Leaflike Structured Multilayer Assembly of Dimercaptothiadiazole on Gold Surface

Abstract

Adsorption of a heteroaromatic dithiol, 2,5-dimercapto-1,3,4-thiadiazole (DMT), on Au surface from a completely deaerated aqueous solution leads to the formation of a multilayer assembly via hydrogen bonding with water molecules, whereas adsorption from acetonitrile, ethanol, dimethyl sulfoxide, and chloroform solutions leads to the formation of a monolayer. Cyclic voltammetry (CV), attenuated total reflectance (ATR) infrared spectroscopy, Raman spectroscopy, high-resolution X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used to characterize the monolayer and multilayer assemblies of DMT on Au surface. Since DMT contains two S−H groups, it chemisorbs on Au surface through one of its two S−H groups, while the other S−H group is pointing away from the surface. The presence of free S−H groups on the Au surface was confirmed by CV, ATR-FT-IR, and XPS. It is presumed that the free S−H groups of DMT on the Au surface form a hydrogen bond with the water molecules. Subsequently, DMT molecules in solution form a hydrogen bond with the water molecules attached with DMT on Au surface, and this type of hydrogen bonding network goes on increasing when the soaking time of the Au surface in an aqueous solution of DMT increases. The involvement of water molecules in the multilayer formation was confirmed from the appearance of a broad stretching band around 3300 cm−1 corresponding to the hydrogen bonded O−H in the ATR-FT-IR spectrum, in addition to a binding energy peak at 533.4 eV due to hydrogen-donating water molecules in the O 1s region of XPS. The absence of a stretching band characteristic for S−S at 537 cm−1 in the Raman spectrum confirmed that the multilayer assembly was not formed via S−S linkage. However, exposure of DMT multilayer to air shows a stretching band characteristic of S−S, indicating that aerial oxidation leads to the formation of S−S bond. SEM images show that DMT forms a leaflike structured multilayer assembly on Au surface.

Surface selective binding of 2,5-dimercapto-1,3,4-thiadiazole (DMTD) on silver and gold nanoparticles: a Raman and DFT study

“…DMTD has wide industrial applications and has been used as additives in the fields of antioxidation, 33 anticorrosion, 34,35 and antifriction, [36][37][38] as metal deactivators 39,40 in motor oils, and also as cross-linkers in polymers. 41,42 They have also been widely used as surface-active agents although their surface chemistry is not very well understood [43][44][45] and relatively few studies quantitatively characterize DMTD [46][47][48][49][50][51][52][53][54][55][56][57][58] . DMTD has four potential electron donating sites that may be available for the adsorption of the molecule on the metal NP surface.…”

One-pot green synthesis of Ag/AgCl nanocube/reduced graphene oxide and its application to the simultaneous determination of hydroquinone and catechol

“…Aer drying, graphite and copper wire were inserted for electrical contact. 44 Then, the CFME was dipped for 30 min in 0.5 mg mL À1 AgNC/rGO solution and dried in air before use. The response of polished electrodes was tested by voltammetry in 0.1 mol L À1 KCl containing 10 mmol L À1 K 3 [Fe(CN) 6 ] at a scan rate of 10 mV s À1 .…”

Ultrasensitive and selective spectrofluorimetric determination of Hg(II) using a dimercaptothiadiazole fluorophore

“…It clearly suggests that DMT makes a complex with Hg(II) [27,28,30]. Job's method was applied to find the stoichiometric composition of the complex formed between Hg(II) and DMT and was found to be 1:2 ( Fig.…”

“…In the solid state, DMT exists as a thiolate tautomer, while in solution it exists as dithiol, thiolate and dithione forms and solvent dependent equilibrium obtained between all forms (Scheme 1). It has acid dissociation constants of pK a 1 ¼ À1.36 and pK a 2 ¼7.5, making its neutral form a very strong acid and its anionic form a weak acid [28,30,31]. DMT has four donor sites, and it can coordinate with either (a) both the nitrogen atoms, or (b) both the thiocarbonyl sulfur atoms or (c) one nitrogen atom and one sulfur atom on either the same side or different sides of the molecule.…”