PHYS 23 |
| In order to determine the structural nature of the mode-specific reorganization energy that nearly exactly balances the driving forces for primary and secondary electron-transfer reactions in the purple-bacterial reaction center, we have examined the low-frequency vibrational coherence arising from hindered translational and librational intermolecular interactions in bacteriochlorophyll and Zn(II)-porphyrin systems. The mean frequency of the intermolecular modes is consistent with a van der Waals potential that contains large terms from the London dispersion and dipole–dipole interactions; ion–dipole and ion–induced-dipole interactions make dominant contributions in charge-transfer products. We will discuss new results from the bacteriochlorophyll proteins B777 and B820 that show that ordered intermolecular interactions with first-shell interactions with groups in the surrounding protein medium and adjacent BChl macrocycles exhibit resonance Raman activities that are many times larger than those from the skeletal modes of the macrocycles themselves. We will also discuss new results from studies of Zn(II) meso-tetrakis(N-methylpyridyl)porphyrin in polar solutions, where excited-state intramolecular charge-transfer turns on the ion–dipole and ion–induced-dipole interactions and produces a large change in the intermolecular mode frequency. |
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Optical Probes of Dynamics in Complex Environments
8:00 AM-12:00 PM, Sunday, April 6, 2008 Morial Convention Center -- Rm. 344, Oral
Division of Physical Chemistry |