ANNIHILATION PROCESSES IN THE ISOLATED D1-D2-CYT-B559 REACTION-CENTERCOMPLEX OF PHOTOSYSTEM-II - AN INTENSITY-DEPENDENCE STUDY OF FEMTOSECOND TRANSIENT ABSORPTION

Citation
Mg. Muller et al., ANNIHILATION PROCESSES IN THE ISOLATED D1-D2-CYT-B559 REACTION-CENTERCOMPLEX OF PHOTOSYSTEM-II - AN INTENSITY-DEPENDENCE STUDY OF FEMTOSECOND TRANSIENT ABSORPTION, Journal of physical chemistry, 100(22), 1996, pp. 9537-9544
Citations number
43
Categorie Soggetti
Chemistry Physical
ISSN journal
00223654
Volume
100
Issue
22
Year of publication
1996
Pages
9537 - 9544
Database
ISI
SICI code
0022-3654(1996)100:22<9537:APITID>2.0.ZU;2-3
Abstract
The excitation intensity dependence of the kinetics of the primary pro cesses and of the yield of radical pair formation in the isolated D1-D 2-cyt-b559 reaction center of photosystem II has been studied by femto second transient absorption spectroscopy. It is shown that the kinetic s is strongly dependent on the excitation intensity. The radical pair yield as a function of excitation intensity is compared with the theor etical annihilation curve and a good agreement between theory and expe riment is observed, indicating that the intensity effects on the kinet ics and radical pair yield arise primarily from annihilation processes . Sufficiently annihilation-free measurements require excitation inten sities that give rise to less than or equal to 0.06 absorbed photons/R C while maintaining a high signal/noise ratio of greater than or equal to 100:1 at most detection wavelengths in order to resolve the comple x kinetics. It is shown that such low excitation intensities give rise to absorption changes that are at the edge of the capabilities of pre sent femtosecond absorption equipment. We also compare the excitation conditions that have been used so far by other research groups for pub lished transient absorption data on the isolated D1-D2-cyt-b559 comple x. This comparison shows that essentially all published data have been obtained under conditions where annihilation or quenching effects are expected to significantly distort the kinetics and time-resolved spec tra and to reduce the radical pair yield.