Understanding the Equilibria of Thio Compounds Adsorbed on Gold by Surface-Enhanced Raman Scattering and Density Functional Theory Calculations

Abstract

The self-assembled monolayers (SAMs) derived from thionicotinamide (TNA), thioisonicotinamide (iTNA), and 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol (Hpyt) on gold have been characterized via surface-enhanced Raman scattering (SERS) as a function of pH and applied potential. Density functional theory calculations performed on the molecule/metal interaction model reinforced the vibrational assignments of the SERS spectra. Despite the structural similarity, these compounds presented different behaviors depending on the pH and applied potential with the iTNA SAM being the most affected. Upon adsorption and at pH 6, Hpyt SAM is not protonated while TNA and iTNA SAMs are partially and completely protonated, respectively. The results presented herein, besides being helpful for the understanding of the formation of the SAMs, can shed light on the understanding of the different responses observed for the cytochrome c metalloprotein by using the SAMs derived from these molecules.

Hydroxyl Radical Generation and DNA Nuclease Activity: A Mechanistic Study Based on a Surface‐Immobilized Copper Thioether Clip‐Phen Derivative

“…In this work, we have deliberately attached a SCH 3 fragment to a clip‐phen derivative to make possible the modification of gold substrates, due to the known affinity of sulfur towards gold . In this way, we could combine data obtained in solution with those obtained by using surface techniques such as surface plasmon resonance (SPR) and scanning electrochemical microscopy (SECM) in an attempt to identify the ROS species generated during the redox processes and, in the end, to better understand the degradation mechanism of DNA by copper complexes.…”

Surface enhanced Raman scattering investigation of two novel piperazine carbodithioic acids adsorbed on Ag and ZnO nanoparticles

“…23,24 In this order, DFT computations have been performed (see DFT analysis). 23,24 In this order, DFT computations have been performed (see DFT analysis).…”

“…The geometry optimization of PZCDT/PZbCDT with single Ag atom (deprotonated PZCDT/ PZbCDT + Ag 1 ) using DFT/Lanl2DZ method [23][24][25][26]44,45 suggested strongly the possibility of bidentate interaction. We rst investigated the possibility of bidentate and monodentate interaction exhibited between adsorbate and substrates.…”

Oxadiazole‐2‐thiol Adsorption on Gold Nanorods: A Joint Theoretical and Experimental Study by Using SERS, XPS, and DFT

“…A close examination of the atoms included in this vibration shows that this mode corresponds to the symmetrical bending of NH bonds involved in the hydrogen‐bonded dimer, which explains the failure of the TN monomer to reproduce this feature. The recent report of Paulo et al10 of combined SERS and DFT study on self‐assembled monolayers (SAMs) derived from 5‐(4‐pyridyl)‐1,3,4‐oxadiazole on a roughened gold surface shows large discrepancies between experimental and simulated normal Raman spectra for this ODT derivative in the solid state. The envisaged model in that case is a monomer of thione, which reveals, as mentioned by the authors, that the vibrational assignment for this ODT derivative in the solid state was not straightforward.…”

“…Very recently, the pH‐dependent behavior of an ODT self‐assembled monolayer on a roughened gold electrode surface was studied by using Raman spectroscopy and correlated to DFT calculations. The theoretical Raman spectra of ODT on a gold surface were simulated for different protonated states of ODT molecule coordinated to one gold atom 10…”