This paper focuses on the results of the first accurate determination of enthalpies of solution of 9-ethenyl-14-ethyl-21-(methoxycarbonyl)-3-{(O-methylcarbamoypethyl} -4,8,13,18-tetramethyl-20-oxo-phorbine (Methylpheophorbide a, 1), [3-(hydroxymethyl)-1-oxido-4-oxoquinoxalin-4-ium-2-yl]methanol (Dioxidine, 2) and their conjugate 9-ethenyl-14-ethyl-3-{[2-(3-hydroxymethyl)]-1-oxido-4-oxoquinoxalin-4-ium-2-methyleneoxy}carbamoyl}ethyl)-4,8,13,18-tet-ramethyl-20-oxo-phorbine (Conjugate 3) in liquid N,N-dimethylformamide (DMF) in the temperature range of 298-318 K. Standard enthalpies and heat capacities of solution (Delta C degrees(P)) have been computed and compared with those for other solid and liquid non-electrolytes to highlight important features of solvation of potential photosensitizers in a simple model of a protein-like environment.
