Neighboring Gold Atoms Research Articles

Computational Nanomaterials Design: Towards The Realization of Nanoparticle Use in Radiotherapy - Case Study 1: Adsorption States of I on Au(111) Surface

Abstract Radioactive iodine (e.g. I-125, I-131) have been used for decades in the medical community for cancer treatment and imaging. Using gold nanoparticles as a carrier for iodine opens possibilities of new treatments for cancer and also for tracking cancerous cells. To design an optimized version of gold nanoparticle for such purpose, we need to understand the bonding mechanism and gauge the strength of such bonding. To this end we performed theoretical calculations on the adsorption state of iodine on gold (111) surface. The results show good adsorption of iodine to gold, most stably on the hollow sites. The bonding mechanism is via the hybridization of the 5p orbital of the iodine with the 6s and 5d orbitals of the neighboring gold atoms. These results act as a first step to designing an optimized gold nanoparticle that can be used in future radiotherapy treatments

Quantum-Chemical Study of Adsorption of Tl+ Ions on Au(111)

A density-functional study of the interaction of Tl+ ions with the gold surface is carried out based on the cluster model of the metal surface. The geometry and energy characteristics are assessed. Ion Tl+ exists on the surface in its ad-ionic form. The electronic state of the Au–$${\text{Tl}}_{{{\text{ads}}}}^{ + }$$ system is analyzed. The involvement of the adsorbed thallium ion and the neighboring gold atoms in the formation of molecular orbitals of this system is assessed. Their formation is preferentially contributed by s-orbitals of thallium and d-orbitals of gold. It is found that in alkaline media, Tl+ ions coadsorb with OH– ions to form TlOH on the surface. The possible geometrical configuration of their associate with OH– ions is determined for the low and high surface coverages by OH– ions.

Quantum-Chemical Study of the Adsorption of Pb2+ on Au(111)

The interaction between the Pb2+ ion and gold is studied using the cluster metal surface model and the density functional method. The geometric and energy characteristics of the interaction between this ion and the gold surface are estimated. The form in which the Pb2+ ion exists on the surface is more ad-ionic than ad-atomic. The electron structure of the Au–Pbads2+ system is analyzed. The participation of the adsorbed lead ion and its neighboring gold atoms in the formation of molecular orbitals in this system is estimated. It is established that the contribution to their formation is predominantly provided by the lead s-orbitals and the gold d-orbitals. The interaction with a solvent decreases the transfer of a charge from an adsorbed lead ion to gold. It is demonstrated that the hydrolyzability of a lead ion decreases upon its transition from the electrolyte phase to the surface.

Understanding of the activity difference between nanogold and bulk gold by relativistic effects

It is a challenge to thoroughly understand the astonishing difference in catalytic activity between nanogold and bulk gold for some oxidation reactions. In this work, the Au–O interactions in various surroundings were investigated by DFT calculations and compared with the Ag–O interactions. We have found the three points. First, only Au–O bond can be significantly strengthened by the linear O–Au–O structure. Second, the Au–O bond is always stronger than the Ag–O bond when the bonds are embedded in common surroundings. Third, the Au–O bond becomes weaker than the Ag–O bond when the number of neighboring Au atoms becomes large, because the Au–O interactions are suppressed by the presence of neighboring gold atoms. The origin of these three points can be attributed to wider spatial extension of d orbitals of gold, induced by strong relativistic effects. The strong relativistic effects make nanogold with smaller coordinate numbers highly active due to the ease in forming strong Au–O bonds, especially for the O–Au–O bond, whereas gold atoms in bulk with larger coordination numbers chemically inert due to the strong suppression by neighboring gold atoms destabilizing the O–Au–O bond.

Up-Conversion Luminescence of Gold Nanospheres When Excited at Nonsurface Plasmon Resonance Wavelength by a Continuous Wave Laser

We show that, when gold nanospheres are excited at the red side of the surface plasmon resonance (SPR) wavelength at 592 nm by a continuous wave (CW) laser, they give substantial up-converted luminescence in the SPR wavelength range. The luminescence intensity scales as a second-order function of the excitation power, with a quantum yield ~1/50 of down-conversion luminescence when illuminated at a power of 30 MW/cm(2). The luminescence spectrum is completely different than the SPR profile, indicating a new emission mechanism possibly involving interband transitions coupled with phonons or localized vibration of neighboring gold atoms. Such luminescence is also observed to be substantial for short gold nanorods with an aspect ratio of ~2 but weak for bulk gold. This study provides new insight to the understanding of gold nanoparticle luminescence and opens a new detection scheme for gold nanoparticle-based biological imaging.

