Abstract
Gold surfaces are widely used in electrochemistry while gold nanoparticles have very many uses, with both the surfaces and the particles often being protected by sulfur-bound organic ligands. The ligands not only provide chemical stability but also directly participate in many desired processes. This review considers the diversity of known atomic structures for gold–sulfur interfaces, how these structures facilitate a diversity of mechanisms in electrochemical applications, and why this is possible based on recent advances in the basic understanding of the electronic structure of gold–sulfur bonds. Believed once to be Au(I)-thiolate in character and hence distinctly different to physisorbed thiols and disulfides, chemisorbed bonds are shown to be Au(0)-thiyls instead. A wide range of in situ STM electrochemical and other data is interpreted from this perspective.
Highlights
For thousands of years, solid gold (Au) has been treasured as an economic investment, for cultural purposes, and as jewelry [1]
On the basis of recent detailed analysis [40], it is concluded that the Au-S link holds a dominant Au(0)-thiyl character resting on strong van der Waals interactions and the aurophilic effect, in addition to secondary covalent and ionic Au-S features
Aspects [40] of the Brust-Schiffrin core nanoparticle synthesis [16,17] can be understood, as well the results of real time imaging on planar Auelectrode surfaces as reported for 1-propanethiol [31] and cysteamine [36], anticipated for more complex molecular selfassembled monolayers (SAMs) [80]
Summary
Solid gold (Au) has been treasured as an economic investment, for cultural purposes, and as jewelry [1]. The reactivity of the immobilized redox metalloproteins is, exceedingly sensitive to the structural details of the SAM This is strikingly illustrated by the voltammetry and in-situ STM and AFM studies of the blue Cu-enzyme nitrite reductase on single-crystal Au(111) electrode surfaces, modified by a broad variety of aliphatic and aromatic thiol SAMs [63,64]. Comprehensive spectroscopy, diffraction and other surface physics supported by theoretical and computational work has disclosed the nature of the Au-S bond [24,38,39,41,42,43,44,46,69,70] These results are consistent with the in-situ STM & AFM studies [71] and provides a detailed understanding of structure and function [40]. Strong Au-Au interactions within surface and in Au-Au compounds [72,73,77,78] shifts the 6s band away from the Au Fermi level and the 5d band [69], causing the filled 5d orbitals to take over bonding to the sulfur atom
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