Metal-mediated electrochemical oxidation of DNA-wrapped carbon nanotubes.

As part of the ongoing effort to describe electron transfer reactions of carbon nanotubes (CNTs), we studied the mediated electrochemical oxidation of CNTs solubilized by wrapping with a T(60) deoxyribooligonucleotide. Cyclic voltammetry revealed that the oxidation of this CNT-DNA material by electrogenerated ML(3)(3+) mediators completes a catalytic cycle that increases the oxidative current compared to that obtained by voltammetry of the mediator alone (M = Fe(III), Ru(III), or Os(III); L = 2,2'-bipyridine or 4,4'-dimethyl-2,2'-bipyridine). We observed a greater increase in current at higher nanotube concentration, slower experimental scan rate, and higher mediator redox potential (E(0)'). Using computer simulation, these observations were shown to be consistent with CNT oxidation involving the removal of multiple electrons from each CNT-DNA moiety (the T(60) oligonucleotide was chosen because it is not oxidized by any of the mediators). The data are well-described by a simulation model based on the classical catalytic mechanism (EC') with the following embellishment: three populations of CNT-DNA redox-active sites with different E(0)' and therefore different oxidation rates are employed to represent the varying redox potentials of different valence band electrons within one CNT chiral type and within the distribution of CNT types present in our sample. This modeling suggests the number of CNT-DNA sites available for oxidation increases with the E(0)' of the mediator. This result can be qualitatively interpreted in terms of CNT band theory.