The effect of methoxy group rotation and hydrogen bonding on the redox properties of ubiquinone

Two critical factors influencing the electron affinity and associated redox potential of ubiqiuinone - the orientation relative to the ring plane of the methoxy groups and the number of hydrogen bond donors to the oxygen atoms are investigated using Density Functional Theory calculations. Increasing the number of hydrogen bond donors to the oxygen atoms leads to an increase of approximately 350 meV for each hydrogen bond donor. The profile for the methoxy group rotation shows that the electron affinity is at a minimum for in plane orientations whereas maximum values of electron affinity are found for orientations nearly perpendicular to the ring plane. Maximum variation in electron affinity values using the methoxy group is around 200 meV. The theoretical dependence of ubiquinone electron affinity values, as a function of variation of methoxy dihedral angles and hydrogen bond donation demonstrates the two principal mechanisms available to the ubiquinone molecule in vivo to adapt its redox potential value to perform efficient electron transfer. (C) 2015 Elsevier B.V. All rights reserved.