Anionic Gold Research Articles

Comparison of the Reactivity for the Solvent Extraction of Gold(iii) from Concentrated HCl Solutions Among D2EHPA, PC 88A, and Cyanex 272

ABSTRACT In this study, the chemical reactivity of three organophosphorus acidic extractants (D2EHPA, PC 88A, and Cyanex 272) was compared for the extraction of the anionic gold(III) complex, AuCl4 −, from the concentrated hydrochloric acid solutions. The extraction behavior was examined by varying the hydrochloric acid concentration from 1 to 9 M. Among the three extractants, only Cyanex 272 showed significant efficiency in extracting Au(III) with the extraction percentage was proportional to hydrochloric acid concentration. In contrast, the extraction of Au(III) by D2EHPA and PC 88A was not significant. FT-IR spectra analysis indicated that the P=O bond in Cyanex 272 weakened after extraction, suggesting its involvement in the process. Based on the structural differences between the extractants and the observed dependence of gold(III) extraction on the hydrochloric acid concentration, a nucleophilic addition reaction was proposed as the extraction mechanism. Specifically, the phosphoryl oxygen of protonated Cyanex 272 likely forms a coordinate bond with the gold ion in AuCl4 −, facilitating its extraction. This mechanism was supported by both extraction and spectroscopic data, making Cyanex 272 a promising candidate for the selective extraction of Au(III) from highly acidic solutions. The findings offer insights into the extraction of metal ions using organophosphorus extractants in highly acidic environments.

Geometric and electronic properties of anionic precious metal gold doped boron clusters AuB n − (n = 10–20)

Recently, the Au–B covalent bonds in gold doped boron clusters has attracted great attention. However, there are fewer theoretical reports on exploration their ground state structures and stabilities, especially for the medium sizes. Here, we study the structural evolution and electronic properties of the anionic Au doped boron clusters with medium sizes of n from 10 to 20 using the unbiased cluster structural searches combined with density functional theory (DFT) calculations. The results reveal that the quasi-planar AuB18 − (1A, C 1) cluster shows excellent stability and a large vertical separation energy (VDE) of 4.25 eV. The good consistency between the computationally simulated photoelectron spectra and the experimental spectra strongly supports the correctness of our low-lying structures. Further bonding analyses show that the well-stabilized aromatic AuB18 − cluster is due to the active σ interactions between Au atom (6s orbitals) and B units (2p orbitals), as well as the large number of σ–bonds in the B18 − moiety with π-aromaticity. These findings enriched the family of Au-B alloy clusters and metal-doped boron-based aromatic clusters, which provide valuable information for the experimental characterization and preparation of boron-rich alloy nanoclusters in the future.

Adsorption of Multiple NO Molecules on Anionic Gold Clusters: Electron Transfer and Disproportionation Enhanced by Molecular Aggregation.

The reactions of Aun- clusters with multiple nitric oxide (NO) molecules are explored at 150 K by utilizing a mini-flow-tube reactor and a time-of-flight mass spectrometer. Adsorption of multiple NO molecules is observed on most Aun-, while disproportionation reactions only occur on even-sized Aun- with n = 4, 6, 8, 20 and odd-sized ones with n = 5 and 7. Theoretical calculations reveal the geometric structures and electronic states of the products containing bimolecular and trimolecular NO units, where two NO molecules typically form dimers. Different from NO monomers that weakly interact with odd-sized Aun- and form electron-sharing covalent bonds with Au10-(D3h) and Au16-, NO dimers can extract significant charge from parent Aun-. Regarding the three NO molecules, a predilection toward condensation into trimers on even-sized Aun- is observed, while the tendency is more toward an adsorption pattern of a dimer plus a monomer on odd-sized Aun-. The NO trimers register even higher charge gain from Aun- as compared with the NO dimers, which leads to an elevated degree of activation and induces the progression of disproportionation reactions. Therefore, when considering the reaction between NO and Aun-, it appears that NO has a propensity to form dimers or trimers on Aun-. This behavior of aggregate formation substantially enhances the ability of NO to absorb negative charges from Aun- although the occurrence of disproportionate dissociation reactions is initiated only for specific sizes.

Third-Generation Anticancer Photodynamic Therapy Systems Based on Star-like Anionic Polyacrylamide Polymer, Gold Nanoparticles, and Temoporfin Photosensitizer.

Photodynamic therapy (PDT) is a non-invasive anticancer treatment that uses special photosensitizer molecules (PS) to generate singlet oxygen and other reactive oxygen species (ROS) in a tissue under excitation with red or infrared light. Though the method has been known for decades, it has become more popular recently with the development of new efficient organic dyes and LED light sources. Here we introduce a ternary nanocomposite: water-soluble star-like polymer/gold nanoparticles (AuNP)/temoporfin PS, which can be considered as a third-generation PDT system. AuNPs were synthesized in situ inside the polymer molecules, and the latter were then loaded with PS molecules in an aqueous solution. The applied method of synthesis allows precise control of the size and architecture of polymer nanoparticles as well as the concentration of the components. Dynamic light scattering confirmed the formation of isolated particles (120 nm diameter) with AuNPs and PS molecules incorporated inside the polymer shell. Absorption and photoluminescence spectroscopies revealed optimal concentrations of the components that can simultaneously reduce the side effects of dark toxicity and enhance singlet oxygen generation to increase cancer cell mortality. Here, we report on the optical properties of the system and detailed mechanisms of the observed enhancement of the phototherapeutic effect. Combinations of organic dyes with gold nanoparticles allow significant enhancement of the effect of ROS generation due to surface plasmonic resonance in the latter, while the application of a biocompatible star-like polymer vehicle with a dextran core and anionic polyacrylamide arms allows better local integration of the components and targeted delivery of the PS molecules to cancer cells. In this study, we demonstrate, as proof of concept, a successful application of the developed PDT system for in vitro treatment of triple-negative breast cancer cells under irradiation with a low-power LED lamp (660 nm). We consider the developed nanocomposite to be a promising PDT system for application to other types of cancer.

Engineering hydroxyls on a metal-organic framework as Adsorbers and high-activity Dehydrochlorination sites for selective gold recovery

Design of stable materials for selective gold extraction from complex sources is of a great challenge due to the poor understanding of the fundamental conversion processes responsible for anionic gold. Herein, engineering terminal hydroxyls is reported to tune the interfacial adsorption of aqueous [AuCl4]−. The energetically favorable nucleation pathway endorses the conversion of [AuCl4]− to Au atoms on the adsorption sites by dehydrochlorination, forming polyhedral Au particles anchored on the Zr6OH-BTC. Compared to the atomically separated adsorption, this terminal hydroxyl‑assisted approach achieved 5.7 times enhancement in the gold recovery capacity. This study paves a new way to comprehend the conversation and adsorption mechanism for alleviating the emerging dilemma of gold recovery.

Structural and Photoluminescent Properties of a Novel Terbium Bis(thiocyanato)aurate, Tb[Au(SCN)2]3·6H2O

The reaction of Tb3+ ions with KAu(SCN)2 results in the formation of the crystalline coordination compound Tb[Au(SCN)2]3·6H2O. Single-crystal X-ray diffraction has been employed to investigate the structural features of this compound. The crystallographic data are as follows (Mo Kα, λ = 0.71073 Å): orthorhombic, Cmcm, a = 12.4907(9) Å, b = 8.5845(6) Å, c = 20.7498(8) Å, V = 3679.72(16) Å3, Z = 4, R1(I > 2(σ)) = 0.0232. This material represents the first known example of a lanthanide dithiocyanatoaurate compound. Au(SCN)2− anions bridge Tb3+ centers in a bidentate fashion to form the [Tb(H2O)4(Au(SCN)2)2]͚+ 1D chains present in the structure. Trimeric Au units in the structure contain short aurophilic bonding interactions with distances of 3.1066(4) Å. The more common O–H‧‧‧O and O–H‧‧‧N H-bonding interactions in the structure are overshadowed by relatively rare O–H‧‧‧S interactions involving the bis(thiocyanato)gold(I) anions. Photoluminescence measurements illustrate that Tb[Au(SCN)2]3·6H2O displays strong Tb3+-based emission, but there is a lack of Au-based emission down to 85 K. Excitation spectra are recorded for the title compound and these measurements demonstrate the presence of a donor–acceptor process within the compound, leading to enhanced Tb3+-based emission.

