摘要:

AbstractThe kinetics of the intramolecular processes of barium(II), zinc(II), cadmium(II) and lanthanum(III) complexes with 2‐hydroxypropane‐1,3‐diaminetetraacetic acid (HPDTA) were investigated by1H NMR spectrometry. A novel result, the slow Δ, Λ conversion process at room temperature for Zn and LaHPDTA chelates, was observed. The best fittings of the experimental spectra were obtained by computer analysis. These indicate that the activation energy of the Δ, Λ conversion process increases with increasing electrostatic potential for t

ISSN:0749-1581    

DOI:10.1002/mrc.1260300502

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractA computer program developed for the simulation of proton spin‐lattice relaxation times (T1) was applied to the conformational analysis of adenosine 5′‐phosphate (5′‐AMP) in neutral D2O solution. TheT1values of all the non‐exchangeable protons of 5′‐AMP were calculated from the atomic coordinates of the hydrogens and the rotational correlation times by numerically solving a simultaneous differential equation for all the proton magnetizations of the molecule. However, no single conformation gave a good enough agreement between the calculated and observedT1values. 5′‐AMP in solution must therefore be in conformational equilibrium.The equilibrium around the C‐4′–C‐5′ bond was fixed asgauche‐trans(16%),gauche‐gauche(68%) andtrans‐gauche(16%) from the spin coupling constant. A correlation was found to exist between two conformational equilibria,anti⇌synand 2′‐endo⇌ 3′‐endo. The best agreement between the calculated and observedT1values was obtained for an equilibrium between three conformers, 2′‐endo‐anti(Z = 60°) 40–53%, 3′‐endo‐anti(Z = 30°) 18–28% and 2′‐endo‐syn(Z = 220–260°) 27–30%. This equilibrium was consistent with all the currently available information about the conformation of 5′‐AMP in solution. 5′‐AMP exists only in theanticonformation in the crystal. This is similar to our results that theantiis the

ISSN:0749-1581    

DOI:10.1002/mrc.1260300503

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

Abstract13C resonances of [d(CGTACGTACG)]2were assigned by heteronuclear multiple quantum coherence and longrange heteronuclear multiple coherence. The maximum likelihood method was used for the sugar regions of the HMQC spectrum, which made it possible to assign unambiguously all the C‐2′ carbons and some of the C‐5′

ISSN:0749-1581    

DOI:10.1002/mrc.1260300504

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractOxygen‐17 NMR spectra of 45 substituted methyl benzoates in acetonitrile were measured at natural abundance. The substituent‐induced chemical shifts (SCS) of the carbonyl oxygen correlate well with the σmand σ p+substituent constants in two separate correlations formetaandparaderivatives; principal component analysis (PCA) is only slightly better [particularly for the N(CH3)2substituent]. The17O SCS generally depend on the same factors as the13C SCS of the β‐carbon of alkenes, provided comparison is made between compounds of similar polarity. SCS of the methoxyl oxygen depend less precisely on σmor σp, with some unexplaine

ISSN:0749-1581    

DOI:10.1002/mrc.1260300505

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe dynamic behaviour of [Lys8]‐vasopressin derivatives, especially ofN‐Gly‐Gly‐Gly‐[Lys8]‐vasopressin in solution, was investigated by NMR relaxation studies. One can derive a set of dynamics data which describe the molecular tumbling in solution from13C spin–lattice relaxation times,T1, spin–spin relaxation times,T2, and heteronuclear nuclear Overhauser enhancements (NOE). Two different approaches, the scheme proposed by Jardetzky and co‐workers and the ‘model‐free’ approximation of Lipari and Szabo, are used to analyse the dynamics and a comparison of the corresponding data is given. In addition to a mobility of 108–109s−1, we observe a faster mobility of the order of 109–1010s−1in addition to slow dynamic contributions. The latter can be associated by means ofT1, measurements with a motion involving the SS linkage in the vasopressin. Some additional motion is described as the overall mobility of an associate. The results from13C relaxation were corroborated by15NT1measurements, performed at the15N natural abundance level by an INEPT–reverse INEPT m

ISSN:0749-1581    

DOI:10.1002/mrc.1260300506

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo types of proton‐detected1H15N correlation experiments were compared with respect to the observation of15N NMR resonances broadened by scalar relaxation of the second kind. Both single‐ and multiple‐quantum experiments gave equal15N line widths inF1, and in all cases the inverse experiments provided a dramatic increase in sensitivity and spectrometer time‐saving compared with the direct observation of15N resonances. Various aminoboranes [B(NHMe)3; B(NHNMe2)3; 2,3‐dihydro‐2‐methyl‐2‐boraperimidine; organo‐substituted 2,5‐dihydro‐1,2,5‐azasilaboroles; organo‐substituted 7,8‐benzo‐1‐oxa‐6‐aza‐2‐sila‐5‐bora‐3‐cyclooctene], organo‐substituted 2,5‐dihydro‐1,2,5‐azasilaboratolates, an amine–borane adduct (organo‐substituted 7,8‐benzo‐6‐oxa‐1‐aza‐2‐sila‐5‐borabicyclo[3.3.0]oct‐3‐ene), and (ligand)transition metal π‐complexes of organo‐substituted 2,5‐dihydro‐1,2,5‐azasilaboroles were studied by two‐dimensional inverse1H{15N} NMR experiments. The straightforward application to the analysis of several mixtures suggests that this technique is

ISSN:0749-1581    

DOI:10.1002/mrc.1260300507

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe chemistry of highly reactive zerovalent copper species represents an active area of research. Recently, active metal chemistry has been successfully accomplished using polymer‐supported triphenylphosphine–copper(I) coordination complexes as precursors. Since the materials are solids, detailed examination of the reagents at vaious stages of chemical reaction can be problematic, since the primary means of examination has historically been proton,13C and31P NMR methods. In this study, cross‐polarization magic angle spinning (CPMAS) experiments, combined with31PT1relaxation measurements (via proton cross‐polarization), provided data which allowed the determination of the role of the phosphine species in the overall chemistry of these materials. Although it is known that the type of phosphine affects the chemistry, it was found here that there is no observable interaction between the reduced copper species and the polymer‐supported triphenyl

ISSN:0749-1581    

DOI:10.1002/mrc.1260300508

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractExtremely broad119Sn resonances, as the result of1J(119Sn,11B) scalar coupling, were readily detected, even for diluted samples (5 mg in 0.5 ml of C6D6), via inverse two‐dimensional1H{119Sn} NMR experiments. Two bis(amino)trimethylstannylboranes and four dialkylaminobis(trimethylstannyl)boranes were studied. The reaction between diisopropylaminobis(trimethylstannyl)borane and trimethoxyborane was monitored by the same technique, leading to the detection of diisopropylaminomethoxytrimethylstannylborane and dimethoxytrimethylstannylborane as reaction products. Crystalline dicyclohexylaminobis(trimethylstannyl)borane was studied by119Sn CP/MAS NMR. In spite of the proximity of119Sn to the quadrupolar11B nucleus, meaningful spectra could be obtained in a short time (≤ 2

ISSN:0749-1581    

DOI:10.1002/mrc.1260300509

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractMultilayer membranes of 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphorylcholine were prepared in D2O and exposed to γ‐radiation. Changes in the chemical structure due to irradiation were studied by1H,13C and31P NMR after lyophilization and dissolution in chloroform‐methanol (1 : 2, v/v). One‐ and two‐dimensional techniques were used. 1‐Palmitoyl‐sn‐glycero‐3‐phosphorylcholine, 2‐palmitoyl‐sn‐glycero‐3‐phosphorylcholine, glycero‐3‐phosphorylcholine and palmitic acid were identified as new components. Their development during irradiation was quantitatively determined. The results were discussed in terms of possible reaction steps re

ISSN:0749-1581    

DOI:10.1002/mrc.1260300510

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractProton NMR spectra of (E)‐ and (Z)‐[1,2‐bis(methoxycarbonyl)vinyl]aminotoluene were obtained in neutral and basic solutions at 25°C. Base‐catalysed NH proton exchange of theEisomer was found to be about 50 times faster than for theZisomer. The results are rationalized by consideration of electronic and hydrogen bonding

ISSN:0749-1581    

DOI:10.1002/mrc.1260300511

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY