This paper is part of a special issue dedicated to Professor J. C. (Tito) Scaiano on the occasion of his 60th birthday.
Psoralen and Coumarin Photochemistry in HSA Complexes and DMPC Vesicles†
Article first published online: 30 APR 2007
Photochemistry and Photobiology
Volume 82, Issue 1, pages 31–37, January 2006
How to Cite
Chen, L., Rinco, O., Popov, J., Vuong, N. and Johnston, L. J. (2006), Psoralen and Coumarin Photochemistry in HSA Complexes and DMPC Vesicles. Photochemistry and Photobiology, 82: 31–37. doi: 10.1562/2005-07-20-RA-616
- Issue published online: 30 APR 2007
- Article first published online: 30 APR 2007
- Received 20 July 2005; accepted 07 September 2005; published online 08 September 2005
The photochemistry and photophysics of several psoralens and coumarins have been examined in human serum albumin (HSA) complexes and dimyristoylphosphatidylcholine (DMPC) vesicles. Fluorescence spectroscopy indicates that there are multiple binding sites with polarities that are intermediate between those of acetonitrile and water for the substrates complexed to HSA. In the case of the 6,7-dimethoxycoumarin-HSA complex, laser flash photolysis experiments provide evidence for the formation of radical cation in addition to triplet. Radical cations are not detected for other coumarin-HSA complexes, either due to a lower yield of formation or to rapid reaction of an initial radical cation with adjacent amino acids. Fluorescence spectra for coumarins indicate that they are primarily solubilized in the polar headgroup region in DMPC vesicles. Consistent with this, radical cations generated by photoionization are detected in transient experiments. For dimethoxycoumarins the radical cation is long-lived, indicating rapid exit from the vesicle and decay in the aqueous phase. However, 4,5′,8-trimethylpsoralen and 7-ethoxy-4-hexadecylcoumarin radical cations are much shorter-lived, presumably due to rapid decay by electron recombination in the vesicle. The results for both HSA complexes and vesicles indicate that radical ions may play a role in psoralen and coumarin photochemistry in a cellular environment.