Luminescent Au(III)-M(I) (M = Cu, Ag) Aggregates Based on Dicyclometalated Bis(alkynyl) Gold Anions†.

The syntheses and structures of a series of complexes based on the C∧C-chelated Au(III) unit (C∧C = 4,4'-bis(t-butyl) 2,2'-biphenyl-1,1'-diyl) are reported, namely, [{(C∧C)Au(C≡CtBu)2}2M2], (C∧C)Au(C≡CR)(C≡NXyl), and [{(C∧C)Au(C≡CR)2}{M(C≡NXyl)}] (M = Ag, Cu; R = tBu, C6H4tBu-4, C6H4OMe-4; Xyl = 3,5-Me2C6H3). The X-ray structures reveal a broad range of dispositions determined by the different coordination modes of Ag(I) or Cu(I). The complexes are bright photoemitters in the solid state and in poly(methyl methacrylate) (PMMA) films. The photoluminescence is dominated by 3IL(C∧C) transitions, with indirect effects from the rest of the molecules, as supported by theoretical calculations. This work opens up the possibility of accessing Au(III) carbon-rich anions to construct photoluminescent aggregates.

Hydrogen-Bonded Matched Ion Pair Gold(I) Catalysis.

The enantioselective reaction of 1,6-enynes with O-, N-, and C-nucleophiles has been developed by matched ion pair gold(I) catalysis in which the chiral gold(I) cation and anion are H-bonded through a urea group. Very high levels of enantiocontrol are achieved (up to >99:1 er) for a broad scope of substrates. DFT studies demonstrate the importance of the H-bond donor group in anchoring the matched chiral cation- and anion-favoring additional noncovalent interactions.

UiO-66-NH2/chitosan with microalgae platform for gold valorization from waste microelectronics

The combination of UiO-66-NH2/chitosan (CTS) and microalgae was effective in precious metal recovery of electronic wastes (E-wastes) from discarded microchips. Herein, zirconium-based metal–organic frameworks were introduced to bind metal ions from the E-waste. Thus, UiO-66-NH2 was linked to CTS as examined by Fourier-transform infrared spectroscopy (FT-IR). Au(III) leachate solutions were prepared via acidic treatments from the microcomputer chips that were used to test metal binding using UV–Vis absorption spectroscopy. The prepared UiO-66-NH2/CTS was tested to recover Au(III) ions from the liquid phase waste, which exhibited higher adsorption capacity than UiO-66, UiO-66-CTS, and UiO-66-NH2. The inclusion of microalgae in UiO-66-NH2/CTS system enhanced gold adsorption efficiency and binding of Au(III) ions onto UiO-66-NH2/CTS and UiO-66-NH2/CTS/microalgae attained equilibrium within a few hours. UiO-66-NH2/CTS showed an adsorption capacity of ∼ 576 mg/g, which increased to ∼ 671 mg/g after the introduction of microalgae of Spirulina maxima. The pH effect on Au(III) binding revealed that electrostatic interactions between the negatively charged UiO-66 particles and gold anions decreased the adsorption capacities at higher pH values. The findings highlighted the potential use of UiO-66-NH2/CTS and microalgae for effective gold recovery from the E-waste.

