DETERMINATION OF THE O-17 QUADRUPOLAR COUPLING-CONSTANT AND OF THE C-13 SHIELDING TENSOR ANISOTROPY IN SOLUTION FOR MOLECULES CONTAINING A COOH GROUP - NMR RELAXATION STUDY AND THEORETICAL CALCULATIONS

The shielding anisotropy (SA) of the C-13-nucleus Delta sigma in COOH groups of some molecules could be deduced, in solution, from the measu rements of the relaxation time T-1 for different values of the magneti c field (contribution of the SA mechanism to the total relaxation rate ) and from the determination of the reorientational correlation time o f these species. Delta sigma was determined in function of the solvent for benzoic acid, in function of pH for glycine and for free and boun d (to Mg2+) ethylene diamine tetraacetate (EDTA) ion. For benzoic acid dissolved in benzene the results were compared to those obtained in a n aqueous solution and in the solid state, and in order to try to expl ain the observed variations, theoretical calculations of Delta sigma w ere performed. O-17 NMR allowed us also to obtain the O-17 quadrupolar coupling constant.