Identification of transient radical species in microbial systems using diffuse reflectance laser flash photolysis

Abstract

Conventional and diffuse reflectance laser flash photolysis are used to study the disulfonated aluminium phthalocyanine radical anion (AlPcS₂^−˙), both in solution and in a microbial cell environment. The transient absorption of the AlPcS₂^−˙ is characterised using model quenchers and the bimolecular quenching rate constants (k_Q) for several chemical components present in the outer membranes/cell structures of the microbes studied with AlPcS₂ are determined. The generation of the AlPcS₂^−˙ by the microbial cells is investigated, and the relative quantum yields of this process are calculated, together with the transient lifetime of the AlPcS₂^−˙ in a microbial cellular environment. Supporting evidence is found for the involvement of type I processes in the overall photodynamic mechanism of AlPcS₂ with the microbes studied. Several biological substrates present in the outer cell structures of the microbial cells studied are capable of quenching the AlPcS₂ triplet state to generate the AlPcS₂ radical anion (AlPcS₂^−˙), which is the reactive species that mediates type I photodynamic mechanisms. The transient absorption band of the AlPcS₂^−˙ is observed in the triplet minus singlet absorption spectra of AlPcS₂ in the presence of each of the microbes.