Thiolate Adsorption Research Articles

Thiol Adsorption on and Reduction of Copper Oxide Particles and Surfaces.

The adsorption of 1-dodecanethiol at room temperature and at 75 °C on submicron cuprous and cupric oxide particles suspended in ethanol has been investigated by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy. Thiol adsorption occurs in all cases via Cu-S bond formation, with partial dissolution of CuO at 75 °C and formation of a copper-thiolate complex replacement layer. Regardless of temperature, the surface of the CuO particles is essentially completely reduced to either Cu2O or metallic copper, as evidenced by loss of the characteristic Cu(2+) XPS features of dried powder samples. Companion ultrahigh-vacuum studies have been performed by dosing clean, oxygen-dosed, and ozone-treated single crystal Cu(111) with methanethiol (MT) gas at room temperature. In the latter case, the surface corresponds to CuO/Cu(111). XPS confirms MT adsorption in all cases, with an S 2p peak binding energy of 162.9 ± 0.1 eV, consistent with methanethiolate adsorption. Heating of MT-covered Cu(111) and oxygen-dosed Cu(111) leads to decomposition/desorption of the MT by 100 °C and formation of copper sulfide with an S 2p binding energy of 161.8 eV. Dosing CuO/Cu(111) with 50-200 L of MT leads to only partial reduction/removal of the CuO surface layers prior to methanethiolate adsorption. This is confirmed by ultraviolet photoelectron spectroscopy (UPS), which measures the occupied states near the Fermi level. For both the colloidal CuO and single crystal CuO/Cu(111) studies, the reduction of the Cu(2+) surface is believed to occur by formation and desorption of the corresponding dithiol prior to thiolate adsorption.

Adsorption, kinetics and biochemical interaction of biotin at the gold–water interface

The adsorption kinetics and surface coverage of free biotin with a thin gold film have been exploited by means of surface plasmon resonance sensing. The material was dissolved in phosphate buffered saline (PBS) aqueous solution and ethanol–PBS mixtures. A micro-fluidic flow cell was used for solute admission. Experimental conditions eliminate contact to ambient air and surface contaminations and maintain a stable, initially hydrophilic metal surface and reproducible adsorption conditions. In the initial binding phase, and at higher solute concentration, biotin films are composed from up to three mono-layers. Rinsing with PBS buffer removes the weakly bound fraction and leaves a single molecular layer at 1.1nm thickness, along with concentration dependent surface coverage. The binding kinetics is well described by a Langmuir adsorption isotherm. The equilibrium constant Keq determines to 2.94×103mol−1, and the free adsorption energy ΔGads to −4.7kcal/mol. Both values are well within the parameter range for alkene–thiolate adsorption to microcrystalline gold films. This supports a chemisorptive binding state, along with the possibility of molecular self-assembly. Both, Neutravidin (NA) and human serum (HS) effectively immobilize onto a biotin monolayer beneath. In the reversed binding sequence, biotin firmly attaches also to NA, but not to HS. Hence, the direct binding route of biotin onto thin gold films can be favorably used in the design of simplified immuno-assays, solely relying on biotinylated antibodies, while avoiding the need for immobilization of an intermediate Neutravidin linker layer.

Thiolate adsorption on Au(${\bm {hkl}}$hkl) and equilibrium shape of large thiolate-covered gold nanoparticles

The adsorption of thiolates on Au surfaces employing density-functional-theory calculations has been studied. The dissociative chemisorption of dimethyl disulfide (CH(3)S-SCH(3)) on 14 different Au(hkl) is used as a model system. We discuss trends on adsorption energies, bond lengths, and bond angles as the surface structure changes, considering every possible Au(hkl) with h, k, l ≤ 3 plus the kinked Au(421). Methanethiolate (CH(3)S-) prefers adsorption on bridge sites on all surfaces considered; hollow and on top sites are highly unfavourable. The interface tensions for Au(hkl)-thiolate interfaces is determined at low coverage. Using the interface tensions in a Wulff construction method, we construct atomistic models for the equilibrium shape of large thiolate-covered gold nanoparticles. Gold atoms in a nanoparticle change their equilibrium positions upon adsorption of thiolates towards shapes of higher sphericity and higher concentration of step-edge atoms.

Electrochemical Properties of Alkanethiol Monolayers Adsorbed on Nanoporous Au Surfaces

Although there have been numerous reports on the fundamental physical and chemical properties of thiolate SAMs on Au surfaces, mo st of them were investigated on flat Au surfaces, typically on well-defined Au(111) surfaces. These previous investigations provide valuable insights on the surface phenomena of thiolate adsorption on Au surfaces; however, the effect of the structure of Au substrates on the basic properties of thiolate monolayers such as electrochemical properties and structures of the adsorbed layers has yet to be understood. A few reports have addressed the structures of thiolate SAMs on different single crystalline Au surfaces.

Photoemission core-level shifts reveal the thiolate-Au(111) interface

The nature of the thiolate/Au(111) interface is a long-standing puzzle. It has been suggested that thiolates drive surface reconstruction, however, a consensus regarding the adsorption configuration is missing. Herein, the density-functional theory is used to evaluate surface core-level shifts (SCLSs) for methyl thiolates on Au(111) assuming a representative set of different surface reconstructions. The SCLSs are found to provide sensitive fingerprints of the anchoring configuration, and it is only thiolate adsorption in the form of MeS-Au-SMe complexes that can be reconciled with experimental data.

Electronic Structure of Thiolate-Covered Gold Nanoparticles: Au102(MBA)44

We present first principles, density functional theory (DFT) calculations of the structural and electronic properties of thiolate-protected gold nanoparticles [Au(102)(MBA)(44) ] that have been recently crystallized and measured by X-ray diffraction. Our calculations yield structural properties in very good agreement with experiment and reveal the impact of thiolate adsorption on both the surface geometry and the electronic structure of the gold core; in particular, within DFT we observe the emergence of an energy gap of about 0.5 eV, upon MBA adsorption. Using a localized orbital analysis, we characterize the electron distribution in the nanoparticle and provide insight into the bonding of thiolates on curved gold surfaces.

First-principles studies: Thiolated Au 2Cr and Au 6Cr clusters

The structural, energetic and magnetic properties of thiol-passivating Au 2Cr and Au 6Cr clusters are investigated by performing first-principles calculation based on density functional theory. We find that the adsorption of thiolate is energetically more favorable than thiol and that the thiolates favor “top” site adsorption on Cr atom in one methanethiolate adsorbed Au 2Cr cluster while they favor “bridge” site adsorption on top of the middle point of Cr–Au bonds in three methanethiolates adsorbed Au 2Cr cluster. In thiol-passivating Au 6Cr cluster, the thiol favor “top” site adsorption on top of atom Au while the thiolate favor “bridge” site adsorption on top of the middle point of Au–Au bonds. The energetics of the reactions indicates that these thiol-passivating Au 2Cr or Au 6Cr clusters can be used as hydrogen storage materials. There are large and positive spin populations on atom Cr. The spin populations of atoms Au, S and H are attributed to both the spin delocalization and the spin polarization mechanisms.

Structure, Bonding Nature, and Binding Energy of Alkanethiolate on As-Rich GaAs (001) Surface: A Density Functional Theory Study

Chemisorption of alkanethiols on As-rich GaAs (001) surface under a low coverage condition was studied using first principles density functional calculations in a periodic supercell approach. The thiolate adsorption site, tilt angle and its direction are dictated by the high directionality of As dangling bond and sulfur 3p orbital participating in bonding and steric repulsion of the first three CH2 units from the surface. Small charge transfer between thiolate and surface, strong dependence of total energy on tilt angle, and a relatively short length of 2.28 A of the S-As bond indicate the highly covalent nature of the bonding. Calculated binding energy of 2.1 eV is consistent with the available experimental data.

Raman Spectroscopy of Benzenethiolates on Nanometer-Scale Gold Clusters

Near-infrared (1064-nm) irradiation of neat solid samples of benzenethiolate monolayer-protected gold clusters (MPCs) yields strong, well-resolved Raman spectra of the thiolate groups, comparable to those obtained for the same groups adsorbed at roughened gold electrodes. These clusters are formulated as TOAZ[AuN(SPh)M]Z-, N >> M and Z = 3-6, with core diameters of 1.7 and 1.5 nm, and were characterized previously by X-ray scattering, mass spectrometry, infrared spectroscopy, optical spectroscopy, nuclear magnetic resonance, and elemental analysis [Price, R. C.; Whetten, R. L. J. Am. Chem. Soc. 2005]. Numerous previous attempts to obtain spectra on various MPCs yielded only diffuse luminescence bands, as did benzenethiolate MPC samples of TOA2[Au44(SPh)28]2-, with 1.1-nm core diameters. The clusters are free of excess tetraoctylammonium bromide (TOABr) from the synthetic procedure, containing only the necessary TOA+ to maintain charge balance. In situ thermometry, using the anti-Stokes/Stokes intensity ratios, indicated the sample temperature remained below the onset of thermal decomposition. The Raman spectra of the clusters bear a strong resemblance to those obtained for nonmetallic (Au(I)SPh)x polymer samples that are not in resonant absorption at the laser wavelength. The smaller of the two cores, nominally TOA6[Au110(SPh)62], shows clearly a band at 505 cm(-1) assigned to a S-S stretch, suggestive of a moiety resembling diphenyl disulfide on the cluster surface. These results are interpreted with reference to recent reports suggesting a substantial "reconstruction" of the outermost gold layer upon thiolate adsorption (SAM formation).

Publisher’s Note: “Tail molecule dependence of thiolate adsorption on Au(111) surface: Theoretical study” [J. Chem. Phys. 121, 970 (2004)

Abstract

Tail molecule dependence of thiolate adsorption on Au(111) surface: Theoretical study.

The adsorption of thiolates with various tail molecules on the Au(111) surface has been investigated by first-principles calculations. We have considered six typical thiolate molecules, that is, methylthiolate, ethylthiolate, ethylenethiolate, acetylenethiolate, benzenethiolate, and thiophenethiolate. It is found that these thiolates exhibit little difference in their stable adsorption geometries. They are adsorbed at the bridge site with being significantly tilted from the surface normal. The adsorption energy of thiolate on Au, on the other hand, largely varies depending on the type of tail molecule, and is linearly proportional to the binding energy of thiolate with H. We discuss the tail molecule dependence in terms of the bonding environment around the C atom connected to the head S atom.

Adsorption modes of cysteine on Au(111): thiolate, amino-thiolate, disulfide.

The adsorption of cysteine on the (111) surface of gold has been studied by means of periodic supercell density-functional theory calculations. A number of different adsorption modes are examined, including adsorption through the thiol group in either thiolate or disulfide form, and adsorption through both the thiol and amino functional groups. We find that at intermediate coverage densities the latter mode of adsorption is favored, followed by thiolate adsorption at the bridge (slightly displace toward fcc) site. The N-Au and S-Au bond strengths in the amino-thiolate adsorption are estimated to be of the order of 6 and 47 kcal/mol, respectively. The electronic structure of the different systems is analyzed, with focus on the total and projected density of states, as well as on the detailed character of the electronic states at the interface. States near the Fermi energy are found to have a metal-molecule antibonding character, whereas metal-molecule bonding states mostly occur near the lower edge of the Au-d band.

Ultrasonic effects on electroorganic processes: Part 24. Rate and saturated amount of the self-assembled adsorption of thiolate species on a gold surface

The rate and saturated amount of the self-assembled adsorption of aromatic thiolate species such as 4-pyridinethiolate and phenylthiolate on a polycrystalline gold surface were clearly increased under ultrasonic irradiation with an intensity higher than the ultrasonic cavitation threshold. On the other hand, in the case of the self-assembled adsorption of an aliphatic thiolate species like carboxy ethane thiolate, only the adsorption rate was increased under the irradiation, while the saturated amount was not. This fact suggests that the adsorption of carboxy ethane thiolate results in the most closely packed and ordered monolayer, regardless of ultrasonic irradiation.

Quenching of Growth of ZnO Nanoparticles by Adsorption of Octanethiol

To exploit the size dependent properties of nanoparticles, it is essential to control the particle size. We show that injection of octanethiol into suspensions of ZnO particles can be used to quench particle growth. X-ray photoelectron spectroscopy studies of the adsorption of octanethiol on ZnO single crystals indicate relatively weak adsorption of thiolate and sulfonate species dependent on the crystal orientation. These results suggest that adsorption of thiolate and sulfonate groups on ZnO particles in suspension prevent dissolution of the solid phase. Furthermore, the octanethiol is adsorbed sufficiently strongly to quench growth but can be easily removed for subsequent surface functionalization.

Interaction of Methanethiol with Sulfur-Covered W(001)

The chemisorption of methanethiol on W(001) resulting in the formation of methyl thiolate decreases linearly as a function of preadsorbed atomic S. The ratio of selective decomposition of methyl thiolate, which results in methane desorption, to total decomposition, resulting in desorbed H2 and adsorbed atomic S and C, remains constant. The S 2p photoemission from methanethiol on W(001) consists of peaks from two methyl thiolate species. The presence of atomic S adsorbed in fourfold hollow sites preferentially inhibits the thiolate species with the higher S 2p binding energy. This suggests that this thiolate species is also adsorbed in a fourfold hollow, and its adsorption is blocked by atomic S. Adsorption of thiolate on the S-precovered surface causes the S 2p peak position of the atomic S to shift to lower binding energy. This is the result of crowding caused by the chemisorption of the thiolate in adjacent sites but is not due either to direct bonding of the thiolate to the preadsorbed S or to a major ...