An Electrochemical Study of the SAMs of 6-Mercaptopurine (6MP) at Hg and Au(111) Electrodes in Alkaline Media

Abstract

A study of the reductive desorption process of 6MP-coated Hg and Au(111) electrodes in alkaline media has been carried out by means of such electrochemical techniques as cyclic voltammetry, chronoamperometry, and capacity−potential curves. The cyclic voltammograms show a single reduction peak whose peak potentials are strongly dependent on the nature of the substrate, Hg and Au(111) in this study. The full widths at half-maximum (fwhm) for Hg and Au(111) electrodes respectively are 19 and 21 mV at a scan rate of 0.1 V/s. These values are generally indicative of the existence of strong lateral interactions between molecules.The chronoamperometric curves have been recorded by single potential step experiments from a potential where the monolayer is stable to different final values within the range of potential where the monolayer is being desorbed. The curve shapes resemble those of systems that follow nucleation and growth mechanisms in the formation or dissolution of two-dimensional layers. In fact, the curve analysis using the nucleation and growth model of etching centers which was carried out in this report is actually in agreement with a mechanism of this kind for the dissolution of the 6MP monolayer at Hg and Au(111) electrodes. This study compares the properties of the 6MP monolayer at the two substrates Hg and Au(111) as well as with other thiol derivative monolayers.

An electrochemical study of 6-thioguanine monolayers on a mercury electrode in acid and neutral solutions

“…Scheme 2 can be proposed for the arrangements of the rows of stacked 6TG molecules. For the 6MP-SAM formed in mercury, a different orientation has been proposed [13], consisting of the interaction of the N1 with the mercury surface, in addition to the covalent SHg bond. The interaction of the nitrogen atoms in the ring with the electrode surface could not be established by electrochemical means alone, but has been observed for 6MP chemisorbed at a silver electrode by surface enhanced Raman spectroscopy [24].…”

“…Recent studies of SAMs on mercury have shown that highly organized, two-dimensional arrays of adsorbed molecules are obtained [6][7][8][9][10][11][12][13]. Demoz and Harrison [6] reported on the formation of an extremely impermeable, low-defect density hexadecanethiol monolayer on mercury.…”

“…We have recently studied the formation of a SAM of 6-mercaptopurine (6MP) on mercury in acidic [12] and alkaline [13] media. The process has been examined by electrochemical means, and the study concludes the existence of a two-dimensional condensed phase at potentials higher than the cathodic/anodic adsorption peaks.…”

Formation and electrochemical characterization of 6-thioguanosine monolayers on the mercury surface

“…On the other hand, interactions among aromatic rings (which are of the π → π stacking type) are stronger than those among aliphatic chains. For this reason (and also due to the rigidity of such rings), a densely packed SAM of 6-mercaptopurine (6MP) is formed on Hg in spite of the small size of its constituent molecules, as reported in several publications [26][27][28][29].…”

Voltammetry of the Reductive Desorption of Thiol Self‐assembled Monolayers from Electrode Surface

“…Other interesting features, which are out of the scope of this chapter, about the reductive desorption of organothiolate SAMs from a metal surface include the micelle-like aggregates that are formed after the desorption [11,12,25,71], the appearance of multiple peaks on the n voltammogram [9,31,33,72], the effects of pH [44], the reoxidative adsorption after the desorption [11,[73][74][75], the effect of the nature of the metal and the facets on SAMs [10,19,[76][77][78][79], the role of solvents used for the formation of SAMs [27,80], the effect of the type of ω-terminal on the desorption behavior [3,14,34,38,81], the rate of the ion penetration [1], the effect of the temperature on the shape of voltammograms [82], and the desorption of SAMs other than alkanethiols [23,24,32,49,50,53,[83][84][85][86].…”