Escherichia coli, as most Gram‐negative bacteria, is insensitive to the photosensitizing action of both lipid‐soluble Zinc‐phthalocyanine (Zn‐Pc) and water‐soluble Zinc‐mono/disulfonated phthalocyanine (Zn‐PcS). Photosensitivity can be induced by alteration of the outer membrane, as obtained by either induction of competence or treatment with Tris‐EDTA. Both phthalocyanines largely bind at the level of the cytoplasmic membrane; however, Zn‐PcS shows a superior photosensitizing activity as compared with Zn‐Pc. Biochemical analyses performed on irradiated cells suggest that the cytoplasmic membrane is an important target of the photoprocess, while DNA is not involved.

A series of derivatives of 5,10,15,20-tetrakis-(4-N-methylpyridyl)-porphine, where one N-methyl group was replaced by a hydrocarbon chain ranging from C6 to C22, were characterized for their photophysical and photosensitizing properties. The absorption and fluorescence features of the various compounds in neutral aqueous solutions were typical of largely monomeric porphyrins, with the exception of the C22 derivative, which appeared to be extensively aggregated. This was confirmed by the very low triplet quantum yield and lifetime of the C22 derivative as compared with 0.2-0.7 quantum yields and 88-167 micros lifetimes for the other porphyrins. The photophysical properties and photosensitizing activity toward N-acetyl-L-tryptophanamide of the C22 porphyrin became comparable to those typical of the other derivatives in 2% aqueous sodium dodecyl sulfate, where the C22 compound is fully monomerized. All the porphyrin derivatives exhibited at micromolar concentrations photoinactivation activity against both Staphylococcus aureus and Escherichia coli, even though the gram-negative bacteria were markedly less photosensitive. The photosensitizing efficiency was influenced by (1) the amount of cell-bound porphyrin, which increased with increasing length of the hydrocarbon chain; and (2) the tendency to undergo partial aggregation in the cell, which seems to be especially important for the C22 derivative.

No abstract

A series of derivatives of 5,10,15,20‐tetrakis‐(4‐N‐methylpyridyl)‐porphine, where one N‐methyl group was replaced by a hydrocarbon chain ranging from C6 to C22, were characterized for their photophysical and photosensitizing properties. The absorption and fluorescence features of the various compounds in neutral aqueous solutions were typical of largely monomeric porphyrins, with the exception of the C22 derivative, which appeared to be extensively aggregated. This was confirmed by the very low triplet quantum yield and lifetime of the C22 derivative as compared with 0.2–0.7 quantum yields and 88–167 μs lifetimes for the other porphyrins. The photophysical properties and photosensitizing activity toward N‐acetyl‐l‐tryptophanamide of the C22 porphyrin became comparable to those typical of the other derivatives in 2% aqueous sodium dodecyl sulfate, where the C22 compound is fully monomerized. All the porphyrin derivatives exhibited at micromolar concentrations photoinactivation activity against both Staphylococcus aureus and Escherichia coli, even though the gram‐negative bacteria were markedly less photosensitive. The photosensitizing efficiency was influenced by (1) the amount of cell‐bound porphyrin, which increased with increasing length of the hydrocarbon chain; and (2) the tendency to undergo partial aggregation in the cell, which seems to be especially important for the C22 derivative.

No abstract