most active compounds against the established cell line KB were the butyl derivatives. © 1997 John Wiley & Sons, Ltd.
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    Mono-organotin(IV) and tin(IV) derivatives of 2-mercaptopyridine and 2-mercaptopyrimidine: X-ray structures of methyl-tris(2-pyridinethiolato)tin(IV) and phenyl-tris(2-pyridinethiolato)tin(IV)·1.5CHCl3 (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 11 (1997), S. 869-888 
    Details
    ISSN: 0268-2605
    Keywords: organotin ; pyridine-2-thiolate complexes ; pyrimidine-2-thiolate complexes ; crystal structure ; Mössbauer ; IR ; NMR ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mono-organotin(IV) and tin(IV) derivatives of 2-mercaptopyridine (HSPy) and 2-mercaptopyrimidine (HSPym), RSnL3 (R=Me, n-Bu, Ph; L=SPy, SPym; R=Bz=benzyl, o-ClBz, o-ClC6H4, p-ClC6H4, o-tolyl, p-tolyl; L=SPy), RSnClL2 (R=Me, n-Bu, Ph; L=SPy, SPym), RSnCl2L (R=Me, n-Bu; L=SPy, SPym) and SnCl4-nLn (L=SPy, SPym; n=2, 4) were obtained from RSnCl3 or SnCl4 and NaL or by neutralization (R=Ph, p-tolyl; L=SPy, SPym). RSnClL2 and RSnCl2L were better prepared by comproportionation of RSnCl3 and RSnL3.MeSn(SPy)3 and PhSn(SPy)3·1.5CHCl3 crystals, as determined by single-crystal X-ray diffraction, are monoclinic. In the discrete monomeric RSn(SPy)3 units, three bidentate SPy ligands together with R form a distorted pentagonal bipyramid around tin. One S and the C(R) atom are in the axial positions. Two S atoms and three N atoms form the pentagonal plane.From 119Sn Mössbauer and IR data, analogous structures are inferred for the other solid RSnL3 compounds, except for R=Bz, o-ClBz, o-ClC6H4 and o-tolyl, in which tin would be hexacoordinated. In the compounds RSnClL2 and RSnCl2L, tin is at the center of an octahedron or a trigonal bipyramid, respectively. For Sn(SPym)4 and SnCl2(SPym)2, the same type of octahedral structure as was previously found for Sn(SPy)4·HSPy and SnCl2(SPy)2 is proposed.According to IR and 1H, 13C and 119Sn NMR data, the solid-state molecular structures are retained in chloroform and dimethyl sulfoxide solution. © 1997 John Wiley & Sons, Ltd.
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    Aliphatic-aromatic poly(ether amide)s containing oxyethylene units. Synthesis and characterization (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 659-667 
    Details
    ISSN: 0887-624X
    Keywords: condensation monomers ; amide-ether copolymers ; solution and interfacial polycondensation ; NMR ; GPC ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and characterization of aromatic polyamides containing oxyethylene units is reported, and the differences observed in polycondensation yields, molecular weights, and molecular weight distributions, as a function of the method of synthesis, are discussed. Four diamines containing oxyethylene units and aromatic rings, meta and para oriented, and their corresponding hydrochlorides were prepared as condensation monomers to be combined with isophthaloyl chloride (IPC) and terephthaloyl chloride (TPC). High molecular weight polyamides were obtained by interfacial and low-temperature solution methods. Values of (OVERLINE)M(/OVERLINE)n up to 6 × 104 g/mol and (OVERLINE)M(/OVERLINE)w up to 2 × 105 g/mol could be measured by gel permeation chromatography using aromatic polyamide standards, and values of (OVERLINE)M(/OVERLINE)n up to 2 × 105 g/mol and (OVERLINE)M(/OVERLINE)w up to 5 × 105 g/mol by using polystyrene standards. © 1996 John Wiley & Sons, Inc.
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    Radical polymerization of vinyl monomers initiated by a mono-captodatively substituted ethane (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 1945-1949 
    Details
    ISSN: 0887-624X
    Keywords: radical polymerization ; captodative ; initiator ; block copolymerization ; primary radical termination ; ESR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Homopolymerization of styrene and methyl methacrylate was carried out at 60-130°C in the presence of a mono-captodatively (cd) substituted ethane bearing nitrile and ethylsulfenyl substituents on the same carbon atom. It was found that the cd-ethane accelerated both styrene and methyl methacrylate polymerizations with no induction period, but the polymerization mode of methyl methacrylate was different from that of styrene. The polymerization rate of styrene was proportional to the 0.46th power of the cd-ethane concentration. However, the cd-ethane produced a reversible radical termination in the case of methyl methacrylate. The mechanism of both polymerizations is discussed in terms of the kinetic and ESR data. © 1996 John Wiley & Sons, Inc.
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    An investigation of radiation-induced structural changes in nitrile rubber (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 2439-2454 
    Details
    ISSN: 0887-624X
    Keywords: radiation ; nitrile rubber ; NMR ; ESR ; radicals ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism of radiation-induced structural changes in nitrile rubber with different acrylonitrile contents were investigated by ESR, NMR, and FTIR. To investigate new structures solid-state NMR methods had to be used due to crosslinking of the irradiated rubbers, and higher probe temperatures were used to obtain better resolution. The radicals generated on the acrylonitrile groups were found to abstract hydrogen from the adjacent butadiene units resulting in the formation of allylic radicals. These allylic radicals reacted to form intermolecular crosslinks and cyclisation. Cyclisation of the butadiene units were found to occur in the initial stages of the irradiation. Radiation yields of radicals increased with acrylonitrile content from 1.42, 1.58, to 2.42 for 18, 30, and 45% acrylonitrile rubbers. The radiation yields for intermolecular crosslinking were higher in rubbers with higher acrylonitrile contents, giving G values of 17.8, 21.3, and 24.5 for 18, 30, and 45% acrylonitrile rubbers, respectively. However, the crosslink clustering was found to be less in the rubbers with a higher acrylonitrile content. © 1996 John Wiley & Sons, Inc.
