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Os 3 (CO) 10 (NCCH 3 ) 2 has been hydrogenated with para-hydrogen to yield H 2 Os 3 (CO) 10 where the two hydrogen nuclei remain magnetically equivalent and therefore in a singlet state. Despite this equivalence, an enhanced longitudinal magnetization is observed to decrease toward thermal equilibrium. It is postulated that this enhanced magnetization is created through a nuclear relaxation interference mechanism (cross-correlation between dipolar interaction and chemical shift anisotropy); decay curves are then successfully analyzed by means of a spin relaxation theory adapted to this situation.

Decylammonium chloride dissolved in water at concentrations of 0.5 and 2.0 M has been studied by multifield carbon-13 and deuterium nuclear magnetic relaxation. Carbon-13 longitudinal relaxation times , and nuclear Overhauser effects have been obtained for all carbons in the aliphatic chain, at frequencies ranging from 15 to 90 MHz. Decylammonium chloride has been selectively deuterated at the a position with respect to the polar head. 2H longitudinal relaxation times T[ and, in some instances, transverse relaxation times T2 have been measured from 2 to 55 MHz. At 0.5 M decylammonium chloride forms spherical micelles. The relevant data are consistently analyzed according to the "two-step model" (Halle, B.; Wennerstrom, H. J. Chem. Phys. 1981, 75, 1928, which implies correlation times associated with the local fast motions, ß (/ = 1, 10), a correlation time associated with the slow overall motion of surfactant molecules, rs, and local order parameters S¡. The 2.0 M solution data required a more elaborate analysis (three-step model), which involves two correlation times (corresponding to rotation about the different axes of an ellipsoid) for describing the slow motions. This is because, at this concentration, micelles have nonspherical shape. In both cases, slow correlation times could be interpreted in terms of micelle tumbling and lateral diffusion of surfactant molecules around the curved surface of the aggregate. Quantitative parameters could be deduced. The radius of spherical micelles is identical with the surfactant extended chain length. At 2 M concentration, micelles are rod-shaped. When approximated by an ellipsoid, it is shown that the minor axis is identical with the radius of spherical micelles whereas the major axis is 9 times as large as the latter. The lateral diffusion coefficient is found to be the same in the two types of micelles D = (1.5 ± 0.2) X 10"10 m2 s"1. The fast correlation times confirm the liquidlike character of the micelle interior and the order parameters exhibit the usual profile starting from 0.2 at the a position to very small values at the terminal methyl.

This article begins with general considerations about enrichment of hydrogen gas into its para isomer (corresponding to nuclear spins in the singlet state); this is a necessary condition to obtain hyperpolarization from transfer of the relevant population excess. This transfer is generally mediated by a hydrogenation reaction such that the two protons become nonequivalent. The energy level populations of this new spin system can be calculated unambiguously using a density matrix formalism. This formalism is reviewed, and the authors propose a simple method that leads to the spin state after the hydrogenation reaction and the insertion of the sample in the NMR magnet. The effect of radiofrequency pulses is also considered.

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In 2001, Pickard and Mauri implemented the gauge including projected augmented wave (GIPAW) protocol for first-principles calculations of NMR parameters using periodic boundary conditions (chemical shift anisotropy and electric field gradient tensors). In this paper, three potentially interesting perspectives in connection with PAW/GIPAW in solid-state NMR and pure nuclear quadrupole resonance (NQR) are presented: (i) the calculation of J coupling tensors in inorganic solids; (ii) the calculation of the antisymmetric part of chemical shift tensors and (iii) the prediction of (14)N and (35)Cl pure NQR resonances including dynamics. We believe that these topics should open new insights in the combination of GIPAW, NMR/NQR crystallography, temperature effects and dynamics. Points (i), (ii) and (iii) will be illustrated by selected examples: (i) chemical shift tensors and heteronuclear (2)J(P-O-Si) coupling constants in the case of silicophosphates and calcium phosphates [Si(5)O(PO(4))(6), SiP(2)O(7) polymorphs and α-Ca(PO(3))(2)]; (ii) antisymmetric chemical shift tensors in cyclopropene derivatives, C(3)X(4) (X = H, Cl, F) and (iii) (14)N and (35)Cl NQR predictions in the case of RDX (C(3)H(6)N(6)O(6)), β-HMX (C(4)H(8)N(8)O(8)), α-NTO (C(2)H(2)N(4)O(3)) and AlOPCl(6). RDX, β-HMX and α-NTO are explosive compounds.

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