Antimicrobial photodynamic inactivation is potentiated by addition of selenocyanate: possible involvement of selenocyanogen?

We previously showed that antimicrobial photodynamic inactivation (aPDI) of Gram-positive and Gram-negative bacteria mediated by the phenothiazinium dye, methylene blue (MB) was potentiated by addition of potassium thiocyanate (10mM). The mechanism was suggested to involve a singlet oxygen mediated reaction with SCN- to form sulfite and cyanide and then to produce sulfur trioxide radical anion. We now report that potassium selenocyanate KSeCN (concentrations up to 100 mM) can also potentiate (up to 6 logs of killing) aPDI mediated by a number of different photosensitizers: MB, Rose Bengal, and TPPS4 (as low as 200 nM). When a mixture of selenocyanate with these PS in solution was illuminated and then bacteria were added after the light, there was up to 6 logs killing (Gram-negative > Gram-positive) but the antibacterial species decayed rapidly (by 20 min). Our hypothesis to explain this antibacterial activity is the formation of selenocyanogen (SeCN)₂ by reaction with singlet oxygen (¹O₂) as shown by quenching of ¹O₂ by SeCN- and increased photoconsumption of oxygen. The fact that lead tetra-acetate reacted with SeCN- (literature preparation of (SeCN)₂) also produced a short-lived antibacterial species supports this hypothesis.

from ORL via alkiviadis.1961 on Inoreader http://ift.tt/2F2qJFu