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"Structures and vibrational frequencies of the quinones in
Rb. Sphaeroides derived by a combined
density functional / molecular mechanics approach." M. Nonella, G. Mathias, M. Eichinger, and P. TavanJ. Phys. Chem. B 107: 316-322 (2003) Abstract: The structures of the ubiquinones QA and QB in the bacterial photosynthetic reaction center of Rb. sphaeroides are calculated by a QM/MM hybrid technique. The orientations of their methoxy groups are found to differ by less than 30o. Calculation of the vibrational spectra reveals that one C=O stretching mode of QA is considerably shifted to lower frequencies in agreement with the experimental data. The orientational differences of the methoxy groups at QA and QB are too small as to provide an explanation for this shift. Instead, it must be due to a very special interaction of the protein with QA. Artificial neutralization of the iron cofactor, while keeping all other structural parameters of the RC fixed, reveals that this interaction arises from the electrostatic field of the Fe2+ ion, within which QA is oriented in a particular way. BMO authors (in alphabetic order): Markus Eichinger Gerald Mathias Marco Nonella Paul Tavan Assoziierte Projekte: QM/MM hybrid descriptions of solutes in complex solvents Vibrational Spectra of Quinones  WWW-Version |