A DFT study on equilibrium geometries, stabilities, and electronic properties of small bimetallic Na-doped Au(n) (n = 1-9) clusters: comparison with pure gold clusters

A systematic study on the geometric structures, relative stabilities, and electronic properties of small bimetallic Au _n Na (n = 1-9) clusters has been performed by means of first-principle density functional theory calculations at the PW91PW91 level. The results show that the optimized ground-state isomers adopt planar structures up to n = 5, and the Na-capped geometries are dominant growth patterns for n = 6-9. Dramatic odd-even alternative behaviors are obtained in the second-order difference of energies, fragmentation energies, highest occupied-lowest unoccupied molecular orbital energy gaps, and chemical hardness for both Au _n Na and Au _n+1 clusters. It is found that Au₅Na and Au₆ have the most enhanced stability. Here, the size evolutions of the theoretical ionization potentials are in agreement with available experimental data, suggesting a good prediction of the lowest energy structures in the present study. In addition, the charge transfer has been analyzed on the basis of natural population analysis.     

A theoretical study of isocyanic acid with hydrogen radical (HNCO + OH) catalysed by Aux (x = 0, 1, 3) cluster: dynamic characterisation

Abstract

The related energy and multi channel HNCO with OH reaction potential energy surface under the catalysis of Au_x (x = 0, 1, 3) cluster and its dynamic characterisation have been investigated with density functional calculations. The geometries were fully optimised with the CCSD(T)//B3LYP level. The calculated results show that the main pathway of the HNCO with OH reaction under the catalysis of Au_x (x = 0, 1, 3) cluster can give the main product P1 (NCO + H₂O), while the minor product is P2 (NH₂ + CO₂). We calculated the rate constant of the main reaction pathway, the calculated dynamic characterisation indicating that the rate constants increase significantly as the temperature increase. According to the dynamic results and the energetically intermediates and transition states involved in the dominant paths, the reaction is expected to be occurred the most rapidly under the catalysis of Au₁. According to our calculation, the singlet atom is the best catalysis and can catalyse the reaction better. The present theoretical studies may provide useful information on the issues of the reaction mechanism and product distributions.     

Synthesis and structural characterization of gold(III) dioximates with anions [AuCl4] and [AuCl2]

Two complexes of Au(III) with dimethylglyoxime of compositions [Au^III(HDMG)₂][Au^IIICl₄] (1) and [Au^III(HDMG)₂][Au^ICl₂] (2) were synthesized and characterized by X-ray structural analysis. It was shown that in [Au^III(HDMG)₂]⁺ cation Au(III) has a square-planar environment, and the oxygen atoms of oxime groups are joined by intramolecular H-bond. The secondary Au?Au and Au?Cl interactions in the crystal are discussed.     

A gas-phase study of the gold-catalyzed coupling of alkynes and alcohols

Mass spectrometric methods are used for an investigation of the C-O bond formation between alkynes and alcohols mediated by cationic gold(I) complexes. In the condensed-phase catalysis, an efficient coupling to the corresponding enol ethers has been observed. In the gas phase, however, kinetic and entropic restrictions are too large for both bare Au⁺ as well as (CH₃)₃PAu⁺ to permit bond formation in strictly bimolecular collisions occurring at thermal energies. The experimental findings are complemented by a theoretical study of the Au⁺/C₂H₂/CH₃OH system using density functional theory.     

Phosphane-stabilized gold clusters: investigation of the stability of [Au13(PMe2Ph)10Cl2]3+

The phosphane-stabilized gold cluster [Au₁₃(PMe₂Ph)₁₀Cl₂]³⁺ was studied using density functional theory. The extraordinary stability of the cluster has been attributed to the stability of the gold core and the protection conferred by ligands. Here, five stability factors of the gold core were explained and verified by investigating the Au₁₃⁵⁺ core in detail. Interactions between the gold core and several PR₃ ligands (R = Me, H, I, Br, Cl, F) were investigated according to the different electron donor abilities of each ligand; bonding energy between the ligand and the gold core was found to increase with the electronegativity of the R substituent. Furthermore, two other aspects of the ligands were clarified: how the ligand stabilizes the Au₁₃⁵⁺ core, and which kind of ligand provides the best stabilization for the cluster.     

DNA interactions and photocatalytic strand cleavage by artificial nucleases based on water-soluble gold(III) porphyrins

The novel gold porphyrin complex (5,10,15-tris(N-methylpyridinium-4-yl)-20-(1-pyrenyl)-porphyrinato)gold(III) chloride, [Au^III(TMPy₃Pyr₁P)](Cl)₄, was prepared and characterized by optical spectroscopy, high-resolution nuclear magnetic resonance (NMR), and electrospray mass spectrometry. This cationic multichromophore compound exhibits excellent water solubility and does not form aggregates under physiological conditions. Binding interactions of this complex and related model compounds with nucleic acid substrates have been studied and characterized by NMR and circular dichroism spectroscopy. The photoreactivity of [Au^III(TMPy₃Pyr₁P)](Cl)₄ was investigated under anaerobic and aerobic conditions in the presence of an excess of purine nucleoside, guanosine, and plasmid DNA. Photocatalytic oxidative degradation of guanosine and the change from supercoiled to circular plasmid DNA upon monochromatic irradiation and polychromatic blue-light exposure with a maximum at 420 nm was explored. The potential of the novel water-soluble cationic metallointercalator complex [Au^III(TMPy₃Pyr₁P)](Cl)₄ to serve as a catalytic photonuclease for the cleavage of DNA has been demonstrated.     

Catalysis of the acetylene hydrochlorination reaction by Si-doped Au clusters: a DFT study

The mechanisms for the acetylene hydrochlorination reaction on pristine Au₇ and Au₈ clusters and on the Si-doped Au clusters Au₆Si and Au₇Si were systematically investigated via density functional theory using the PBE functional. The band gap (?E_g) of the Au₇Si cluster was found to smaller than that of its undoped equivalent (Au₈), thus enhancing its catalytic activity, and Au₇Si presented a significantly reduced activation barrier (16.69 kcal mol^?1) for the acetylene hydrochlorination reaction compared with the pristine Au₈ cluster (21.83 kcal mol^?1). On the other hand, the activation barrier for the acetylene hydrochlorination reaction was not lower for the Au₆Si cluster than for the pristine Au₇ cluster because the band gap (?E_g) of Au₆Si was found to be larger than that of Au₇. Hence, the current work shows that the catalytic activities of gold clusters can be systematically modified by doping them. Our findings also suggest how to enhance the acetylene hydrochlorination reaction by doping foreign atoms into Au clusters.

Open image in new window

Graphical abstract The Si-doped Au₇Si cluster showed stronger catalytic activity for the acetylene hydrochlorination reaction compared with the pristine Au₈ cluster.

     

Amplification of blue emission of Tm3+ ions in Li2O-HfO2-SiO2 glass system by means of Au0 metallic particles

Li₂O-HfO₂-SiO₂-Tm₂O₃:Au₂O₃ glass samples (containing fixed content of Tm₂O₃ and different concentration of Au₂O₃) were prepared and characterized. Bearing of Au⁰ metallic particles (MPs) on improving blue emission of thulium ions (Tm³⁺) ions was explored. Optical absorption (OA) spectra exhibited multiple bands excited from ³H₆ of Tm³⁺. Additionally, a broad peak in the wavelength range 500–600 nm due to surface plasmon resonance (SPR) of Au⁰ MPs was noticed in the spectra. Photoluminescence (PL) spectra (of thulium free glasses) indicated a peak in the visible range due to sp → d electronic transition of Au⁰ MPs. Luminescence spectra of Tm³⁺ and Au₂O₃ co-doped glasses exhibited intense blue emission with substantial increase of intensity with increase of Au₂O₃ content. Bearing of Au⁰ MPs on the reinforcement of blue emission of Tm³⁺ was discussed in detail with kinetic rate equations.     

Optimization of Carbon‐ and Binder‐Free Au Nanoparticle‐Coated Ni Nanowire Electrodes for Lithium‐Oxygen Batteries

A Au nanoparticle‐coated Ni nanowire substrate without binder or carbon is used as the electrode (denoted as the Au/Ni electrode) for Li‐oxygen (Li‐O₂) batteries. A minimal amount of Au nanoparticles with sizes of <30 nm on a Ni nanowire substrate are coated using a simple electrodeposition method to the extent that maximum capacity can be utilized. This optimized, one body, Au/Ni electrode shows high capacities of 921 mAh g^?1_Au, 591 mAh g^?1_Au, and 359 mAh g^?1_Au, which are obtained at currents of 300 mAg^?1_Au, 500 mAg^?1_Au, and 1000 mAg^?1_Au respectively. More importantly, the Au/Ni electrode exhibits excellent cycle stability over 200 cycles.     

