Solvation descriptors for porphyrins (porphines)

Abstract

Literature data on partition coefficients for porphyrin and literature data on solubilities in organic solvents for substituted porphyrins have been used to obtain Abraham descriptors, or properties, of porphyrin and of sixteen substituted porphyrins. The obtained descriptors are not exceptional, although the descriptor A, for hydrogen bond acidity is appreciably less than the sum of A-values for two pyrrole rings, probably because of steric restraints on the approach of hydrogen bond bases to the porphyrin ring system. One extra property that we can obtain is a calculated solubility in water. From this, and calculated values of water–solvent partition coefficients we can then predict solubilities in other organic solvents, as well as, of course, numerous predicted water–solvent partition coefficients. For the substituted porphyrins, the solubility in water is far too low to be experimentally obtainable, and water–solvent partition coefficients are correspondingly far too high to be experimentally obtainable.