Unveiling electrostatic portraits of quinones in reduction and protonation states

Abstract

Quinones are known to perform diverse functions in a variety of biological and chemical processes as well as molecular electronics owing to their redox and protonation properties. Electrostatics chiefly governs intermolecular interaction behaviour of quinone states in such processes. The electronic distribution of a prototypical quinone, viz., p-benzoquinone, with its reduction and protonation states (BQS) is explored by molecular electrostatic potential (MESP) mapping using density functional theory. The reorganization of electronic distribution of BQS and their interaction with electrophiles are assessed for understanding the movement of ubiquinone in bacterial photosynthetic reaction centre, by calculating their binding energy with a model electrophile viz., lithium cation (Li +) at B3LYP/6-311+G(d,p) level of theory. The changes in the values of the MESP minima of BQS states alter their interacting behaviour towards Li +. A good correlation is found between the value of MESP minimum of BQS and the Li + binding strength at the respective site. To acquire more realistic picture of the proton transfer process to quinone with respect to its reduction state in the photosynthetic reaction center, interaction of BQS with model protonated motifs of serine, histidine as well as NH + 4 is explored. Further, the electronic conjugation of the reduced states of 9,10-anthraquinone is probed through MESP for understanding the switching nature of their electronic conductivity.

Atoms to Phenotypes: Molecular Design Principles of Cellular Energy Metabolism

“…The diving motif applies to both quinone and quinol because both share similar binding pockets. Quinol is more polar than quinone, correlating with faster binding to the pocket (Pingale et al, 2018). With the RC-to-bc 1 diffusion time of 101 ms determined here (Figure S4C), we infer that the rate-determining step is not the nm-scale diffusion of the quinone in the bilayer, even while traversing the densely packed LH2 environment (Cartron et al, 2014), but, rather, its angstrom-scale binding from RC-LH1 and the associated conformational changes in the quinonebinding pocket.…”