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Gold(III) complexes containing trifluoromethyl ligands are efficient catalysts in the hydration of alkynes, operating at low catalyst loadings, without additives, using environmentally friendly solvents and at mild conditions (60 °C). Hydration of terminal and internal alkynes provides the corresponding ketones in quantitative yields without special precautions as dry solvents or inert atmospheres. Remarkably, hydration of asymmetric internal alkynes proceeds with moderate to notable regioselectivities, providing mixtures of the two possible isomers with ratios up to 90 : 10. [ABSTRACT FROM AUTHOR]

The direct auration of arenes is a key step in numerous gold‐catalyzed reactions. Although reported more than 100 years ago, understanding of its underlying mechanism has been hampered by the difficulties in the isolation of relevant intermediates given the propensity of gold(III) species to undergo reductive elimination. Here, we report the synthesis and isolation of a new family of intriguing zwitterionic [C(sp3)^C(sp2)]‐auracyclopentanes, as well as of their alkyl‐gold(III) precursors and demonstrate their value as mechanistic probes to study the C(sp2)‐Au bond‐forming event. Experimental investigations employing Kinetic Isotope Effects (KIE), Hammett plot, and Eyring analysis provided important insights into the formation of the auracycle. The data suggest a SEAr mechanism wherein the slowest step might be the π‐coordination between the arene and the gold(III) center, en route to the Wheland intermediate. We also show that these auracyclopentanes can work as catalysts in several gold‐promoted transformations. [ABSTRACT FROM AUTHOR]

To elucidate an antitumor drug exhibiting enhanced activity relative to cisplatin, a novel dinuclear gold(III) complex was synthesized, incorporating 1,5-naphthyridine as a bridging ligand. Subsequently, the newly synthesized complex underwent comprehensive characterization using various techniques to validate its structural attributes. The stability of the complex in both water and PBS buffer was assessed through UV–Vis spectroscopy. DNA binding studies were conducted employing UV–Vis, fluorescence spectroscopy, and viscosity measurements. Competitive studies with ethidium bromide (EB) or 4′-hydroxyethidium (HOE) were performed utilizing fluorescence spectroscopy. The findings indicated that the dinuclear gold(III) complex interacts with calf thymus DNA (CT-DNA) through a groove binding mode. Moreover, the investigated complex exhibited significant binding constants for its interaction with human serum albumin (HSA) and bovine serum albumin (BSA) and interactions in the presence of site markers (eosin Y or ibuprofen). The dinuclear gold(III) complex demonstrated notable cytotoxicity against HCT116 and MDA-MB-231 cancer cell lines at 24 and 72 h post-treatment. Furthermore, the complex displayed selectivity by inducing significantly lower cytotoxic activity in healthy cells than in cancerous ones. In support of its antitumor activity, the complex exhibited proapoptotic effects, as evidenced by increased caspase 9 activity and low percentages of necrosis. Molecular docking simulations were employed to corroborate all experimentally obtained results. [ABSTRACT FROM AUTHOR]

A new method utilizing sugarcane bagasse-derived ash (SB-dA) to remove and convert gold(III) to valuable noble gold metal has been developed. The SB-dA was purified with a mixed solution of 0.1 mol/L HCl and 0.3 mol/L HF, followed by 3 mol/L HNO3, resulting in a silica-rich material with silanol (Si–OH) and siloxane (Si–O–Si) groups, along with an aromatic component. The gold(III) removal was endothermic (ΔHo of 34.51 kJ/mol) and spontaneous (ΔGo ranging from −27.72 to −29.81 kJ/mol as temperature increased from 30 to 50 °C). The activation energy (Ea) and standard entropy (ΔSo) values were 35.15 and 0.2 kJ/mol, respectively, indicating increased interfacial irregularity during gold(III) removal. At an optimum pH of 4.2, the removal followed the Langmuir isotherm and the second-order kinetics models. The rate constant (k2) enhanced from 3.32 to 7.56 × 102 L/mol·min, and Langmuir's removal capacity (b) rose from 0.18 to 0.25 × 10⁻⁴ mol/g as temperature increased from 30 to 50 °C. Silanol and siloxane groups played crucial role in gold(III) removal through adsorption, with silanol also active in reducing gold(III) to gold metal, a process that intensified by increasing temperatures.

Pyridoxal and pyridoxal 5′-phosphate are aldehyde forms of B6 vitamin that can easily be transformed into each other in the living organism. The presence of a phosphate group, however, provides the related compounds (e.g., hydrazones) with better solubility in water. In addition, the phosphate group may sometimes act as a binding center for metal ions. In particular, a phosphate group can be a strong ligand for a gold(III) ion, which is of interest for researchers for the anti-tumor and antimicrobial potential of gold(III). This paper aims to answer whether the phosphate group is involved in the complex formation between gold(III) and hydrazones derived from pyridoxal 5′-phosphate. The answer is negative, since the comparison of the stability constants determined for the gold(III) complexes with pyridoxal- and pyridoxal 5′-phosphate-derived hydrazones showed a negligible difference. In addition, quantum chemical calculations confirmed that the preferential coordination of two series of phosphorylated and non-phosphorylated hydrazones to gold(III) ion is similar. The preferential protonation modes for the gold(III) complexes were also determined using experimental and calculated data. [ABSTRACT FROM AUTHOR]