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    End group chemistry of fluoro-oligomers: Highly selective syntheses of diepoxy, diallyl, and tetraol derivatives (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 3263-3275 
    Details
    ISSN: 0887-624X
    Keywords: end group chemistry ; chemical modification ; fluoropolyether ; oligomer ; allyl ; epoxide ; polyol ; tetraol ; oxidation ; etherification ; NMR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Different synthetic methods for the preparation of polyfunctional fluorinated oligomers were explored and the results compared. Fluoropolyether macromonomers bearing epoxy, allyl, and polyhydroxy end groups were synthesized and spectroscopically characterized. For obtaining a polyol (namely tetraol) functionality, a highly selective route was the reaction of the fluoropolyether macrodiol ZDOL with allylic halides and subsequent oxidation reaction at the C=C double bond by means of peroxyacids. This approach made it possible to obtain a segmented structure RH-RF-RH in which the molecular body RF consisted of a perfluoropolyether block endcapped by two hydrogenated segments RH, where RH = - CH2OCH2CH(OH)CH2OH. Unlike other more conventional syntheses, which always produce byproducts and higher molecular weight species such as RH-(RF-RH)n-RF-RH or RH-RF-(RH)n-, the described method offers high yields and selectivity. The fluoropolyether polyfunctional derivatives offer the possibility to prepare a variety of highly crosslinked fluorinated materials and, owing to their well defined regularly segmented structures, they also constitute interesting models for the understanding of basic structure-property relations of fluoro-oligomers and their copolymers. © 1996 John Wiley & Sons, Inc.
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    Mechanism of radiation degradation of polyisobutylene (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 971-984 
    Details
    ISSN: 0887-624X
    Keywords: radiation ; polyisobutylene ; NMR ; GC/MS ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: GC, GC/MS, GPC, and Solution NMR spectra were used to study the γ radiolysis of polyisobutylene (PIB) in vacuum to different total doses (0-900 kGy) and at different temperatures (77-423 K). NMR spectra show a large number of new resonances with relatively narrow line widths, and a variety of NMR techniques have been employed to determine and quantify the structures associated with these new resonances. Chemical shift assignments were made by comparison with those for small molecule model compounds and predictions based upon calculations according to several different schemes. Chain-end structures have been proposed that account well for the majority of the new resonances, all being the result of an initial chain scission reaction initiated by the radiation. These assignments support some previous proposals for the mechanism of radiation degradation of polyisobutylene and exclude others. For example, NMR provides no evidence for the formation of ethyl chain ends and some of the main chain unsaturated structures previously proposed. NMR also indicate that at higher doses the chain end products formed during initial stages undergo secondary reactions. GC/MS data show the formation of oligomers during irradiation, which may be due to a backbitting mechanism. © 1996 John Wiley & Sons, Inc.
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    EPR Study of the Radical Ions of Aryl-Substituted Propellanes (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1533-1539 
    Details
    ISSN: 0947-3440
    Keywords: ESR ; Radical cations ; Radical anions ; Propellanes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The radical anions and the radical cations of 1-3 in which three π systems are connected in three dimensions by a strained propellane spacer were studied by ESR/ENDOR/TRIPLE spectroscopy. The hyperfine data of acenaphthene (4) are compared with those of the fused π systems 5-10. In the relatively persistent radical anions of 1-3, the spin is mainly confined to the two naphthalene moieties. Whereas the radical cation of 2 resembles a naphthalene trimer, the radical cations of intact 1 and 3 cannot be detected. The ESR spectra recorded upon one-electron oxidation of 1 and 3 are assigned to the radical cations of 9 and 10, respectively, formed by the loss of one naphthalene moiety from the parent molecules.
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    A friction factor analysis of the coupling between polymer/solvent self- and mutual-diffusion: Polystyrene/toluene (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 2759-2766 
    Details
    ISSN: 0887-6266
    Keywords: self-diffusion ; mutual-diffusion ; solution thermodynamics ; friction coefficients ; polystyrene ; toluene ; NMR ; forced rayleigh scattering ; photon correlation spectroscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Bearman statistical mechanical theory, which couples the mutual-diffusion and self-diffusion coefficients via friction factors, has been applied to polystyrene/toluene solutions with polystyrene molecular weights of 18 kDa and 900 kDa. Toluene and polystyrene self-diffusion coefficients, obtained from the literature and measured here, along with polystyrene/toluene binary mutual-diffusion coefficients and thermodynamic data, were employed to independently calculate the three friction coefficients (ζ12, ζ11, and ζ22) required to describe transport within binary solutions. Results reveal that the frequently used geometric mean approximation (GMA) for relating the friction coefficients consistently underestimates ζ22 and worsens with increasing polymer molecular weight. The GMA is found to be appreciably more accurate than the arithmetic mean approximation. A formalism recently proposed by Vrentas et al. has also been evaluated for this system and is found to describe the concentration dependence of ζ11 very well. The Vrentas model, therefore, can accurately predict mutual-diffusion coefficients from solvent self-diffusion coefficients for polystyrene/toluene solutions. © 1996 John Wiley & Sons, Inc.
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    The Use of Proton Chemical Shifts to Define the Solution Structure of a Dimeric Peptide (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 2 (1996), S. 233-239 
    Details
    ISSN: 1075-2617
    Keywords: NMR ; chemical shift estimation ; restrained refinement ; Chemistry ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For flexible peptides, nuclear Overhauser Effects (NOE) experiments do not provide enough information to ensure a correct definition of their solution structure. The use of distance constraints, derived from the knowledge of proton chemical shifts, is developed to restrict the number of possible conformations. In the case of flexible molecules, randomization appears as an important factor of the correct estimation of the chemical shifts from the 3D structure. The refinement of the solution structure of the highly flexible AVP-like parallel dimer is described to illustrate this process.
