Electron‐Transfer Reactions through the Associated Interaction between Cytochrome c and Self‐Assembled Monolayers of Optically Active Cobalt(III) Complexes: Molecular Recognition Ability Induced by the Chirality of the Cobalt(III) Units
You can manage bookmarks using lists, please log in to your user account for this.
Media type:
E-Article
Title:
Electron‐Transfer Reactions through the Associated Interaction between Cytochrome c and Self‐Assembled Monolayers of Optically Active Cobalt(III) Complexes: Molecular Recognition Ability Induced by the Chirality of the Cobalt(III) Units
Description:
<jats:title>Abstract</jats:title><jats:p>Self‐assembled monolayers (SAMs) of optically active Co<jats:sup>III</jats:sup> complexes ((<jats:italic>S</jats:italic>)‐<jats:bold>2</jats:bold>/(<jats:italic>R</jats:italic>)‐<jats:bold>2</jats:bold>) that contain (<jats:italic>S</jats:italic>)‐ or (<jats:italic>R</jats:italic>)‐phenylalanine derivatives as a molecular recognition site were constructed on Au electrodes ((<jats:italic>S</jats:italic>)‐<jats:bold>2</jats:bold>–Au/(<jats:italic>R</jats:italic>)‐<jats:bold>2</jats:bold>–Au). Molecular recognition characteristics induced by the <jats:italic>S</jats:italic> and <jats:italic>R</jats:italic> configurations were investigated by measurements of electron‐transfer reactions with horse heart cytochrome <jats:italic>c</jats:italic> (cyt <jats:italic>c</jats:italic>). The electrochemical studies indicate that the maximum current of cyt <jats:italic>c</jats:italic> reduction is obtained when the Au electrode is modified by <jats:bold>2</jats:bold> with a moderate coverage of approximately 4.0×10<jats:sup>−11</jats:sup> mol cm<jats:sup>−2</jats:sup>. Since the Au electrode is not densely packed with the Co<jats:sup>III</jats:sup> units at this concentration, we conclude that the penetrative association process between cyt <jats:italic>c</jats:italic> and the Co<jats:sup>III</jats:sup> unit plays an important role in this electron‐transfer system. The differences in the electron‐transfer rates of (<jats:italic>S</jats:italic>)‐<jats:bold>2</jats:bold>–Au and (<jats:italic>R</jats:italic>)‐<jats:bold>2</jats:bold>–Au increase with increasing scan rates, a result indicating that the chiral ligand has an influence on the rate of association of the complexes with cyt <jats:italic>c</jats:italic>. <jats:bold>3</jats:bold>–Au has a mixed monolayer composed of <jats:bold>2</jats:bold> and hexanethiol and exhibits electron‐transfer behavior comparable to <jats:bold>2</jats:bold>–Au. The difference in the association rates of (<jats:italic>S</jats:italic>)‐<jats:bold>3</jats:bold>–Au and (<jats:italic>R</jats:italic>)‐<jats:bold>3</jats:bold>–Au is larger than that between (<jats:italic>S</jats:italic>)‐<jats:bold>2</jats:bold>–Au and (<jats:italic>R</jats:italic>)‐<jats:bold>2</jats:bold>–Au, which indicates that the molecular recognition ability of <jats:bold>3</jats:bold>–Au has been enhanced by filling the gap between molecules of <jats:bold>2</jats:bold> with hexanethiols. The differences in the oxidation rates of cyt <jats:italic>c</jats:italic><jats:sup>II</jats:sup> between (<jats:italic>S</jats:italic>)‐<jats:bold>2</jats:bold>–Au and (<jats:italic>R</jats:italic>)‐<jats:bold>2</jats:bold>–Au and between (<jats:italic>S</jats:italic>)‐<jats:bold>3</jats:bold>–Au and (<jats:italic>R</jats:italic>)‐<jats:bold>3</jats:bold>–Au were larger than the differences in the rates of the reduction of cyt <jats:italic>c</jats:italic><jats:sup>III</jats:sup>; this suggests that the size of the heme crevice varies according to the oxidation state of cyt <jats:italic>c</jats:italic>.</jats:p>