The kinetics of the substitution reactions between bifunctional Au(III) complexes, [AuCl2(bipy)]+, [AuCl2(dach)]+ and [AuCl2(en)]+ (bipy = 2,2″-bipyridine, dach = (1 R,2R)-1,2-diaminocyclohexane, en = ethylenediamine), with biologically relevant ligands such as glutathione (GSH), L-methionine (L-Met) and L-cysteine (L-Cys) is determined. All kinetic studies are performed in 25 mM Hepes buffer (pH = 7.2) in the presence of NaCl (25 mM) to prevent hydrolysis of the complexes. The reactions were followed under pseudo-first-order conditions using stopped-flow UV–Vis spectrophotometry at determined working wavelengths at three different temperatures (288.2, 298.1, and 309.8 K). DFT theoretical approach was applied to calculate thermodynamic and kinetic parameters that determined an operative mechanism of substitution reactions for all complexes and L-Cys as a selected model substituent. The obtained kinetic data showed that all complexes have similar reactivity; [AuCl2(bipy)]+ is the most reactive while [AuCl2(en)]+ is the least reactive. The second step of the substitution reaction is much faster than the first. The reactivity of the studied nucleophiles decreases in order L-Met > L-Cys > GSH. According to the values of the activation parameters determined experimentally and theoretically, all substitutions follow an associative model. [ABSTRACT FROM AUTHOR]

The solvent extraction of gold(III) by undiluted 2-ethylhexanol or dissolved in toluene from a HCl solution has been investigated in this paper. The numerical analysis of gold distribution data suggests the formation of HAuCl4·L and HAuCl4·2L (L = 2-ethylhexanol) species in the organic phase, with formation constants K11 = 38 and K12 = 309, respectively. The results derived from gold(III) distribution have been implemented in a solid-supported liquid membrane system. The influence of several variables on gold transport has been considered: feed and receiving phases' stirring speeds, HCl and gold concentrations in the feed phase, and carrier concentration in the membrane phase as well as the presence of base metals (Fe, Cu, Ni) and platinum-group metals (PGMs) in the feed phase. Gold transport is influenced by the stirring speed of the feed phase and the variation in HCl and gold (feed phase) and carrier (membrane phase) concentrations. Also, diffusional resistances to mass transfer are estimated, and the contribution of each resistance to gold transport is estimated. Gold is recovered as zero-valent nanoparticles. [ABSTRACT FROM AUTHOR]

The synthesis of gold(III) and gold(I)–gold(III) complexes with phosphide bridges is still a matter that requires solutions for their marked instability, in spite of the affinity of this metal in both oxidation states for phosphorous donor ligands. In the course of our studies, we realized that the presence of perhalophenyl groups of the type pentafluorophenyl or 3,5-dichlorotrifluorophenyl in the complexes gives rise to an increase in their stability that eases their isolation and structural characterization. In this paper, we describe two new fully characterized neutral compounds of this type to extend the knowledge on this family of compounds, [{Au(C6Cl2F3)2}2(µ-PPh2)2] (1) and [{Au(C6Cl2F3)2(µ-PPh2)2Au}2] (2). In this work, we analyze the role of the perhalophenyl groups in the stability of these complexes by using quantum chemical topology methodologies, specifically employing an analysis of the non-covalent interactions (NCIs) in real space and evaluating the electrostatic potential surfaces (ESP). Our findings reveal the existence of appreciable π-stacking interactions among the perhalophenyl and phenyl groups in both compounds, significantly contributing to the stability of the systems. [ABSTRACT FROM AUTHOR]

Cyanoaurate complexes represent a broad class of compounds with diverse structures. In particular, coordination polymers based on these complexes have numerous potential practical applications, including in microelectronics, nanotechnology, materials science, and medicine. In the development of new functional materials, significant attention is given to the possibility of molecules and other structural units participating in noncovalent interactions, which play a crucial role in determining the physicochemical properties and biological activity of these materials. Thus, the presence of aurophilic contacts or halogen–halogen interactions in cyanoaurate complexes only intensifies researchers' interest in this class of compounds. At present, study of the chemistry of gold cyanides continues to develop rapidly, making the synthesis and exploration of new cyanoaurate compounds, as well as the systematization of the knowledge gained, relevant tasks. This review, encompassing a description of contemporary achievements in the methods of synthesis, investigation of structural features, and potential practical applications of metal dicyanoaurates, tetracyanoaurates, and dihalodicyanoaurates of both molecular and ionic types, is based on an analysis of publications, with the majority of sources published before 2022. Some more recent studies are also included in the review. The information presented in this article is fundamentally important and undoubtedly valuable for specialists in the field of inorganic and organometallic chemistry of gold. [ABSTRACT FROM AUTHOR]

We report on a comprehensive reactivity study starting from [AuF3(SIMes)] to synthesize different motifs of monomeric gold(III) fluorides. A plethora of different ligands has been introduced in a mono‐substitution yielding trans‐[AuF2X(SIMes)] including alkynido, cyanido, azido, and a set of perfluoroalkoxido complexes. The latter were better accomplished via use of perfluorinated carbonyl‐bearing molecules, which is unprecedented in gold chemistry. In case of the cyanide and azide, triple substitution gave rise to the corresponding [AuX3(SIMes)] complexes. Comparison of the chemical shift of the carbene carbon atom in the 13C{1H} NMR spectrum, the calculated SIMes affinity and the Au−C bond length in the solid state with related literature‐known complexes yields a classification of trans‐influences for a variety of ligands attached to the gold center. Therein, the mixed fluorido perfluoroalkoxido complexes have a similar SIMes affinity to AuF3 with a very low Gibbs energy of formation when using the perfluoro carbonyl route. [ABSTRACT FROM AUTHOR]

Pyridoxal and pyridoxal 5′-phosphate are aldehyde forms of B6 vitamin that can easily be transformed into each other in the living organism. The presence of a phosphate group, however, provides the related compounds (e.g., hydrazones) with better solubility in water. In addition, the phosphate group may sometimes act as a binding center for metal ions. In particular, a phosphate group can be a strong ligand for a gold(III) ion, which is of interest for researchers for the anti-tumor and antimicrobial potential of gold(III). This paper aims to answer whether the phosphate group is involved in the complex formation between gold(III) and hydrazones derived from pyridoxal 5′-phosphate. The answer is negative, since the comparison of the stability constants determined for the gold(III) complexes with pyridoxal- and pyridoxal 5′-phosphate-derived hydrazones showed a negligible difference. In addition, quantum chemical calculations confirmed that the preferential coordination of two series of phosphorylated and non-phosphorylated hydrazones to gold(III) ion is similar. The preferential protonation modes for the gold(III) complexes were also determined using experimental and calculated data.

The synthesis of gold(III) and gold(I)–gold(III) complexes with phosphide bridges is still a matter that requires solutions for their marked instability, in spite of the affinity of this metal in both oxidation states for phosphorous donor ligands. In the course of our studies, we realized that the presence of perhalophenyl groups of the type pentafluorophenyl or 3,5-dichlorotrifluorophenyl in the complexes gives rise to an increase in their stability that eases their isolation and structural characterization. In this paper, we describe two new fully characterized neutral compounds of this type to extend the knowledge on this family of compounds, [{Au(C6Cl2F3)2}2(µ-PPh2)2] (1) and [{Au(C6Cl2F3)2(µ-PPh2)2Au}2] (2). In this work, we analyze the role of the perhalophenyl groups in the stability of these complexes by using quantum chemical topology methodologies, specifically employing an analysis of the non-covalent interactions (NCIs) in real space and evaluating the electrostatic potential surfaces (ESP). Our findings reveal the existence of appreciable π-stacking interactions among the perhalophenyl and phenyl groups in both compounds, significantly contributing to the stability of the systems.

Background: There has been a continuous interest in the development of luminescent gold(III) complexes as emitters for OLED applications in recent years. Objective: To design and synthesize a series of luminescent bis‐alkynylgold(III) complexes with bidentate C^N‐type ligands and to compare their properties with related tridentate cyclometalated complexes. Methods: A series of bis‐alkynylgold(III) complexes with bidentate C^N‐type ligands derived from 2‐phenylpyridine and 7,8‐benzoquinoline has been designed and synthesized. The photophysical properties of the complexes have been studied by electronic absorption and emission spectroscopies. Results: All of the complexes were observed to exhibit rich photophysical and electrochemical properties. In particular, the complexes were strongly emissive at ambient conditions, showing vibronic‐structured emission bands peaked at 433–557 nm in dichloromethane solutions at 298 K. Conclusions: By comparing the structural features, luminescence properties and electrochemistry of the bidentate complexes with related tridentate C^N^C and C^N^N‐type alkynylgold(III) complexes, a better understanding on the structure‐property relationship of the alkynylgold(III) system has been obtained. [ABSTRACT FROM AUTHOR]

Gold(III) complexes with different ligands can provide researchers with a measure against pathogenic microorganisms with antibiotic resistance. We reported in our previous paper that the UV-Vis spectra of different protonated species of complexes formed by gold(III) and five hydrazones derived from pyridoxal 5′-phosphate are similar to each other and to the spectra of free protonated hydrazones. The present paper focuses on the reasons of the noted similarity in electron absorption spectra. The geometry of different protonated species of complexes of gold(III) and hydrazones (15 structures in total) was optimized using the density functional theory (DFT). The coordination polyhedron of gold(III) bond critical points were further studied to identify the symmetry of the gold coordination sphere and the type of interactions that hold the complex together. The UV-Vis spectra were calculated using TD DFT methods. The molecular orbitals were analyzed to interpret the calculated spectra. [ABSTRACT FROM AUTHOR]

Solvent extraction of gold(III) from HCl media using pseudo-protic ionic liquids (PPILs) dissolved in toluene as the extractant phase is investigated. Three PPILs are generated from the reaction of commercially available amines and 1 M HCl solution and named as pri-NH2H+Cl− (derived from the primary amine Primene 81R), sec-NHH+Cl− (derived from the secondary amine Amberlite LA2) and ter-NH+Cl− (derived from the tertiary amine Hostarex A327). In the above structures, -NH2H+Cl−, -NHH+Cl− and -NH+Cl− represented the active groups (anion exchangers) of the respective PPIL. In the case of gold(III) extraction, the experimental variables investigated included the equilibration time (2.5–30 min), temperature (20–60 °C), HCl concentrations (1–10 M) in the aqueous phase, gold(III) concentration (0.005–0.05 g/L) in this same phase, and PPILs concentrations in the organic phase. From the experimental data, and using the Specific Interaction Theory, the interaction coefficients (ε) for the pair AuCl4−, H+ are estimated for the systems involving the three PPILs. Gold(III) is recovered from the metal-loaded organic phases using sodium thiocyanate solutions, and from these, gold is finally recovered by the precipitation of zero-valent gold (ZVG) nanoparticles. [ABSTRACT FROM AUTHOR]

In this paper, we describe a series of diphenylphosphane and diphenylphosphanide gold(III) and gold(III)/gold(I) complexes containing 3,5-C6Cl2F3 as aryl ligands at gold that have been synthesized due to the arylating and oxidant properties of the new polymeric thallium(III) complex [TlCl(3,5-C6Cl2F3)2]n (1). Its reaction with [Au(3,5-C6Cl2F3)(tht)] (tht = tetrahydrothiophene) produces the gold(III) complex [Au(3,5-C6Cl2F3)3(tht)] (2), which allows the synthesis of the diphenylohosphane derivative [Au(3,5-C6Cl2F3)3(PPh2H)] (3). Its treatment with acetylacetonate gold(I) derivatives leads to two novel AuIII/AuI phosphanido-bridged complexes, [PPN][Au(3,5-C6Cl2F3)3(µ-PPh2)AuCl] (4) and [PPN][{(3,5-C6Cl2F3)3Au(µ-PPh2)}2Au] (5). All these complexes have been characterized, and the crystal structures of 1, 2, 4 and 5 have been established by single crystal X-ray diffraction methods, showing a novel polymeric arrangement in 1. [ABSTRACT FROM AUTHOR]

The reaction of a solution of H[AuCl4] with 1,10-phenanthroline (Phen) in acetonitrile gave the complex (H2Phen)[AuCl4]Cl (I). According to X-ray diffraction data (CCDC no. 2165199), Phen exists in I as an unusual doubly protonated (cationic) form (H2Phen)2+. Binding of ionic structural units ([AuCl4]–, Cl–, and (H2Phen)2+) by D–H···Cl hydrogen bonds (D = N, C) gives rise to supramolecular 2D pseudo-polymer layers. The biological activity of I was measured for human ovarian carcinoma cells (SKOV3). Using MTT assay results, the half-maximal inhibitory concentration was calculated, demonstrating high selectivity of I to cancer cells in combination with low toxicity towards normal fibroblasts. [ABSTRACT FROM AUTHOR]

Today, complexes of gold(I) and gold(III) are recognized as promising drugs for the treatment of bacterial infectious diseases and oncological diseases, respectively. It is of interest to broaden the area of potential use of gold(III) compounds to the pathogenic microorganism as well. The first step towards the development of new antibacterial drugs based on Au3+ complexes is the study of their stability in an aqueous solution. The present contribution reports on the investigation of gold(III) complexation with five hydrazones derived from a well-known biologically active compound, pyridoxal 5′-phosphate (one of the aldehyde forms of the B6 vitamin). The complex formation in aqueous solutions was confirmed by mass spectrometry and fluorescent spectroscopy. The stoichiometric composition of the complexes formed and their stability constants were determined using a UV–Vis titration method. The complexes are quite stable at physiological values of pH, as the speciation diagrams show. The results of the paper are helpful for further studies of gold(III) complexes interaction with biomacromolecules. [ABSTRACT FROM AUTHOR]

A series of (C^S)-cyclometallated Au(III) cationic complexes of general formula [Au(dppta)(dtc)] + , [Au(dppta)(azmtd)] + and [Au(dppta)(azc)Cl] + (dppta = N,N-diisopropyl-P,P-diphenylphosphinothioic amide-κ 2 C,S; dtc = dithiocarbamate-κ 2 S,S'; azc = azolium-2-dithiocarboxylate-κ 1 S; azmdt = azol(in)ium-2-(methoxy)methanedithiol-κ 2 S,S') were synthetized and tested against a panel of bacterial strains belonging to different Gram-positive and Gram-negative species of the ESKAPE group of pathogens. Among the tested compounds, complex 4c had the higher Therapeutic Index (TI) against multidrug resistant strains of S. aureus, S. epidermidis and A. baumannii, showing a more favourable cytotoxicity profile than the reference gold metalloantibiotic Auranofin. © 2024 xxxxxxxx. Hosting by Elsevier B.V. All rights reserved., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Sara M. Soto has patent A gold(III) complex, a conjugate of the gold(III) complex, a pharmaceutical composition comprising the gold(III) complex and uses and a process for preparing the gold(III) complex issued to Institute of Global Health of Barcelona. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

The direct auration of arenes is a key step in numerous gold-catalyzed reactions. Although reported more than 100 years ago, understanding of its underlying mechanism has been hampered by the difficulties in the isolation of relevant intermediates given the propensity of gold(III) species to undergo reductive elimination. Here, we report the synthesis and isolation of a new family of intriguing zwitterionic [C(sp 3 )^C(sp 2 )]-auracyclopentanes, as well as of their alkyl-gold(III) precursors and demonstrate their value as mechanistic probes to study the C(sp 2 )-Au bond-forming event. Experimental investigations employing Kinetic Isotope Effects (KIE), Hammett plot, and Eyring analysis provided important insights into the formation of the auracycle. The data suggest a S E Ar mechanism wherein the slowest step might be the π-coordination between the arene and the gold(III) center, en route to the Wheland intermediate. We also show that these auracyclopentanes can work as catalysts in several gold-promoted transformations., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

[Display omitted] • Silver(I) and gold(III) complexes with miconazole were synthesized. • The structure of silver(I) complex was determined by X-ray diffraction analysis. • DFT was used for determination of the structure of complexes in solution. • The synthesized complexes showed significant antibacterial and antifungal activity. • Gold(III) complex with miconazole significantly reduced pyocyanin production. To develop a new antimicrobial agent, we used the clinically approved antifungal azole, miconazole (mcz), as a ligand for the synthesis of silver(I) and gold(III) complexes. The new complexes [Ag(NO 3 - O)(mcz- N) 2 ] (1) and [AuCl 3 (mcz- N)] (2) were synthesized and characterized by 1H NMR, IR and UV–Vis spectroscopy and mass spectrometry, while the crystal structure of 1 was determined by single-crystal X-ray diffraction analysis. From the results obtained, it can be concluded that in both complexes, mcz is monodentately coordinated to the silver(I) and gold(III) ions through the imidazole nitrogen atom N3. In the solid state, complex 1 contains two mcz ligands and monodentately coordinated nitrate in the third position, while in the case of 2 gold(III) ion is coordinated by one mcz and three chlorido ligands, resulting in the expected square-planar arrangement around the metal center. DFT and TDDFT calculations were employed to elucidate the electronic structures and thermodynamic stability of the synthesized complexes in solution to complement the experimental findings. The coordination of mcz to silver(I) and gold(III) ions leads to an enhancement of its activity against Gram-negative Escherichia coli and Pseudomonas aeruginosa strains, while against the panel of Staphylococcus aureus and Candida species, only 2 shows improved activity compared to mcz. Both complexes 1 and 2 were tested in vitro for their antimycobacterial activity against the strain Mycobacterium tuberculosis H37Rv and showed good growth inhibition with minimum inhibitory concentration (MIC) values of 3.12 and 8.69 μM, respectively, with complex 1 being twice effective as mcz (MIC = 7.50 μM). Complex 2 significantly reduced the production of pyocyanin, a virulence factor in P. aeruginosa controlled by quorum sensing, while this effect was not observed for 1. [ABSTRACT FROM AUTHOR]

Gold(III) complexes with different ligands can provide researchers with a measure against pathogenic microorganisms with antibiotic resistance. We reported in our previous paper that the UV-Vis spectra of different protonated species of complexes formed by gold(III) and five hydrazones derived from pyridoxal 5′-phosphate are similar to each other and to the spectra of free protonated hydrazones. The present paper focuses on the reasons of the noted similarity in electron absorption spectra. The geometry of different protonated species of complexes of gold(III) and hydrazones (15 structures in total) was optimized using the density functional theory (DFT). The coordination polyhedron of gold(III) bond critical points were further studied to identify the symmetry of the gold coordination sphere and the type of interactions that hold the complex together. The UV-Vis spectra were calculated using TD DFT methods. The molecular orbitals were analyzed to interpret the calculated spectra.

Solvent extraction of gold(III) from HCl media using pseudo-protic ionic liquids (PPILs) dissolved in toluene as the extractant phase is investigated. Three PPILs are generated from the reaction of commercially available amines and 1 M HCl solution and named as pri-NH2H+Cl− (derived from the primary amine Primene 81R), sec-NHH+Cl− (derived from the secondary amine Amberlite LA2) and ter-NH+Cl− (derived from the tertiary amine Hostarex A327). In the above structures, -NH2H+Cl−, -NHH+Cl− and -NH+Cl− represented the active groups (anion exchangers) of the respective PPIL. In the case of gold(III) extraction, the experimental variables investigated included the equilibration time (2.5–30 min), temperature (20–60 °C), HCl concentrations (1–10 M) in the aqueous phase, gold(III) concentration (0.005–0.05 g/L) in this same phase, and PPILs concentrations in the organic phase. From the experimental data, and using the Specific Interaction Theory, the interaction coefficients (ε) for the pair AuCl4−, H+ are estimated for the systems involving the three PPILs. Gold(III) is recovered from the metal-loaded organic phases using sodium thiocyanate solutions, and from these, gold is finally recovered by the precipitation of zero-valent gold (ZVG) nanoparticles.

A catalytic method to synthesize a broad array of cyclometalated (C^N)gold(III) complexes is reported here. An unprecedented Rh‐to‐AuIII transmetalation allows the facile transfer of (C^N) ligands between these two metals in a redox‐neutral process. The reaction employs commercially available precursors and proceeds under mild and environmentally benign conditions. Both experimental and computational studies support a multistep transmetalation from rhodium to gold as the underlying mechanism for these transformations. This process involves first, a rate‐determining transfer of the C ligand followed by the subsequent incorporation of the N donor to form the monocyclometalated (C^N)gold(III) species. [ABSTRACT FROM AUTHOR]

A simple and efficient method to detect and quantify Fe(II) and Au(III) cations in environmental water samples was developed. The detection principle is based on the 1:1 mol‐ratio complex formation between the probe molecule (tannic acid, TA) and Fe(II)/or Au(III), which yields visual color change and strong light absorbance at 518 nm and 534 nm, respectively. The association constant Ka for Fe(II) and Au(III) cations 4.01 × 104 and 4.13 × 104 M−1, respectively, was determined from Benesi–Hildebrand plot, indicating strong interactions between TA and target ions. This TA probe performed well in 50 mM phosphate buffer (PB, pH 9.0) solution and demonstrated an outstanding selectivity over 16 potential interfering metal ions and a good selectivity over Fe(III). The linear range in this study for Fe(II) and Au(III) cations was 0.25–100 μM and 1.0–100 μM, respectively. The detection limit of the TA probe for Fe(II) and Au(III) cations was found to be 0.080 and 0.50 μM, respectively. The spike recovery for both metal ions in three environmental aqueous samples (spring water and pond water) was ranged 90.2%–117.2%. This study demonstrated that the TA probe is a simple and convenient detection method for analyzing water samples obtained from fresh water sources. [ABSTRACT FROM AUTHOR]

Abstract Background There is an emerging field to put into practice new strategies for developing molecules with antimicrobial properties. In this line, several metals and metalloids are currently being used for these purposes, although their cellular effect(s) or target(s) in a particular organism are still unknown. Here we aimed to investigate and analyze Au3+ toxicity through a combination of biochemical and molecular approaches. Results We found that Au3+ triggers a major oxidative unbalance in Escherichia coli, characterized by decreased intracellular thiol levels, increased superoxide concentration, as well as by an augmented production of the antioxidant enzymes superoxide dismutase and catalase. Because ROS production is, in some cases, associated with metal reduction and the concomitant generation of gold-containing nanostructures (AuNS), this possibility was evaluated in vivo and in vitro. Conclusions Au3+ is toxic for E. coli because it triggers an unbalance of the bacterium’s oxidative status. This was demonstrated by using oxidative stress dyes and antioxidant chemicals as well as gene reporters, RSH concentrations and AuNS generation.

Au(III)-NHC-oxazolyl complexes are prepared by oxidation and anion exchange of the corresponding Au(I)Cl-NHC-oxazolyl precursors, which are synthesized from appropriate imidazolium pre-ligands. As the Au(III) complexes are too unstable for proper isolation and spectroscopic characterization, selective 15N NMR techniques provide valuable knowledge of N-coordination to gold by formation of N-ligated Au(III) complexes. The changes in 15N-shift values (Δδ15N), observed by 1H,15N-HMBC 2D NMR studies, going from Au(I)Cl, via Au(III)Cl3 to the C,N-Au(III) NHC-oxazolyl complexes, afford important information of the oxidation and the anion exchange processes. In particular, the huge up-field shift of the oxazoline-N by anion exchange (Δδ15NAE: −71.3 ppm), represents significant evidence that oxazoline-N-coordination to Au(III) takes place by anion exchange, and, hence, that the target six-membered bidentate C,N-Au(III)-NHC-oxazoline chelated complex is formed.

In this paper, we describe a series of diphenylphosphane and diphenylphosphanide gold(III) and gold(III)/gold(I) complexes containing 3,5-C6Cl2F3 as aryl ligands at gold that have been synthesized due to the arylating and oxidant properties of the new polymeric thallium(III) complex [TlCl(3,5-C6Cl2F3)2]n (1). Its reaction with [Au(3,5-C6Cl2F3)(tht)] (tht = tetrahydrothiophene) produces the gold(III) complex [Au(3,5-C6Cl2F3)3(tht)] (2), which allows the synthesis of the diphenylohosphane derivative [Au(3,5-C6Cl2F3)3(PPh2H)] (3). Its treatment with acetylacetonate gold(I) derivatives leads to two novel AuIII/AuI phosphanido-bridged complexes, [PPN][Au(3,5-C6Cl2F3)3(µ-PPh2)AuCl] (4) and [PPN][{(3,5-C6Cl2F3)3Au(µ-PPh2)}2Au] (5). All these complexes have been characterized, and the crystal structures of 1, 2, 4 and 5 have been established by single crystal X-ray diffraction methods, showing a novel polymeric arrangement in 1.

Today, complexes of gold(I) and gold(III) are recognized as promising drugs for the treatment of bacterial infectious diseases and oncological diseases, respectively. It is of interest to broaden the area of potential use of gold(III) compounds to the pathogenic microorganism as well. The first step towards the development of new antibacterial drugs based on Au3+ complexes is the study of their stability in an aqueous solution. The present contribution reports on the investigation of gold(III) complexation with five hydrazones derived from a well-known biologically active compound, pyridoxal 5′-phosphate (one of the aldehyde forms of the B6 vitamin). The complex formation in aqueous solutions was confirmed by mass spectrometry and fluorescent spectroscopy. The stoichiometric composition of the complexes formed and their stability constants were determined using a UV–Vis titration method. The complexes are quite stable at physiological values of pH, as the speciation diagrams show. The results of the paper are helpful for further studies of gold(III) complexes interaction with biomacromolecules.

The reactions of N-alkyl-N′-picolyl-benzimidazolium bromides or N,N′-dipicolyl-benzimidazolium bromide with silver oxide yielded the silver dicarbene complexes of the type [Ag(NHC)2][AgBr2] 1–4 (NHC = picoline-functionalized benzimidazolin-2-ylidene). The silver complexes 1–4 have been used in carbene transfer reactions to yield the gold(I) complexes of the type [AuCl(NHC)] 5–8 in good yields. A halide exchange at the metal center of complexes 5–8 with lithium bromide yielded the gold bromide complexes 9–12. Finally, the oxidation of the gold(I) centers in complexes 9–12 with elemental bromine gave the gold(III) complexes of the type [AuBr3(NHC)] 13–16. Molecular structures of selected Au(I) and Au(III) complexes have been determined by X-ray diffraction studies. [ABSTRACT FROM AUTHOR]

Poly(N-2-sulfoethylethylenimine) (SEPEI) with a degree of modification equal to 0.30, 0.58, and 0.74, cross-linked with diethylene glycol diglycidyl ether, demonstrates efficient sorption properties with respect to PtIV, PdII, and AuIII ions. The selectivity coefficient KPd/Au in a HCl solution with pH 0.8 decreases from 90 to 61, and the selectivity coefficient KPd/Pt in a HCl solution with pH 3.9 increases from 0.94 to 480 with an increasing degree of modification. A thiourea hydrochloric acid solution effectively removes metal ions; the desorption of PtIV, PdII, and AuIII from the SEPEI surface reaches 100, 96.9, and 83.8%, respectively. [ABSTRACT FROM AUTHOR]

Dependencies for the sorption of palladium(II), gold(III), and platinum(IV) chloro complexes from individual and binary solutions with sorbents based on sulfoethylated polyallylamine and poly(aminostyrene) have been obtained. It has been found that predominant sorption mechanism is complexation with functional groups of the sorbents for gold(III) and palladium(II) and ion exchange for platinum(IV). It has been shown that increase in the sulfoethylation degree of aminopolymer matrix leads to decrease of platinum(IV) sorption and therefore, to increase in palladium(II) sorption selectivity relative to this ion. This effect is the largest for the sorbents based on polyallylamine. The conditions of quantitative desorption of the studied metals from sorbent surface have been determined. The sorption of gold(III) by the sorbent based on polyallylamine has been shown to be complicated by gold(III) reduction in sorbent phase. [ABSTRACT FROM AUTHOR]

In aqueous solutions, gold(III) complexes with organic ligands in the presence of DNA can dissociate releasing metal ion. A degree of dissociation depends on the stability of gold(III) complexes with DNA and a small molecule. This paper reports on the stability constants of the complexes formed by chlorohydroxy complexes of gold(III) and DNA. [Display omitted] • Nature of gold(III) species interaction with DNA depends on C(Cl-). • Log K of gold(III) species binding with DNA are determined. • AFM confirms the gold(III)-DNA interaction. • Speciation diagram for the system of gold(III)-hydrazone-DNA is drawn. Gold(III) complexes resemble cisplatin and other similar platinum(II) complexes in structure and electron properties. Because of this similarity, the coordination compounds formed by gold(III) can find application in medicine. They are considered to bind with DNA, disrupting its normal replication. However, there are a few available papers devoted to the study of the interaction between tetrachloroaurate(III), which is used often for the synthesis of other gold(III) complexes, and DNA. The stability constants of gold(III) and DNA are also useful for studying the reactions between gold(III) complexes and DNA, as the dissociation of the metal complex is possible. Therefore, this paper describes the interactions between [AuCl 4 ]- and its hydrolyzed species and DNA in pure water and aqueous 0.1 M NaCl solution. Binding mode and binding constants are determined from the results of UV–Vis and circular dichroism titration, while the kinetic fluorescent measurements are used to study the ethidium bromide replacement. Atomic force microscopy is also used to show the influence of gold(III) species on DNA. The calculated equilibrium constants are used to calculate the speciation diagram for the solution containing chlorohydroxyaurate(III) species, hydrazone derived from pyridoxal 5′-phosphate, and DNA at different pH values. [ABSTRACT FROM AUTHOR]

The title compound, an (N^C)-cyclometalated gold(III) diazide, namely, diazido[5-ethoxycarbonyl-2-(5-ethoxycarbonylpyridin-2-yl)phenyl-κ2C1,N]gold(III), [Au(C17H16NO4)(N3)2] or Au(ppyEt)(N3)2, was synthesized by reacting Au(ppyEt)Cl2 with NaN3 in water for 24 h. The complex has been structurally characterized and features a gold center with a square-planar environment. The Au—N(azide) bond lengths are significantly different depending on the influence of the atom trans to the azide group [Au—N(trans to C) of 2.067 (2) Å versus Au—N(trans to N) of 2.042 (2) Å]. The azide groups are twisted in-and-out of plane by 56.2 (2)°.

A new family of cationic, bidentate (P^N)gold(III) fluoride complexes has been prepared and a detailed characterization of the gold‐fluoride bond has been carried out. Our results correlate with the observed reactivity of the fluoro ligand, which undergoes facile exchange with both cyano and acetylene nucleophiles. The resulting (P^N)arylgold(III)C(sp) complexes have enabled the first study of reductive elimination on (P^N)gold(III) systems, which demonstrated that C(sp2)−C(sp) bond formation occurs at higher rates than those reported for analogous phosphine‐based monodentate systems. [ABSTRACT FROM AUTHOR]

The use of gold in medicine has a long history. Recent clinical applications include anti-inflammatory agents for the treatment of rheumatoid arthritis (chrysotherapy), and is currently being developed as potential anticancer chemotherapeutics. Gold(III), being isoelectronic to platinum(II) as in cisplatin, is of great interest but it is inherently unstable and redox-reactive under physiological conditions. Coordination ligands containing C and/or N donor atom(s) such as porphyrin, pincer-type cyclometalated and/or N-heterocyclic carbene (NHC) can be employed to stabilize gold(III) ion for the preparation of anticancer active compounds. In this review, we described our recent work on the anticancer properties of gold(III) compounds and the identification of molecular targets involved in the mechanisms of action. We also summarized the chemical formulation strategies that have been adopted for the delivery of cytotoxic gold compounds, and for ameliorating the in vivo toxicity.

The title compound, an (N^C)-cyclo­metalated gold(III) diazide, namely, di­azido­[5-eth­oxy­carbonyl-2-(5-eth­oxy­carbonyl­pyridin-2-yl)phenyl-κ²C¹,N]gold(III), [Au(C17H16NO4)(N3)2] or Au(ppyEt)(N3)2, was synthesized by reacting Au(ppyEt)Cl2 with NaN3 in water for 24 h. The complex has been structurally characterized and features a gold center with a square-planar environment. The Au—N(azide) bond lengths are significantly different depending on the influence of the atom trans to the azide group [Au—N(trans to C) of 2.067 (2) Å versus Au—N(trans to N) of 2.042 (2) Å]. The azide groups are twisted in-and-out of plane by 56.2 (2)°. [ABSTRACT FROM AUTHOR]

A new family of phosphine‐ligated dicyanoarylgold(III) complexes has been prepared and their reactivity towards reductive elimination has been studied in detail. Both, a highly positive entropy of activation and a primary 12/13C KIE suggest a late concerted transition state while Hammett analysis and DFT calculations indicate that the process is asynchronous. As a result, a distinct mechanism involving an asynchronous concerted reductive elimination for the overall C(sp2)−C(sp)N bond forming reaction is characterized herein, for the first time, complementing previous studies reported for C(sp3)−C(sp3), C(sp2)−C(sp2), and C(sp3)−C(sp2) bond formation processes taking place on gold(III) species. [ABSTRACT FROM AUTHOR]

Background: There is an emerging field to put into practice new strategies for developing molecules with antimicrobial properties. In this line, several metals and metalloids are currently being used for these purposes, although their cellular effect(s) or target(s) in a particular organism are still unknown. Here we aimed to investigate and analyze Au3+ toxicity through a combination of biochemical and molecular approaches. Results: We found that Au3+ triggers a major oxidative unbalance in Escherichia coli, characterized by decreased intracellular thiol levels, increased superoxide concentration, as well as by an augmented production of the antioxidant enzymes superoxide dismutase and catalase. Because ROS production is, in some cases, associated with metal reduction and the concomitant generation of gold-containing nanostructures (AuNS), this possibility was evaluated in vivo and in vitro. Conclusions: Au3+ is toxic for E. coli because it triggers an unbalance of the bacterium's oxidative status. This was demonstrated by using oxidative stress dyes and antioxidant chemicals as well as gene reporters, RSH concentrations and AuNS generation. [ABSTRACT FROM AUTHOR]

A new method is presented here for liquid-liquid extractive spectrophotometric determination of gold(III). The current method is based on complexation between 4-(4'-flurobenzylideneimino)-3-methyl- 5-mercapto-1,2,4-triazole (FBIMMT) as a chromogenic reagent and gold(III) in presence of potassium iodide solution to form a yellow complex which was quantitatively extracted in chloroform at room temperature from 0.8 mol L -1 of hydrochloric acid medium. The (1:2) [Au(III)-FBIMMT] complex in chloroform exhibited maximum absorption at λ max 390 nm and was stable for more than 24 hrs. The values of molar absorptivity and Sandell's sensitivity of [Au(III)-FBIMMT] complex were found to be 0.98485 × 104 L mol -1 cm-1 and is 0.01858 μg cm-2 respectively. The extraction system follows Beer's law from 4.0-17.5 μg mL-1 however Ringbom's plot suggests favourable concentration range as 4.5-17.5 μg mL-1. The values of both LOD and LOQ were found to be as 0.20 and 0.78 μg mL-1 respectively. [ABSTRACT FROM AUTHOR]

In a systematic study of the extraction of gold(III) in acidic chloride solutions by a number of aliphatic esters with the focus on dibasic esters, it was found that di- or tribasic esters are more effective extractants than monobasic esters. The equilibrium for the extraction of gold(III) by a series of dibasic esters C2H5OCO(CH2)nCOOC2H5 (n = 0 to 8) has been studied. Diethyladipate (n = 4) was found to be the most reactive. The extraction of gold by diethyl adipate increases with increasing proton and with increasing chloride ion concentrations. The latter is due to the effect of chloride ions on the activity coefficient of the proton in concentrated HCl solutions. Gold is extracted more effectively by the use of diluents with a high dielectric constant. Gold is extracted as the tetrachloro-complex ion. Slope analysis has shown that the extracted gold complex contains three molecules of the ester and one hydrated proton. The Donor number obtained by calorimetric measurements increases with increasing number of methylene groups and is constant for greater than 3 methylene groups. The distribution coefficient correlates with the Donor number up to 4 methylene groups with steric effects resulting in a decrease in extraction for the higher chain length esters. It is proposed that gold is extracted as an ion-pair in the organic phase with a hydrated proton solvated by the esters. [ABSTRACT FROM AUTHOR]

Value and high demand for gold have encouraged its exploration and recoverability from secondary sources. This study is aimed to investigate the extraction recovery of gold(III) from hydrochloric acid media using 1-butyl-3-methylimidazolium hexafluorophosphate and 1-octanol. The influence of initial ion concentration, 1-butyl-3-methylimidazolium hexafluorophosphate concentration, acidity of solution, volumetric ratio of aqueous to organic phase, and extraction time are examined. Central composite design in response-surface methodology was applied for the optimization of the effective parameters. The extraction recovery higher than 99% is achieved at the optimum conditions, which is close to the predicted response by the model (99.999%). [ABSTRACT FROM AUTHOR]

The transport of gold(III) across a supported liquid membrane containing the ionic liquid Cyphos IL102 (trihexyl(tetradecyl)phosphonium bromide) in Solvesso 100 has been investigated. The investigation was carried out under various experimental variables affecting to the transport process: stirring speed in the aqueous feed solution, HCl and gold(III) concentrations in this same phase, and carrier concentration in the membrane phase. The transport of gold(III) was compared against the transport of Fe(III), Cu(II), and Ni(II) from aqueous solutions containing the four elements, whereas the performance of Cyphos IL102 was compared, with respect to the gold transport, against other potential carriers for gold(III) from this acidic medium. Gold can be recovered in the strip solution as zero valent gold nanoparticles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bacterial infection confronts the World's population. • Antimicrobial resistance demands new and effective therapeutics. • Gold(I) compounds exhibit broad range activity against Gram-positive bacteria. • Gold(III) complexes exert broad-range antibacterial activity. • Repurposing the anti-arthritis drug Auranofin®: a way forward? Bacterial infections pose a significant threat to public health and the global economy. The misuse of antibiotics in the treatment of bacterial infections has led to a rapid development of antibiotic-resistant bacteria which demands the development of new antibiotics for effective therapy. Gold complexes manifest prominent antibacterial activities against a broad panel of bacterial strains, indicating their great potential for development as potent antibiotics. The present review article provides an overview of the antibacterial activity of gold complexes since the year 2000, with an emphasis on the past decade, and with separate sections dedicated to the discussion of gold(I) and gold(III) complexes. Further, a summary is provided on the repurposing of Auranofin for antibacterial purposes, along with a summary of the reported associated mechanism(s) of action. This overview is provided to offer insight into the rational design of gold complexes with bio-efficacy. [ABSTRACT FROM AUTHOR]

Three novel gold(III) complexes (1–3) of general composition [Au(Bipydc)(S2CNR2)]Cl2 (Bipydc = 2,2′-bipyridine-3,3′-dicarboxylic acid and R = methyl for dimethyldithiocarbamate (DMDTC), ethyl for diethyldithiocarbamate (DEDTC), and benzyl for dibenzyldithiocarbamate (DBDTC)) have been synthesized and characterized by elemental analysis, FTIR and NMR spectroscopic techniques. The spectral results confirmed the presence of both the Bipydc and dithiocarbamate ligands in the complexes. The in vitro cytotoxic studies demonstrated that compounds 1–3 were highly cytotoxic to A549, HeLa, MDA-231, and MCF-7 cancer cells with activities much higher (about 25-fold) than cisplatin. In order to know the possible mode of cell death complex 2, [Au(Bipydc)(DEDTC)]Cl2 was further tested for induction of apoptosis towards the MCF-7 cells. The results indicated that complex 2 induces cell death through apoptosis.

A gold(III) salt of composition [AuCl2(C12H8N2)]PF6 was prepared and characterized by elemental and mass spectrometric analysis (ESI(+)–QTOF–MS), 1H nuclear magnetic resonance measurements and by single-crystal X-ray diffraction. The square-planar coordination sphere of AuIII comprises the bidentate 1,10-phenanthroline ligand and two chloride ions, with the AuIII ion only slightly shifted from the least-squares plane of the ligating atoms (r.m.s. = 0.018 Å). In contrast to two other previously reported AuIII-phenantroline structures that are stabilized by interactions involving the chlorido ligands, the packing of the title compound does not present these features. Instead, the hexafluoridophosphate counter-ion gives rise to anion...π interactions that are a crucial factor for the crystal packing.

Chemical properties and biological activity of Au(III) compounds obtained from dichlorido[2‐(dimethylaminomethyl)phenyl‐C1,N]gold(III), [Au(damp‐C1,N)Cl2], and halogenated, potentially tridentate thiosemicarbazones have been studied. The results of this work show that the complexation of the halogenated thiosemicarbazones with Au(III) enhances their stability against hydrolysis and retains or enhances their anti‐parasitic activity. Fluorination in the periphery of the ligands has expectedly no influence on the structural chemistry of the obtained Au(III) complexes, but modulates their biological behaviour. Best results with a remarkably high selectivity index for the trypomastigote form of Trypanosoma cruzi were obtained with the complex containing the ligand, which presents a 3,5‐fluorine substitution in meta‐position of an aromatic ring, [Au(dampH)(L‐3,5‐F)]Cl. [ABSTRACT FROM AUTHOR]