摘要:

AbstractThe combination of 1D and 2D NMR techniques, especially the long‐range heteronuclear chemical shift correlation experiment, has permitted the reassignment of some carbons and protons of scopolamine free base in CDCl3solution and the differentiation of each atom of the piperidine ring. In contrast to literature data, and to the protonated state conformation, these studies showed that the methyl group is equatorially disposed relative to the piperidine ring. NMR and IR spectroscopic results demonstrated that the OH group is connected by a hydrogen bond to the phenyl ring at a low concentration, but an intermolecular hydrogen bond is formed at high concentratio

ISSN:0749-1581    

DOI:10.1002/mrc.1260290402

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe13C NMR characteristics of sodium acetate and complexes of ethylenediaminetetraacetic acid (EDTA, H4edta) with La3+and VO2+in the presence of the paramagnetic relaxant [Gd(H2O)nedta]−are reported. The observed selective paramagnetic line broadening of the uncoordinated glycinate arms in [VO2edta]3−permits an assignment of the13C resonances and independent ligand denticity determination. For COO resonances the selectivity was found to beca. 18. A large difference was also observed between the13C transverse relaxation times for the uncoordinated COO groups of CH3COO−and the coordinated COO groups of [La(H2O)3edta]−. The magnitude of the selectivity provides clear advantages in aiding the13C NMR assignment and the establishment of the true denticity for the complexes of polydentate

ISSN:0749-1581    

DOI:10.1002/mrc.1260290403

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

Abstract13C,13C coupling constants in benzene and cyclohexane were measured using monodeuteriated derivatives where13C,13C two‐spin subsystems become slightly non‐equivalent (benzene,1J= 55.88,2J= 2.46,3J= 10.04; cyclohexane,1J= 33.10,2J= 2.12, =3J2.05; all couplings in hertz within the error limits of 0.01 Hz).12C/13C isotope effects for the13C chemical shifts were found to be non‐add

ISSN:0749-1581    

DOI:10.1002/mrc.1260290404

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractAn analysis of the11B relaxation rates was carried out for different solutions ofcloso‐borane dianions B12H 122−and B10H 102−and for a solution ofo‐carborane, C2B10H12. The temperature dependence of these relaxation rates shows the similar interactions of these molecules with the medium. Foro‐carborane,13C relaxation rate measurements provide an evaluation of the correlation time τcand of the microviscosity of the medium. By using these values it is possible to estimate the quadrupole coupling constants for the borane dianions. The results are supported by theoretical data on the electric field gradient using the

ISSN:0749-1581    

DOI:10.1002/mrc.1260290405

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractTwo‐dimensional heteronuclear chemical shift correlation experiments which attempt decoupling inf1have been shown to give artifacts in strongly coupled systems. In particular, COLOC and HETRES experiments on methylene groups show an artifact midway between the two proton lines. This paper provides an explanation of the artifact intensity behaviour with respect to the strength of coupling between the methylene protons. Experimental results on 1,2‐dibromoethylbenzene are presented, and theoretical calculations were carried out on the COLOC experiment and a mathematical model was developed which predicted the artifact appearance and intensity. Simulations were also performed using the simulation program SIMPLTN to verify the experimental and theoretical resu

ISSN:0749-1581    

DOI:10.1002/mrc.1260290406

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of a series of 2‐(n‐butylthiomethylene) cycloalkanones and 2‐(n‐butylthiomethylene) 1‐decalones were recorded and unequivocally assigned by the study of correlation signals in DQCOSY and HETCOR experiments. The effect caused by the introduction of then‐butylthiomethylene group in comparison with the corresponding parent compounds i

ISSN:0749-1581    

DOI:10.1002/mrc.1260290407

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractAn extensive application of two‐dimensional proton–proton and proton–carbon shift correlated spectroscopy allowed the structural elucidation of isosaraine‐2, a minor component of an unique family of alkaloids from the spongeRenier

ISSN:0749-1581    

DOI:10.1002/mrc.1260290408

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe complete resonance assignments and the conformation of the hormone [Tyr8]‐bradykinin, a nonapeptide, in DMSO‐d6have been determined using 2D1H NMR techniques. NMR parameters such as the chemical shifts, coupling constants, temperature coefficients of the backbone NH protons and NOEs have been analysed in the light of the known conformation of the native peptide. The results indicate that the peptide loses conformational rigidity on the replacement of Phe‐8 b

ISSN:0749-1581    

DOI:10.1002/mrc.1260290409

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe1H and13C NMR spectra of tallysomycin s10b(TLM), a third‐generation analog of bleomycin, were completely assigned through the use of two‐dimensional NMR experiments (NOESY, HOHAHA, HMQC, HMBC) in D2O at pH 2.5 and 6.8 (uncorrected values). Significant differences in the resonances for the β‐aminoalanine, β‐hydroxyhistidine and pyrimidinylpropionamide residues were observed owing to the protonation/deprotonation of these moieties. The assignments for TLM at pH 6.8 were compared with the latest 2D NMR‐based assignments of bleomycin A2(BLM A2) at pH 6.7. In general the agreement was excellent, in view of the size and complexity of these anticancer antibiotics. Of the several differences found, most can be attributed to the different substitution patterns in the variable regions of the larger TLM and the BLM A2. Both drugs have similar structures in the region of protonation. For this invariant region of the molecules, comparison of the TLM13C data at pH 2.5 with the 1D BLM A213C data at low pH revealed that protonation induced similar changes in chemical shift for the corresponding signals in the two drugs. It is particularly noteworthy that the glucose and mannose13C signals shift in a very similar manner for both drugs. Since the protonation shifts of the signals of these two sugars are much too large to be attributed to inductive effects, it is highly likely that both drugs, despite the structural differences in the variable region, undergo the same conformationl changes of the gulose and mannose moieties. These chemical shift similarities at both low and high pH confirm the validity of the assignments made independently on these two large drug molecules. The few differences between the two most recent13C assignments of BLM A2, which are based on modern 2D NMR methods, can be resolved using the TLM

ISSN:0749-1581    

DOI:10.1002/mrc.1260290410

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe application of a Hahn spin–echo extended X–1H shift‐correlated (X =13C,29Si,119Sn,207Pb) two‐dimensional NMR technique to carbon–, silicon–, tin– and lead–nitrogen compounds is described. This allows complete suppression of the central line (representing the isotopomer with14N), leaving solely the15N satellites in the two‐dimensional spectrum leading both to accurate measurement of long‐range15N1H spin–spin coupling constants and to the determination of the relative signs of the15NX and15N1H couplings.15N/14N isotope effects on119Sn and207Pb chemical shifts were measured ap

ISSN:0749-1581    

DOI:10.1002/mrc.1260290411

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY