Isomeric N-alkylpyridylporphyrins and their Zn(II) complexes: inactive as SOD mimics but powerful photosensitizers.

The ortho, meta, and para isomers of cationic N-alkylpyridylporphyrins and their Zn(II) complexes were compared in terms of their photodynamic properties. The ortho Zn(II) complex was found to be the most efficient in causing photooxidation of NADH in vitro. In Escherichia coli, however, the para and meta isomers were better photosensitizers than their ortho analogs. The lower potency of the ortho compound in vivo seems to be due to its lower intracellular concentration. All porphyrins tested were more efficient in killing E. coli and in photooxidizing NADH than the hematoporphyrin derivative. Antibiotic resistance did not affect the photokill, which implies that the cationic N-alkylpyridylporphyrins, as their Zn(II) complexes, can be used as bactericidal agents against antibiotic-resistant strains of gram-negative bacteria.