In this work, monolayers of metal complexes were covalently attached to the surface of carbon electrodes with the goal of binding monolayers of histidine-tagged proteins with a controlled molecular orientation and a maintained biological activity. In this novel method, which is simple, versatile, and efficient, the covalent attachment was accomplished in a single step by the electrochemical reduction of aryl diazonium ions that were substituted with a nitrilotriacetic (NTA) or an imminodiacetic (IDA) ligand at the para position. The transient aryl radicals that were generated in the reduction were grafted to the surfaces of glassy carbon, highly oriented pyrolitic graphite, and graphite-based screen-printed electrodes, producing dense monolayers of the ligands. The NTA- and IDA-modified electrodes were shown to efficiently chelate Cu(II) and Ni(II) ions. The presence of the metal was established using X-ray photoelectron spectroscopy and electrochemistry. Surface coverages of the ligands were indirectly determined from the electroactivity of the copper(II) complex formed on the electrode surface. Studies on the effect of electrodeposition time and potential showed that, at sufficiently negative potentials, the surface coverage reached a saturating value in less than 2 min of electrodeposition time, which corresponds to the formation of a close-packed monolayer of ligand on the electrode surface. Once loaded with a metal ion, the modified electrode was able to bind specifically to histidine-tagged proteins such as the horseradish peroxidase (His-HRP) or to an enhanced, recombinant green-fluorescent protein via its N-terminal hexahistidine tail. In the case of His-HRP, the amount of active enzyme specifically immobilized by metal-chelating binding was determined from the analysis of electrocatalytic currents using cyclic voltammetry. The electrochemical grafting makes it possible to accurately controlled and electronically address the amount of deposited ligand on the conductive surfaces of carbon electrodes with any size and shape.

We measured single-molecule conductances for three different redox systems self-assembled onto gold by the STMBJ method and compared them with electrochemical heterogeneous rate constants determined by ultrafast voltammetry. It was observed that fast systems indeed give higher conductance. Monotonous dependency of conductance on potential reveals that large molecular fluctuations prevent the molecular redox levels to lie in between the Fermi levels of the electrodes in the nanogap configuration. Electronic coupling factors for both experimental approaches were therefore evaluated based on the superexchange mechanism theory. The results suggest that coupling is surprisingly on the same order of magnitude or even larger in conductance measurements whereas electron transfer occurs on larger distances than in transient electrochemistry.

Electron transfer inside self-assembled monolayers made from complex redox-active oligophenylenevinylene molecular wires is examined by ultrafast cyclic voltammetry. Rate constants above 10(6) s(-1) are measured when the electroactive moieties are easily accessible to counterions from the electrolyte. These counterion movements are necessary to compensate the local charge created upon electron transfer. Conversely, if the redox center is buried within long hydrophobic diluents, the counterion movement towards the redox entity becomes rate limiting, thus drastically altering the rate magnitude and its physical meaning. This change in the mechanism is examined both for superexchange or when one electron-hopping step is involved.

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A new electrochemical methodology is reported for monitoring in homogeneous solution the enantiospecific binding of a small chiral analyte to an aptamer. The principle relies on the difference of diffusion rates between the targeted molecule and the aptamer/target complex, and thus on the ability to more easily electrochemically detect the former over the latter in a homogeneous solution. This electrochemical detection strategy is significant because, in contrast to the common laborious and time-consuming heterogeneous binding approaches, it is based on a simple and fast homogeneous binding assay which does not call for an aptamer conformational change upon ligand binding. The methodology is here exemplified with the specific chiral recognition of trace amounts of l- or d-tyrosinamide by a 49-mer d- or l-deoxyribooligonucleotide receptor. Detection as low as 0.1% of the minor enantiomer in a nonracemic mixture can be achieved in a very short analysis time (<1 min). The assay finally combines numerous attractive features including simplicity, rapidity, low cost, flexibility, low volume samples (few microliters), and homogeneous format.

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New hybrid organic-inorganic materials are prepared by hydrolysis and polycondensation, or cocondensation with tetraethoxysilane, of iron porphyrins bearing a trifluorosilyl function; despite their insolubility, these

The halogen bond donor properties of iodo-tetrathiafulvalene (I-TTF) can be electrochemically switched and controlled via reversible oxidation in the solution phase. Interestingly the activation of only one single halogen bond yielded already a strong and selective interaction, quantified by cyclic voltammetry. The standard potentials of the redox couples I-TTF(0/1+) and I-TTF(1+/2+) were observed to shift upon the addition of halides. These anions selectively stabilize the cationic I-TTF species through halogen bonding in polar liquid electrolytes. The thermodynamic affinity constants for chloride and bromide binding to the oxidized species have been determined. Competition in halide binding between I-TTF(1+) and other halogen bond donors allowed for comparing the relative donor strength of the respective electrophilic species. Furthermore it has been shown that halogen bonding can prevail over hydrogen bonding in the investigated system.