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

Abstract

Self-assembled monolayers (SAMs) of optically active Co(III) complexes ((S)-2/(R)-2) that contain (S)- or (R)-phenylalanine derivatives as a molecular recognition site were constructed on Au electrodes ((S)-2-Au/(R)-2-Au). Molecular recognition characteristics induced by the S and R configurations were investigated by measurements of electron-transfer reactions with horse heart cytochrome c (cyt c). The electrochemical studies indicate that the maximum current of cyt c reduction is obtained when the Au electrode is modified by 2 with a moderate coverage of approximately 4.0 x 10(-11) mol cm(-2). Since the Au electrode is not densely packed with the Co(III) units at this concentration, we conclude that the penetrative association process between cyt c and the Co(III) unit plays an important role in this electron-transfer system. The differences in the electron-transfer rates of (S)-2-Au and (R)-2-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 c. 3-Au has a mixed monolayer composed of 2 and hexanethiol and exhibits electron-transfer behavior comparable to 2-Au. The difference in the association rates of (S)-3-Au and (R)-3-Au is larger than that between (S)-2-Au and (R)-2-Au, which indicates that the molecular recognition ability of 3-Au has been enhanced by filling the gap between molecules of 2 with hexanethiols. The differences in the oxidation rates of cyt c(II) between (S)-2-Au and (R)-2-Au and between (S)-3-Au and (R)-3-Au were larger than the differences in the rates of the reduction of cyt c(III); this suggests that the size of the heme crevice varies according to the oxidation state of cyt c.

Insights into the formation and operation of polyaniline sulfonate/cytochrome c multilayer electrodes: contributions of polyelectrolytes’ properties

“…[11][12][13][14][15][16][17] Intensive work in the area of bioelectrochemistry during the last two to three decades has certainly been devoted to the metalloprotein cytochrome c (cyt c). 12,[18][19][20][21][22][23][24][25][26][27] Strategies have been developed for producing cyt c monolayers on coated electrodes with different properties, 19,[28][29][30][31][32] and their applications as sensors for superoxide and peroxide have been shown. [33][34][35][36][37][38] By means of the LBL process the formation of electroactive multilayers on the electrode could also be demonstrated.…”

Optically Activated Uptake and Release of Cu2+ or Ag+ Ions by or from a Photoisomerizable Monolayer-Modified Electrode

“…For example, Ag + - or Hg 2+ -functionalized monolayer-modified electrodes revealed electroswitchable hydrophobic/hydrophilic properties upon the reduction/oxidation of the ions. , Sensing of metal ions (e.g., Cu 2+ ) was demonstrated with a thiolated acetylacetonate monolayer associated with electrodes, and the association of proteins to electrodes via Ni 2+ -Histag ligands was reported . Also, chiroselective electron transfer to redox proteins (cytochrome C) using a chiral metal complex monolayer acting as a mediator was reported . Supramolecular Cu 2+ catenane or rotaxane complexes were assembled as monolayers on electrodes, and the electrochemically driven pirouetting within these molecular devices was reported .…”