Calorimetric study of the oxidation of dithiothreitol

The enthalpy changes of the eoxidation of dithiothreitol (DTT) by ferricyanide was measured calorimetrically in the pH range of 6 to 13 in various buffer solutions at 298 K. By combining the results of potentiometric titrations with the pH dependence of the observed enthalpy changes, the enthalpy changes of DTT oxidation and of the ionization of DTT sulfhydryls were evaluated. The enthalpy changes of oxidation of the non-ionized and the fully ionized DTT were found to be delta HDTT (non-ionized) = 32 +/- 3 kJ mol-1 and delta HDTT (fully ionized) = -38 +/- 3 kJ mol-1, respectively. The enthalpy changes of the first and the second ionizations of DTT sulfhydryls were found to be delta H1 = 48 +/- 2 kJ mol-1 and delta H2 = 21 +/- 3 kJ mol-1, respectively.