Surface Plasmon Resonance and Enhanced Fluorescence Application of Single-step Synthesized Elliptical Nano Gold-embedded Antimony Glass Dichroic Nanocomposites

A novel series of elliptical gold (Au⁰) nanoparticles (18–40 nm) embedded antimony glass (K₂O-B₂O₃-Sb₂O₃) dichroic nanocomposites have been synthesized by a single-step melt-quench in-situ thermochemical reduction technique. X-ray and selected area electron diffractions manifest growth of Au⁰ nanoparticles along the (111) and (200) crystallographic planes. The transmission electron microscopic image reveals elliptical Au⁰ nanoparticles having an aspect ratio varying in the range 1.2–2.1. The dichroic behavior of the nanocomposites arises due to elliptical shape of the Au⁰ nanoparticles. These nanocomposites show strong surface plasmon resonance (SPR) band of Au nanoparticles in the range 610–681 nm and it exhibit red-shifts with increasing Au concentration. They, when co-doped with Sm₂O₃ and excited at 949 nm, exhibit about sevenfold enhancement of the upconverted red emission transition of ⁴G_5/2→⁶H_9/2 at 636 nm due to local electric field enhancement effect of Au⁰ nanoparticles induced by its SPR. These nanocomposites are the promising materials for laser, display, and various nanophotonic applications.     

A systematic search for the structures,stabilities, and electronic properties of bimetallic Ca<Subscript>2</Subscript>-doped gold clusters: comparison with pure gold clusters

The local meta-GGA exchange correlation density functional (TPSS) with a relativistic effective core potential was employed to systematically investigate the geometric structures, stabilities, and electronic properties of bimetallic Ca₂Au _n (n = 1–9) and pure gold Au _n (n ≤ 11) clusters. The optimized geometries show that the most stable isomers for Ca₂Au _n clusters have 3D structure when n > 2, and that one Au atom capping the Ca₂Au _n−1 structure for different-sized Ca₂Au _n (n = 1–9) clusters is the dominant growth pattern. The average atomic binding energies and second-order difference in energies show that the Ca₂Au₄ isomer is the most stable among the Ca₂Au _n clusters. The same pronounced even–odd alternations are found in the HOMO–LUMO gaps, VIPs, and hardnesses. The polarizabilities of the Ca₂Au _n clusters show an obvious local minimum at n = 4. Moreover, the inverse corrections to the polarizabilities versus the ionization potential and hardness were found for the gold clusters.     

Genetic relationships among three chlorophyll-deficient mutants in peanut,Arachis hypogaea L.

Summary The genetic relationships of three chlorophyll-deficient mutant peanuts, lutescens (lu), aureus (au), and virescent (v) were studied under field and greenhouse conditions. The F₁ plants from crosses between these mutants produced phenotypically normal green. In F₂, aureus X virescent segregated 675 normal green : 225 virescent : 45 aureus : 15 virescent aureus : 64 seedling lethal, and lutescens X virescent segregated 45 normal green : 15 virescent : 3 lutescens : 1 seedling lethal. (Lutescens peanuts were seedling lethal in the field.) As previously reported, the F₂ of aureus X lutescens gave 225 normal green : 15 aureus :15 lutescens : 1 seedling lethal. The three chlorophyll-deficient factors (au, lu, and v) show independent inheritance. The recessive combinations from the parental types between aureus and virescent and between aureus and lutescens would produce plants with a combination of their respective parental characteristics, but the recessive combination between lutescens and virescent was nearly albino. The v-au and lu-au seedlings have a longer life span than the v-lu seedling has. The genotypes for the three mutants are tentatively identified as lutescens VV Au ₁ Au ₁ Au ₂ Au ₂ lu ₁ lu ₁ lu ₂ lu ₂ L ₁ L ₁ L ₂ L ₂, aureus VV au₁au₁ au₂au₂ Lu₁Lu₁ Lu₂Lu₂ L₁L₁ l₂l₂, and virescent vv Au₁Au₁ Au₂Au₂ lu₁lu₁ Lu₂Lu₂ l₁l₁ L₂L₂.     