Understanding Structure, Size, and Charge Effects for the H2 Dissociation Mechanism on Planar Gold Clusters

The H2 dissociation on several planar Aunq gold clusters, with n = 4, ..., 10 and charges q = 0, ±1, has been studied in detail as a function of the nuclear configuration of the cluster and at different sites of attack. It is found that the formation of a well in the entrance channel is a necessary condition for the dissociation to occur. This well always appears in sites of Aunq where there is a defect in the electronic density with respect to that of the n neutral and isolated gold atoms or, in other words, where there is a positive charge due to the polarization of the electronic density associated to the electronic correlation. When H2 attacks on linear sides of three atoms, on the middle gold atom, the reactivity is fully determined by this entrance well. On the contrary, when attacking corners there is a second step, in which a b2 antibonding orbital crosses the a1 HOMO orbital. The b2 orbital is strongly stabilized by an important bonding overlap between the H2 and the two neighboring gold atoms or...

Metallic Corner Atoms in Gold Clusters Supported on Rutile Are the Dominant Active Site during Water−Gas Shift Catalysis

Au/TiO(2) catalysts used in the water-gas shift (WGS) reaction at 120 °C, 7% CO, 22% H(2)O, 9% CO(2), and 37% H(2) had rates up to 0.1 moles of CO converted per mole of Au per second. However, the rate per mole of Au depends strongly on the Au particle size. The use of a nonporous, model support allowed for imaging of the active catalyst and a precise determination of the gold size distribution using transmission electron microscopy (TEM) because all the gold is exposed on the surface. A physical model of Au/TiO(2) is used to show that corner atoms with fewer than seven neighboring gold atoms are the dominant active sites. The number of corner sites does not vary as particle size increases above 1 nm, giving the surprising result that the rate per gold cluster is independent of size.

X-ray Absorption Spectroscopy Unveils the Formation of Gold Nanoparticles in Corn

In this study, X-ray absorption spectroscopy was used to determine the possible gold biotransformation by Zea mays (corn) var. Golden, germinated and grown in a medium spikedwith KAuCl4. In addition, the gold uptake capacity of corn assisted by thiourea and ammoniumthiocyanate was investigated. Results showed that up to 160 mg/L, gold did no treduce corn seed germination or plant growth. Both thiourea and ammonium thiocyanateresulted in a 6-fold increase of gold concentration in roots and thiourea promoted a 10-fold increase of gold concentration in shoots. X-ray absorption near edge structure studies demonstrated that approximately 91% of the gold present in plant samples was Au(0). Theremaining 9% was present as Au(III). In addition, extended X-ray absorption fi ne structureresults showed that in corn roots, the gold coordination number was around 9,5 neighboringgold atoms at approximately 2,86 Å, indicating an incomplete fi rst coordination shell,which imply the presence of a nano-phase. The results demonstrated that Z. mays was ableto produce gold nanoparticles with a size of 10,36 nm.

Stabilization of gold(I) and gold(III) complexes by pyridil bis{3-hexamethylene-iminylthiosemicarbazone}: spectroscopic, structural and computational study

The reaction of pyridil bis{3-hexamethylene-iminylthiosemicarbazone} (H2Plhexim) with dichloro[2-(dimethylaminomethyl)phenyl-C1,N]-gold(III) ([Au(damp-C1,N)Cl2]) led to the isolation of the complexes [Au2(H2Plhexim)(Hdamp-C1)2Cl4]Cl(2).2H2O () and [Au(H2Plhexim)]2Cl2.S(8).6H2O (). The spectroscopic data for suggests that the bisthiosemicarbazone is coordinated to two different Au(III) atoms through the sulfur atoms. The fourfold coordination of the gold atoms is completed by one protonated Hdamp ligand, with the corresponding cleavage of an Au-N bond, and by two chloro ligands. The coordination mode and structure has been rationalized by means of DFT calculations. The crystal structure of shows the neutral bisthiosemicarbazone coordinated through the sulfur atoms in a linear S-Au-S geometry. Gold-gold interactions are not observed and this is due to the steric hindrance of the bulky groups present in the ligand, which prevent the approach of two neighboring gold atoms. During the reaction, the reduction of Au(III) to Au(I) takes place with the bisthiosemicarbazone oxidized to the elemental sulfur, S8, which is present in the complex. (H2O)12 clusters are also located in the void spaces. The in vitro antitumor activity against the HeLa-299 cell line was also investigated. The IC50 values are slightly higher than that of cisplatin. In comparison to the value for cisplatin, the maximum antiproliferative activity is higher in the Au(I) complex and similar in Au(III) complex, thus, the Au(I) complex exhibits greater activity against the human cervix carcinoma cell line.

