Thermodynamics of the formation of copper(II) complexes with L-histidine in aqueous solution

The heat effects from the reaction between L-histidine solutions and Cu(NO3)(2) solutions at 298.15 K in the 0.2 to 1.0 (KNO3) range of ionic strength are measured by means of direct calorimetry. The experimental data is treated with allowance for the simultaneous proceeding of several processes. The heat effects of the formation of complexes Cu(His)(+), Cu(His)(2), CuHHis(2+), CuH(His) (2) (+) and CuH2(His) (2) (2+) are calculated from calorimetric measurements. The standard enthalpies of formation for complexes of L-histidine with Cu2+ ions are obtained via extrapolation to zero ionic strength. The relationship between the thermodynamic characteristics of the formation of complexes of copper(II) with L-histidine and their structure is determined.