摘要:

AbstractConformational and dynamic features of ranitidine were delineated by1H and13C NMR 1D and 2D spectroscopy. Spin–lattice relaxation rates and homo‐ and hetero‐nuclear NOEs were measured. An extended conformation was shown to predominate in solution, with restricted segmental motion. The main reorientational motion and some of the internal motions were characterized in terms of stochastic internal motion around a molecular axis that reorients isotropically. Selective irradiation methods were used to obtain relevant conformational param

ISSN:0749-1581    

DOI:10.1002/mrc.1260261202

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe27Al chemical shift, line widths and intensities have been measured for a series of sodium aluminate solutions with a range of sodium and aluminium concentrations. The aluminium is present entirely as the anion [Al(OH)4]−in all but the most concentrated solutions, where intensity is lost owing to the formation of species with very broad lines. The viscosities of the solutions were also measured and it was shown that these accounted to a great extent for the observed changes in line width, so that the unusually wide lines seen in the most concentrated solutions cannot be said to arise from dimeric specie

ISSN:0749-1581    

DOI:10.1002/mrc.1260261203

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe usefulness of1H bi‐selective relaxation times (T 1BS) and selective relaxation times (T 1s) for structure and conformation determination is emphasized. A pulse sequence has been devised which provides the apparent observedT 1BS. The cross‐relaxations (σij) orFijvalues are derived from the observedT 1BSandT 1Svalues. The σijvalues can be correlated with the HH distances (rij) and can be used for conformational analysis or structure determination. TheFijvalues, which indicate the fractional contribution to the dipolar relaxation of protonivia the interaction with protonj(i ≠ j), can be compared with the NOE values. 2‐Vinylpyridine was chosen as a model compound and three types ofT1values were measured for its protons. Its conformation in CDCl3solution is discussed based on the correlation between the σijobtained and therijvalues. A conformational eq

ISSN:0749-1581    

DOI:10.1002/mrc.1260261204

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractWhen the proton–proton decoupled heteronuclear two‐dimensional chemical shift correlation experiment is applied to a molecule containing methylene groups, the spectra show not only the expected signals at the two proton chemical shifts, but also a strong artifact. This artifact appears at the average of the two proton chemical shifts, and arises from coherence transfer between the two protons caused by the BIRD pulse. It is not caused by strong coupling between the protons, and so may appear in any spectrum. The dependence of this artifact on experimental conditions was analysed, and is illustrated with results obtained on the methylene groups from the cyclophane ring inN6′,N9‐octamethylenepurinecyc

ISSN:0749-1581    

DOI:10.1002/mrc.1260261205

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractC‐Glycopyranosides andC‐glycofuranosides were identified using13C and1H chemical shift and coupling constant data. Full assignments for all α‐ and β‐anomers were made possible by recourse to carbon–proton chemical shift correlation spectroscopy. Greater steric shielding effects were observed on the carbon atoms incis‐1,2‐substituted compounds compared with theirtranscounterparts. Consistent proton chemical shift differences were also noted in that the anomeric protons resonate at lower field in all

ISSN:0749-1581    

DOI:10.1002/mrc.1260261206

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractIn previous work a modified COLOC sequence combined with a selective BIRD pulse which allows one to obtain one‐bond13C1H shift‐correlated spectra with full1H1H decoupling and good (ca15 Hz)f1resolution, in addition to improved sensitivity over earlier sequences measured under the same conditions, was developed. In this paper it is demonstrated that a further modification of this sequence to allow the pair of1H and13C 180° pulses to traverse the entire fixed evolution period allows excellent (ca7–8 Hz)f1resolution plus a further increase in sensitivity (in the same time) of almost √2. Factors contributing to the sensitivity advantages relative to other sequences were examined. Whereas some artifacts are noted for tightly coupled CH2groups, these may actually aid in the accurate determination of very small chemical shift differences. The precision of measurement of1H chemical shi

ISSN:0749-1581    

DOI:10.1002/mrc.1260261207

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe mechanism of195Pt spin–lattice relaxation in aqueous solutions of Pt(CN) 42−and 62−has been elucidated from variable‐temperatureT1measurements at 4.70 and 8.48 T. For Pt(CN) 42−both the chemical shielding anisotropy and spin rotation mechanisms are important; for Pt(CN) 62−the spin rotation mechanism completely dominates. The value of Δσ obtained for Pt(CN) 42−is 2350 ppm, which is in excellent agreement with the value previously measured for the tetracyanoplatinate(II) ion in a variety of

ISSN:0749-1581    

DOI:10.1002/mrc.1260261208

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractTo determine the feasibility of using77Se NMR spectroscopy to characterize bis(alkylthio)selenides formed by reaction of selenite with thiol groups of biological molecules,77Se NMR spectra have been measured for bis(alkylthio)selenides formed by reaction of selenite with cysteine, homocysteine, penicillamine,N‐acetylpenicillamine, 2‐mercaptopropanoic acid, mercaptosuccinic acid, cysteamine and glutathione. The77Se chemical shift is extremely sensitive to the nature of the alkylthiol group, covering a range greater than 150 ppm for this series of thiols. The chemical shift is also sensitive to the stereochemistry of the alkylthiol group, and resolved resonances are observed formesoandD,L‐stereoisomers, e.g. themesoandD,L‐stereoisomers of bis(cysteine)selenide.77Se NMR spectra were also measured for mixed bis(alkylthio)selenides (RSSeSŔ) formed by reaction of selenite with two‐component mixtures of the various thiols. The effect of the two alkylthiol groups on the77Se chemical shift is additive, with77Se chemical shifts of the mixed bis(alkylthio)selenides located mid‐way between those of the two symmetric compounds. The77Se chemical shift is also sensitive to the protonation state of carboxylic acid and ammonium groups of the alkylthiol, and pKAvalues were determined from77Se chemical shift vs pH titration curves for selected symmetrical and mixed bis(alkylthio)selenides. The results demonstrate that77Se NMR is a sensitive method for the characterization and study of bis(alkylth

ISSN:0749-1581    

DOI:10.1002/mrc.1260261209

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractNMR line widths (13C) and spin–lattice relaxation times (13C and2H) were measured over a wide temperature region in liquid and solidtert‐butyl chloride (1) andtert‐butyl nitrate (2). Molecular self‐diffusion, with activation energies in the range 29–37 kJ mol−1, is responsible for the considerable line narrowing observed for the13C resonances in solid I of these substances.An analysis of the13C and2H spin–lattice relaxation times (T1) in the liquid and solid phases of 1 and 2 is reported. Rotational correlation times, activation energies and pre‐exponential factors for the appropriate motions were obtained from the Arrhenius equation. The13C and2HT1data suggest that the overall reorientation occurring in solid I of 1 and 2 is slightly retarded by the melting process. The13CT1data show that the faster motion in the ordered phases of 1 and 2 is the uniaxialC3′ reorientation with an activation energy of 12–14 kJ mol−1, while the slower motion is theC3methyl reorientation with an activation ene

ISSN:0749-1581    

DOI:10.1002/mrc.1260261210

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractTwo‐dimensional relayed‐NOESY spectra are of utility in assigning connectivities in crowded spectra. A modified version of this pulse sequence is described which removes uniformative diagonal peaks and one other type of unwanted peak. The resulting spectra are less crowded and can be interpreted more eas

ISSN:0749-1581    

DOI:10.1002/mrc.1260261211

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY