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Structures and Properties of Ubiquinone-1 and Its Radical Anion from Hybrid Hartree−Fock/Density Functional Studies

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journal contribution
posted on 07.08.1997 by Scott E. Boesch, Ralph A. Wheeler
Ubiquinones and their semiquinone radical anionselectron transfer cofactors vital for respiration and photosynthesisare 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 CO and CC stretching frequencies calculated for UQ and to shift methoxy and/or methyl CH bending modes away from one CO stretching band of UQ•-.

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