摘要:

AbstractThe1H and2H NMR spectra of a number of edible oils were investigated. The average numbers of hydrogens and deuteriums for the olefinic, methylene and methyl sites in mixtures of triacylglycerols were determined, and some parameters describing the different fractionation of deuterium in the various sites were obtained. These results are discussed in connection with the biosynthesis steps involved in the elongation and desaturation processes of the fatty acid components.

ISSN:0749-1581    

DOI:10.1002/mrc.1260330302

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe configurational and conformational properties of six 4‐trimethylammoniummethyl 2,2‐disubstituted 1,3‐dioxolanes were studied using NOE experiments and vicinal coupling constants. Selective 1D NOE experiments proved to be effective tools in the configurational assignment of C‐2 relative to C‐4. The preferred conformation of the dioxolane ring and the exocyclic group at C‐4 was obtained by employing vicinal coupling constants and NOE results. The1H and13C NMR chemical shifts show stereochemically dependent trends. Quantitative analysis of conformer populations was performed using Haasnootet al's equation. The N+(CH3)3group was found to be synclinal with respect to the heterocyclic O‐3 atom and points outside the ring. When a phenyl group is present at C‐2, the 4‐CH2N+— group in atransrelationship to the 2‐phenyl ring was found to occur prevalently in a pseudo‐axial orientation, whereas it was established to be prevalently pseudo‐equatorial whenciswith

ISSN:0749-1581    

DOI:10.1002/mrc.1260330303

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractIsotropically shifted19F NMR signals were observed for novel mononuclear Co(II) complexes, (Et4N)2[Co(Z‐Cys‐Pro‐Leu‐Cys‐Gly‐X)2] (Z = benzyloxycarbonyl, X = NHC6H4‐p= F, NHC6H4‐m‐F and NHCH2CH2C6H4‐p‐F). Such isotropically shifted signals show very short19F spin‐lattice relaxation times (T1) in the range 20–150 ms compared with the corresponding SH‐free peptide ligands, Z‐Cys(SH)‐Pro‐Leu‐Cys(SH)‐Gly‐X, which revealed signals with19FT1values in the range 1600–3200 ms. The observed19F NMR isotropic shifts and short19FT1values in the Co(II)‐cysteine‐peptide complexes are ascribed to the formation of NH—S hydrogen bonds and the presence of interactions of aromatic groups with the s

ISSN:0749-1581    

DOI:10.1002/mrc.1260330304

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractFrom the marine brown algaDictyopteris delicatulaLamaouroux, two new (1, 3) and two previously reported sesquiterpenes (2, 4) were isolated and characterized. Compound 1 was identified as 4β,5α‐dihydroxycubenol and 2 was found to be a non‐racemic mixture of (±)‐torreyol. Compound 3 was characterized as cubenol‐3‐one and 4 was identified as cubenol. For the assignment of the complete relative stereochemistry of compounds 1 and 2, it was necessary to employ extensive 2D NMR methodologies in combination with the lanthanide shift reagent europium(III) tris(1,1,1,2,2,3,3)‐heptafluoro‐7,7‐dimethyl‐d6‐octane‐4,6‐dione‐d3[Eu(fod)3]. Anomalous proton shielding effects which occurred on addition of Eu(fod)3to compound 1 suggested that classical lanthanide‐induced shift (LIS) analysis for predicting proton chemical shifts was not applicable. Application of 2D NOESY measurements to NMR samples of 1 and 2 containing Eu(fod)3clearly demonstrated an alternative to classical methods for interpreting lanthanide‐induced shifts. The enhanced value of shift reagnents of this type as an aid to structure determination and as for ass

ISSN:0749-1581    

DOI:10.1002/mrc.1260330305

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe relative configuration and conformation of the 8‐methyl‐5‐nitro‐1‐oxo‐Δ8(8a)‐octahydronaphthalene isomers were elucidated by various1H and13C NMR methods. The structure of the tricyclic by‐products was

ISSN:0749-1581    

DOI:10.1002/mrc.1260330306

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

Abstract77Se was measured by inverse proton detection using multiple‐quantum1H‐{77Se} correlation spectroscopy. One‐and two‐dimensional heteronuclear multiple quantum coherence (HMQC) experiments are reported for selenophene, benzeneselenol, dimethyl selenide, dimethyl diselenide, and D,L‐selenomethionine with a range of77Se1H coupling constants from 9.5 to 54.2 Hz. In these compounds having protons with different77Se1H coupling constants the different correlations can be selectively enhanced by varying the mixing time. The enhancement for indirect versus direct77Se detection was estimated for dimethyl selenide yielding a value close to the theoretica

ISSN:0749-1581    

DOI:10.1002/mrc.1260330307

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractLong‐range proton‐carbon coupling constants,nJCH, were measured for some simple norbornene derivatives. Among the influence of substitution pattern, a study of the experimental influence of the double bond in the norbornene skeleton on2JCHand3JCHwas made, taking into account the previously published experimental data for analogous saturated systems. These experimental data show that structural groups which are several bonds away from the coupling sites, but close in space, can provide important alternative mechanisms for transmission of the heteronuclear coupl

ISSN:0749-1581    

DOI:10.1002/mrc.1260330308

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe BIRD pulse sequence is widely used to distinguish between protons that are directly bonded to a13C nucleus and those that are not. It consists of a proton 90° pulse, a delay of 1/(21JCH), simultaneous carbon and proton 180° pulses, a further delay of 1/2Jand a final proton 90° pulse. For two spins at equilibrium, the effect of this sequence can be easily understood, but for complex systems the behaviour can be counter‐intuitive. This paper explains the general behaviour of the BIRD sequence using theoretical equations and numerical simulations, and discusses some practical applications of the BIRD pulse train. The theoretical equations are derived using tables of general behaviour for the spin systems AX, AX2and AX3. The tables allow the exact calculation of the effect of any pulse sequence on these spin systems, including all multiple quantum effects. The simulations show that the sequence is usually robust with respect to pulse imperfections and non‐ideal spin systems. In other cases, particularly when signals should be suppressed, small errors can have dramatic consequences. The results derived here are for a BIRD sequence inserted into an INEPT experiment, but many of the conclusions can be applied to all of the more standard applications of th

ISSN:0749-1581    

DOI:10.1002/mrc.1260330309

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractFollowing earlier studies on the development of one‐ and two‐dimensional NMR methods based on selection of coherences via maximum‐quantum pathways and using inverse1H detection, a pulse sequence is now described for analogous direct heteronuclear detection for use in laboratories which do not have access to inverse detection technology. The method has been applied to the assignment of all of the1H and13C NMR resonances of sodium taurocholate, an important component of bile. The assignment of the resonances of major bile salts is important for the assignments of NMR resonances in bile itself to yield understanding of altered biochemistry in disease states. The effect of deliberately missetting the refocusing delay in the pulse sequence is shown to be beneficial in the assignment pr

ISSN:0749-1581    

DOI:10.1002/mrc.1260330310

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractHigh‐speed magic angle spinning at high magnetic field was used to obtain high‐resolution solid‐state23Na NMR spectra of anhydrous Na2SO3(P3,Z= 2). Observation of the spinning sidebands of the23Na satellite (± 3/2 ↔ ± 1/2) transitions allows the identification of the three crystallographic sites that could not be distinguished in the central transition region of the NMR spectrum. The23Na sites in this salt were characterized by NMR for the first time and assigned to the crystallographic sites on the basis of a point‐charge model of the electric field gradient tensors a

ISSN:0749-1581    

DOI:10.1002/mrc.1260330311

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY