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Observation of a bacteriochlorophyll anion radical during the primary charge separation in a reaction center

โœ Scribed by W. Holzapfel; U. Finkele; W. Kaiser; D. Oesterhelt; H. Scheer; H.U. Stilz; W. Zinth

Publisher
Elsevier Science
Year
1989
Tongue
English
Weight
605 KB
Volume
160
Category
Article
ISSN
0009-2614

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โœฆ Synopsis

The primary light-induced charge separation in reaction Centers of Rkfobacter sphueroides was investigated with femtosecond time resolution. The absorption changes in the time range 100 fs to 1 ns observed after direct excitation of the primary donor P at 860 mn could only be explained by a kinetic model which uses three time constants. This fmding supports the following reaction scheme: (i) the electronically excited primary donor P* decays with a time constant of 3.5 ps and populates a very short-lived intermediate involving a reduced accessory bacteriochlorophyll molecule; (ii) with a time constant of 0.9 ps the electron is transferred to the neighboring bacteriopheophytin molecule; and (iii) from there within 200 ps to the quinone.

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Using continuous wave EPR spectroscopy with a high time resolution, a new short-lived signal at g = 2 is observed in bacterial photosynthetic reaction centers in which electron transfer past the bacteriopheophytin @A is blocked. This signal decays with a time constant equal to the rise time of the t