Chemical-shift anisotropy experimental determination

The process of spin-lattice relaxation involves the transfer of magnetization between the magnetic nuclei (spins) and their environment (the lattice). The rate at which this transfer of energy occurs is the spin-lattice relaxation-rate (/ , in s ). The inverse of this quantity is the spin-lattice relaxation-time (Ti, in s), which is the experimentally determinable parameter. In principle, this energy interchange can be mediated by several different mechanisms, including dipole-dipole interactions, chemical-shift anisotropy, and spin-rotation interactions. For protons, as will be seen later, the dominant relaxation-mechanism for energy transfer is usually the intramolecular dipole-dipole interaction. 

The characterisation of the angular dependence of the interaction of two dipole tensors A1 A2 and B B2 is therefore straightforward, namely it depends on the projection angle of the two bonds between A1 and A2 and between B1 and B2. The orientation and magnitude of the chemical shift anisotropy (CSA) tensor, which also can cause cross-correlated relaxation, is not know a priori and therefore needs to be determined experimentally or... 

USA, in press) that this phenomena is due to an exchange of ATP with bound state where its Linewidth is determined by chemical shift anisotropy. Do you have any experimental or theoretical data on the chemical shift anisotropy of the phosphorus atoms in ATP ... 

Three cis-dioxovanadium(V) complexes with similar N-salicylidenehy-drazide ligands modeling hydrogen bonding interactions of vanadate relevant for vanadium haloperoxidases are studied by solid-state NMR spectroscopy. Their parameters describing the quadrupolar and chemical shift anisotropy interactions are determined both experimentally and theoretically using DFT methods. 

Oldfield et al. have reported the experimental determination of the chemical shift tensors of Ala, Leu, Val, Phe and Met in a number of polycrystalline peptides with known X-ray or de novo solid-state NMR structures. The 700 Hz dipolar coupling between and (directly bonded to C ) permitted extraction of both the magnitude and the orientation of the shielding tensor with respect to the bond vector. The chemical shift anisotropy... 

Ring currents cannot be directly determined by experimental methods. However, comparison of experimental values of magnetic susceptibilities and their exaltations and anisotropies as well as of H-NMR chemical shifts with the respective data calculated from the ring current model points to the adequacy of this model for the interpretation of experimental results. The magnetic susceptibility associated with the ring current / (83BCJ1853), known as the London susceptibility, is given by... 

All the same, the quantitative determination of the aromaticity and antiaromaticity from the ring current model may be complicated by at least two problems. First, experimentally observable values of magnetic susceptibilities and their exaltations and anisotropies as well as the H-NMR chemical shifts are not necessarily determined exclusively by ring currents hence, all other effects have to be identified and removed. Naturally, for this model to work, the contribution by the ring current must be predominant. Another problem is that the calculated results on ring current intensities for molecules from the diatropic-paratropic border area may vary qualitatively depending on the method of calculation (80PAC1541). 

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