Structures and Properties of Ubiquinone-1 and Its Radical Anion from Hybrid Hartree−Fock/Density Functional Studies
journal contributionposted on 07.08.1997 by Scott E. Boesch, Ralph A. Wheeler
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Ubiquinones and their semiquinone radical anionselectron transfer cofactors vital for respiration and photosynthesisare typically characterized in proteins by measuring their vibrational or electron spin resonance spectra. This contribution presents calculated geometries and spin properties for ubiquinone-1 (UQ1) and its radical anion (UQ1•-), as well as vibrational frequencies for a model with the methyl groups on the isoprenyl side chain of UQ1 replaced by hydrogens (UQ and UQ•). Computations were done by using the hybrid Hartree−Fock/density functional B3LYP method with the 6-31G(d) and [632|41] basis sets. Bond distance changes upon reducing UQ1 to UQ1•- are qualitatively consistent with results for other p-benzoquinones. Proton and 13C hyperfine coupling constants calculated by using Chipman's [632|41] basis set agree exceptionally well with experimental measurements and reflect the distribution of unpaired spin. We suggest isotopic substitution experiments to resolve the nearly overlapping CO and CC stretching frequencies calculated for UQ and to shift methoxy and/or methyl CH bending modes away from one CO stretching band of UQ•-.