Theoretical study on the series of [Au3Cl3M2] complexes, with M = Li, Na, K, Rb, Cs

The prediction of the series of complexes [Au₃Cl₃M₂] with M = Li, Na, K, Rb and Cs, has been achieved at the ab initio level of theory. All geometries were fully optimized at the MP2 level of theory; the central Au₃ cluster is capped by chlorine atoms and the alkaline metals lie above and below the plane of the central ring; aurophilic interactions were found on the metal cluster, and also a strong aromatic character coming from the delocalized d-electrons of the Au atoms according to nuclear independent chemical shift calculations. On the other hand, the chemical hardness parameter was used to test the stability of the series of complexes, and the Fukui indexes of electrophilic and nucleophilic attack were employed to explore possible sites where chemical reactivity may play a role. Figure Molecular representations of the series of complexes [Au₃Cl₃M₂] (M = Li, Na, K, Rb, Cs) and their corresponding chemical hardness     

Density functional study of bare gold clusters: the ten-vertex neutral system

Four novel Au₁₀ structures have been located by means of density functional methods and their geometry and electronic structure are discussed. Furthermore, the behavior of less extensive basis sets in conjunction with the B3PW91 functional is compared to a highly accurate and more extensive energy-consistent scalar-relativistic pseudopotential and basis set for neutral ten-vertex gold clusters. The values obtained for several structural parameters for known and novel optimized Au₁₀ systems are discussed.     

The Dissociation Rate of Unlabelled Drugs from Receptor Sites: A Poorly Investigated,Yet Important Aspect in Receptor Research. Studies on the Serotonin-S2 Receptor

Abstract

The labelling by ³H-spiperone of serotonin-S₂ receptors in rat frontal cortex tissue adsorbed to glass fibre filters was investigated. For 12 unlabelled serotonin antagonists the dissociation time from serotonin-S₂ receptors was measured using rat frontal cortex tissue preparations adsorbed to glass fibre filters. The dissociation half-time varied from 4.8 min for pipamperone to 160 min for ritanserin. The drug-receptor dissociation time was not related to a particular class of chemical structure, or to the lipophilicity or the acid dissociation constant of the drugs. The essential requirement of experimental determination of the drug-receptor dissociation time for each drug individually is illustrated. The possible applications of the knowledge of the drug-receptor dissociation time in in vitro and in vivo receptor studies, in pharmacological and pharmaco-kinetic studies and in drug design and receptor modelling is discussed. For various serotonin-S₂ antagonists, the type of inhibition produced by the drug on ³H-ketanserin binding to serotonin-S₂ receptors was determined using suspensions of rat frontal cortical tissue. The observed patterns of inhibition were clearly related to the drug-receptor dissociation times: rapidly dissociating drugs produced competitive inhibition, drugs with dissociation half-times between 15-30 min produced mixed type inhibition, and the very slowly dissociating ritanserin produced non-competitive inhibition.     

Polymeric and macrocyclic gold(I) complexes with bridging dithiolate and diphosphine ligands

The reaction of digold(I) diphosphine complexes [Au₂(O₂CCF₃)₂(μ-Ph₂P-X-PPh₂)] with dithiols HS-Y-SH can give either macrocyclic complexes [Au₂(μ-S-Y-S)(μ-Ph₂P-X-PPh₂)] or polymeric complexes [Au₂(μ-S-Y-S)(μ-Ph₂P-X-PPh₂)]_n. The structures of the macrocyclic complex [Au₂{μ-(S-4-C₆H₄)₂S}{μ-Ph₂P(CH₂)₄PPh₂}], and the polymeric complexes [Au_n{μ-(S-CH₂CO₂CH₂CH₂O)₂-1,4-C₆H₄}_n(μ-trans-Ph₂PCHCHPPh₂)_n] and [Au_n{μ-(S-CH₂CO₂CH₂CH₂O)₂-1,5-C₁₀H₆}_n(μ-trans-Ph₂PCHCHPPh₂)_n] have been determined. Evidence is presented that the complexes exist primarily as macrocycles in solution and that, in favorable cases, ring-opening polymerization occurs during crystallization.     

