Protonation Constants of Uridine 5′-Monophosphate in Different Aqueous Solutions of Methanol

Abstract

The protonation equilibria of uridine 5′-monophosphate disodium salt (UMP) was determined in binary solvent mixtures of water–methanol containing 0, 10, 15, 20, 25, 30, 35, 40, 45, and 50 % (v/v) methanol, using a combination of spectrophotometric and potentiometric methods at 25 °C and constant ionic strength (0.1 mol·dm−3 NaClO4). The protonation constants were analyzed using Kamlet, Abboud, and Taft parameters. A good linear correlation of the protonation constants (on the logarithmic scale) was obtained. Dual-parameter correlation of log10K versus π* (dipolarity/polarizability) and α (hydrogen-bond donor acidity), as well as π* and β (hydrogen-bond acceptor basicity), gave good results in various aqueous solutions of methanol. Finally, the results are compared with CMP, a homolog of UMP, and are discussed in terms of the effect of the solvent on the protonation constants.