title: Modulation of quinone PCET reaction by Ca2+ ion captured by calix[4]quinone in water.
abstract: Calix[4]arene-triacid-monoquinone (CTAQ), a quinone-containing water-soluble ionophore, was utilized to investigate how proton-coupled electron transfer (PCET) reactions of quinones were influenced by redox-inactive metal ions in aqueous environment. This ionophoric quinone derivative captured a Ca(2+) ion that drastically altered the voltammetric behavior of quinone, showing a characteristic response to pH and unique redox wave separation. Spectroelectrochemistry verified significant stabilization of the semiquinone, and electrocatalytic currents were observed in the presence of Ca(2+)-free CTAQ. Using digital simulation of cyclic voltammograms to clarify how the thermodynamic properties of quinones were altered, a simple scheme was proposed that successfully accounted for all the observations. The change induced by Ca(2+) complexation was explained on the basis of the combined effects of the electrostatic influence of the captured metal ion and hydrogen bonding of water molecules with the support of DFT calculation.
authors.affiliation: Department of Chemistry, Seoul National University , Seoul 151-747, Korea.
authors.forename: Yang-Rae
authors.initials: YR
authors.lastname: Kim
authors.forename: R Soyoung
authors.initials: RS
authors.lastname: Kim
authors.forename: Sun Kil
authors.initials: SK
authors.lastname: Kang
authors.forename: Myung Gil
authors.initials: MG
authors.lastname: Choi
authors.forename: Hong Yeong
authors.initials: HY
authors.lastname: Kim
authors.forename: Daeheum
authors.initials: D
authors.lastname: Cho
authors.forename: Jin Yong
authors.initials: JY
authors.lastname: Lee
authors.forename: Suk-Kyu
authors.initials: SK
authors.lastname: Chang
authors.forename: Taek Dong
authors.initials: TD
authors.lastname: Chung