Estimated ionic B-coefficients from NMR measurements in aqueous electrolyte solutions

O-17-NMR spin-lattice relaxation times T-1 of D2O molecules were measured at 5-85 degrees C in D2O solutions of alkali metal halides (LiCl similar to CsCl, KBr and KI), DCl, KOD, Ph4(P)Cl, NaPh(4)B, and tetraalkylammonium bromides (Me(4)NBr similar to Am4NBr) in the concentration range 0.1-1.4 mol-kg(-1). The B-coefficients of the electrolytes obtained from the concentration dependence of relaxation rates R(1) = 1/T-1 were divided into the ionic B-coefficients by three methods: (i) the assumption of B(K+) = B(Cl-), (ii) the assumption of B(Ph(4)P(+)) = B(Ph(4)B(-)), and (iii) the use of B(Br-) obtained from a series of B(R(4)NBr). It was found that Methods (ii) and (iii) resulted in an abnormal temperature dependence of the B-coefficients of alkali metal ions and a negative values of rotational correlation times tau(c) at lower temperatures for hydroxide and halide ions. These results suggest that the methods based on the van der Waals volume are not adequate for the ionic separation of NMR B-coefficients. From the analysis using the assumption of B(K+) = B(Cl-), it was found that D3O+, OD-, and Me(4)N(+) ions are the intermediates between structure makers and breakers, and that the hydrophobicity of phenyl groups is weaker than that of alkyl groups due to the interactions between water molecules and pi-electrons in phenyl groups.