EFFECT OF IONS ON THE O-17 AND H-1-NMR CHEMICAL-SHIFTS OF WATER

The O-17 and H-1 NMR chemical shifts of water, correspondingly the del ta((OH2)-O-17) and delta((H2O)-H-1) values, have been measured in aque ous solutions of various salts. The effect of these electrolytes on th e delta((OH2)-O-17) and delta((H2O)-H-1) values is discussed. The indi vidual ionic O-17 and H-1 molal chemical shifts, delta((OH2)-O-17)(m) and delta((H2O)-H-1)(m) values, respectively, are evaluated and correl ated with the different properties of ions. In general, within a serie s of ions of one type, an increase in ionic radius causes an increase in delta((OH2)-O-17) (deshielding) and a decrease in delta((H2O)-H-1) (increased shielding). This was observed (with exceptions) for the cat ions as well for the anions. There is no general correlation between t he delta((OH2)-O-17)(m) and delta((H2O)-H-1)(m) for all ions considere d. The contribution of specific ion-solvent interactions on the delta( (OH2)-O-17) and delta((H2O)-H-1) values is important for the complex a nions (SO42-, NO3-, ClO4-, SCN-) and protonated or deprotonated water clusters. Compared with the Mg2+, Ca2+, Sr2+, Ba2+, and Na+, K+, Rb+, Cs+ ions, the relatively small Be2+ and Li+ ions behave differently. T he delta((OH2)-O-17) and delta((H2O)-H-1) values are largely specific quantities and the division of electrolytes by their effect on the wat er delta((OH2)-O-17) and delta((H2O)-H-1) into water 'structure breake rs' or 'structure makers' is confusing and not well founded.