Linear dichroism of electric field oriented bacteriochlorophyll a-protein from green photosynthetic bacteria |
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Authors: | William B. Whitten Robert M. Pearlstein Edwin F. Phares Nicholas E. Geacintov |
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Affiliation: | 1. Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tenn. 37830 U.S.A.;2. Biology Division, Oak Ridge National Laboratory, Oak Ridge, Tenn. 37830 U.S.A.;3. Chemistry Department, New York University, New York, N.Y. 10003 U.S.A. |
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Abstract: | Bacteriochlorophyll a-protein from Prosthecochloris aestuarii strain 2K was oriented in a pulsed electric field. The room temperature linear dichroism spectrum of the oriented protein in the Qy region of the bacteriochlorophyll a absorption exhibits a single asymmetrical peak at 813 nm with a shoulder extending to the blue. The ≈12 nm fullwidth of the linear dichroism peak is only about half that of the 300 K absorption spectrum. The linear dichroism at 813 nm was not saturated at field strengths of up to 15 kV/cm. The time dependence of the linear dichroism suggests that the orienting particles are aggregates of at least some tens of bacteriochlorophyll a-protein trimers. The linear dichroism peak coincides in wavelength with the 813-nm peak of the 300 K, 4th derivative absorption spectrum of the protein and is therefore attributed to the bacteriochlorophyll a Qy exciton transition observed in absorption at the same wavelength. |
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Keywords: | Bchl bacteriochlorophyll CD circular dichroism LD linear dichroism |
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