Redox-Stable SAMs in Water (pH 0–12) from 1,1′-Biferrocenylene-Terminated Thiols on Gold

Abstract

Redox-active alkyl and acyl SAMs (self-assembled monolayers) on gold prepared from BFD-terminated thiols (BFD = bis(fulvalene)diiron, 1,1′-biferrocenylene) have been investigated in aqueous buffered solutions at various pH values by electroanalytical methods, and their redox potentials were determined at pH 7. Excellent redox stability over the whole range from pH 0 to 12, far superior to that of the corresponding ferrocene-terminated SAMs, is established by oxidizing alkanethiol BFD-SAMs to alkanethiol BFD + -SAMs for more than 1 h without any significant decomposition (<3%). The high stability and full reversibility suggests profitable use for diverse redox applications in aqueous solution. As a proof of concept, the utility of alkanethiol BFD SAMs for controlling surface wetting properties is demonstrated in contact angle changes of 25°by triggering the BFD/BFD + redox process.

A Single-Level Tunnel Model to Account for Electrical Transport through Single Molecule- and Self-Assembled Monolayer-based Junctions

“…Let us focus now on some very recent experiments in SAM-based molecular junctions where a record-high rectification ratio of three orders of magnitude has been achieved 22 . Figure 5 shows a sketch of the molecular junction formed by a SAM of S(CH 2 ) 11 Fc 2 molecules (with Fc 2 representing a biferrocenylene (Fc = Fc) head group) sandwiched in between /EGaIn (top) and Ag (bottom) electrodes (see refs 22 , 46 for synthesis and experimental details). In these junctions, the Fc 2 lies at the end of a long insulating alkyl chain, providing a non-covalent contact (van der Waals coupling) to the top electrode.…”

A Molecular Diode with a Statistically Robust Rectification Ratio of Three Orders of Magnitude

“…This observation of stable rectification from the SAMs with the biferrocenylene terminal groups is in good agreement with the redox stability of these SAMs monitored by CV measurements. 41 The fact that the values of R do not change as a function of the cycle number despite the large applied bias indicates that the Ga 2 O 3 cond layer does not change, i.e., anodic growth of the Ga 2 O 3 cond layer does not occur. 45 Figure 4 shows the log-average J(V) traces, the values of R versus V, and histograms of R for applied V at the highest value of R (R max ) of the three types of junctions.…”

Reversible binding and quantification of heparin and chondroitin sulfate in water using redox-stable biferrocenylene SAMs

“…The anodic peak potential E pa is 0.13 AE 0.02 V SCE , which is consistent with previous results in perchlorate solution at pH ¼ 7. 17 Although the oxidation and reduction charge is exactly identical, the full width at half maximum (FWHM) is 150 and 105 mV for the anodic and cathodic peaks, respectively. Thus, both FWHM values are larger than the theoretical value of 90.6 mV, but still in the range found for ferrocene SAMs as well.…”

“…bisfulvalene diiron) monocation over that of ferrocenium in basic solution (pH ¼ 7-12) 16 and at surfaces. 17 Stimulated by these results, BFD-SAMs made from 1 (Scheme 1) are used in this work to assess their utility for quantitative determination of polysulfates in aqueous biological buffer solution with good selectivity. Moreover, in the case of heparin, binding and release was electrochemically achieved by switching the BFD surface between the monocationic and neutral states.…”