Force Decomposition Analysis: A Method to Decompose Intermolecular Forces into Physically Relevant Component Contributions

Computational quantum chemistry can be more than just numerical experiments when methods are specifically adapted to investigate chemical concepts. One important example is the development of energy decomposition analysis (EDA) to reveal the physical driving forces behind intermolecular interactions. In EDA, typically the interaction energy from a good-quality density functional theory (DFT) calculation is decomposed into multiple additive components that unveil permanent and induced electrostatics, Pauli repulsion, dispersion, and charge-transfer contributions to noncovalent interactions. Herein, we formulate, implement, and investigate decomposing the forces associated with intermolecular interactions into the same components. The resulting force decomposition analysis (FDA) is potentially useful as a complement to the EDA to understand chemistry, while also providing far more information than an EDA for data analysis purposes such as training physics-based force fields. We apply the FDA based on absolutely localized molecular orbitals (ALMOs) to analyze interactions of water with sodium and chloride ions as well as in the water dimer. We also analyze the forces responsible for geometric changes in carbon dioxide upon adsorption onto (and activation by) gold and silver anions. We also investigate how the force components of an EDA-based force field for water clusters, namely MB-UCB, compare to those from force decomposition analysis.

Anionic N-heterocyclic carbenes featuring weakly coordinating perfluoroalkylphosphorane moieties.

The anionic 1-methyl-3-(tris(pentafluoroethyl)difluorophosphorane)imidazoline-2-ylidenate 3 and the 1,3-bis(tris(pentafluoroethyl)difluorophosphorane)imidazoline-2-ylidenate dianion 4 were obtained in high yield by deprotonation of {(C2F5)3PF2}-methylimidazole 1 and the {(C2F5)3PF2}2-imidazolate anion 2. Carbenes 3 and 4 are first examples for a novel class of NHCs carrying weakly coordinating anions (WCA-NHCs). First reactions of these new ligands with elemental selenium and chloro(phosphine)gold(I) complexes to result in an anionic selenium adduct (5) and WCA-NHC gold complexes (6 and 7) have been undertaken. The structural and spectroscopic properties of these NHC derivatives in conjunction with data from quantum chemical calculations provide an insight into the electronic and steric properties of the WCA-NHCs 3 and 4. Especially the combination of properties such as weakly coordinating periphery combined with the coordinative carbene center, negative charge, large buried volume (%Vbur), and strong σ-donor as well as efficient π-acceptor ability render NHCs 3 and 4 unique and promising new ligands.

Adsorption of multiple NO molecules on Au10- and Au9Zn- planar clusters. A comparative DFT study.

The doping of atomic clusters with transition-metal atoms modifies to a lesser or greater extent the catalytic properties of the pure forms. Here we study by means of density functional theory (DFT) the adsorption of up to six NO molecules on Au10- and Au9Zn- clusters, both with well-tested D3h planar geometry, to learn how precise modifications of the atomic and electronic environment, namely one atom and a valence electron, affect the bonding of multiple NO molecules to anionic gold clusters. First, we confirm that these clusters have D3h symmetry as determined by L. S. Wang and coworkers using photoelectron spectroscopy experiments [Kulichenko et al., J. Phys. Chem. A, 2021, 125, 4606]. Second, we verify that Au10(NO)n- with n ≤ 6 does not form adsorbed (NO)2 dimers, as realized by the experiments of Ma and coworkers [Ma et al., Phys. Chem. Chem. Phys., 2020, 22, 25227] using a mini flow-tube reactor at 150 K. Third, we discover that the ground state of the doped Au9Zn(NO)6- compound forms a (NO)2cis-dimer bridging two non-corner Au atoms of the Au9Zn(NO)4- compound. The discussion of adsorption energies, spin multiplicities, bond lengths, charge trends, vibrational strength frequencies of adsorbed NO's, and projected density of states (PDOS), brings additional testable differences between Au10(NO)n- and Au9Zn(NO)n- compounds (n ≤ 6).

Peptide valence-induced breaks in plasmonic coupling.

Electrostatic interactions are a key driving force that mediates colloidal assembly. The Schulze-Hardy rule states that nanoparticles have a higher tendency to coagulate in the presence of counterions with high charge valence. However, it is unclear how the Schulze-Hardy rule works when the simple electrolytes are replaced with more sophisticated charge carriers. Here, we designed cationic peptides of varying valencies and demonstrate that their charge screening behaviors on anionic gold nanoparticles (AuNPs) follow the six-power relationship in the Schulze-Hardy rule. This finding further inspires a simple yet effective strategy for measuring SARS-CoV-2 main protease (Mpro) via naked eyes. This work provides a unique avenue for fundamental NP disassembly based on the Schulze-Hardy rule and can help design versatile substrates for colorimetric sensing of other proteases.

Magnetic Alignment for Plasmonic Control of Gold Nanorods Coated with Iron Oxide Nanoparticles.

Plasmonic nanoparticles that can be manipulated with magnetic fields are of interest for advanced optical applications, diagnostics, imaging, and therapy. Alignment of gold nanorods yields strong polarization-dependent extinction, and use of magnetic fields is appealing because they act through space and can be quickly switched. In this work, cationic polyethyleneimine-functionalized superparamagnetic Fe3 O4 nanoparticles (NPs) are deposited on the surface of anionic gold nanorods coated with bovine serum albumin. The magnetic gold nanorods (MagGNRs) obtained through mixing maintain the distinct optical properties of plasmonic gold nanorods that are minimally perturbed by the magnetic overcoating. Magnetic alignment of the MagGNRs arising from magnetic dipolar interactions on the anisotropic gold nanorod core is comprehensively characterized, including structural characterization and enhancement (suppression) of the longitudinal surface plasmon resonance and suppression (enhancement) of the transverse surface plasmon resonance for light polarized parallel (orthogonal) to the magnetic field. The MagGNRs can also be driven in rotating magnetic fields to rotate at frequencies of at least 17Hz. For suitably large gold nanorods (148nm long) and Fe3 O4 NPs (13.4nm diameter), significant alignment is possible even in modest (<500Oe) magnetic fields. An analytical model provides a unified understanding of the magnetic alignment of MagGNRs.

Anionic Ultrasmall Gold Nanoparticles Bind to Coagulation Factors and Disturb Normal Hemostatic Balance

Ultrasmall gold nanoparticles (usNPs) and nanoclusters are an emerging class of nanomaterials exhibiting distinctive physicochemical properties and in vivo behaviors. Although understanding the interactions of usNPs with blood components is of fundamental importance to advance their clinical translation, currently, little is known about the way that usNPs interact with the hemostatic system. This study describes the effects of a model anionic p-mercaptobenzoic acid-coated usNP on the coagulation cascade, with particular emphasis on the contact pathway. It is found that in a purified system, the anionic usNPs bind to and activate factor XII (FXII). The formed usNP-FXII complexes are short-lived (residence time of ∼10 s) and characterized by an affinity constant of ∼200 nM. In human plasma, the anionic usNPs activate the contact pathway and promote coagulation. The usNPs also exhibit anticoagulant activity in plasma by interfering with the thrombin-mediated cleavage of fibrinogen. Taken together, these findings establish that anionic usNPs can disturb the normal hemostatic balance, which in turn may hinder their clinical translation. Finally, it is shown that usNPs can be designed to be nearly inert in plasma by surface coating with the natural peptide glutathione.

Back Cover: Supported Anionic Gold Nanoparticle Catalysts Modified Using Highly Negatively Charged Multivacant Polyoxometalates (Angew. Chem. Int. Ed. 34/2022)

Supported gold nanoparticle catalysts have attracted growing interest in aerobic oxidation reactions. In their Research Article (e202205873), Kazuya Yamaguchi, Kosuke Suzuki et al. describe a method for the design of supported anionic gold nanoparticle catalysts using negatively charged multivacant polyoxometalates. The electronic states of the catalysts can be sequentially modulated, and the catalyst prepared using [SiW9O34]10− acted as a reusable heterogeneous catalyst, showing superior catalytic activity and enhanced stability compared to conventional catalysts.

Rücktitelbild: Supported Anionic Gold Nanoparticle Catalysts Modified Using Highly Negatively Charged Multivacant Polyoxometalates (Angew. Chem. 34/2022)

Goldnanopartikel-Katalysatoren sind von großem Interesse für aerobe Oxidationsreaktionen. In ihrem Forschungsartikel (e202205873) beschreiben Kazuya Yamaguchi, Kosuke Suzuki et al. eine Methode für die Entwicklung von Katalysatoren aus anionischen Goldnanopartikeln mithilfe von negativ geladenen, mehrwertigen Polyoxometallaten. Die elektronischen Zustände der Katalysatoren können moduliert werden, und der unter Verwendung von [SiW9O34]10− hergestellte Katalysator fungierte als wiederverwendbarer heterogener Katalysator mit überlegener katalytischer Aktivität und verbesserter Stabilität im Vergleich zu herkömmlichen Katalysatoren.

Supported Anionic Gold Nanoparticle Catalysts Modified Using Highly Negatively Charged Multivacant Polyoxometalates

AbstractAlthough supported anionic gold nanoparticle catalysts have been theoretically investigated for their efficacy in activating O2 in aerobic oxidation reactions, limited studies have been reported due to the difficulty of designing these catalysts. Herein, we developed a feasible method for preparing supported anionic gold nanoparticle catalysts using multivacant lacunary polyoxometalates with high negative charges. We confirmed the strong and robust electronic interaction between gold nanoparticles and multivacant lacunary polyoxometalates, and the electronic states of the supported gold nanoparticle catalysts can be sequentially modulated. Particularly, the catalyst prepared using [SiW9O34]10− acted as an efficient reusable heterogeneous catalyst, showing superior catalytic performance for the oxidative dehydrogenation of piperidone derivatives to the corresponding enaminones and remarkably higher stability than supported gold nanoparticle catalysts without this modification.

Supported Anionic Gold Nanoparticle Catalysts Modified Using Highly Negatively Charged Multivacant Polyoxometalates.

Although supported anionic gold nanoparticle catalysts have been theoretically investigated for their efficacy in activating O2 in aerobic oxidation reactions, limited studies have been reported due to the difficulty of designing these catalysts. Herein, we developed a feasible method for preparing supported anionic gold nanoparticle catalysts using multivacant lacunary polyoxometalates with high negative charges. We confirmed the strong and robust electronic interaction between gold nanoparticles and multivacant lacunary polyoxometalates, and the electronic states of the supported gold nanoparticle catalysts can be sequentially modulated. Particularly, the catalyst prepared using [SiW9 O34 ]10- acted as an efficient reusable heterogeneous catalyst, showing superior catalytic performance for the oxidative dehydrogenation of piperidone derivatives to the corresponding enaminones and remarkably higher stability than supported gold nanoparticle catalysts without this modification.

Heterobimetallic Ln(III)‐Containing Materials Based on One‐Dimensional Aurophilic Chains of Gold(I) Dithiolate Dimers and Their Vapochromic Response to DMF

AbstractThe synthesis, characterization, X‐ray structures and luminescence of a series of lanthanide coordination polymers containing anionic gold(I) iso‐maleonitriledithiolate units ([Au2(i‐mnt)2]2−; {Au2[S2C=C(CN)2]2}2−) are described. Crystals of (nBu4N)Ln(DMF)8[Au2(i‐mnt)2]2 (Ln=Gd, Tb, Eu) contain 1‐D aurophilic chains of [Au2(i‐mnt)2]2− units and DMF‐saturated Ln(III) cations. The Ln=Gd and Tb systems are emissive, with λmax=596 and 625 nm respectively, attributable to the aurophilic chains. The luminescence intensities and emission energies qualitatively correlate to the local concentration of DMF vapour, where emission‐quenched (nBu4N)Ln(DMF)5[Au2(i‐mnt)2]2 is formed upon sample removal from a DMF atmosphere for 24 hours; the emissive species was regenerated by exposure to fresh DMF vapour. A similar turn‐on luminescence effect was also observed when a quenched sample of (nBu4N)Tb(DMF)5[Au2(i‐mnt)2]2 powder was exposed to pyridine, resulting in emission with λmax=625 nm. Structure‐property correlations show that the emission maximum is influenced not only by the intermolecular Au−Au distances but also by a combination of the Au−Au−Au angles and other geometric factors in the [Au2(i‐mnt)2] units.