Thermodynamics of Solution of Hemato- and Deuteroporphyrins in N,N-Dimethylformamide

This paper focuses on the results of the first accurate study of thermodynamics of solution for two blood porphyrins in the model of a protein-like environment liquid N,N-dimethylformamide (DMF) in the physiological temperature range. The solubility of hematoporphyrin dimethylether dimethylester (HDEDE) and deuteroporphyrin dimethylester (DDE) in DMF has been obtained from (288 to 318) K. Free energies, enthalpies, entropies, and heat capacities of solution have been computed from solubility data and compared with those obtained from the previously reported calorimetric data via the Gibbs-Helmholtz equation. We have shown that for the solutes studied it is more correct to compute thermodynamic functions from the temperature dependence of the enthalpy and solubility/activity at the reference temperature. This approach allows to reproduce qualitatively both free energies of solution and solubility of porphyrins for the physiological temperature range.