The protonation state of thiols in self-assembled monolayers on roughened Ag/Au surfaces and nanoparticles

Abstract

The protonation state of thiols in self-assembled monolayers (SAMs) on Ag and Au surfaces and nanoparticles (NPs) has been an issue of contestation. It has been recently demonstrated that deuterating the thiol proton produces ostentatious changes in the Raman spectra of thiols and can be used to detect the presence of the thiol functional group. Surface enhanced Raman spectroscopy (SERS) of H/D substituted aliphatic thiols on Ag surfaces clearly shows the presence of S-H vibration between 2150-2200 cm(-1) which shifts by 400 cm(-1) upon deuteration and a simultaneous >20 cm(-1) shift in the C-S vibration of thiol deuteration. Large shifts (>15 cm(-1)) in the C-S vibration are also observed for alkyl thiol SAMs on Au surfaces. Alternatively, neither the S-H vibration nor the H/D isotope effect on the C-S vibration is observed for alkyl thiol SAMs on Ag/Au NPs. XPS data on Ag/Au surfaces bearing aliphatic thiol SAMs show the presence of both protonated and deprotonated thiols while on Ag/Au NPs only deprotonated thiols are detected. These data suggest that aliphatic thiol SAMs on Au/Ag surfaces are partially protonated whereas they are totally deprotonated on Au/Ag NPs. Aromatic PhSH SAMs on Ag/Au surfaces and Ag/Au NPs do not show these vibrations or H/D shifts as well indicating that the thiols are deprotonated at these interfaces.

Competition of van der Waals and chemical forces on gold–sulfur surfaces and nanoparticles

“…These Au(I)thiolate species are thus not really protectants at all as their formation is associated with surface destruction. On the other hand, the binding of thiols or disulfides to surfaces subsequent to initial physisorption 90,91 does not involve Au(I)-thiolate production, but results instead in surfaces protected by Au(0)-thiyl species. Chemical reaction conditions that access Au(I)-thiolate potential-energy surfaces lead to products that are fundamentally different in structure and properties to those that proceed only along Au(0)-thiyl pathways.…”

Metal–ligand bond strength determines the fate of organic ligands on the catalyst surface during the electrochemical CO2 reduction reaction

“…In the as-synthesised sample, the broad peak can be deconvoluted into two major components, corresponding to the protonated form (thiol; S2p 1/2 at 164.30 eV) and deprotonated form (thiolate; S2p 1/2 at 162.85 eV) of DDT, respectively. 31 One can assume that the thiolate is the one binding to the surface, while the thiol is simply physisorbed. Following CO 2 RR, the contribution from the thiol component is much lower.…”

Effects of Gold Salt Speciation and Structure of Human and Bovine Serum Albumins on the Synthesis and Stability of Gold Nanostructures

“…Noticeable is the appearance of a band at 2150 cm −1 for the albumins capping GNPs at pH 6. This band is assigned to the coordination of protonated SH with the gold surface (Bandyopadhyay et al, 2015 ). The absence of this contribution in the spectra of the GNPs synthesized at pH 7 is consistent with the lowered p K a of the SH group in the albumin structure that makes this group predominantly deprotonated at pH 7.…”