*On sabbatical leave from the Department of Physics, Bar Ilan University, Ramat Gan, Israel.
Kinetics and Yield of Singlet Oxygen Photosensitized by Hypericin in Organic and Biological Media
Article first published online: 2 JAN 2008
Photochemistry and Photobiology
Volume 68, Issue 2, pages 135–140, August 1998
How to Cite
Ehrenberg, B., Anderson, J. L. and Foote, C. S. (1998), Kinetics and Yield of Singlet Oxygen Photosensitized by Hypericin in Organic and Biological Media. Photochemistry and Photobiology, 68: 135–140. doi: 10.1111/j.1751-1097.1998.tb02479.x
- Issue published online: 2 JAN 2008
- Article first published online: 2 JAN 2008
- Received 16 January 1998; accepted 24 April 1998
The spectroscopy and photophysics of the photosensitizer hypericin when in homogeneous solutions and when bound to liposomes were studied. Hypericin was found to partition efficiently into DMPC liposomes, with a binding constant of 58 (mg lipid/mL)−1. In these liposomes the singlet oxygen production quantum yield was 0.43 ± 0.09. To determine the deactivation constant of singlet oxygen in lipid bilayers for the first time, we calculated extrapolated values from its quenching by DMPC and lecithin in homogeneous solutions and obtained decay times of 36.4 and 12.2 μs, respectively. We also measured the quenching of singlet oxygen, sensitized by hypericin in DMPC liposomes, by NaN3, diphenyl isobenzofuran and H2,O: D2O mixtures and explained the results on the basis of singlet oxygen diffusing rapidly out of the lipid bilayer into the aqueous medium. The observed temperature effect on the lifetime of singlet oxygen of about 50% over a 15°C range in liposome suspension contrasts with a 3% change in a homogeneous solution in 1-nonanol and is explained by the temperature effect on the diffusion out of the liposome. A strong pH effect was observed, indicating that the deprotonated species formed above about pH 10 is a much weaker photosensitizer of singlet oxygen than the native, protonated species.