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    Polymer characterization and gas permeability of poly(1-trimethylsilyl-1-propyne) [PTMSP], poly(1-phenyl-1-propyne) [PPP], and PTMSP/PPP blends (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 2209-2222 
    Details
    ISSN: 0887-6266
    Keywords: poly(1-trimethylsilyl-1-propyne) ; poly(1-phenyl-1-propyne) ; blends ; gas and vapor transport ; NMR ; Maxwell model ; Bruggeman model ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Pure gas and hydrocarbon vapor transport properties of blends of two glassy, polyacetylene-based polymers, poly(1-trimethylsilyl-1-propyne) [PTMSP] and poly(1-phenyl-1-propyne) [PPP], have been determined. Solid-state CP/MAS NMR proton rotating frame relaxation times were determined in the pure polymers and the blends. NMR studies show that PTMSP and PPP form strongly phase-separated blends. The permeabilities of the pure polymers and each blend were determined with hydrogen, nitrogen, oxygen, carbon dioxide, and n-butane. PTMSP exhibits unusual gas and vapor transport properties which result from its extremely high free volume. PTMSP is more permeable to large organic vapors, such as n-butane, than to small, permanent gases, such as hydrogen. PPP exhibits gas permeation characteristics of conventional low free volume glassy polymers; PPP is more permeable to hydrogen than to n-butane. In PTMSP/PPP blends, both n-butane permeability and n-butane/hydrogen selectivity increase as the PTMSP content of the blends increases. © 1996 John Wiley & Sons, Inc.
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    Mapping of motional heterogeneity in organic-inorganic nanocomposite gels (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 2533-2542 
    Details
    ISSN: 0887-6266
    Keywords: organic-inorganic nanocomposites ; sol-gel ; poly(ethyleneoxide) ; EPR ; NMR ; molecular and macromolecular dynamics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Organic-inorganic nanocomposite gels comprising poly(ethyleneoxide) chains grafted between silica particles have been studied by electron paramagnetic and nuclear magnetic resonances. Motional heterogeneity has been investigated as a function of gelation and drying by paramagnetic probes dissolved in the organic phase or grafted onto the inorganic nodes. The organic phase exhibits marked variations in dynamic behavior with the liquid-like mobility of the polymer chains strongly hindered at the silica nodes. The conclusions of the EPR study are confirmed by liquid- and solid-state carbon-13 NMR measurements. © 1996 John Wiley & Sons, Inc.
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    Microstructure of copoly(3-hydroxyalkanoates) produced in the anaerobic-aerobic activated sludge process (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 39 (1996), S. 183-189 
    Details
    ISSN: 0959-8103
    Keywords: polyhydroxyalkanoate ; copolyester ; microstructure ; NMR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The sequence structures of bacterially synthesized copoly(3-hydroxyalkanoates), isolated from the sludge developed in the anaerobic-aerobic waste-water treatment process containing propionate as a carbon source, were analysed by 13C NMR spectroscopy. These copolyesters were composed of four different monomer units, 3-hydroxybutyrate, 3-hydroxyvalerate, 3-hydroxy-2-methylbutyrate and 3-hydroxy-2-methylvalerate. By using water/acetone mixed solvent, one of the copolyester samples was fractionated into fractions by differences in average molecular weights as well as in monomer compositions. The carbonyl carbon resonances, split due to differences in diad sequences, were analysed on the basis of Bernoullian statistics. It is suggested that these copolyesters were mixtures of random copolymers with different monomer compositions.
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    Proton NMR studies of molecular-level mobility in vulcanised and epoxidised natural rubber (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 40 (1996), S. 63-71 
    Details
    ISSN: 0959-8103
    Keywords: NMR ; relaxation ; rubber ; vulcanisation ; epoxidisation ; additives ; mobility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Proton spin-lattice relaxations in the laboratory and rotating frames, together with transverse relaxation (free induction decay), have been measured for natural and epoxidised rubber, plus a series of vulcanised samples. The data have been analysed by fitting procedures to give characteristic times which are discussed in terms of the mobility of the various parts of the samples, and of their compositions (including the effects of paraffin wax and oil additives). Interpretation has been aided by recording free induction decays following a period of spin-locking. Carbon-13 magic-angle spinning spectra have also been measured.
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    New thermostable systems: structure/property relationships of nadic terminated telechelic fluorine polyimides (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 41 (1996), S. 135-149 
    Details
    ISSN: 0959-8103
    Keywords: telechelic polyimides ; nadimide ; endo/exo isomerization ; NMR ; HPLC ; thermomechanical properties ; α and β transitions ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polyimides were synthesized by polycondensation of nadic anhydride monoester (NE), hexafluoroisopropylidene-2,2-bis (phthalic acid anhydride) (6HFDA) and Cardo diamine in aprotic/polar medium. After examining the microstructure and the composition of systems with a polymerization index n̄ = 2.075 and 5.18 by high performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) spectroscopy (1H and 13C), their thermomechanical properties were investigated. The rheology curves obtained in the temperature range 50-400°C showed the presence of an α transition (glass transition temperature Tg) and a sub-glass β transition. The temperature of the maximum of the loss modulus G″ of these two transitions varied in the domain of molar mass M̄n studied.The effect of endo/exo isomerization of the nadimide extremities on the values of the glass transition temperature has also been shown. When the percentage of exo isomer of a given polymer increased, the glass transition temperature Tg increased by 50°C.
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    δ-Selective Opioid Peptides Containing a Single Aromatic Residue in the Message Domain: An NMR Conformational Analysis (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 2 (1996), S. 290-308 
    Details
    ISSN: 1075-2617
    Keywords: opioid peptides ; selectivity ; antagonism ; conformation ; NMR ; Chemistry ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sequence of deltorphin I, a δ-selective opioid agonist, has been systematically modified by inserting conformationally constrained Cα,α disubstituted apolar residues in the third position. As expected, substitution of Phe with Ac6c, Ac5c and Ac3c yields analogues with decreasing but sizeable affinity. Surprisingly, substitution with Aib yields an analogue with almost the same binding affinity of the parent compound but with a greatly increased selectivity. This is the first case of a potent and very selective opioid peptide containing a single aromatic residue in the message domain, that is, only Tyr1. Here we report a detailed conformational analysis of [Aib3]deltorphin I and [Ac6c3]deltorphin I in DMSO at room temperature and in a DMSO/water cryomixture at low temperature, based on NMR spectroscopy and energy calculations. The peptides are highly structured in both solvents, as indicated by the exceptional finding of a nearly zero temperature coefficient of Val5 NH resonance. NMR data cannot be explained on the basis of a single structure but it was possible to interpret all NMR data on the basis of a few structural families. The conformational averaging was analysed by means of an original computer program that yields qualitative and quantitative composition of the mixture. Comparison of the preferred solution conformations with two rigid δ-selective agonists shows that the shapes of [Aib3]deltorphin I and [Ac6c3]deltorphin I are consistent with those of rigid agonists and that the message domain of opioid peptides can be defined only in conformational terms.
