Partition of methylpheophorbide a , dioxidine and their conjugate in the 1-octanol/phosphate saline buffer biphasic system

The 1-octanol/phosphate saline buffer partition coefficients (P) for the well-established antimicrobial drug “Dioxidine” and its conjugate with the chlorin e6 molecule have been determined between the temperatures 298.15 K and 318.15 K and compared with corresponding quantities for several chlorophyll-type photosensitizers (PSs). The lipid-like phase is found to be enriched by solute molecules for all cases and the effect strongly depends on the solute structure. The temperature changes of partition coefficient are very small for chlorin e6-type PSs but significant for methylpheophorbide a and its glycol derivative. Thermodynamic calculations indicate that all solutes are better solvated in OctOH than in phosphate saline buffer mainly due to the favorable enthalpic term. The entropic term contributes to the behavior of phorbin-type pigments in an opposite manner but favors solvation of two chlorin e6-type PSs in a lipid-like phase.