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The antibacterial photodynamic effects of uncharged (o-tetrahydroxyphenyl porphine [THPP], m-THPP and p-THPP), cationic (5,10,15,20-tetra[4-N-methylpyridyl]porphine [TMPyP]) and anionic (5,10,15,20-tetra[4-sulfonatophenyl porphine] [TPPS4]) porphines on Staphylococcus aureus and Escherichia coli bacteria inactivation were examined. The results show that uncharged porphines provoked antibacterial photodynamic activity on S. aureus, and also on E. coli in the presence of the membrane-disorganizing peptide polymixin B nonapeptide (PMNP). The TMPyP compound was highly photoactive toward gram-positive bacteria but only marginally effective on gram-negative cells, whereas TPPS4 showed no activity on either gram-positive or gram-negative bacteria. The photoactivity of TMPyP is due to the electrostatic attraction between the positively charged sensitizer molecule and the negatively charged membrane of the gram-positive target cells. For TPPS4, the inactivity toward gram-positive bacteria is due to electrostatic repulsion between the charged sensitizer molecule and the cell membrane. For gram-negative bacteria, the inactivity is conceivably due to preferential (electrostatic) binding to the positively charged PMNP, which is an adjuvant for membrane disorganization, but has no effect on cell viability. For hydrophobic sensitizers, the photoactivity depends on the state of aggregation. The extent of deaggregation of the different THPP isomers was determined by fluorescence measurements of bound sensitizers and could be positively correlated with their photoinactivation capacity. We conclude that the structure-activity relationships of these porphines are affected by their net charge and by aggregation.

— Measurement of singlet oxygen production by porphyrin-type photosensitizers in simple buffer solutions show that TPPS is more efficient than PII (Photofrin II) or than hematoporphyrin. This behavior was observed using three independent analytical detection methods for 1O2: RNO bleaching, tryptophan degradation, and oxygen consumption. Similar results were obtained when irradiating with a classical light source or with a pulsed dye laser. Addition of EPC liposomes to the buffer solution caused a decrease of efficiency for TPPS and an increase for PII. Addition of BSA shows the same relative pattern: a small increase of efficiency for TPPS and a tenfold increase for PII. These changes can be ascribed to specific interactions between the sensitizer molecules and the organized medium. Since changes in the fluorescence properties are also due to interactions with the medium, we monitored the emission of the sensitizers as a function of the environment. The fluorescence peak positions (at 648, 705 nm for TPPS and at 615, 677 nm for PII) were all red shifted. The intensities show an increase, particularly for PII in liposomes, due to a marked change in the microviscosity.