Synthesis and investigation of water-soluble chlorophyll pigments for antimicrobial photodynamic therapy

Abstract This study focuses on synthesis, identification, distribution and interaction of water-soluble chlorophyll pigments with bacteria and fungi as new potential photosensitizers for antimicrobial photodynamic therapy. Pheophorbide 17(3)-methyl ester was functionalized by covalent attachment of one, two or three charged –N(CH 3 ) 3 + groups to reach sufficient solubility in an aqueous medium and enhance the PS antibacterial activity towards different bacterial strains. The pigments have been identified via UV-VIS, emission, IR-, NMR- and MS-spectra. All species are found to be well-soluble in water and stable both in a solution and a solid state. They are able to generate singlet oxygen with a sufficient quantum yield and reveal affinity to lipid cell membranes. The latter effect, however, strongly depends on the intrinsic charge of a pigment molecule. Microbiological studies do indicate that even highly diluted pigment solutions efficiently kill Gram-positive bacteria and fungi but not Gram-negative bacterial cells. The increase of photosensitizer concentration and addition of certain agents enhancing the permeability of the outer membrane of Gram-negative bacteria provide total inactivation of opportunistic microflora. These results reveal a great potential of charged chlorophyll pigments to treat wound infections and bacterial biofilms that often reveal significant resistance to standard antibiotic therapy.