Wide-line 1H Research Articles

31P and 2H NMR studies of structure and motion in bilayers of phosphatidylcholine and phosphatidylethanolamine.

The structural and motional properties of mixed bilayers of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) have been examined by using wide-line 31P, 14N, and 2H NMR. 2H and 14N NMR data showed that in mixed bilayers containing both PC and PE the conformations of the head-group moieties are essentially identical with those observed for bilayers containing a single phospholipid species. Equimolar amounts of cholesterol induce also only a small change in head-group conformation. 31P T1 relaxation measurements (at 300 MHz) at various temperatures of bilayers containing phospholipids with a mixture of phosphocholine and phosphoethanolamine head-groups and unsaturated fatty acid residues revealed in all cases a clearly defined minimum corresponding to the condition omega O tau C-1 approximately 1. For all phospholipid mixtures studied, the 31P T1 relaxation was homogeneous over the whole powder spectrum and could be fitted to a single-exponential decay. The 31P vs temperature profiles were analyzed by a simple correlation model following the analysis of Seelig et al. (1981) [Seelig, J., Tamm, L., Hymel, L., & Fleischer, S. (1981) Biochemistry 20, 3922-3932]. Rotational diffusion of the phosphate moiety in bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was slower than that of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), and the activation energy was increased by a factor of 1.7 to 31.4 kJ mol-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Reactive hydrogen species in the copper-chromium oxide system

Mixed copper chromium oxides are excellent catalysts for selective hydrogenation of unsaturated organic compounds, but the reaction mechanism has not been completely elucidated. The use of thermogravimetry, wide-line 1H NMR and catalytic hydrogenation revealed the presence of some reactive hydrogen species in a reduced cubic copper chromite spinel catalyst. Quantitative evaluations of this hydrogen have been obtained. It is not possible to be precise about the location and the charge of this species but we suggest that it is located in the bulk of the catalyst and closely associated with this spinel phase.

Anisotropic mobility of water in hydrated layered chalcogenides A+x(H2O)y[TaS2]x− and A+x(H2O)y [NbS2]x− as studied by NMR

Wideline 1H NMR studies have been carried out in various hydrated layered chalcogenides of the type A+x(H2O)y [TaS2]x− at temperatures from 148 to 300 K, where A=Na, K, NH4, Cs, and Ca. Some measurements have been made at 77, 363, 398, and 425 K, respectively, and a sample with Nb instead of Ta has also been examined. Depending upon the temperature range and upon the particular compound, three different types of spectra have been observed. The rigid lattice H2O spectra are characterized by intra- and intermolecular dipole–dipole interactions. At elevated temperatures, the spectrum equals rather perfectly the theoretical shape of the proton spectrum for an isolated two-spin system. This suggests the occurance of a range of activated ordered mobility which is explained by a two-dimensional diffusion of water inside the interlayer space. For compounds with bilayers rather than monolayers of water, rotation of H2O about its C2 axis is also activated. This is supported by measurements of the spin–lattice relaxation time T1. Finally, an additional narrow line, which appears at high temperature, is attributed to a subphase of water undergoing random motion.

1: 13- und 1: 14-Heteropolyvanadate des Phosphors(V) / 1:13- and 1:14- Heteropolyvanadates of Phosphorus(V)

Deep red heteropolyvanadates of phosphorus(V) n M2O:P2O5: 13 V2O5 · aq (n = 3, 5, 6; M = Na, K, Rb, Cs, NH4) and n M2O: P2O5: 14 V2O5 · aq (n = 4, 7; M = K, Rb, Cs, NH4, (n-C4H9)4N) were prepared. Recrystallization of 1: 13- and 1: 14-heteropolyvanadates and determination of molecular weight by ultracentrifuge technique in solutions from V2O5 and NaH2PO4 indicate 1: 14-heteropolyvanadate ions to be stable species over a wide range of pH, while 1: 13-heteropolyvanadate ions are only stabilized in higher acidified solutions containing H2PO4 - or as slightly soluble salts. Wide line 1H NMR spectra are interpreted in terms of OH groups and H2O of cristallization, the isolated heteropolyvanadates of both series consisting of protonated anions; the basicity of heteropolyvanadic acids of phosphorus(V) is unknown.