Strong interactions through the XAu–Y bridge: the Au bond?

The interaction between AuOH and the lone-pair donors (HF, H₂O) is shown to result in well-bound complexes whose structure resembles that of the corresponding H-bonded systems with the gold atom replacing hydrogen. The dissociation energies are estimated to be 10.7 and 27.4 kcal/mol for HFAu–OH and H₂OAu–OH, respectively. However, the interaction between AuOH and the lone pair donors is found to involve significant charge transfer. Furthermore, the Au–O stretching frequency increases upon the complex formation. It is concluded that, in spite of certain similarity to the H-bonded species, the Au-bonded complexes should be considered as Lewis acid–base pairs.     

Adenine–Au and adenine–uracil–Au. Non-conventional hydrogen bonds of the anions and donator–acceptor properties of the neutrals

This is a study of adenine–Au and adenine–uracil–Au (neutral, anionic and cationic), applying the B3LYP density-functional approach. In these systems, the interaction is directly related to the charge; so that as the metal atomic charge increases, the bond strength also increases. Neutral molecules are weakly bonded, the interaction in the case of cations is mainly electrostatic and in the case of the anions, the extra electron is localized on the metal atom and consequently, non-conventional hydrogen bonds are formed. In the case of adenine–Au (anion), the H dissociation energy is similar to the electron dissociation energy, and therefore both reactions may be possible. Moreover, the Au anionic atom modifies the hydrogen bonds of the uracil–adenine base pair. This may be significant in the study of point mutations that may occur in the Watson–Crick dimmer of nucleic basis. The electron-donator properties of these compounds are analyzed with the aid of the donator–acceptor map (DAM), previously described. Adenine–Au, uracil–Au and adenine–uracil–Au are more effective electron donors, but poorer electron acceptors than adenine, uracil and adenine–uracil. If the electron acceptor properties of carotenoids such as β-carotene and astaxanthin are compared, there are indications that astaxanthin may act as an oxidant instead of an antioxidant with the uracil–adenine base pair. The oxidation of nucleic acid bases by carotenoids may have important consequences, as oxidative damage of DNA and RNA appears to be linked to cancer. This is something that demands further studies and for this reason, work concerning the reactivity of carotenoids with DNA-nitrogen bases is in progress.     

Phase equilibria in the palladium-rich part of the Pd–Au–Cu–Sn quaternary system

The solubility of tin in the phases of Pd–Au–Sn and Pd–Cu–Sn ternary systems and a Pd–Au–Cu–Sn quaternary system with a fixed Pd: Au: Cu ratio of 11.1: 1: 4.6 is studied via microstructural, X-ray diffraction, and energy dispersive analysis. It is found that a quaternary alloy in equilibrium with a solid solution based on Pd, Au, and Sn contains a τ₁ compound with structure which is derivative of the In type. It contains ~15 at % Sn and is a solid solution of the same compounds identified earlier in Pd–Au–Sn and Pd–Cu–Sn ternary systems. In addition, a quaternary alloy with a content of 20 at % Sn also contains a τ₂ compound with the Pd₂CuSn own type and can barely dissolve gold. The obtained data are used to construct a three-dimensional model of the Pd-rich part of the isothermal tetrahedron of the Pd–Au–Cu–Sn system and diagrams of the tin solubility isolines in palladium-rich alloys of the quaternary system at 500°С.     

Experimental investigation and thermodynamic modeling of the Au–Ge–Ni system

Abstract  

Phase equilibria in the Au–Ge–Ni ternary system were studied by means of scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and differential scanning calorimetry. The phase relations in the solid state at 600 °C as well as a vertical section at Au₇₂Ge₂₈–Ni were established. No ternary compound was found at 600 °C. On the basis of the experimental phase equilibria data, a thermodynamic model of the Au–Ge–Ni ternary system was developed using the CALPHAD method. Thermodynamically calculated phase diagrams are shown at 600 °C, in two vertical sections and the liquidus projection. Reasonable agreement between the calculations and the experimental results was achieved.     

Model studies of the chemisorption of hydrogen and oxygen on the Au (1 0 0) surface

 The convergence of chemisorption energy for hydrogen and oxygen on gold clusters is studied. Two theoretical approaches have been employed; wavefunction methods at the self-consistent-field second–order M?ller–Plesset level and density functional theory and the two methods are compared. Relativistic effective core potentials exploited in the former approach were developed in this work. Received: 25 October 1999 / Accepted: 21 February 2001 / Published online: 11 October 2001     

DFT Study of the BH4− Hydrolysis on Au(111) Surface

The mechanism of the catalytic hydrolysis of BH₄⁻ on Au(111) as studied by DFT is reported. The results are compared to the analogous process on Ag(111) that was recently reported. It is found that the borohydride species are adsorbed stronger on the Au⁰-NP surface than on the Ag⁰-NP surface. The electron affinity of the Au is larger than that of Ag. The results indicate that only two steps of hydrolysis are happening on the Au(111) surface and the reaction mechanism differs significantly from that on the Ag(111) surface. These remarkable results were experimentally verified. Upon hydrolysis, only three hydrogens of BH₄⁻ are transferred to the Au surface, not all four, and H₂ generation is enhanced in the presence of surface H atoms. Thus, it is proposed that the BH₄⁻ hydrolysis and reduction mechanisms catalyzed by M⁰-NPs depend considerably on the nature of the metal.     

Protective properties of gold in the composition of nanoparticles and Au—rutin complexes

Protective properties of gold nanoparticles and gold—rutin complexes were studied. Aurophilic bacteria Micrococcus luteus and methanotrophic bacteria Methylococcus capsulatus were studied. Gold—rutin nanoparticles and complexes protect the respiratory activity of the bacteria against toxins. Pretreatment of the cells with gold is more efficient than the treatment after the action of toxin.     

Reactions of Au+ and Au− with benzene and fluorine-substituted benzenes

Reactions of gold anions and cations generated by laser desorption/ionization were studied in the FTICR spectrometer. Au⁻ associated with C₆F₆ to give the novel Au⁻(C₆F₆) complex, whose binding energy was estimated to be 24 ± 4 kcal mol⁻¹ from analysis of the radiative association (RA) kinetics. Au⁺ associated with C₆F₅H to give Au⁺(C₆F₅H), with binding energy estimated to be 31 kcal mol⁻¹. Au⁺ reacted with C₆H₆ to form the well known Au⁺(C₆H₆) and Au⁺(C₆H₆)₂ complexes. The observation of rapid charge transfer from Au⁺(C₆H₆) to C₆H₆ was interpreted as showing that benzene binds more strongly to neutral Au than to Au⁺. The neutral Au–C₆H₆ bond is accordingly concluded to be stronger than about 70 kcal mol⁻¹.     

Does core size matter in the kinetics of ligand exchanges of monolayer-protected Au clusters?

This paper compares the kinetics of exchanges of phenylethanethiolate ligands (PhC2S-) of the monolayer-protected clusters (MPCs) Au(38)(SC2Ph)(24) and Au(140)(SC2Ph)(53) with p-substituted arylthiols (p-X-PhSH), where X = NO(2), Br, CH(3), OCH(3), and OH. First-order rate constants at 293 K for exchange of the first ca. 25% of the ligands on the molecule-like Au(38)(SC2Ph)(24) MPC, measured using (1)H NMR, vary linearly with the in-coming arythiol concentration; ligand exchange is an overall second-order reaction. Remarkably, the second-order rate constants for ligand exchange on Au(38)(SC2Ph)(24) are very close to those of corresponding exchange reactions on the larger nanoparticle Au(140)(SC2Ph)(53) MPCs. These are the first results that quantitatively show that the chemical reactivity of different sized nanocrystals is almost independent of size; presumably, this is because the locus of the initial ligand exchanges is a common kind of site, thought to be the nanocrystal vertexes. The rates of later stages of exchange (beyond ca. 25%) differ for Au(38) and Au(140) cores, the latter being much slower presumably due to its larger terrace-like surface atom content. The reverse exchange reaction was studied for Au(38)(p-X-arylthiolate)(24) MPCs (X = NO(2), Br, and CH(3)), where the in-coming ligand is now phenylethanethiol. Remarkably, the rate constants of both forward and reverse exchanges display identical substituent effects, which implies a concurrent bonding of both in-coming and leaving ligands to the Au core in the rate-determining step, as in an associative mechanism. X = NO(2) gives the fastest rates, and the ratio of forward and reverse rate constants gives an equilibrium constant of K(EQ,PE) = 4.0 that is independent of X.     

Structural organization and dimensionality at the hands of weak intermolecular Au···Au, Au···X and X···X (X = Cl, Br, I) interactions

The salts K[AuCl(2)(CN)(2)]·H(2)O (1), K[AuBr(2)(CN)(2)]·2H(2)O (2) and K[AuI(2)(CN)(2)]·?H(2)O (3) were synthesized and structurally characterized. Compound 1 crystallizes as a network of square planar [AuCl(2)(CN)(2)](-) anions separated by K(+) cations. However, 2 and 3 feature 2-D sheets built by the aggregation of [AuX(2)(CN)(2)](-) anions via weak, intermolecular X···X interactions. The mixed anion double salts K(3)[Au(CN)(2)](2)[AuBr(2)(CN)(2)]·H(2)O (4) and K(5)[Au(CN)(2)](4)[AuI(2)(CN)(2)]·2H(2)O (5) were also synthesized by cocrystallization of K[Au(CN)(2)] and the respective K[AuX(2)(CN)(2)] salts. Similarly to 2 and 3, the [Au(CN)(2)](-) and [AuX(2)(CN)(2)](-) anions form 2-D sheets via weak, intermolecular Au(I)···X and Au(I)···Au(I) interactions. In the case of 5, a rare unsupported Au(I)···Au(III) interaction of 3.5796(5) ? is also seen between the two anionic units. Despite the presence of Au(I) aurophilic interactions of 3.24-3.45 ?, neither 4 nor 5 exhibit any detectable emission at room temperature, suggesting that the presence of Au(I)···X or Au(I)···Au(III) interactions may affect the emissive properties.     

Au2、Au3小团族分子的结构和势能函数

原子团簇的结构和性质研究是当今物理学和材料学中的一个热门课题,过渡金属团簇特别是Au团簇,由于其独特的物理和化学性质而被广泛地应用于催化反应、材料吸附[1-2]和光的吸收中[3]。近年来,人们用不同的理论方法研究金原子团簇。H儯kkinen等人利用GGA方法研究了中性和阴离Au2-10团簇的性质[4];Bravo-P啨rez等人采用从头计算的HF和post-HF方法研究Au2-Au6小团簇[5],这些计算结果与实验值相比,相差较大。由于金团簇电子结构的复杂性,对Au体系考虑旋—轨耦合和电子相关效应是很重要的,这种计算的不确定性对Au的影响比IB簇的其它金属团…     

Mn3O4–Au nanozymes as peroxidase mimic and the surface-enhanced Raman scattering nanosensor for the detection of hydrogen peroxide

The artificial enzyme-mimicking system using nanomaterials has attracted significant research interest in chemical and biological sensing for industrial and environmental applications. Mn₃O₄ nanostructure serves as an effective catalyst in oxidation and reduction reactions that mimic natural peroxidase enzymes. In this study, we synthesized Mn₃O₄–Au spindle nanocomposites (Mn₃O₄–Au SNCs) stabilized by L-cysteine using a simple hydrothermal reduction. The enzyme-mimicking peroxidase activity of these Mn₃O₄–Au SNCs with hydrogen peroxide (H₂O₂) was investigated in the presence of a chromogenic substrate, 3,3′,5,5′-tetramethylbenzidine that catalyzed reduction of H₂O₂ in water and milk giving rise to a blue color inferring the nanozyme activity of Mn₃O₄–Au SNCs. The exceptional enzyme-like catalytic activity of Mn₃O₄–Au SNC probes later proved to be excellent surface-enhanced Raman scattering (SERS) sensor nanoprobes for sensitive H₂O₂ detection over a wide concentration range from 0.005 to 10 μM. The developed Mn₃O₄–Au SERS sensor exhibited a lower detection limit (LoD) of 2 nM in water and 0.6 μM in spiked milk indicating sensitivity for H₂O₂ detection with excellent selectivity, reproducibility, and long-term stability. The developed Mn₃O₄–Au nanoprobes demonstrated unique combination of properties with visual and SERS methods for sensitively detecting H₂O₂ in food, overcoming limitations of existing H₂O₂ sensors. The developed SERS method using nanozymes potentially be extended to detecting a variety of other redox chemicals or explosives in industries, environments, and biomedical fields.     

Investigation of the Adsorption and Self Assembly of Isocyanide Derivatives on Au（111） Surface

The adsorption and self-assembly of isocyanide derivatives on Au（111） surface were investigated by density functional theory （DFF） and molecular dynamics simulation. The calculation for phenyl isocyanide by DFT was based on cluster and slab models. The self-assembled monolayers of 2-isocyanoazulene and 1,3-diethoxycarbony 1- 2-isocyanoazulene on Au（111） were simulated using Au-C force field parameters developed by us. It was found that the top site was the most preferred position, and the isocyanoazulene and its derivatives could form the ordered face to edge self-assembled monolayer on gold surface indeed, and the molecules stood on the gold surface vertically.     

Transformations of [Au(CN)2]− at the contact with activated carbon surface

We have studied the processes occurring when alkaline aqueous solution of Na[Au(CN)₂] is brought in contact with activated carbon surface. It has been shown that the adsorption of the gold cyanide complex occurs via several independent routes, one of them being accompanied with the partial breakdown of the inner sphere of the compound and free cyanide ions release into the solution. The latter process decreases the gold recovery by aqueous NaOH during the high-temperature (150°C) desorption. A prolonged storage of the adsorbent saturated with [Au(CN)₂]^? in air produces a similar result. The reasons of the observed phenomena have been discussed.     

纳米团簇Au19Pd和Au19Pt催化解离N2O

采用密度泛函理论研究Au-Pd和Au-Pt 纳米团簇催化解离N₂O. 首先根据计算得到Au₁₉Pd和Au₁₉Pt 团簇的最优构型(杂原子均位于团簇的表面). 以Au₁₉Pd催化解离N₂O为例研究催化解离的反应机理. 对此主要考虑两个反应机理, 分别是Eley-Rideal (ER)和Langmuir-Hinshelwood (LH). 第一个机理中N₂O解离的能垒是1.118 eV, 并且放热0.371 eV. N₂分子脱附后, 表面剩余的氧原子沿着ER路径消除需要克服的能垒是1.920eV, 这比反应沿着LH路径的能垒高0.251 eV. 此外根据LH机理, 氧原子在表面的吸附能是-3.203 eV, 而氧原子在表面转移所需的能垒是0.113 eV, 这表明氧原子十分容易在团簇表面转移, 从而促进氧气分子的生成. 因此, LH为最优反应路径. 为了比较Au₁₉Pd和Au₁₉Pt 对N₂O解离的活性, 根据最优的反应路径来研究Au₁₉Pt 催化解离N₂O, 得到作为铂族元素的铂和钯对N₂O的解离有催化活性, 尤其是钯. 同时, 将团簇与文献中的Au-Pd合金相比较, 得到这两种团簇对N₂O 解离有较高的活性, 尤其是Au₁₉Pd团簇. 再者, O₂的脱附不再是影响反应的主要原因, 这可以进一步提高团簇解离N₂O的活性.     

Nano Au enhanced upconversion in dichroic Nd3+:Au–antimony glass nanocomposites

Dichroic Nd³⁺:Au–antimony glass (K₂O–B₂O₃–Sb₂O₃) nanocomposites (NCs) have been synthesized by single-step melt-quench thermochemical reduction process. The UV–Vis–NIR spectra show surface plasmon resonance (SPR) band of Au⁰ nanoparticles (NPs) and absorption peaks of Nd³⁺ ions. XRD and SAED results indicate growth of Au⁰ NPs along (200) plane. TEM image reveals elliptical Au⁰ NPs having sizes 12–21 nm (aspect ratio ～1.2) responsible for the dichroic behavior. Photoluminescent upconversion under excitation at 805 nm exhibit two emission bands of Nd³⁺ ions at 540 (green) and 650 (red) nm due to ⁴G_7/2 → ⁴I_9/2 and ⁴G_7/2 → ⁴I_13/2 transitions respectively. Both bands undergo maximum 8 and 11 fold intensity enhancements respectively at 0.03 wt% Au⁰ (4.1 × 10¹⁸ atoms/cm³). Local field enhancement (LFE) induced by Au⁰ SPR and energy transfer (ET) from Au⁰ → Nd³⁺ is found to be responsible for enhancement while ET from Nd³⁺ → Au⁰ and optical re-absorption due to Au⁰ SPR for quenching.