Nuclear magnetic resonance studies on the protonation equilibria of oxoanions in polysaccharide gels as models for biological media

Abstract

The protonation equilibria of phosphinate, phosphite and acetate ions in Sephadex gels with different degrees of crosslinking have been investigated by ³¹P and ¹³C NMR methods. These oxoanions gave different NMR chemical shift values for the gel phase and the corresponding aqueous solution, the chemical shift for the gel phase being of higher field in all cases. The protonation constants of these oxoanions in the gel phase were determined for the first time. The constants for the gel phase were always larger than those for the corresponding aqueous solution and became larger in accordance with an increase in the degree of crosslinking and with a decrease in the ionic strength. Problems in intracellular pH measurements are discussed in the light of the results obtained for the polysaccharide gels.