Magnetic Resonance in Chemistry

Martin, Gary E.; Crow, Frank W.; Kaluzny, Brian D.; Marr, J. Gordon; Fate, Gwendolyn D.; Gilbertson, Terry J.

doi: 10.1002/(SICI)1097-458X(199809)36:9<635::AID-OMR348>3.0.CO;2-Cpmid: N/A

Early efforts to utilize 15N NMR spectroscopy in structure elucidation studies were often frustrated by the low gyromagnetic ratio (γN) and the low natural abundance (0.37%) of the nuclide. The advent of 1H and inverse‐detected 2D NMR methods has eliminated many of the difficulties inherent to the use of 15N as a structural probe. This paper reports the partial assignment of the 15N NMR resonances of the thiopeptide antibiotic sulfomycin‐I produced by Streptomyces viridochromogenes. With the exception of two tertiary nitrogen resonances that had no two‐ or three‐bond coupling pathways, assignments were made either through direct correlation 1H–15N GHSQC or one‐bond optimized 1H–15N GHNMQC or via two or three bonds using 1H–15N GHNMQC spectra. Assignments are also reported for the heterocyclic nitrogen resonances of two thiazole and one oxazole moiety contained in the structure of the antibiotic via 3J(N,H) coupling from the heterocyclic ring protons. Despite the suggestion that these coupling pathways, suspected to be ca. 2 Hz, might be difficult to observe since they are comparable to the linewidths of the thiazole and oxazole protons in question, they were still exploitable for assignment purposes. © 1998 John Wiley & Sons Ltd.

Delepierre, Muriel; Roux, Pascale; Chaffotte, Alain‐F.; Goldberg, Michel E.

doi: 10.1002/(SICI)1097-458X(199809)36:9<645::AID-OMR353>3.0.CO;2-Ppmid: N/A

Magic angle spinning (MAS) has long been used as a powerful technique in studies of heterogeneous samples such as powdered solids, compartmentalized liquids and heterogeneous solid–liquid mixtures. Recently it has been shown that higher resolution could be achieved if high‐resolution magnetic susceptibility matching probe technology was used in conjunction with MAS (Nano‐probe). In this paper the possibilities and advantages of generating high‐resolution spectra of liquids is illustrated using the Nano.nmr probe for the study in solution of lysozyme subjected to various treatments. © John Wiley & Sons Ltd.

Xu, F.; Cross, T. A.

doi: 10.1002/(SICI)1097-458X(199809)36:9<651::AID-OMR341>3.0.CO;2-6pmid: N/A

Changes in the solvent dielectric properties are correlated with changes in polypeptide conformer populations. Gramicidin A, a peptide native to membrane environments, forms a variety of well defined dimeric conformations in relatively low dielectric organic solvents. However, changes in this environment lead to changes in the conformer populations with the lowest dielectric solvents favoring the conformers with the lowest net dipole moment. Such changes were characterized by cross‐peak intensities in GCOSY solution NMR spectra. In studying membrane‐bound polypeptides, it is very important to recognize that the structure is not dictated by just the amino acid sequence, but that the environment plays a very significant role in defining the polypeptide conformation. © 1998 John Wiley & Sons, Ltd.

Screttas, Constantinos G.; Heropoulos, George A.; Steele, Barry R.; Bethell, Donald

doi: 10.1002/(SICI)1097-458X(199809)36:9<656::AID-OMR339>3.0.CO;2-5pmid: N/A

The nuclear magnetic resonance shifts, δobs, induced to 31P in Ph3P, (MeO)3P and (MeO)3PO by alkali metal fluorenone radical anions in tetrahydrofuran solutions were measured. These parameters, which depend significantly on the cation for a given ligand, and also on the ligand for a given cation, were used to extract the corresponding 31P contact shifts, δc(M). The latter parameters are proposed as a measure of the ligand affinity of a given phosphorus compound for a particular alkali metal. Trimethyl phosphate exhibits the greatest affinity for the lithium cation. The magnitudes of δc(M) imply some covalency between the cation and the radical anion and the ‘paradox’ of a heavier alkali metal such as potassium being covalently bonded to fluorenone radical anion has been explained. The transferability of the reported ligand affinities of Li+, Na+ and K+ is discussed. © John Wiley & Sons, Ltd.

Hilmersson, Göran; Rebek, Julius

doi: 10.1002/(SICI)1097-458X(199809)36:9<663::AID-OMR350>3.0.CO;2-1pmid: N/A

13C NMR spin–lattice relaxation and 13C–{1H} nuclear Overhauser measurements were performed on the encapsulation complex between (2.2)paracyclophane and a dimeric capsule known as the hydroxy ‘softball.’ The data were analyzed using the formalism for an isotropically diffusing sphere. The binding constant for the complex is (3.5±0.5)×103 l mol‐1 in CDCl3 at 295 K. The average dipole–dipole relaxation time is 0.45±0.04 s for the CH vectors of the encapsulated (2.2)paracyclophane and 0.30±0.03 s for the skeleton of the hydroxy ‘softball.’ The correlation time for the skeleton of the hydroxy ‘softball’ is 2.7×10‐10 s. The corresponding correlation time for the encapsulated (2.2)paracyclophane is calculated to be 1.2×10‐10 s. This results in an average dynamic coupling constant, χ, of 0.47, indicating shape complementarity and correlated motion between the hydroxy ‘softball’ and the (2.2)paracyclophane. © 1998 John Wiley & Son Ltd.

Dalvit, Claudio; Böhlen, Jean‐Marc

doi: 10.1002/(SICI)1097-458X(199809)36:9<670::AID-OMR356>3.0.CO;2-Spmid: N/A

The performance of the 1H 2D PFG‐DQ experiment is analysed with theory and with some practical examples. The use of different angles for the detection pulse allows sensitivity optimization and spectral editing. Almost complete water suppression, high sensitivity, predominantly absorption lineshape, very low t1 noise and absence of strong diagonal signals make the method very suitable for the analysis of complex mixtures, e.g. biofluids, cell cultures, natural product extracts and combinatorial chemistry samples. The method is also compared with the well known TOCSY and COSY experiments. © John Wiley & Sons Ltd.

Zalibera, Ľubomír; Milata, Viktor; Ilavský, Dušan

doi: 10.1002/(SICI)1097-458X(199809)36:9<681::AID-OMR346>3.0.CO;2-Ppmid: N/A

A series of 14 3‐substituted 4‐oxoquinolones with or without a substituent (methyl, ethyl) in position 1 were prepared. Literature and measured data were used to study the influence of the substituent on the shifts of carbon atoms of these compounds, which are model compounds for antibacterial drugs of the nalidixic acid type. ©1998 John Wiley & Sons, Ltd.