Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1260250901pmid: N/A

Pattaroni, Christian; Lauterwein, Jürgen

doi: 10.1002/mrc.1260250902pmid: N/A

The 13C spin‐lattice relaxation times and nuclear Overhauser enhancement factors of all‐trans‐retinal were measured in acetone‐d6 at two different magnetic field strengths. The extent to which the chemical shift anisotropy mechanism was found to contribute to the relaxation rate of the quaternary olefinic carbons was between 23 and 37% at 4.70 T and between 48 and 66% at 8.45 T. Assuming anisotropic molecular motion and an asymmetric chemical shift tensor, the shielding anisotropies of carbons C‐5, C‐6, C‐9 and C‐13 were calculated to be 185, 172, 188 and 228 ppm, respectively. These are qualitatively similar to those obtained in a recent 13C NMR study of all‐trans‐retinal in the solid state. In contrast, the quaternary aliphatic carbon C‐1 was much less relaxed by the chemical shift anisotropy mechanism (contribution <11%). The relaxation of the proton‐bearing carbons was independent of the magnetic field and determined only by the dipole—dipole interaction mechanism.

Zektzer, Andrew S.; John, Boban K.; Martin, Gary E.

doi: 10.1002/mrc.1260250903pmid: N/A

A modified long‐range heteronuclear chemical shift correlation pulse sequence which eliminates modulations of response intensity due to one‐bond proton‐carbon [1 J(CH)] spin couplings is described. The ‘decoupling’ of one‐bond modulation has been accomplished through the use of a bilinear rotational decoupling (BIRD) pulse of the type 90° x(1H)‐τ‐180° x(1H)/180° x(13C)‐τ‐90° ‐x(1H) midway through the second magnetization transfer delay, Δ2.

Iyer, Radhakrishnan P.; Ratnam, Rakesh K.; Kulkarni, Subodh P.; Zubair, M. A.; Coutinho, Evans C.; Sonaseth, Mariam S.; Gopalan, Balasubramanian

doi: 10.1002/mrc.1260250904pmid: N/A

The structures of open‐chain bis‐Reissert analogues and their salts were investigated using 13C NMR spectroscopy. Evidence is presented to show that the former exists in the acyclic form in solution. Detailed structural studies and the 13C NMR data clearly show that, in solution, the open‐chain bis‐Reissert salt analogues exist predominantly as the amino tautomer.

Szalontai, G.; Bakos, J.; Tóth, I.; Heil, B.

doi: 10.1002/mrc.1260250905pmid: N/A

13C, 1H and 31P NMR investigations were carried out to confirm the stereochemistry of novel bis[(4R,6R)‐4,6‐dimethyl‐1,3,2‐dioxaphosphorinan‐2‐yloxy]alkanes. The 13C NMR spectra exhibited second‐order features at room temperature. Substantial coupling was found between P atoms six bonds apart. The possibility of a through‐space contribution was tested. Spatially close P atoms and the strongly electronegative P substituents (oxygen atoms) are thought to be responsible for the enhanced P… P coupling.

Wasser, R; Diehl, P

doi: 10.1002/mrc.1260250906pmid: N/A

The rα structures of ethylene and 1,1‐difluoroethylene have been determined by NMR of partially oriented molecules, considering the interaction between the solute molecule and the liquid crystal solvent which leads to a correlation between molecular vibration and rotation. The analysis of the data also provides the interaction parameters which characterize the torques acting on the individual molecular bonds, deforming and simultaneously orienting the solute. A linear relationship between the interaction parameters for the C  H bonds of the two solutes and methane in the same solvents has been found.

MacBride, J. A. Hugh; Leow, Mei Ling; Wright, (the late) Peter M.; Kilcoyne, John P.; Wakefield, Basil J.

doi: 10.1002/mrc.1260250907pmid: N/A

The 13C chemical shifts for 2,7‐, 1,8‐ and 1,6‐diazabiphenylenes are reported, together with some coupling constants and the 13C chemical shifts of a benzothiophene analogue of biphenylene. The results can be explained by the existence of a paramagnetic ring current in the four‐membered ring of the nitrogen‐containing compounds which is absent in the case of the benzothiophene. A possible explanation is offered.

Nelson, John H.; Affandi, Salina; Gray, George A.; Alyea, Elmer C.

doi: 10.1002/mrc.1260250908pmid: N/A

Proton and 13C NMR parameters have been determined for phenyldibenzophosphole and its oxide, sulfide, selenide and W(CO)5 complex from high‐resolution one‐ and two‐dimensional (COSY, HETCOR and 2DJ) experiments at 4.7, 7.1 and 9.4 tesla. Assignments of chemical shifts and coupling constants have been made and verified by computer simulation of the proton spectra. The data are discussed in relation to the geometry and electron density at phosphorus and the diamagnetic anisotropy of the W(CO)5 group.

Bischofberger, Karl; Bull, James R.; Chalmers, Anthony A.

doi: 10.1002/mrc.1260250909pmid: N/A

The 500 MHz 1H spectra of the 3‐methyl ethers of estrone, estradiol and their 14α‐methyl analogues were assigned by proton decoupling and analysed by second‐order calculations for chemical shifts and coupling constants. Introduction of a 14α‐Me group effects consistent deshielding of 1,3 diaxially disposed protons. Coupling constant values show characteristic changes for ring D protons, and suggest that some minor perturbation in the H‐9α, ‐11α, ‐11β region is caused by the additional methyl group.

Berman, Elisha

doi: 10.1002/mrc.1260250910pmid: N/A

Two O‐linked glycopeptides were isolated by protease digestion of calf fetuin. Using 13C and 1H NMR spectroscopy, it was established that both carry identical trisaccharide side‐chains, but they were found to possess different peptide moieties. Therefore, they must originate from different regions of the polypeptide backbone of fetuin. The two glycopeptides carry a total of three oligosaccharide chains, in accordance with previously published data. One glycopeptide was found to carry two side‐chains: one is linked to a serine and the other to a threonine that are separated by one alanine only. The other glycopeptide carries one sugar chain linked to a serine residue. It was not possible to isolate any glycopeptide which contained a second sialic acid residue directly linked to the N‐acetylgalactosamine, as reported earlier. Some long‐range chemical shift effects were observed in the NMR spectra of the glycopeptide, indicating a specific conformation for this glycopeptide as a result of the proximity of the two oligosaccharide side‐chains.