ISSN:0030-4921    

DOI:10.1002/mrc.1270070612

出版商:John Wiley&Sons Limited    

年代:1975

数据来源: WILEY

摘要:

AbstractThe Carr‐Purcell experiment first used by Allerhand and Gutowsky for the determination of chemical exchange rates has been applied to the study of an enzyme inhibitor complex. Chemical shift and relaxation time data obtained by analysis of pulsed fluorine NMR data collected at 51 MHz are shown to be consistent with high resolution results assembled at 94° 1 MHz. The rate constants for dissociation of theN‐trifluoroacetyl‐D‐tryptophan‐α‐chymotrypsin complex were determined to be 1 × 104s−1at 26°C and 2 × 103s−1at 6·5°C. The resonance position of the fluorine nuclei of the inhibitor is shifted downfield ∼1 ppm upon complexation to the enzyme, and the trifluoromethyl group suffers some restriction of molecular motion in the bound state as

ISSN:0030-4921    

DOI:10.1002/mrc.1270070602

出版商:John Wiley&Sons Limited    

年代:1975

数据来源: WILEY

摘要:

AbstractCarbon‐13 spin‐lattice relaxation times have been measured in glycine and the tripeptide pro‐leu‐gly‐NH2. These times are compared with those measured in the same compounds where the glycine α‐carbon has been deuterated. In this manner evidence is obtained which indicates that mechanisms other than dipolar interactions with covalently bonded protons may contribute to carbon‐13 spin‐lattice relaxation. The effect of these additional mechanisms is found to be non‐negligible for the carbonyl carbon of glycine and the glycine α‐carbon of the tripeptide. The implication of these findings for deducing motional information from carbon‐13 relaxation measuremen

ISSN:0030-4921    

DOI:10.1002/mrc.1270070603

出版商:John Wiley&Sons Limited    

年代:1975

数据来源: WILEY

摘要:

AbstractMagnetic resonance techniques have been used to study the ionization behavior of the catalytic triad of the serine protease, α‐lytic protease, in the tetrahedral, hemiacetal complex it forms with the aldehyde inhibitor, N‐ac‐L‐ala‐L‐pro‐L‐alaninal. Chemical shift, coupling constant and relaxation measurements of a carbon‐13 nucleus specifically incorporated in C‐2 of the imidazole ring of the single histidine residue of the protein show that, above pH 7, the imidazole ring of the catalytic triad in the enzyme + aldehyde complex is neutral. We suggest, further, that a neutral carboxylic acid group for Asp 102 and an oxyanion for the hemiacetal are most likely to describe the state of ionization of the other groups above pH 7. Around pH 6·25, both the oxyanion and the histidine become protonated in a co‐operative process which forces the histidine away from its rigidly localized position as a member of the catalytic triad into a so

ISSN:0030-4921    

DOI:10.1002/mrc.1270070604

出版商:John Wiley&Sons Limited    

年代:1975

数据来源: WILEY

摘要:

AbstractThe proton magnetic resonance spectra of catechol, epinephrine, dopamine, synephrine, tyramine and amphetamine have been analysed by computer simulation. The chemical shifts and coupling constants are discussed, with their molecular implications. Convenient parameters are introduced for the additivity of substituent effects on chemical shifts of aromatic protons. The additivity rule of coupling constants is extended to these compounds.

ISSN:0030-4921    

DOI:10.1002/mrc.1270070605

出版商:John Wiley&Sons Limited    

年代:1975

数据来源: WILEY

摘要:

AbstractDer diamagnetische und paramagnetische Term der chemischen Verschiebung wird durch semiempirische CNDO/II Ladungsdichte‐und Bindungsordnungswerte ausgedrückt. Es wird untersucht ob ein linear funktionaler Zusammenhang zwischen den berechneten Termen und der chemischen Verschiebung von19F‐ und13C‐Atomen besteht. In Form einer linearen Regression werden eine Reihe unterschiedlicher Ansätze–unter Berücksichtigung von s̀diasowie s̀dia+ s̀para—untersucht. Es zeigt sich, daß die Beziehung δA=a+bqA+cQAB+dqAπQABden kleinsten mittler

ISSN:0030-4921    

DOI:10.1002/mrc.1270070606

出版商:John Wiley&Sons Limited    

年代:1975

数据来源: WILEY

摘要:

AbstractThe 300 MHz spectra of 2‐methyl‐, 2‐phenyl‐, 2‐(2‐chlorophenyl)‐ and 2‐(4‐chlorophenyl)‐oxetanes were recorded in CCl4and C6D6. The chemical shifts and the proton‐proton coupling constants were solved through iterative calculations. The results were discussed in the light of structural factors and theoretical calculations. The average angle of pucker for the oxetane ring was estimated atc. 5°, in fair agreement with the value of 3·3° derive

ISSN:0030-4921    

DOI:10.1002/mrc.1270070607

出版商:John Wiley&Sons Limited    

年代:1975

数据来源: WILEY

摘要:

AbstractVingt‐six monoalcoxyfluorophosphoranes comportant un group asymétrique et appartenant aux types R1PF3(OR2*) (1), R1*PF3(OR2) (2), R1R3PF2(OR2*) (3) et R21PF2(OR2*) (4) ont été préparés. La non‐équivalence des fluors occupant les sites apicaux de la bipyramide trigonale est mise en évidence par RMN de19F pour les types1(δFa) – δF′a∼ 0,5 à 3,8 ppm.J(FaFa′) ∼ (10 Hz),2δFa– δF′a∼ 1,1 à 1,5 ppm,J(FaFa)′ ∼ 14 Hz et3δFa‐ δF′a∼ 0,2 ppmJ(FaFa′) ∼ 10 Hz, mais non pour les types4R12PF2(OR2*) Elle est attribuée à la diastéréotopie de ces fluors apicaux. La possibilité d'une gěne à la rotation des substituants est exclue.

ISSN:0030-4921    

DOI:10.1002/mrc.1270070608

出版商:John Wiley&Sons Limited    

年代:1975

数据来源: WILEY

摘要:

AbstractL'analyse complète du spectre de résonance du proton du composé du titre est mise à profit pour une étude conformationnelle de la molécule au niveau C‐4—C‐5. La position relative des protons vis à vis de la liaison S=O est fixée grâce à l'utilisation du complexe de l'Europium Eu(fod)3. Les résultats obtenus sont tout à fait cohérents avec ceux trouvés pour des composés similaires contenant, ou non, u

ISSN:0030-4921    

DOI:10.1002/mrc.1270070609

出版商:John Wiley&Sons Limited    

年代:1975

数据来源: WILEY

摘要:

Abstract1H NMR spectra of substituted cyclotrisilazanes are discussed in terms of conformational analysis. Experimental spectra are consistent with an equilibrium involving chair conformers, following from simulating the effect of phenyl substituents and the temperature dependence of methyl proton chemical shifts. The barrier to chair‐chair interconversion in hexamethyl‐cyclotrisilazane is estimated. An analysis is carried out of the shielding of non‐equivalent methyl groups in substituted cyclotrisila

ISSN:0030-4921    

DOI:10.1002/mrc.1270070610

出版商:John Wiley&Sons Limited    

年代:1975

数据来源: WILEY