Photochemical hole-burning spectroscopy of a photosynthetic reaction center mutant with altered charge separation kinetics: properties and decay of the initially excited state
| Autor: | Laura T. Mazzola, Thomas R. Middendorf, Steven G. Boxer, Craig C. Schenck, Dale Gaul |
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| Rok vydání: | 1991 |
| Předmět: | |
| Zdroj: | The Journal of Physical Chemistry. 95:10142-10151 |
| ISSN: | 1541-5740 0022-3654 |
| Popis: | Photochemical hole-burning spectra have been obtained for the lowest energy electronic absorption band of the primary electron donor P of photosynthetic reaction centers (RCs) that exhibit different rates for the initial charge separation step. Wild type (WT) and Tyr(M)210 - Phe mutant [(M)Y210F] RCs from Rhodobacter sphaeroides were studied at 1.5 K in 50% glycerol/buffer glasses. In both types of RC, difference spectra obtained by using narrow-bandwidth excitation on the low-energy edge of the P band display weak, narrow zero-phonon holes coincident with the laser wavelengths, in addition to a broad background bleach of much larger amplitude. The zero-phonon hole width in each type of RC corresponds quantitatively to the broadening expected from the excited-state lifetime. These results are inconsistent with electronic relaxation of the excited state of P prior to electron transfer. The agreement between the time- and frequency-domain experiments may result from vibrational thermalization prior to electron transfer. An alternative mechanism, which does not invoke subpicosecond vibrational thermalization and which is consistent with a wide range of data, is also presented. Quantitative estimates were obtained for the total electron-phonon coupling strength (Huang-Rhys factor) S and for the magnitudes of the homogeneous and inhomogeneous broadening in the P absorption band from self-consistent simulations of the 1.5 K absorption and hole spectra from a linear electron-phonon coupling model. The vibronic and line-width parameters deduced from the simulations are very similar for WT and (M)Y2lOF RCs. |
| Databáze: | OpenAIRE |
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