Thiols adsorption

Immobilization strategies for electrochemical detection may involve physical adsorption, thiol-finking chemistries to gold electrodes, and organosilane finking chemistries to oxidized silicon or glass substrates. Immobilization... 

SSIMS has also been used to study the adsorption of propene on ruthenium [3.29], the decomposition of ammonia on silicon [3.30], and the decomposition of methane thiol on nickel [3.31]. 

Forda, M.J., Hoft, R.C. and Gale, J.D. (2006) Adsorption and dimerisation of thiol molecules on Au(lll) using a Z-matrix approach in density functional theory. Molecular Simulation, 32, 1219-1225. 

Kruger, D., Fuchs, H., Rousseau, R., Marx, D. and Parinello, M. (2001) Interaction of short-chain alkane thiols and thiolates with small gold clusters Adsorption structures and energetics. Journal of Chemical Physics, 115, 4776-4786. 

Sulfiir-anchored SAMs and thin films, mostly from organosulfiir precursors, have been discussed at length by a number of authors [10, 181]. SAMs of organosulfiir compounds (thiols, disulfides, sulfides) form on gold substrates by spontaneous adsorption from either the liquid or the vapor phase. A number of experimental factors can affect the formation and structure of SAMs such as choice of solvent, temperature, concentration, immersion time, purity of adsorbate, oxygen concentration in solution, cleanliness, and structure of the adsorbate. Interestingly, the... 

The adsorption of collectors on sulfide mineral occurs by two separate mechanisms chemical and electrochemical. The former results in the presence of chemisorbed metal xanthate (or other thiol collector ion) onto the mineral surface. The latter yields an oxidation product (dixanthogen if collector added is xanthate) that is the hydrophobic species adsorbed onto the mineral surface. The chemisorption mechanism is reported to occur with galena, chalcocite and sphalerite minerals, whereas electrochemical oxidation is reportedly the primary mechanism for pyrite, arsenopyrite, and pyrrhotite minerals. The mineral, chalcopyrite, is an example where both the mechanisms are known to be operative. Besides these mechanisms, the adsorption of collectors can be explained from the point of interfacial energies involved between air, mineral, and solution. 

Interest in the adsorption of sulfur-containing molecules at metal surfaces been stimulated by a desire to elucidate the decomposition mechanisms of thiols during the catalytic removal of sulfur from feedstocks and the position of thiols as the favoured head groups for adsorbates used to construct self-assembled monolayers. We shall not survey the extensive self-assembled film literature but restrict our discussion to the simpler thiols. 

The smallest molecule in the class is methanethiol, which has been studied at several surfaces as an indicator for the behaviour of larger thiols. On all metals, except gold, adsorption results in the dissociation of the S H bond. Yates and co-workers suggested47 that the S-H bond of methanethiol is also stable on silver, dissociation being catalysed by adsorbed sulfur present at defect sites. However, this contradicts Jaffey and Madix s results,56 which showed S-H bond cleavage below 350 K in their study of ethanethiol on Ag(lll). 

The initial step of the adsorption of thiols on a Mo(100) surface is the formation of adsorbed thiolate groups. Phenyl thiolate is formed upon adsorption of thiophenol at 120 K on a clean Mo(110) surface.381 The thiolate intermediate subsequently undergoes competing C-S bond hydrogenolysis to form benzene, or C-S and C-H bond scission to form surface benzyne. The adsorption of thiophenol was also studied on a sulfur-covered Mo surface382 Phenyl disulfide is formed via S-H bond scission and S-S bond formation. The S-S linkage is oriented perpendicular and the phenyl ring parallel to the surface. 

Analyses of enzyme reaction rates continued to support the formulations of Henri and Michaelis-Menten and the idea of an enzyme-substrate complex, although the kinetics would still be consistent with adsorption catalysis. Direct evidence for the participation of the enzyme in the catalyzed reaction came from a number of approaches. From the 1930s analysis of the mode of inhibition of thiol enzymes—especially glyceraldehyde-phosphate dehydrogenase—by iodoacetate and heavy metals established that cysteinyl groups within the enzyme were essential for its catalytic function. The mechanism by which the SH group participated in the reaction was finally shown when sufficient quantities of purified G-3-PDH became available (Chapter 4). 

Inhibitors form a film on the surface that blocks the dissolution of the substrate. Adsorption of an alkyl-thiol to the surface of the CU3AU alloy resulted in an inaeased surface tension of the gold film this is observed as an increase in the value of <., which depresses dissolution of copper. This behavior resembles inhibition of copper corrosion on a pure copper surface where benzotriazole increases the potential to start significant copper dissolution this was demonstrated by Cruickshank et using in situ AFM. However, when the critical potential for benzotriazole film... 

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