Thiols electrocatalytic reduction

A further system providing photoswitchable redox-activated properties with amplification features via a secondary electrocatalytic vectorial electron transfer reaction has been exemplified by diarylethene (45) molecules incorporated into a long-chain thiol monolayer adsorbed on a Au electrode due to hydrophobic interactions [85]. In the closed isomeric state (45a), the monolayer demonstrates well-defined reversible cyclic voltammetry, whereas the open (45b)-state is completely redox-inactive. The electrochemically active 45a-state provides electrocatalytic reduction of Fe(CN)g-, thus enabling a vectorial electron cascade that amplifies the photonic input. 

Zak J, Yuan H, Ho M, Woo LK, Porter MD (1993) Thiol-derivatized metalloporphyrins monomolecular films for the electrocatalytic reduction of dioxygen at gold electrodes. Langmuir 9 2772—2774... 

Hutchison, J.E., T.A. Postlethweite, and R.W. Murray (1993). Molecular films of thiol-derivatized tetraphenylporphyrins on gold Film formation and electrocatalytic dioxygen reduction. Langmuir 9, 3277-3283. 

Table 7.6 shows that the potentials for the reduction of nitrite on MPc complexes are relatively high compared to when Hb, Mb, or FeTMPyP/DNA are employed. Zagal, Bedioui, and coworkers employed CoPc adsorbed (as monomer) or electropolymerized onto a vitreous carbon electrode (VCE), to catalyze the oxidation of nitrite . The activity of the electrode was found not to increase with the amount of CoPc adsorbed onto the electrode . At low potentials (at the foot of the electrocatalytic wave), the proposed mechanism is similar to that as proposed for thiols Equations (7.4)-(7.7). 

Metalloporphyrin SAMs also play an important role in catalysis. Several thiol-derivatised metalloporphyrins have been prepared that contain zinc [151,152], manganese [153] or cobalt [152,154-156]. Such metalloporphyrin systems bound to gold electrodes have been used to investigate the reduction of oxygen to hydrogen peroxide [154-156]. The electrocatalytic activity of this process depends on the interfacial architecture of the metalloporphyrin SAMs [155]. Metalloporphyrins in which the porphyrin rings are coplanar to the Au-surface show a higher electrocatalytic activity than... 

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