ACIDITY CONSTANTS OF ADENOSINE-5'-MONOPHOSPHATE AND DIPHOSPHATE IN VARIOUS WATER-ORGANIC SOLVENT MIXTURES

The acidity constants of adenosine-5'-mono- and diphosphate (AMP and A DP) were determined at 25.00 +/- 0.1-degrees-C by potentiometric titra tion in pure water and different solvent mixtures (methanol, ethanol, N,N-dimethylformamide, dimethylsulfoxide, acetone, and dioxane). The i onization of AMP and ADP depends on both the proportion and the nature of the organic solvent used. The pK(a1 values for both AMP and ADP ar e slightly influenced as the solvent is enriched in ethanol and methan ol and remains practically constant in presence of different amounts o f DMF and DMSO. A pronounced change in the pK(a1) values is observed a s the solvent is enriched in acetone or dioxane. It is concluded that the electrostatic effect has only a relatively small influence on the dissociation equilibrium, whereas other solvent effects such as solven t basicity, hydrogen bonding and protonsolvent interactions play an im portant role.