摘要:

AbstractAn ‘anomalous’ variation of β‐fluorine chemical shifts with respect to the inductive effect in the19F NMR of a series of 1‐halo‐F‐adamantanes is reported. These fluorine chemical shifts are similar to the hydrogen chemical shift anomaly found in the corresponding hydrocarbon halides. Whereas the γ‐hydrogen chemical shifts can be rationalized by the inductive effect, the γ‐fluorine chemical shifts have the same ‘anomalous’ variation as found in the β

ISSN:0749-1581    

DOI:10.1002/mrc.1260311103

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractPelargonidin‐3‐O‐β‐glucopyranoside was isolated from an acidified methanolic extract of frozen strawberries, purified by several chromatographical techniques and subjected to homo‐ and heteronuclear proton and carbon NMR analysis, including selective decoupling, DQF‐COSY, NOESY, SEFT, HMQC and HMBC. Several strategies for the unambiguous assignment of the aglycone H‐6 and H‐8 resonances are discussed. Secondary isotope effects and different deuterium exchange rates of the pr

ISSN:0749-1581    

DOI:10.1002/mrc.1260311104

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe estrogen receptor ligandmeso‐hexestrol has been synthesized with13C enrichment (98 at.%) at every position.13C NMR spectra of the intermediates were obtained and13C−13C coupling patterns analyzed. The complex13C NMR spectrum of [13C18]‐meso‐hexestrol was simplified through the use of selective13C decoupling. Several13C−13C coupling constants were estimated from the decoupled spectra and refined via iterative simulation. Some additional coupling constants were measured in selective one‐dimensional13C COSY spectra. Coupling constants are reported to an accuracy of ±0.4–1 Hz. This study demonstrates the feasibility of determining13C−13C coupling constants in highly13C−substituted compounds; such compounds are expected to be used with increased frequency in studying receptor‐ligand interactions by polarizat

ISSN:0749-1581    

DOI:10.1002/mrc.1260311105

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

Abstract15N NMR spectra of dialkyl sulphur diimides (1) [R1(NSN)R2; R1= R2= Me (a), Et (b),nPr (c),iPr (d),nBu (e),tBu (f),tOct (g)], N‐alkyl‐N′‐phenyl sulphur diimides (2) [R1(NSN)R2; R1= Me (a), Et (b); R2= Ph] and diphenyl sulphur diimide (3) were measured at variable temperature. The assignment is based on the comparison with data for the correspondingN‐sulphinylamines R1(NSO). The Z/E configuration is always preferred at low temperature, whereas the minor isomer adopts the Z/Z configuration. In the presence of bulky substituents (If and g), only the isomer withZ/Econfiguration is observed. At room temperature,15N NMR signals were not observed for symmetrically substituted sulphur diimides, but a single averaged14N resonance can be measured. The unsymmetrically substituted sulphur diimides 2a and b adopt theZ/Econfiguration with the alkyl group Z and the phenyl groupE.There are no indications of other isomers at low temperature.14N NMR spectra at room temperature prove that the (Z)‐phenyl/(E)‐alkyl isomer contributes little to th

ISSN:0749-1581    

DOI:10.1002/mrc.1260311106

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

Abstract13C and1H NMR spectra of six Schiff bases formed from 2‐hydroxy‐1‐naphthaldehyde and substituted anilines were measured and assigned in a variety of solvents. Based on the13C chemical shifts and3J(CH,NH), the ratio of the keto‐amine and phenol‐imine tautomers was derived using both13C chemical shifts and1H−1H coupling constants, the two methods giving comparable results. The solid‐state13C NMR spectra of two of these Schiff bases were also measured and interpreted. Based on chemical shift assignments from solution NMR, which showed a relationship between certain shifts and the proportions of the tautomers, it has been shown that these compounds exist essentially as the keto‐amine form in the solid, the tautomer previously shown to be the more thermodyn

ISSN:0749-1581    

DOI:10.1002/mrc.1260311107

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractRaman magnetic resonance (RMR) with direct and indirect detection schemes features 1D display of multiple quantum (MQ) transitions. Consequently, useful information such as couplings and correlations can be easily extracted from the RMR approach. In this paper, RMR experiments are demonstrated to determine heteronuclear chemical shift correlations, homonuclear and heteronuclear long‐range coupling constant values and their relative signs, with typical samples. It is shown that this approach is useful for the study of small molecules and groups of special interest in a complex molecul

ISSN:0749-1581    

DOI:10.1002/mrc.1260311108

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractTypically the13C CP/MAS spectra of proteins have low signal‐to‐noise ratios and broad lines, which considerably degrade the value of such spectra. The origins of these effects were examined using a model protein, lysozyme. The effects of hydration, relaxation time and crystallinity were systematically investigated. It is concluded that low signal‐to‐noise ratios are the result of the typically low density of protein preparations and not an intrinsic magnetic resonance phenomenon, and that line broadening is principally the result of poor molecular packing in noncrystalline protein prepa

ISSN:0749-1581    

DOI:10.1002/mrc.1260311109

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe selective detection of the arylamine aromatic protons in a 15‐mer DNA duplex modified by the carcinogen 4‐aminobiphenyl was accomplished using one‐dimensional multiple quantum filtration experi

ISSN:0749-1581    

DOI:10.1002/mrc.1260311110

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

Abstract17O NMR longitudinal and tranverse relaxation rates and chemical shifts were measured at variable temperature at three magnetic fields (1.4, 4.7 and 9.4 T) for aqueous solutions of the complexes [Gd(H2O)8]3+and [Gd(PDTA)(H2O)2]−. The transverse relaxation rates and chemical shifts were analysed in the light of recent EPR line width measurements to obtain the parameters for water exchange kinetics:k ex298= (8.30 ± 0.95) × 108and (1.02 ± 0.10) × 108s−1, ΔH‡= 14.9 ± 1.3 and 11.0 ± 1.4 kJ mol−1and ΔS‡ = −24.1 ± 4.1 and −54.6 ± 4.6 J K−1mol−1for [Gd(H2O)8]3+and [Gd(PDTA)(H2O)2]−, respectively. The longitudinal relaxation rates were used to obtain the parameters for the rotation time of the complexes: τ c298= (2.9 ± 0.2) × 10−11and (7.9 ± 0.3) × 10−11s andEc= 15.1 ± 1.5 and 19.2 ± 1.1 kJ mol−1for [Gd(H2O)8]3+and [Gd(PDTA)(H2O)2]−, respectively. The17O NMR transverse relaxation rates were measured at variable pressure, and were used to determine the activation volumes for the water exchange process: ΔV0‡= −3.3 ± 0.2 and −1.5 ± 0.5 cm3mol−1for [Gd(H2O)8]3 +and [Gd(PDTA)(H2O)2]−, respectively. It can be concluded that water exchange occurs via an associative limiting A mechanism for [Gd(H2O)8]3 +(without excluding Ia) and an associative interchange, Ia, mechanism for [Gd(PDTA)(H2O)2]−. These water exchange kinetic and mechanistic results are compared with those for the

ISSN:0749-1581    

DOI:10.1002/mrc.1260311111

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe first example of 3D NMR spectroscopy involving1H,13C and31P nuclei is described. The use of this technique for difficult signal assignments in organophosphorus chemistry is demonstrated.

ISSN:0749-1581    

DOI:10.1002/mrc.1260311112

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY