Thiol/thiolate alkanethiol

For example, Wuelfing et al. reported on the synthesis of Au NPs using the thiolated polymer, a-methoxy-co-mercapto-poly(ethylene glycol) (PEG-SH), as stabilizer in a modification of the Brust-Schiffrin method using a 1/12 polymer thiol/ AuC14 ratio. Transmission electron microscopy showed that the product had modestly polydisperse Au cores of average diameter 2.8 1 nm. This nanomaterial led to characteristics uniquely different from alkanethiolate MPCs, notably aqueous solubility, thermal and chemical stability, ligand footprint size, and ionic conductivity [66]. 

Thiol monolayers are not removed by solvents, but by sulfur-active chemicals which pass through the surface monolayers. Laser desorption mass spectrometry has shown that thiolate molecules are intact on the gold surface, but through air oxidation, some sulfonates develop. The relative stability of alkanethiol SAMs on gold to air oxidation is to be expected due to the covalent nature of the S—Au bond. Photooxidation via UV excitation of electrons in the metal surface is, however, possible and leads to sulfonate salts which have again been characterized by mass spectrometry as well as by XPS . Alkene-thiolate monolayers can best be desorbed from gold by a one-electron reductive path. Stable monolayers on gold were also obtained with benzenesulfinate. 

The energy of the adsorption process could be estimated on toe basis of toe literature data using bond energies for RS—H, H2, RS—SR and RS—Au at 87, 104, 74 and 40kcalmol , respectively . Values of —5 and —6 kcalmol per gold thiolate unit are obtained for adsorption of thiols and disulphides, respectively. Schlenoff and coworkers estimated values of —5 and —12 kcalmoP for adsorption of thiols and disulphides, from his own and earher published data on toe voltammetric curves corresponding to the thermodynamically controlled (equiUbrium) electrodeposition of alkanethiolates on gold . Recently, accurate thermodynamic parameters were obtained... 

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