Tuning the redox properties of metalloporphyrin- and metallophthalocyanine-based molecular electrodes for the highest electrocatalytic activity in the oxidation of thiols.
In this work we discuss different approaches for achieving electrodes modified with N(4) macrocyclic complexes for the catalysis of the electrochemical oxidation of thiols. These approaches involve adsorption, electropolymerization and molecular anchoring using self assembled monolayers. We also discuss the parameters that determine the reactivity of these complexes. Catalytic activity is associated with the nature of the central metal, redox potentials and Hammett parameters of substituents on the ligand. Correlations between catalytic activity (log i at constant E) and the redox potential of catalysts for complexes of Cr, Mn, Fe, Co, Ni and Cu are linear with an increase of activity for more positive redox potentials. For a great variety complexes bearing the same metal center (Co) correlations between log i and E(o') of the Co(II)/Co(I) couple have the shape of an unsymmetric volcano. This indicates that the potential of the Co(II)/Co(I) couple can be tuned using the appropriate ligand to achieve maximum catalytic activity. Maximum activity probably corresponds to a DeltaG of adsorption of the thiol on the Co center equal to zero, and to a coverage of active sites by the thiol equal to 0.5.
Bedioui
Fethi
F
INSERM, U 640, CNRS, UMR 8151, Ecole Nationale Supérieure de Chimie de Paris, René Descartes Paris 5, Chemical and Genetic Pharmacology Laboratory, Paris, France.
Griveau
Sophie
S
Nyokong
Tebello
T
Appleby
A John
AJ
Caro
Claudia A
CA
Gulppi
Miguel
M
Ochoa
Gonzalo
G
Zagal
José H
JH
D002384:Catalysis; D004563:Electrochemistry; D004566:Electrodes; D007211:Indoles / Q000737:chemistry*; D054833:Isoindoles; D046911:Macromolecular Substances / Q000737:chemistry; D008665:Metalloporphyrins / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013499:Surface Properties
D007211:Indoles; D054833:Isoindoles; D046911:Macromolecular Substances; D008665:Metalloporphyrins; D013438:Sulfhydryl Compounds; C013647:phthalocyanine