Spectral and photosensitizing properties of bacteriochlorin a and its monomethyl and dimethyl esters

Abstract

We have carried out a comparative study of the photosensitizing activity of bacteriochlorin a (BCA) and its methylated derivatives: monomethyl and dimethyl esters of BCA (BCA MME and BCA DME). We have shown that BCA and its derivatives are bound to the erythrocyte membranes in monomolecular form, and upon photoexcitation in the region of their long-wavelength Qy absorption band, they sensitize oxidation of the major membrane components: proteins and lipids. We have established that despite greater binding of the methylated BCA derivatives to the membranes, their specific activity in photosensitization of peroxide oxidation of membrane lipids and membrane protein tryptophanyls is lower than for BCA. At the same time, BCA MME and BCA DME sensitize oxidation of a larger number of SH groups in membrane proteins, which suggests methylated BCA is predominantly localized in the erythrocyte membrane close to the protein sulfhydryl groups. We also show that the rate of erythrocyte photohemolysis sensitized by BCA MME and BCA DME is significantly faster than for sensitization by BCA. This correlates with the lipophilicity of BCA, BCA MME, and BCA DME, which is responsible for the ability of bacteriochlorins to bind to cell membranes and cells.