New multinuclear Scaffold molybdocene-gold lidocaine complex: DNA/HSA binding,molecular docking,cytotoxicity and mechanistic insights

The new heteronuclear molybdocene-gold complex 1, [(η⁵-Cp)₂Mo^II[(μ²-η²-dtc)₂Nap]Au^III(LC)](PF₆), (η⁵-Cp: η⁵-cyclopentadienyl, (dtc)₂Nap: 2,7-bis(dithiocarbamate)naphthalene, LC: lidocaine) was synthesized and evaluated for biological activity. With the aim of assessing the possible DNA-binding mode, the interaction of the complex 1 with calf thymus DNA (CT DNA) was investigated by UV spectroscopy, emission titration, and viscosity measurement. Also, the binding of the complex to human serum albumin (HSA) was considered by UV–Vis and fluorescence emission spectroscopy. Moreover, molecular docking was used for modeling of the binding of the complex to DNA and HSA. These experimental results were confirmed by the results of molecular docking concerning the lowest binding energy. The cytotoxicity of the heterometallic complex 1 has been evaluated against a panel of several cancer cell lines with low micromolar IC₅₀ (72?h) values, according to its cellular uptake and also versus HEK293 nonmalignant fibroblasts. Moreover, the complex 1 showed the induction of apoptotic process.

Communicated by Ramaswamy H. Sarma     

Well-defined linear Au<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 2–4) chains encapsulated in SWCNTs: a DFT study

One-dimensional (1D) gold nanostructures have been extensively studied due to their potential applications in nanoelectronic devices. Using first-principles calculations, composites consisting of a well-defined linear Au _n (n?=?2–4) chain encapsulated in a (9,0) single-walled carbon nanotube (SWCNT) were studied. The translational energy barrier of a single Au atom in a (9,0) SWCNT was found to be 0.03 eV. This low barrier guaranteed the formation of Au _n @ (9,0) SWCNT (n?=?1–4) composites. Bond lengths, differential charge densities, and electronic band structures of the composites were studied. The average Au–Au bond lengths in the composites were found to be almost the same as those in the corresponding free-standing linear Au _n . The average bond length increased as the number of Au atoms increased. Charge transfer in all of these composites was slight, although a few valence electrons were transferred from the (9,0) SWCNT and the Au chains to intercalations. The conductivities of the encapsulated linear Au _n (n?=?2–4) chains were enhanced to some extent by encapsulating them in the SWCNT.     

State-sensitive monitoring of gold nanoparticle sites on titania and the interaction of the positive Au site with O2 by Au Lα1-selecting X-ray absorption fine structure

The heterogeneity of gold sites in various Au/TiO₂ catalysts was studied by means of state-sensitive Au L₃-edge X-ray absorption fine structure (XAFS) combined with high energy-resolution X-ray fluorescence spectrometry. A series of Au/TiO₂ catalysts were prepared via deposition-precipitation method on anatase-type or mesoporous (amorphous) TiO₂ added with NaOH (lower Au loading) or urea (higher Au loading). The mean Au particle size ranged between 29 and 87 Å based on high-resolution TEM (transmission electron microscope) measurements. The Au Lα₁ emission peak energy for Au/mesoporous-TiO₂ in air and Au/anatase-TiO₂ in CO (5%) corresponded to Au⁰ state. The emission peak energy for Au/anatase-TiO₂ in air shifted toward that of Au^I state. For relatively greater Au particles (average 87 Å) dispersed on mesporous TiO₂, the major valence state discriminated by Au Lα₁-selecting XANES (X-ray absorption near-edge structure) spectrum tuned to Au Lα₁ emission peak top was Au⁰, but the Au^δ− state could be successfully monitored by Au Lα₁-selecting XANES tuned to the emission energy at 9707.6 eV, of which population was relatively small compared to the case of smaller Au particles (average 29 Å) on anatase-type TiO₂. On the other hand, negative charge transfer from Au 5d to support was demonstrated in Au^δ+-state sensitive XANES tuned to 9718.3-9718.7 eV. The Au^δ+-state sensitive XANES spectra resembled theoretically generated XANES for interface Au^δ+ sites model on TiO₂ in contact with surface Ti sites. Further charge transfer was demonstrated from Au to adsorbed O₂ for Au/anatase-TiO₂ catalyst.     

Effect of Age on the Kinetics of the Binding of Iodocyanopindolol to a Membrane Preparation of Rat Lungs

Abstract

The association (k₊₁) and dissociation (k_-1) rate constants, and the equilibrium thermodynamic binding parameters (ΔG°, ΔH° and ΔS°) of the β-adrenergic ligand [¹²⁵Iodo]cyanopindolol (ICYP) were studied in a crude lung membrane preparation of rats of different ages. There was no difference in k₊₁-values for the different age groups, while the k_-1-values were in all cases difficult to measure: almost no dissociation of ICYP from its binding site occurs. The thermodynamic properties were not affected by age. It is concluded that, in these experimental conditions, age has no effect on the kinetic parameters of the binding of ICYP to the β-adrenoceptors in rat lung.