摘要:

AbstractWe have studied the dynamics of binding of19F labelled haptens by mouse plasmacytoma antibody MOPC‐315, a protein which shows specificity for nitrophenyl haptens. The off‐rates for the dissociation of hapten from MOPC‐315 proteins (7S, Fab′ and Fv) were determined by the application of several methods including a technique which, in certain cases, allows the direct determination of the rate of exchange of nuclei between magnetically non‐equivalent sites without requiring prior knowledge of intrinsic line widths. Used in conjunction with independently determined data on line widths, chemical shifts, and binding affinities, these studies show that the rates for hapten association to, or dissociation from, the intact 7S antibody, the Fab′ fragment, and the Fv fragment of MOPC‐315 are essentially the same. They also indicate the presence, probably in the Fv region, of a low affinity (K∼ 103M−1) site(s) for hapten binding. The mobility of the hapten combining site decreases as the size of the protein increases. These rate data, which were determined at relatively high protein concentrations (up to 40 mg ml−1), agree with on‐rates determined at much lower protein concentrations (≤1 mg ml−1); we therefore conclude that protein aggregation, if it does occur, does not significantly affect

ISSN:0030-4921    

DOI:10.1002/mrc.1270130102

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractA study has been made of the13C chemical shifts of a number of acyclic alkanes, alkenes, nitriles and ketones which contain quaternary carbon atoms. Similar data have also been obtained for the series of compounds involved in the synthesis of triisopropylacetic acid. Substituent effects and steric factors in these highly substituted compounds are discussed in relation to the chemical shifts.

ISSN:0030-4921    

DOI:10.1002/mrc.1270130103

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe synthesis of [1‐15N]nicotinamide adenine dinucleotide is described. Chemical shift data from15N NMR studies are presented for the pyridine ring nitrogen of labeled NAD and related compounds. The results indicate a15N label in the N‐1 position to be highly sensitive to the redox‐state of the pyridine moiety, with an upfield shift of over 100 ppm observed upon reduction of NAD+to NADH. The feasibility of conducting15N NMR studies of pyridine nucleotide binding to dehydrogenases is disc

ISSN:0030-4921    

DOI:10.1002/mrc.1270130104

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe NMR spectra of a number of 2,4‐disubstituted 1,3‐dioxolanes have been recorded and the proton chemical shifts and coupling constants derived from complete spectral analysis. Vicinal coupling constants were found to be dependent on the substituent at C‐4 and this effect is more pronounced forJ(trans)of the C‐4‐C‐5 fragment. These coupling constants also indicate a homogeneous behaviour within a series with either acisortransconfiguration, although thecisbehaviour differs from that oftransisomers. This has been interpreted in terms of definite ring conformations in substituted derivatives, while the unsubstituted 1,3‐dioxolane undergoes free pesudorotation. Calculations of coupling constants were performed by semi‐empirical MO methods, both for unsubstituted 1,3‐dioxolane and for C‐4 substituted derivatives in a large number of conformations, in order to compare calculated and experimental values; the correct order ofJ(cis)andJ(trans)for 1,3‐dioxolane is obtained only by employing energies fromab‐initioMO calculations averaged over the pseudorotation circuit. For the C‐4 substituted compounds calculated coupling constants were employed in a ‘trial and error’ process for the identification of the preferred conformations of these compounds; a set of two torsional angles for each compound was derived which allows a tentative description of the geometry of each molecule. A criticism of these geometries is given according to the evidence available on the structure

ISSN:0030-4921    

DOI:10.1002/mrc.1270130105

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe carbon‐13 NMR spectra have been recorded for representatives of three previously unexamined classes of pentacyclic triterpenes—lupanes, fernanes and arboranes. In addition to the spectra of lupeol methyl ether, cylindrin and arundoin, the spectra of a number of other triterpene methyl ethers are also recorded. The effect of methyl ether formation on the shilding values for carbons in the 3β‐hydroxy‐4,4‐dimethyl‐ ring A syste

ISSN:0030-4921    

DOI:10.1002/mrc.1270130106

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe carboxyl substituent effects for branched carboxylic acids have been determined by carbon‐13 Fourier ransform nuclear magnetic resonance of eighteen measured and reported branched acids. For α‐branched systems the substituent effects are α = 15.3 ppm, β = 2.6 ppm, γ = −1.9 ppm, δ = 0.9 ppm and ϵ = 0.5 ppm. For other branched acids, the determined carboxyl substituent effects are α = 19.2 ppm, β = 2.1 ppm, γ = −1.4 ppm, δ = 0.6 ppm