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    Elucidation of the structure of constrained bicyclopeptides in solution by two-dimensional cross-relaxation spectroscopy: Amatoxin analogues (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 2 (1996), S. 3-13 
    Details
    ISSN: 1075-2617
    Keywords: Structure of amatoxin analogues ; constrained bicyclopeptides ; NMR ; molecular dynamics ; Chemistry ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The evaluation of peptide structures in solution is made feasible by the combined use of two-dimensional NMR in the laboratory (NOESY) and rotating frames (ROESY), and by the use of molecular dynamics calculations. The present paper describes how both the NMR method and molecular dynamics calculations were applied to very rigid synthetic bicyclic peptides that are analogues of natural amatoxins. The NMR theory, which allows the estimate of interatomic distances between interacting nuclei, is briefly discussed. The experimental data were compared with those of known solid-state structures. Three amatoxin analogues have been examined. Of these, one is biologically active (S-deoxo γ[R] OH-Ile3-amaninamide) and its structure in the solid state has recently been worked out. The second and third analogues (S-deoxo-Ile3 -Ala5-amaninamide and S-deoxo-D-Ile3 -amaninamide, respectively) are inactive and their solid-state structures are unknown. The data presented confirm the authors' previous hypothesis that lack of biological activity of S-deoxo-Ile3-Ala5- amaninamide is due to the masking of the tryptophan ring by the methyl group of L-Ala and not to massive conformational changes of the analogue.
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    Malolactic fermentation by engineered Saccharomyces cerevisiae as compared with engineered Schizosaccharomyces pombe (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 12 (1996), S. 215-225 
    Details
    ISSN: 0749-503X
    Keywords: Saccharomyces cerevisiae ; Schizosaccharomyces pombe ; Lactococcus lactis ; malolactic enzyme ; malolactic fermentation ; heterologous expression ; NMR ; Life Sciences ; Life Sciences (general)
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The ability of yeast strains to perform both alcoholic and malolactic fermentation in winemaking was studied with a view to achieving a better control of malolactic fermentation in enology. The malolactic gene of Lactococcus lactis (mleS) was expressed in Saccharomyces cerevisiae and Schizosaccharomyces pombe. The heterologous protein is expressed at a high level in cell extracts of a S. cerevisiae strain expressing the gene mleS under the control of the alcohol dehydrogenase (ADH1) promoter on a multicopy plasmid. Malolactic enzyme specific activity is three times higher than in L. lactis extracts. Saccharomyces cerevisiae expressing the malolactic enzyme produces significant amounts of l-lactate during fermentation on glucose-rich medium in the presence of malic acid. Isotopic filiation was used to demonstrate that 75% of the l-lactate produced originates from endogenous l-malate and 25% from exogenous l-malate. Moreover, although a small amount of exogenous l-malate was degraded by S. cerevisiae transformed or not by mleS, all the exogenous degraded l-malate was converted into l-lactate via a malolactic reaction in the recombinant strain, providing evidence for very efficient competition of malolactic enzyme with the endogenous malic acid pathways. These results indicate that the sole limiting step for S. cerevisiae in achieving malolactic fermentation is in malate transport. This was confirmed using a different model, S. pombe, which efficiently degrades l-malate. Total malolactic fermentation was obtained in this strain, with most of the l-malate converted into l-lactate and CO2. Moreover, l-malate was used preferentially by the malolactic enzyme in this strain also.
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    Synthese der Stannatetraphospholane (tBuP)4SnR2 (R = tBu, nBu, C6H5) und (tBuP)4Sn(Cl)nBu Molekül- und Kristallstruktur von (tBuP)4Sn(tBu)2Professor Ekkehard Fluck zum 65. Geburtstag gewidmet (1996)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 622 (1996), S. 1167-1172 
    Details
    ISSN: 0044-2313
    Keywords: Phosphorus tin heterocycles ; syntheses ; crystal structure ; NMR ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis of the Stannatetraphospholanes (tBuP)4SnR2 (R = tBu, nBu, C6H5) and (tBuP)4Sn(Cl)nBu Molecular and Crystal Structure of (tBuP)4Sn(tBu)2The reaction of the diphosphide K2[tBuP-(tBuP)2-PtBu] 4 with the halogenostannanes (tBu)2SnCl2, (nBu)2SnCl2, (C6H5)2SnCl2 or nBuSnCl3 in a molar ratio of 1 : 1 leads via a [4 + 1]-cyclocondensation reaction to the stannatetraphospholanes (tBuP)4SnR2 3 b-3 d and (tBuP)4Sn(Cl)nBu 3 e, respectively, with the binary 5-membered P4Sn ring system. 3 b was characterized by a single crystal structure analysis; the 5-membered ring exists in a planar conformation. The compounds 3 b-3 e were identified by NMR and also by mass spectroscopy; the 31P{1H}-NMR spectra of 3 b-3 d showed an AA′MM′ (AA′MM′X), 3 e on the other hand an ABCD (ABCDX) spin system.
    Notes: Bei der Reaktion zwischen dem Diphosphid K2[tBuP-(tBuP)2-PtBu] 4 und den Halogenstannanen (tBu)2SnCl2, (nBu)2SnCl2, (C6H5)2SnCl2 bzw. nBuSnCl3 im Molverhältnis 1 : 1 findet eine [4 + 1]-Cyclokondensationsreaktion statt, bei der die Stannatetraphospholane (tBuP)4SnR2 3b-3d bzw. (tBuP)4Sn(Cl)nBu 3 e mit dem binären Fünfringgerüst P4Sn gebildet werden. Von 3 b wurde eine Einkristallstrukturanalyse durchgeführt; das Fünfringgerüst zeigt eine planare Konformation. Die Verbindungen 3 b-3 e wurden Massen- und NMR-spektroskopisch charakterisiert; 3 b-3 d liefern im 31P{1H}-NMR-Spektrum ein AA′MM′-(AA′MM′X)-, 3 e dagegen ein ABCD- (ABCDX)-Spinsystem.
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    1,2-Bis(dimethylamino)-3,4,5-triphenyl-3,4,5-triphospha-1,2-diborolan und 1,2-Bis(dimethylamino)-3,4,5,6-tetra-tbutyl-3,4,5,6-tetraphospha-1,2-diborin: Synthese und Struktur sowie Berechnungen zur MolekülstrukturProfessor Hans-Georg von Schnering zum 65. Geburtstage gewidmet (1996)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 622 (1996), S. 1462-1470 
    Details
    ISSN: 0044-2313
    Keywords: 1,2-Bis(dimethylamino)-3,4,5-triphenyl-3,4,5-triphospha-1,2-diborolane ; 1,2-bis(dimethylamino)-3,4,5,6-tetra-tbutyl-3,4,5,6-tetraphospha-1,2-diborine ; preparation ; NMR ; molecular structures ; ab initio calculations ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: 1,2-Bis(dimethylamino)-3,4,5-triphenyl-3,4,5-triphospha-1,2-diborolane and 1,2-Bis(dimethylamino)-3,4,5,6-tetra-tbutyl-3,4,5,6-tetraphospha-1,2-diborine: Synthesis and Structure as well as Calculations on the Molecular StructureThe diphosphides K2[(C6H5)P—(C6H5)P—P(C6H5)], 4 or K2[(tBuP)—(tBuP)2—P(tBu)], 5, react with (ClBNMe2)2 to form the binary 5-membered ring system 1,2-bis(dimethylamino)-3,4,5-triphenyl-3,4,5-triphospha-1,2-diborolane (C6H5P)3(BNMe2)2, 2a, and the 6-membered ring system 1,2-bis(dimethylamino)-3,4,5,6-tetra-tbutyl-3,4,5,6-tetraphospha-1,2-diborine, (tBuP)4(BNMe2)2, 3a, respectively. 2a and 3a could be obtained in a pure form and characterized NMR spectroscopically and by X-ray structure analyses. The two ring systems are folded; 2a exists in the „envelope“- 3a in the „boat“-conformation. Ab initio computations for 3,4,5-triphospha-1,2-diborolane M5 show that the global minimum is characterized by one B—P double bond. The parent compound geometry M6 is characterized by transannular bonding in the PH—BH—BH—PH moiety which differs in character from those in the four- and five-membered rings (BH)2(PH)2 and (BH)2(PH)3 M5 d, respectively. Explicit calculation of the influence of amino substituents on boron improved agreement of the bond length between computed and X-ray data.
    Notes: Die Diphosphide K2[(C6H5)P—(C6H5)P—P (C6H5)], 4, bzw. K2[(tBuP)—(tBuP)2—P(tBu)], 5, reagieren mit (ClBNMe2)2 zu dem binären Fünfringsystem 1,2-Bis(dimethylamino)-3,4,5-triphenyl-3,4,5-triphospha-1,2-diborolan (C6H5P)3(BNMe2)2, 2a, bzw. dem Sechsringsystem 1,2-Bis(dimethylamino)-3,4,5,6-tetra-tbutyl-3,4,5,6-tetraphospha-1,2-diborin, (tBuP)4(BNMe2)2, 3a. 2a und 3a konnten in reiner Form isoliert, NMR-spektroskopisch und durch Röntgenstrukturanalysen charakterisiert werden. Beide Ringsysteme sind gefaltet; 2a zeigt eine „envelope“- 3a eine „Wannen“-Konformation.Ab initio Berechnungen an 3,4,5-Triphospha-1,2-diborolan M5 zeigen, daß im globalen Minimum eine B—P-Doppelbindung mit annähernd planarem σ3-Phosphor vorliegt. Die Geometrie der Stammverbindung des Sechsringes M6 weist „durch-den-Ring“-Bindung in der PH—BH—BH—PH-Baugruppe auf, welche sich von jenen im Vier- und Fünfring M5 d unterscheidet. Durch die explizite Berechnung des Einflusses von Aminosubstituenten an Bor auf die Geometrien des Fünf- und Sechsringes verbessert sich die Übereinstimmung der Bindungslängen mit den Daten der Röntgenstrukturanalyse.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/zaac.19966220906
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    Synthesis of Oligomeric Axially Bridged Ruthenium Phthalocyanines and 2,3-Naphthalocyanines (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 10 (1996), S. 649-660 
    Details
    ISSN: 0268-2605
    Keywords: naphthalocyanine ; ruthenium ; bridged ; oligomers ; solid state ; NMR ; conductivity ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bridged 2,3-naphthalocyaninatoruthenium oligomers {[MacRu(L)]n} were synthesized and characterized using solid-state methods. For comparison, soluble t-butyl substituted phthalocyaninatoruthenium oligomers were prepared and their chain length examined by 1H NMR spectroscopy. The powder conductivities of all bridged compounds ([MacRu(L)]n) were measured and the dependence of the conductivities on the bridging ligands is discussed.
