Formation and Reductive Desorption of Mercaptohexanol Monolayers on Mercury

Abstract

The formation and reductive desorption of self-assembled monolayers of 6-mercaptohexanol on mercury has been studied by using cathodic stripping voltammetry and capacitative transients, including the possibility of expanding or contracting the electrode area at the end of the preconcentration step. Experimental evidence shows the existence of three sequential stages during the formation of a thiol self-assembled monolayer. Each of these stages can be associated to the presence of (i) a low surface density state of oxidized thiol molecules, characterized by a single electrodimerization wave, (ii) a high surface density state, characterized by the emergence of a second voltammetric wave, and (iii) an ordered monolayer, which gives rise to a voltammetric spike. On the basis of electrode expansion experiments, a method is described to determine the surface concentrations of oxidized products, which does not require a baseline subtraction of the voltammograms to account for the nonfaradaic current. Quantitative voltammetric fits are consistent with the initial formation of a mixture of noninteracting monomers and dimers of oxidized thiol. The value of the maximum surface concentration and the ability to block the Ru(NH 3 ) 6 3+ electron transfer reveal that oxidized thiol molecules adopt a nearly perpendicular orientation in the high surface density state, which hampers ionic permeation. A theoretical model is proposed to account for the observed voltammetric behavior. The transition from the lower to the higher surface density states is modeled as a chemical step involving the exchange of metal free sites. Capacitative transients are also interpreted in terms of the three-stages model.

Electrochemical formation and electron transfer through self-assembled monolayers of 4-mercaptophenol on mercury

“…Their formation under potential control will be monitored at different times during the deposition process, by comparing the areas and shapes of the corresponding cathodic stripping voltammograms. As it was shown previously in the case of 6-mercaptohexanol monolayers [27], 4-mercaptophenol SAMs grow satisfactorily on mercury in the presence of the RuðNH 3 Þ 3þ 6 redox probe in solution, so that tunneling experiments on freshly prepared monolayers can be performed in a straightforward way. Besides, the acid character of the phenolic group offers the possibility to assess the influence of the molecular bridge protonation on its efficiency as a molecular wire.…”

“…Mercury provides a highly reproducible, defect free and atomically flat surface, and it allows to mimic Langmuir balance experiments by expanding/ contracting its surface [25][26][27]. In a recent report [27], the electrochemical formation and reductive desorption of 6-mercaptohexanol SAMs on mercury were studied, and evidence was given for the presence of three sequential stages during SAM formation. These three stages were associated with the growth of: (i) a low surface density monolayer, (ii) a high surface density monolayer and (iii) a passivating highly ordered monolayer, respectively.…”

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

“…The existence of energetically distinct monolayers of thio derivatives chemisorbed on Hg has previously been reported [4,21]. Namely, one lowdensity and one high-density monolayer of n-alkanethiolates were successively formed by scanning potential in the positive direction [4] (but note that such a scan does not lead to the formation of both the low-and high-density monolayers characterized above).…”

“…Namely, one lowdensity and one high-density monolayer of n-alkanethiolates were successively formed by scanning potential in the positive direction [4] (but note that such a scan does not lead to the formation of both the low-and high-density monolayers characterized above). Alternatively, three mercaptohexanol monolayers were formed at distinct exposure periods when chemisorption took place at a fixed potential [21].…”

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].…”