Protonation of D-gluconate and its complexation with Np(V) in acidic to nearly neutral solutions

Abstract

Thermodynamic properties of the protonation of D-gluconic acid (HGH4(aq)) and its complexation with Np(V) have been studied in acidic to nearly neutral solutions at t =25 °C and I=1 M NaClO4 by potentiometry, spectrophotometry and calorimetry. The protonation constant (logK H) and enthalpy (ΔH H) of the carboxylate group are determined to be (3.30±0.10) and −(4.03±0.07) kJ mol-1, respectively. Gluconate forms two Np(V) complexes in nearly neutral solutions. The formation constants and enthalpies of complexation are: log β1 = (1.48±0.03) and ΔH 1 = −(7.42±0.13) kJ mol-1 for NpO2(GH4)(aq), log β2=(2.14±0.09) and ΔH 2= −(12.08±0.45) kJ mol-1 for NpO2(GH4)2 -. The thermodynamic parameters indicate that gluconic acid, like isosaccharinic acid and other α-hydroxycarboxylic acids, is a slightly stronger acid and forms stronger complexes with Np(V) than simple monocarboxylic acids.