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    Synthesis and characterization of organotin complexes with 2-mercaptopyridine derivatives (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 10 (1996), S. 35-45 
    Details
    ISSN: 0268-2605
    Keywords: organotin ; esters of 2-mercaptopyridine-5-carboxylic acid ; 2-mercaptopyridine ; Mössbauer ; IR ; NMR ; crystal structure ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By reaction of diphenyltin(IV) chloride and triphenyltin(IV) hydroxide with esters of the 2-mercaptopyridine-5-carboxylic acid (OVERBAR)NH(CS)CHCHC(COOR)(/OVERBAR)CH (HTNME, R = methyl; HTNEE, R = ethyl; HTNIPE, R = isopropyl) the complexes Ph3Sn(L), Ph2SnCI(L) (L = TNME, TNEE and TNIPE) and Ph2Sn(TNEE)2 have been prepared and characterized by IR, NMR and Mössbauer spectroscopies. Moreover, the Ph2SnCl2/2-mercaptopyridine (HMP) system has been found to yield either the Ph2SnCl2(HMP)2 adduct or the Ph2SnCl(MP) complex.The structures of Ph2SnCl(TNEE) and Ph2SnCl(MP) have been determined by X-ray single-crystal diffraction studies. The two structures are similar. Both ligands behave as bidentate chelating groups forming a four-membered ring with an identical small N(SINGLE BOND)Sn(SINGLE BOND)S bite angle of 63.7°. The tin atom is pentacoordinated, presenting a severely distorted trigonal bipyramidal geometry with apical Cl(SINGLE BOND)Sn(SINGLE BOND)N angles of 155.0(2)° [Ph2SnCl(TNEE)] and 155.7(7)° [Ph2SnCl(MP)] and equatorial C(SINGLE BOND)Sn(SINGLE BOND)C angles of 114.9(2)° and 125.0(3)° respectively. On the basis of 119Sn Mössbauer data, all the complexes should present analogous structures except Ph2Sn(TNEE)2 and Ph2SnCl2(HMP)2, for which an octahedral coordination geometry with a trans arrangement of the phenyl groups can be proposed. The effect of dimethyl sulphoxide on Ph2SnCl(L) and Ph2SnCl2(HMP)2 is also discussed.
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    Main chain scission reaction of poly(methyl methacrylate) caused by two-photon ionization of dopant (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 1969-1978 
    Details
    ISSN: 0887-624X
    Keywords: poly(methyl methacrylate) ; TMPD ; two-photon ionization ; main chain scission ; ESR ; GPC ; radical anion ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The main chain scission reaction of poly(methyl methacrylate) (PMMA) doped with N,N,N,′,N′-tetramethyl-p-phenylenediamine (TMPD) was examined by ESR spectroscopy and GPC measurement, and the scission mechanism was analyzed. The two-photon ionization of TMPD with excimer laser excitation at 77 K produced an ester radical anion of PMMA (PMMA·m̌), which becomes the main chain tertiary radical —CH2—C·(CH3)—CH2—after the detachment of the ester side group by annealing of the sample at room temperature. The main chain scission radical ·C(CH3)(COOCH3)—(PMMA·) which was produced by the β-scission from—CH2—·C(CH3)—CH2—showed the 13-line ESR spectrum instead of the ordinary 9-line, due to the fast quenching of the sample to 77 K. The change of the molecular weight distribution was measured by GPC after several irradiation-and-annealing operations. The simulation of the GPC curve confirmed that the scission re-action occurs at random in the PMMA chain in the solid and the main chain scission yield from the ester radical anion, [PMMA·]/[PMMA·m̌], is 0.30. © 1995 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/pola.1995.080331203
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    Preparation and characterization of fluoropropyl-substituted polysilane copolymers: Poly(3,3,3,-trifluoropropylmethylsilane-co-methylpropylsilane) (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 2279-2283 
    Details
    ISSN: 0887-624X
    Keywords: polysilane ; fluoropropyl side chain ; copolymer ; polymerization ; NMR ; UV absorption ; thermochromism ; thermogravimetry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1995.080331323
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    Cyclopolymerization. XXI. Radical cyclopolymerization of n,n-diallylmethacrylamide (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 2681-2690 
    Details
    ISSN: 0887-624X
    Keywords: radical polymerization ; cyclopolymerization ; dially compound ; N,N-disub-stituted methacrylamide ; ESR ; five-membered ring ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N,N-Diallylmethacrylamide (DAMA) was synthesized and its radical cyclopolymerizability was investigated. Polymerizations of DAMA were found to proceed according to the standard kinetic equation for radical polymerization except for the diffusion controlled termination reactions owing to higher viscosity of DAMA, in spite of the fact that it contains two allyl groups. DAMA yields polymers with slightly higher degree of cyclization than 50% in dilute solution polymerization. With increasing monomer concentration, the degree of cyclization decreases gradually and it becomes slightly lower value than 50% in concentrated solution polymerizations. It was found that about 86% of pendant unsaturations is allyl group and the rest is methacryloyl group. Structural studies on repeating units showed that possibility for the presence of bicyclic structures (those formed with consumption of three double bonds involved in DAMA) and structural units with two pendant unsaturations (those formed with one double bond in DAMA participated in polymerization) is extremely small. Main repeating cyclic unit was assigned to five-membered monocyclic lactam with an allyl group on its nitrogen, the content of which is estimated to be approximately 86% based on the allyl content. The main fraction of the rest of repeating cyclic structures was attributed to monocyclic pirolidine ring with a methacryloyl group on its nitrogen. These structural investigations and ESR studies of DAMA revealed that the methacryloyl group of DAMA is less reactive than its allyl group as in the case of N-methyl-N-allylmethacrylamide which has already been reported. © 1995 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/pola.1995.080331601
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    Enantiomeric separation and recognition mechanism of 2-arylpropionic acid derivatives by high-performance liquid chromatography using a chiral column (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 28-33 
    Details
    ISSN: 0899-0042
    Keywords: ibuprofen ; loxoprofen ; CS-670 ; loxoprofen and CS-670 trans-alcohols ; enantiomer ; diastereoisomer ; chiral HPLC ; chiral recognition ; NMR ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An optical resolution of the amide derivatives of ibuprofen and the carbamate-alkylester derivatives of the trans-alcohol metabolite of loxoprofen and an analogous compound, CS-670, was studied by chiral high-performance liquid chromatography (HPLC). The chiral columns SUMIPAX OA-4000 and OA-4100 were used to investigate the enantiomeric separation behavior of these derivatives using both reversed and normal mobile phases. A better separation factor (α) of the amide and the carbamate ester derivatives was obtained in the normal mobile phase than in the reversed mobile phase HPLC. In addition, the recognition mechanisms of both amide and carbamate ester enantiomers were investigated by 1H-nuclear magnetic resonance (NMR). It is suggested that the important driving forces for the enantiomeric separation are the formation of hydrogen bonding and the charge transfer complex between these derivatives and an active site of the chiral stationary phase. © 1995 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/chir.530070106
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    NMR investigations of the enantiomeric excess effects in solutions with weak intermolecular association (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 326-330 
