Investigation of the demetallation of 10-aryl substituted synthetic chlorins under acidic conditions

Abstract

The acidic demetallation of a series of sparsely substituted Zn(II) chlorins is reported. The chlorins were functionalized in the 10-position with substituents ranging from strongly electron donating mesityl and p-methoxyphenyl to electron-withdrawing p-nitrophenyl and pentafluorophenyl groups. The demetallation kinetics were investigated using UV–Visible absorption spectroscopy. Demetallation was carried out by exposing the metallochlorins dissolved in CH2Cl2 to an excess of trifluoroacetic acid. Reasonable correlation was found between the Hammett constant of the 10-substituent and the rate constant of the loss of the metal ion. The largest differences were observed between the p-methoxyphenyl and p-nitrophenyl-substituted Zn(II) chlorins, undergoing loss of Zn(II) with pseudo first order rate constants of 0.0789 × 10–3 and 3.70 × 10–3 min–1, respectively. Taken together, these data establish the dramatic influence even subtle changes can have in altering the electronic properties of chlorins, which in turn impacts metallochlorin function.