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 aprototypical 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 themovement 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 thephotosynthetic 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.
Volume 133, 2021
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