    Details
    ISSN: 0899-0042
    Keywords: enantioselectivity ; NMR ; self-association ; achiral solvents ; dimerization ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The main features of statistically controlled associate diasteromerism (SCAD) in solution as measured by nuclear magnetic resonance (NMR) are discussed. In an achiral solvent, (R)- and (S)-enantiomers can demonstrate distinct NMR signals, with the intensity ratio equal to the concentration ratio. The previous theory of SCADA (anisochronism of nuclear magnetic moments caused by SCAD) is supplemented by treatment of enantiomeric excess phenomena in relation with the hypothesis that a sample consists totally of short-living diastereomeric dimers which are involved in fast (on the NMR time scale) exchange by enantiomers. Thermodynamic parameters of SCAD as well as limits for enantioselectivity phenomena are estimated. © 1995 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/chir.530070503
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    NMR imaging of polyethylene pipes (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 571-576 
    Details
    ISSN: 0887-6266
    Keywords: NMR ; imaging ; polyethylene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1H nuclear magnetic resonance (NMR) imaging techniques have been used to image the extrusion aid (EA) in polyethylene (PE) pipe samples. The resulting two-dimensional images show the distribution of EA within the pipe. EA is found to be uniformly distributed in a normal pipe. Examples of degraded pipes, due to exposure to extreme conditions, show migration of EA to the pipes' wall surfaces. NMR images of a normal pipe and two examples of damaged pipes are presented. The imaging technique and the results are discussed. © 1995 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/polb.1995.090330405
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    NMR characterization of styrene-divinylbenzene gel beads using freezing point depression of benzene (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 445-451 
    Details
    ISSN: 0887-6266
    Keywords: unfrozen benzene ; NMR ; polystyrene gel ; cross-linking ; pore size ; freezing point depression ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Freezing processes of benzene in the presence of styrene-divinylbenzene gel beads were investigated by proton nuclear magnetic resonance spectroscopy. Some portion of benzene in the pore did not freeze below its freezing point, which was detected until -80°C. Temperature dependence of the amount of unfrozen benzene was discussed in relation to the pore size and the cross-linking density of gel beads. The small pore size and high crosslinking density increased the amount of unfrozen benzene, whereas the polymer matrix concentration showed little effect on the freezing processes. © 1995 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/polb.1995.090330313
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    Rotor-synchronized two-dimensional 13C CP/MAS NMR studies of the orientational order of polymers 2. Melt-extruded poly(ethylene terephthalate) fibers (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 63-69 
    Details
    ISSN: 0887-6266
    Keywords: orientational order ; poly(ethylene terephthalate) ; NMR ; fibers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Determination of the orientational order of morphological components in polyethylene terephthalate (PET) is sought through quantitative application of two-dimensional rotor synchronized magic angle spinning (ROSMAS) 13C NMR technique. Previous study in our laboratories had established a procedure for resolution of the carbonyl carbon (CA) and glycol ethylene carbon (GE) resonances into those corresponding to four morphological components.1 Due to paucity of sidebands in the GE resonances, the focus has been on the CA resonances in this attempt to obtain orientation distributions. A set of PET fibers possessing a broad range of crystalline and orientational order has been used to infer the meaning of NMR-based orientation measurements vis-a-vis other techniques. A surprising finding of this study is the observation that the orientational orders of the broad component in the 13C CP/MAS spectrum and the narrow component are very similar in these fibers. ©1995 John Wiley & Sons, Inc.
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    Solid state 15N NMR study of 15N enriched melamine-formaldehyde resins (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 1449-1460 
    Details
    ISSN: 0887-6266
    Keywords: NMR ; melamine-formaldehyde ; resins structure ; cross-linked ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Molecular dynamics and structure of uncured and cured melamine-formaldehyde resins isotopically 15N enriched at amine sites were studied by solid-state 15N nuclear magnetic resonance (NMR). Spectra recorded with direct (DP) and cross-polarization (CP) pulse sequences reflect two motionally different regions arising from similar chemical structures. DP spectra of uncured resins at higher temperatures have narrow lines and the detection of slightly different structural units is possible. With increasing crosslinking resonances broaden and overlap and the direct detection of individual signals in cured resins is not possible. On the basis of variable contact time, variable spinning speed, and interrupted decoupling experiments three protonated and one nonprotonated group of signals are identified in the CP spectra for all samples. Short polarization-transfer rates, TNH, for nonprotonated nitrogen in uncured and lightly cured samples reveal more effective hydrogen bonding in viscous and rubber-like resins compared to the highly cured rigid resins. The rigid portions of the resins exhibit longer T1 and short T1ρ relaxation times, while the shorter T1 times and longer T1ρ times are associated with the more mobile portion of samples. ©1995 John Wiley & Sons, Inc.
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    NMR and DSC investigations of the miscibility of blends of cis-1,4-polyisoprene with polybutadienes of different microstructures (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 167-178 
    Details
    ISSN: 0887-6266
    Keywords: cis-1,4-polyisoprene/polybutadiene blends ; NMR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Differential scanning calorimetry and torsional braid analysis investigations of the phase diagram of cis-1,4-polyisoprene/polybutadiene blends as a function of the polybutadiene microstructure were reported by several authors. Polybutadienes containing a high vinyl content were shown to be miscible with cis-1,4-polyisoprene on the DSC spatial scale, whereas polybutadienes containing a low vinyl content were immiscible. In this article, we used variable-temperature determinations of 1H NMR free induction decays and low-temperature, high-resolution solid-state 13C NMR measurements of proton spin-lattice relaxation times in the rotating frame to probe the phase behavior of the cis-1,4-polyisoprene/polybutadiene blends at the smaller spatial scale of the NMR technique. Blends of cis-1,4-polyisoprene with a polybutadiene having a large number of vinyl 1,2 linkages appeared to be miscible on the molecular scale, in spite of small regions in which the polybutadiene component is not uniformily dispersed in the other polymer. On the contrary, blends in which the polybutadiene has a low content of vinyl 1,2 sequences were phase separated over the whole temperature range considered and no intermixed regions could be detected. The limiting case was observed with the polybutadiene containing 33 wt % vinyl 1,2 units, for which miscibility on a molecular scale is highly dependent on the blend composition. © 1995 John Wiley & Sons, Inc.
