Surface Chemistry of Thiomalic Acid Adsorption on Planar Gold and Gold Nanoparticles

Abstract

The self-assembly of thiomalic acid (TMA) on Au(111) and on preformed Au nanoparticles (AuNPs) protected by weak ligands has been studied by X-ray photoelectron spectroscopy (XPS) and electrochemical techniques. Results show that TMA is adsorbed on the Au(111) surface as thiolate species with a small amount of atomic sulfur (∼10%) and a surface coverage lower than that found for alkanethiols due to steric factors. The amount of atomic sulfur markedly increases when the TMA is adsorbed on AuNPs by the ligand exchange method. We propose that the atomic sulfur is produced as a consequence of C-S bond cleavage, a process that is more favorable at defective sites of the AuNPs surface. The bond scission is also assisted by the presence of the electron-withdrawing carboxy moiety in the α-position relative to the C-S bond. Moreover, the high local concentration of positively charged species increases the stability of the negatively charged leaving group, leading to a higher amount of coadsorbed atomic sulfur. Our results demonstrate that the terminal functionalities of thiols are conditioning factors in the final structure and composition of the adlayers.

Self-assembled monolayers of thiolates on metals: a review article on sulfur-metal chemistry and surface structures

“…211 Solvent-mediated decomposition and sulfidization have also been reported for MT. 212 In the case of TMA SAMs on Au(111) the mechanism involves the charge withdraw by the S atom from the gold surface, and the stabilization of the negatively charged leaving group by electronic resonance with the carboxylic group at alpha position to C-S bond 66 . Also Au can exhibit some catalytic activity for organic reactions, including C-S bond breaking, due to the presence of a high defect density at nanoparticle surfaces.…”

“…65 There are other interesting experimental observations that deserve attention. Thiols with functional terminal groups distinct from alkyl, such as thiomalic acid (TMA) 66 , and small aromatic thiols such as mercaptobenzoic acid (MBA), 67 and 6-mercaptopurine 68 Table 2. The staple stability arises from surface Au sites that contain single Au-S coordination, anchoring the staple units to the substrate, and some Au-Au coordination.…”

“…82,83 This S1 component is enhanced in some aromatic thiols and is also more evident in AuNPs (S1 S 2p component in Figure 1d). In this case this can be accounted by the increased reactivity of the curved NP surfaces 66 or by the presence of different thiolate species on the facets or by S contamination/formation during NP synthesis. 64 85 are protected by two types of "staple" motifs (RS-Au ad -SR and RS-Au ad -RS-Au ad -SR) 86 , i.e.…”

Gold-Induced Desulfurization in a Bis(ferrocenyl) Alkane Dithiol

“…where the decomposition product is relatively stable). [67][68][69][70] However, while their results confirmed the formation of a sulfur-rich layer on the substrate from a range of different organic thiols, no direct experimental evidence for the reaction products in solution were reported. This would nevertheless be useful, in order to gain further insight into the reaction mechanism and to assess potential further implications of the effect.…”

Understanding the adsorption of branched polyamine on surface of gold nanoparticles by molecular dynamics simulations

“…The structure and dynamics of the interface between solution molecules and metals continue to be intensively investigated by both experimental and computational methods . The understanding of this interface can contribute toward many significant industrial processes, such as in materials synthesis and catalysis as well as for biosensors.…”