Christelle Gautier

Phase segregation on electroactive self-assembled monolayers: a numerical approach for describing lateral interactions between redox centers.

A numerical method is proposed in order to differentiate a random distribution from a phase segregation of redox centers on (mixed) SAMs. This approach is compared to Lavirons interactions model and voltammetric data of nitroxylalkanethiolate SAMs.

Nitroxyl Radical Self-Assembled Monolayers on Gold: Versatile Electroactive Centers in Aqueous and Organic Media

Since the pioneering work by Nuzzo and Allara in 1983, selfassembled monolayers (SAMs) of alkanethiols have gained much attention in the interfacial electrochemistry and other research fields. 3] During the last decade, 5] increasing attention has been dedicated to the design and elaboration of redox-responsive SAMs. Employing redox SAM-modified electrodes for catalysis, recognition and sensing have resulted in some elegant examples that incorporate sophisticated receptors on the electrode surfaces. However, to the best of our knowledge, no redox-responsive SAM was designed to be active and stable in both aqueous (on wide range of pH) and organic media. TEMPO (2,2,6,6-Tetramethylpiperidine-1-oxyl) and its derivatives (under their oxoammonium form) have been extensively studied in the search for organic synthesis as a redox mediator, mostly, for the oxidation of primary alcohols. The electrochemical oxidation of TEMPO is known to be a stable and reversible one-electron process in both aqueous and non-aqueous electrolytes. 13] Despite the wide electrochemical applications of nitroxyl radical, rare works have been devoted to design and elaborate of redox-responsive TEMPO SAMs. In 1997, Fuchigami et al. reported the first preparation of stable self-assembled TEMPO-modified electrodes in acetonitrile : the electrochemical stability was only reached with highly diluted mixed SAMs of nitroxyl radical derivative and hexadecanethiol. In 1999, Kashiwagi et al. reported electrocatalysis attempts of amines with a mixed SAM of chiral nitroxyl radical derivative and hexadecanethiol : as mentioned by authors, results could be applied to the determination of optical purity of chiral amines. After a ten-years pause, Finklea et al. worked on Au-SACHTUNGTRENNUNG(CH2)10C(O)N(H)-TEMPO SAM to the first estimation of the standard rate constant and the reorganization energies of TEMPO/TEMPO in 1 m H2SO4. Herein, we raised the challenge of a design of redox-responsive TEMPO SAMs to be active, stable and providing electrocatalytic activities in both aqueous and non-aqueous solvents. To reach this goal, we synthesized the three nitroxyl radical derivates 1 a, 1 b and 1 c shown in Scheme 1. The synthesis of 1 a, 1 b and 1 c were carried out as outlined in Scheme 1. w-thioACHTUNGTRENNUNGacetyl carboxylic acids with different carbon chains length 2 a–c were synthesized from the corresponding w-bromocarboxylic acids by nucleophilic displacement with potassium thioACHTUNGTRENNUNGacetate in DMF. 4-aminoTEMPO was coupled to w-thioacetyl carboxylic acids 2 a-c via the active ester method, using diACHTUNGTRENNUNGcyclohexylcarbodiimide (DCC) and 1-hydroxybenzotriazole (HOBT) in methylene chloride (CH2Cl2), to give the TEMPO derivatives 3 a–c in good yields (77 to 84 %). The thioacetates 3 a–c were subsequently deprotected to thiols 1 a–c, under basic conditions, using CsOH.H2O in a mixture of THF and MeOH (yields: 50 to 91 %). Cyclic voltammograms (CVs) of 3 a, 3 b or 3 c exhibit a reversible one-electron process in CH2Cl2 and CH3CN, close to 0.56 V and 0.41 V (vs Ag/AgNO3 in 0.1 m Bu4NPF6) respectively. The kinetics for the formation of SAMs, prepared on Au substrate from 1 mm solution of 1 a, 1 b or 1 c in CH2Cl2 or CH3CN, were followed by using quartz crystal microbalance (QCM) measurements. By employing, the Langmuir adsorption isotherm model, it is possible to establish that deposition kiScheme 1. Synthesis of nitroxyl radical derivatives 1 a, 1 b and 1 c.

Electrochemical transduction on self-assembled monolayers: are covalent links essential?

Electrochemical transduction without covalent links between redox and complexant units in a complexing self-assembled monolayer has been established. The results demonstrate that transduction depends on the crown ether/ferrocene ratio and appears to be tunable.

Evidence of electrochemical transduction of cation recognition by TEMPO derivatives

This work reports the first example of electrochemical cation binding transductionvianitroxyl groups. It shows the possibility to transduce a complexation without a π-conjugated bridge between the redox and the host moieties. As expected, we confirm that the host/redox probe distance is a key point for transduction.

Click Chemistry: A Versatile Method for Tuning the Composition of Mixed Organic Layers Obtained by Reduction of Diazonium Cations

Postfunctionalization of glassy carbon electrodes previously modified by reduction of 4-azidobenzenediazonium was exploited to conveniently synthesize controlled mixed organic layers. Huisgen 1,3-dipolar cycloaddition was used to anchor functional entities to azide platform. By this way, ((4-ethynylphenyl)carbamoyl)ferrocene (ϕ-Fc) was coimmobilized with a set of acetylene derivatives: 1-ethynyl-4-nitrobenzene (ϕ-NO2), 4-ethynylaniline (ϕ-NH2) or ethylnylbenzene (ϕ). The composition of the resulting organic layers was tuned by adjusting the acetylene derivatives ratio in the postfunctionalization binary solution. Electronic properties of the substituents beared by the aromatic rings were found to have a strong impact on the cycloaddition kinetics toward the confined azide moieties. From this study, rules to prepare finely tuned bifunctional organic layers can be anticipated.