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    1H NMR studies of molecular relaxations of poly-1-butene (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 1235-1247 
    Details
    ISSN: 0887-6266
    Keywords: NMR ; poly-1-butene ; NMR line shape ; spin-lattice relaxations ; Williams Watt correlation function ; polymorphism ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The temperature dependance of the proton NMR line shape, T1 and T1ρ of isotactic poly-1-butene forms I, I′, II, and III have been studied between 100 and 400 K (up to melting). The usual line shape decompositions concerning rigid vs. crystalline and mobile vs. amorphous phases are discussed. The rigid-lattice second moments were calculated introducing a fast rotation of the methyl group.Complex spin-lattice decays were analyzed as a continuous distribution of rates. Relaxation behavior was analyzed in terms of a Williams-Watt correlation function. Motions in the crystalline parts of samples in forms II and III very similar to the amorphous one were revealed, leading us to compare form II to a condis crystal during the crystal form transformation. © 1995 John Wiley & Sons, Inc.
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    A nuclear magnetic resonance study of toluene-polyisobutylene solutions. 3. Spin-lattice relaxation: Rotational and segmental motion (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 1515-1522 
    Details
    ISSN: 0887-6266
    Keywords: segmental motion ; chain dynamics ; polyisobutylene ; toluene ; Hall-Helfand ; NMR ; free volume ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The spin-lattice relaxation times are determined for the methylene carbon of polyisobutylene (PIB), as well as for the ortho carbon of toluene in toluene-polyisobutylene solutions. The Hall-Helfand correlation function combined with restricted anisotropic rotational diffusion was used to treat the T1 data of the methylene carbon of PIB. A simple exponential correlation function was used to describe the local motion of toluene in the solutions which falls in the extreme narrowing limit for the solutions studied. Both models described satisfactorily the temperature and field dependence of the spin-lattice relation times. From the temperature dependence of the correlation times for the polymer segmental motion, the free volume of the solution at each concentration is extracted and compared with the values obtained from previous studies of the translational motion of the toluene penetrant. The free volume values extracted from the T1 data for the methylene carbon of PIB and the self-diffusion data for the toluene were found to be in substantial agreement. The interrelationship of the timescale of segmental motion of the polymer and the translational diffusion of the toluene was also examined and it was found that the two types of motion seem to be correlated in high polymer concentrated solutions. The toluene reorientational motion was found to be much faster than both the polymer segmental motion and the toluene translational diffusion leading to the conclusion that the toluene reorientational motion is uncoupled from these two motions. ©1995 John Wiley & Sons, Inc.
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    Glass transition and film formation of VeoVa/vinyl acetate latices; role of water and co-solvents (1995)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 6 (1995), S. 291-295 
    Details
    ISSN: 1042-7147
    Keywords: film formation ; latex ; vinyl acetate ; glass transition temperature ; differential scanning calorimetry ; VeoVa ; NMR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The physical forces causing deformation of latex particles during the film formation process have been witley studied. However, the forces resisting particle deformation are still poorly characterized. It is clear that the extent of particle deformation is dependent on the viscoelastic nature of the polymer. In an emulsion, the latex particles will normally contain water, surfactants and “free” monomers which lead to plasticization of the polymer. Although this effect has been recognized, so far it has been studied only on films that had been dried and then partially or completely swollen by water.In this work, plasticization of the emulsion polymers by water and co-solvent has been quantified via differential scanning calorimetry investigation directly on the aqueous latex dispersions. More specifically, the plasticizing effect of water on VeoVa/vinyl acetate copolymer latices and its influence on minimum film-forming temperature (MFFT) has been studied. A linear correlation has been found between Tg and MFFT for the wet latices. This new direct method should help to improve our understanding of the forces resisting latex film formation.Additionally, the homogeneous distribution of the hydrophobic and hydrophilic monomers (VeoVa and vinyl acetate respectively) in the latex particles was verified via a 13C-NMR (nuclear magnetic resonance) study performed directly on the latices. This study confirmed that no significant core/shell type of morphology had influenced latex film formation.
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    Utility of pulsed-field gradient - HMBC indirect detection NMR experiments for polymer structure determinationPresented at ‘MacroAkron '94, 35th IUPAC Symposium on Macromolecules’, Akron, Ohio, 11-15 July 1994. (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 36 (1995), S. 177-185 
    Details
    ISSN: 0959-8103
    Keywords: NMR ; pulsed-field gradient ; heteronuclear multiple bond correlation ; block copolymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The utility of pulsed-field gradient (PFG)-heteronuclear multiple bond correlation (HMBC) 2D NMR experiments for characterizing polymer structure is demonstrated. Heteronuclear multiple quantum coherence (HMQC) and HMBC indirect detection experiments provide correlations indicating the presence of one-bond and two-or three-bond connectivities, respectively; this information is vital for polymer structure determination. When HMBC methods are combined with PFG techniques artifacts are eliminated which normally limit the utility of HMBC. The elimination of these artifacts lowers the detection limit by almost two orders of magnitude, making it feasible to detect signals from the small number of repeat units bonded to defect structures, chain ends, branch points and block junctions, despite the presence of much larger resonances from the main-chain repeat units. Spectra of poly(isobutylene-b-butadiene) diblocks and poly(isoprene-b-styrene) diblocks are used to illustrate these advantages.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pi.1995.210360208
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