Proton-Dependent switching of a novel amino chlorin derivative as a fluorescent probe and photosensitizer for acidic media

Abstract

A novel chlorin derivative (TPCF20-NMe2) was synthesized as a syn adduct of a pyrrolidinefused chlorin carrying an C-linked N,N-dimethylaminophenyl residue. The absorption spectrum of TPCF20-NMe2 was basically identical to that of TPCF20 in N,N-dimethylformamide, indicating a very weak interaction between the chlorin macrocycle and the amine group in the ground state. However, the fluorescence emission of the chlorin moiety in TPCF20-NMe2 was effectively quenched by the attached amine unit. In addition, TPCF20-NMe2 was not able to produce tripletexcited state or photosensitize singlet molecular oxygen. Spectroscopic and redox properties indicated that in this chlorin intramolecular photoinduced electron transfer can take place from the N,N-dimethylaminophenyl group to the chlorin macrocycle. Thus, the addition of an acid medium was used to protonate the amino group leading to a considerable increase in the fluorescenceemission, triplet excited state formation and singlet molecular oxygen production. Photodynamic inactivation of Escherichia coli sensitized by TPCF20-NMe2 was negligible at neutral pH. However, this chlorin becomes highly effective in inactivating E. coli cells under acidic conditions. Therefore,these results indicate that TPCF20-NMe2 is an interesting molecular structure in which protonation of amino group can be used as an off/on molecular switch activating red fluorescence emission and photodynamic activity capable of eradicating bacteria