摘要:

AbstractA comparative study of the spin‐lattice relaxation times (T1) of proton‐bearing carbons in bilirubin and its derivatives is reported. TheNT1values of the backbone carbons indicate that the overall reorientation of the molecule is isotropic. In dimethyl sulphoxide solutions, the segmental motion of the propionic side chains is very limited in bilirubin, bilirubin dimethyl ester and mesobilirubin dimethyl ester, faster in dimethoxybilirubin dimethyl ester and is very fast in the propionic residue of vinylneoxanthobilirubinic acid methyl ester. The relative mobilities of the propionic residues are interpreted on the basis of intramolecular hydrogen bonding in which the solvent participates. The dimeric form of bilirubin dimethyl ester in chloroform solutions is confirmed by the correlation time of tumbling of the backbone. In this solvent the segmental motion of the propionic side chains is rapid, indicating the probable absence of hydrogen‐bonding. In bilirubin, bilirubin dimethyl ester and dimethoxybilirubin dimethyl ester, internal rotation is rapid for theendo‐vinyl group and slow for theexogroup, correlating with reported differences in the chemical behaviour of these residues in bile p

ISSN:0030-4921    

DOI:10.1002/mrc.1270170202

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractPhosphorylation of the tetrapeptide Gly‐Gly‐His‐Ala by phosphoamidate provides a model peptide for proteins which, in the course of their reaction, bind a phosphoryl group to an imidazole ring.31P‐ and1H‐NMR data, including chemical shift and pK values, for this peptide and its three phospho‐derivatives are presented. These data show that it is possible, by NMR studies, to decide whether or not a peptide or a protein is phosphorylated at the N‐1 or at the N‐3 position of an imidazole ring, and how this information

ISSN:0030-4921    

DOI:10.1002/mrc.1270170203

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe Bunte salt derivative was prepared from bovine insulin‐A isolated from natural sources, and was purified by chromatography. Natural abundance 40.55 MHz15N NMR spectra were measured in water and dimethyl sulphoxide. The latter solvent gave the best resolution, and 20 of the 22 possible amide nitrogen signals were detected. Several model oligopeptides were also measured and their usefulness for assignments is discusse

ISSN:0030-4921    

DOI:10.1002/mrc.1270170204

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractTwo‐bond13C13C coupling constants are discussed on the basis of INDO‐SCPT calculations. The dependence of2J(CC) on bond angle variation and on methyl substitution is evaluated, and it is shown that2J(CC) depends linearly on the bond orbitals‐character product of the terminal carbon atoms, whereas no systematic relationship with the hybridization of the central carbon atom was obtained. Alkyl group substituent effects are found to be additive. The coupling constants of a number of cyclobutane derivatives are discussed on the basis of these structural relationships; it is shown that the experimental findings can be interpreted quite consistently by assuming a dual‐pathway coupling

ISSN:0030-4921    

DOI:10.1002/mrc.1270170205

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractConfigurations and preferred conformations of a number of hexahydro[1,3]thiazolo[3,2‐a]pyridines have been assigned on the basis of their1H and13C NMR spectra. The conformational preferences of these compounds have been interpreted in terms of the minimization of dipolar type interactions, arising from 1,3 arrangements of the heteroatoms, which are increased by the electron donor induction effect of the alkyl groups. The stereochemistry of the salts of these bases is very different from that of the free compounds. For thegem‐disubstituted compound, an explanation in terms of the ‘gem‐dimethyl effect’ and a slight deformation at the nitrogen atom is

ISSN:0030-4921    

DOI:10.1002/mrc.1270170206

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe1H and13C NMR spectra of 2,3‐disubstitutedexo‐5,6‐ andendo‐5,6‐bicyclo[2.2.2]octanes, and the corresponding alkanes, have been investigated to determine the effects exerted by an oxirane ring. The1H NMR study showed that theantiprotons, H‐7aand H‐8a, are significantly shielded and thesynprotons, H‐7sand H‐8s, are deshielded, although to a smaller extent, by theexo‐oxirane. Anendo‐oxirane has practically no effect on the same protons. The stereochemistry of epoxybicyclo[2.2.2]octanes is, thus, easily deduced from1H NMR data. The13C NMR study of the epoxy compounds provided an estimate of the value of α, β, γsynand γantieffects (to the epoxide oxygen) of an oxirane ring. In these rigid bicyclic molecules, of known geometry, the γsynand the γantieffects are of the same value, even though the dihedral angles are v

ISSN:0030-4921    

DOI:10.1002/mrc.1270170207

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

Abstract13C NMR shifts of 54 chalcones and their thiophene and furan analogues are analyzed by principal component analysis. Thus, a mathematical model is derived for the variation of the carbon shifts in each of seven classes. Two component models are found to be adequate by cross‐validation. The first component corresponds to ordinary σparavalues, while the second one differentiates benzenes, thiophenes and furans. This type of data analysis is a useful tool for checking the consistencies of spectral parameters. The model parameters, which describe systematic variations within each class, are also used for the study of substituent effects and discussed in relation to substituent constants in linear free energy relationshi

ISSN:0030-4921    

DOI:10.1002/mrc.1270170208

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe effect of silver ion complexation on the13C NMR of several rigid olefin structures has been determined. The silver ion induced chemical shifts (AgIS) are not amenable to easy interpretation. Addition of Yb(fod)3forms binuclear Ag–Yb complexes with the olefin. Lanthanide induced shifts (LIS) fall off rationally with distance from the site of complexation and the averaged position of the lanthanide. The complexes may be used as probes of olefin stereochemistr

ISSN:0030-4921    

DOI:10.1002/mrc.1270170209

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

Abstract15N Chemical shifts ofcis‐decahydroquinoline,N‐methyl‐cis‐decahydroquinoline, and of 19 methyl substituted NH‐ and NCH3‐cis‐decahydroquinolines are reported. Shift values of conformationally homogeneous compounds can be used to determine the chemical shifts of the possible conformations of the mobile compounds. Equilibrium constants derived from the shifts of the contributing conformations agree with results of low temperature13C NMR

ISSN:0030-4921    

DOI:10.1002/mrc.1270170210

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of four thiocarbamates and their correspondingS‐oxides andS,S‐dioxides are reported. Both βSOand β SO 2effects are deshielding and range from 20.44 to 21.68 ppm. The βSO′ effects are slightly deshielding (0.20 ∼ 0.0.77 ppm). The β′ SO 2effects, on the contrary, are shielding and range from −6.54 to −6.98 ppm. The γ′, δ′, ξ′,

ISSN:0030-4921    

DOI:10.1002/mrc.1270170211

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY