Determination of the singlet oxygen quantum yield of bacteriochlorin a: a comparative study in phosphate buffer and aqueous dispersion of dimiristoyl-L- -phosphatidylcholine liposomes

The production of singlet oxygen (O2) by bacteriochlorin a (BCA) was studied in phosphate buffer and in dimyristoyl--α-phosphatidylcholine (DMPC) unilamellar liposomes. The comparative method used to measure O2 production was a quantitative analysis of photooxidation reactions leading to the loss of absorbance of the water-soluble specific probe: anthracene-9,10-dipropionic acid. Rose Bengal, whose O2 quantum yield (Φ ) is well known in alcohols and phosphate buffer, was used as the standard for the quantification of the BCA singlet oxygen production. Our results confirm quantitatively that solubilization of BCA in liposomes leads to an increase in O2 production. Indeed, the quantum yield of O2 production by BCA (Φ ) is 0.05 in phosphate buffer and 0.33 in DMPC liposomes. Furthermore, the diffusion characteristics of O2 produced by BCA bound to liposome were also examined using the isotopic lifetime enhancement effect of D2O. It was shown that O2 spent at least 70% of its lifetime in the vesicular environment.