Quantum mechanical calculations quinones

If subsequent experiments do indeed demonstrate that excited-state H-atom transfer does not occur in hypomycin B, then one may draw the conclusion that multiple transfers (either concerted or stepwise) must occur in these pery-lene quinones and that by frustrating the process in one half of the molecule, the process in the other half is impeded. At this point, such reasoning is speculative and contrary to the growing body of evidence provided by theory and experiment. As indicated above, quantum mechanical calculations indicate that the double-H-atom transfer in hypericin [67] and in the perylene quinone nucleus [75] of hypocrellin is energetically unfavorable compared to the single-transfer event. Experiments for hypericin in which one half of the molecule cannot participate in H-atom transfer owing to protonation of the carbonyl group (or even perhaps complexation with a metal ion) [76] also indicate that the transfer process can still occur. 

Quantum mechanical calculations on the structure of the triplet intermediates in the photochromic reactions of phenoxy quinones show that photochemically induced phenyl migration occurs non-adiabatically with generation of the spiro form of the triplet biradical. Details of a range of new photochromic compounds have appeared in both the scientific and patent literature. ... 

Solvation free energy calculations in combination with quantum mechanical calculations have been utilized to reproduce and predict the aqueous redox properties of quinones and the aqueous one-electron reduction potential of trimethyl-p-benzoquinone and plastoquinone-1 and selected p-benzoquinones. Shifts in the redox pair potential on mutation of the reaction center of Rhodobacter sphaerodes calculated using the FEP method have been reported by Apostolakis et al. ... 

Oxidation by direct H transfer from the a-carbon of alcohols to the pyrroloquinoline quinone (PQQ) cofactor of alcohol dehydrogenases was studied using ab initio quantum mechanical methods <2001JCC1732>. Energies and geometries were calculated at the 6-31G(d,p) level of theory, results were compared to available structural and spectroscopic data, and the role of calcium in the enzymatic reaction was explored. Transition state searches at the semi-empirical and STO-3G(d) level of theory provided evidence that direct transfer from the alcohol to C-5 of PQQ is energetically feasible. 

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