Electronic Structure and Photochemical Properties of a Monolayer-Protected Gold Cluster

The electronic structure of a monolayer-protected gold cluster, [Au13(SCH3)8]3+, has been investigated by performing density functional calculations. The cluster has a characteristic structure with Oh molecular symmetry, and eight (111) facets of a centered cuboctahedral Au13 core cluster are fully passivated by eight methanethiolates. The bond distance between two neighboring gold atoms (3.673 A) is much larger than that of the bare Au13 cluster (2.929 A), whereas the Au−S bond distance is 2.403 A. This atomic rearrangement means that the methanethiolates stabilize the enlarged bare Au13 cluster by bonding to the (111) hollow sites of the bare cluster. The absorption spectrum of the [Au13(SCH3)8]3+ cluster is simulated within time-dependent density functional theory. The spectrum shows clear absorption peaks and each peak is assigned to specific excitation processes.

Solid-state luminescence and crystal structures of novel gold(I) benzenethiolate complexes

A series of mononuclear bis(benzenethiolato)gold(I) complexes, [n-Bu4N][Au(SC6H4R)2] [R = H (1), o-Me (2), o-OMe (3), o-Cl (4), m-Me (5), m-OMe (6), m-Cl (7), p-Me (8), p-OMe (9) or p-Cl (10)] showed luminescence in the solid state at room temperature. The emission maxima ranged from 438 (blue emission) to 529 nm (green emission). The luminescence of these complexes is affected by substituent effects: electron-donating substituents (R = Me or OMe) on the benzene rings tend to shift the emission maxima toward shorter wavelengths, but the electron-withdrawing substituents (R = Cl) make the emission maxima shift toward longer wavelengths when compared to the maximum of the non-substituted species. This suggests that the luminescence properties could come from excited states due to a metal-to-ligand charge-transfer (MLCT) or ligand-centred (LC) transition. Complexes 2, 4, and 7 show normal linear S–Au–S geometries but exhibit no gold–gold interactions owing to the steric hindrance of the bulky counter cations, [n-Bu4N]+, which prevent the approach of two neighboring gold atoms. Both 2 and 4 show asymmetric configurations of the two thiolate ligands. On the other hand, 7 shows a completely symmetric configuration, where the gold atom is positioned at a center of symmetry.

Structure and conductance of a gold atomic chain

The conductances of linear chains of gold atoms suspended between two electrodes were calculated while the distance between the electrodes was increased. The stable structures of the linear chains of the gold atoms at low temperature were initially determined by using the ab initio local spin-density-functional approach. As the average bond length $〈d〉$ increased, the spacings of the neighboring gold atoms modulated similarly to the Peierls transition. The maximum tensile force of a linear four-atom-chain was 0.91 nN and occurred at $〈d〉\ensuremath{\approx}3.1$ \AA{}. The electric conductances were then calculated using the recursion transfer-matrix method. The calculation indicated that the conductance at the Fermi level of the modulated chain decreased from ${1G}_{0}{(=2e}^{2}/h)$ as the chain was stretched.

Formation of well-ordered surface compounds by coadsorption of thallium and bromide on the Au(111) electrode surface

The structures of the adlayers formed on Au(111) in acid solution containing thallium and bromide have been investigated by using in situ surface X-ray diffraction. At the most positive potentials, where Br forms close-packed rotated-hexagonal monolayers, the surface is free of Tl. The Br adlayer disorders at the potential where thallium starts to coadsorb. With further decreasing potential, two well-ordered commensurate and one weakly-ordered incommensurate phases appear over a 0.7 V potential region prior to the formation of the close-packed rotated-hexagonal Tl monolayer. The structure factor analysis for the commensurate phases shows the formation of TlBr 2 and TlBr surface compounds in the 3-( 13 × 13 ) and 2-(3× 3 ) phases, respectively. In addition, an adlayer-induced subsurface relaxation has been observed. Under the 2TlBr-(3× 3 ) adlayer, where bromide ions are at the bridge sites and thallium ions are situated near the hollow sites, the top layer of Au atoms displaces laterally along the 3 direction. This results in more uniform spacings between Tl and the three neighboring gold atoms, as well as an increase of the Br–Au separation.