ISSN:0030-4921    

DOI:10.1002/mrc.1270130107

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe proton spectra of the compounds propene (1) and 3‐methylbutene‐1 (2) have been measured in various solvents and, as neat liquids, at variable temperature. The effects of solvent and temperature on 1 are found to be small, but not negligible. The effect of temperature on the coupling constants of 2 are more pronounced, which is explained in terms of ananti‐gaucheequilibrium. To obtain a consistent ΔE° value from each temperature dependent coupling constant it is necessary to correct for the non‐conformational temperature effects (obtained from 1) as well as to correct for changes in the geometry of the entire molecule, which are concurrent with a conformational transition. Such geometry changes have been calculated by a consistent force field technique, which, when coupled with INDO‐MO calculated dependencies of coupling constants on valence (and torsional) angles, provided the changes in coupling constants. The observed temperature dependence of the coupling constants of the H2CCH— moiety of 2 could be satisfactorily explained in this fashion. The difference in energy between theantiandgaucheforms of 2 were determined as ΔE° = 1

ISSN:0030-4921    

DOI:10.1002/mrc.1270130108

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractDoublets can be observed for carbons α and β to the hydroxyl in aliphatic alcohols containing equimolar amounts of OH and OD dissolved in (CH3)2SO containing CaSO4desiccant. Isotopic doublets are also observed for theipsoandorthocarbons in alkyl substituted phenols.Paraisotopic doublets are observable inpara‐substituted phenols containing a large 2‐substituent. The isotope shift is positive (low field) for theparacarbon, opposite to the negative shifts usually obs

ISSN:0030-4921    

DOI:10.1002/mrc.1270130109

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractIn order to separate inductive and lone pair effects on geminal and vicinal coupling constants in a stereochemically well‐defined system, the1H NMR spectra of phenylcyclopropane (1),N‐methyl‐2‐phenylaziridine (2), styrene oxide (3) and 1,1‐dimethyl‐2‐phenylaziridinium fluorosulfonate (4) were compared. In D2O the heterocyclic ring protons of 4 were split into an ABX pattern which gaveJ(cis)= 8.5,J(trans)= 7.4 andJ(gem)= −4.8 Hz (signs consistent with INDOR results). From the small solvent effects onJ(vic) determined from 4‐d1, it was concluded that J(gem) is −5.0 ± 1.0 Hz in methylene chloride. The absolute values for the coupling constants for 1 and 4 provide a measure of the inductive effect of the ring hetero group onJ.Values ofJ(gem) for 2 and 3 deviated from those predicted on the basis of the above inductive effect, suggesting lone pair contributions toJ(gem) ofc.+5.5 Hz per lone pair. With this estimate it was possible to predict accurately theJ(gem) values for 2‐t‐butyloxaziridine and 1‐t‐butyldiaziridine. The values ofJ(cis)andJ(trans)for 2 and 3 likewise suggested a contribution of −2.5 Hz toJ(cis)and −2.7 Hz toJ(trans)per lone pair. The present results suggest that the major factors causing positiveJ(gem) values in epoxides and aziridines are increasedscharacter to the CH bonds and lone pair effects, while the so‐called electronegativity effect actually operates in the opposite direction todecrease J(gem). Also, the unusually lowJ(vic) values of epoxides relative to cyclopropanes are now seen to be due more to negative lone pair contributions than to the el

ISSN:0030-4921    

DOI:10.1002/mrc.1270130110

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractVarious cyclodipeptides containing glycine, alanine, leucine, valine, phenylalanine, phenylglycine and sarcosine units were synthesized by cyclization of dipeptide pentachlorophenyl esters. The13C and natural abundance15N NMR spectra of these heterocycles were measured in trifluoroacetic acid and compared with the spectra of the corresponding amino acids and polypeptides. The13C NMR carbonyl signals of all cyclodipeptides show a 1.5–4.0 ppm upfield shift relative to the corresponding polypeptides. The15N NMR signals show no such consistent relationship. The substituent effects and the neighbouring residue effects observed in the15N NMR spectra of the cyclodipeptides are different from those of polypeptides, while the one bond NH coupling constant ofcisandtransamide groups was almost identical. The nitrogen and the carbonyl signal of the Gly units in cyclo‐Gly‐Phe show an extraordinary downfield shift, reflecting the interaction of the phenyl group with the 2,5‐dioxopipera

ISSN:0030-4921    

DOI:10.1002/mrc.1270130111

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY