Complexation Of Gold Research Articles

Arsole‐Containing π‐Conjugated Polymer by the Post‐Element‐Transformation Technique

AbstractA synthetic method to obtain an arsole‐containing π‐conjugated polymer by the post‐transformation of the organotitanium polymer titanacyclopentadiene‐2,5‐diyl unit with an arsenic‐containing building block is described. The UV/Vis absorption maximum and onset of the polymer were observed at 517 nm and 612 nm, respectively. The polymer exhibits orange photoluminescence with an emission maximum (Emax) of 600 nm and the quantum yield (Φ) of 0.05. The polymer proved to exhibit a quasi‐reversible redox behavior in its cyclic voltammetric (CV) analysis. The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were estimated to be −5.43 and −3.24 eV, respectively, from the onsets for oxidation and reduction signals in the CV analysis. Further chemical modification of the arsole unit in the π‐conjugated polymer by complexation of gold(I) chloride occurred smoothly resulting in the bathochromic shift of the UV/Vis absorption and lowering of the LUMO energy level.

ESI FT-MS and DFT studies of aqueous Au(I) complexes with cysteine and its disulfide form cystine

Aqueous complexes of [Au(CySSCy)(CySH)n]+ containing gold(I), cysteine (CySH) and the disulfide cystine (CySSCy) have been examined by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, and the identities of individual Au complexes have been confirmed by infrared multiphoton dissociation (IRMPD)- and collision-induced dissociation (CID) experiments. Results from positive-mode ESI–MS experiments show that the aqueous Au(III)/cysteine system has a strong tendency to auto-oxidize toward cystine and form aurous-disulfide complexes of the type [Au(CySSCy)]+ and [Au(CySSCy)(CySH)n]+. An examination of the concentration- and time-dependent complexation behavior of Au(I) with CySSCy and CySH shows that the abundance of [Au(CySSCy)(CySH)]+ and [Au(CySSCy)(CySH)2]+ increases with increasing ESI solution concentration, consistent with the aqueous ionization of cysteine at pKa1=1.92. In general, the response of individual ESI mass spectra of [Au(CySSCy)(CySH)n]+ to changes in solution concentration is indicative of a direct correlation between gas-phase and aqueous Au speciation, a feature that is likely rooted in gold complexation processes occurring in solution prior to electrospraying. Finally, equilibrium geometries of Au(I) complexes with cystine and cysteine have been predicted using M06 and PCM/TD-DFT calculations, and these results have been employed to predict stepwise complexation energies of [Au(CySSCy)(CySH)n]+ and to pinpoint the most important UV–vis absorption features in aqueous solution.

Gold remobilisation and formation of high grade ore shoots driven by dissolution-reprecipitation replacement and Ni substitution into auriferous arsenopyrite

Both gold-rich sulphides and ultra-high grade native gold oreshoots are common but poorly understood phenomenon in orogenic-type mineral systems, partly because fluids in these systems are considered to have relatively low gold solubilities and are unlikely to generate high gold concentrations. The world-class Obuasi gold deposit, Ghana, has gold-rich arsenopyrite spatially associated with quartz veins, which have extremely high, localised concentrations of native gold, contained in microcrack networks within the quartz veins where they are folded. Here, we examine selected samples from Obuasi using a novel combination of quantitative electron backscatter diffraction analysis, ion microprobe imaging, synchrotron XFM mapping and geochemical modelling to investigate the origin of the unusually high gold concentrations. The auriferous arsenopyrites are shown to have undergone partial replacement (∼15%) by Au-poor, nickeliferous arsenopyrite, during localised crystal-plastic deformation, intragranular microfracture and metamorphism (340–460°C, 2kbars). Our results show the dominant replacement mechanism was pseudomorphic dissolution-reprecipitation, driven by small volumes of an infiltrating fluid that had relatively low ƒS2 and carried aqueous NiCl2. We find that arsenopyrite replacement produced strong chemical gradients at crystal-fluid interfaces due to an increase in ƒS2 during reaction, which enabled efficient removal of gold to the fluid phase and development of anomalously gold-rich fluid (potentially 10ppm or more depending on sulphur concentration). This process was facilitated by precipitation of ankerite, which removed CO2 from the fluid, increasing the relative proportion of sulphur for gold complexation and inhibited additional quartz precipitation. Gold re-precipitation occurred over distances of 10μm to several tens of metres and was likely a result of sulphur activity reduction through precipitation of pyrite and other sulphides. We suggest this late remobilisation process may be relatively common in orogenic belts containing abundant mafic/ultramafic rocks, which act as a source of Ni and Co scavenged by chloride-bearing fluids. Both the preference of the arsenopyrite crystal structure for Ni and Co, rather than gold, and the release of sulphur during reaction, can drive gold remobilisation in many deposits across broad regions.

Effect of Gamma-irradiation on biosynthesized gold nanoparticles using Chenopodium murale leaf extract

Eco-friendly synthesized gold nanoparticles (Au NPs) were successfully prepared via facile biosynthesis of Chenopodium murale (C. murale) leaf extract. Biosynthesized Au NPs were characterized by Ultraviolet/Visible spectroscopy (UV/vis.), Fourier transform infra-red spectroscopy (FT-IR), X-ray diffraction and transmission electron microscopy (TEM) techniques. The study was extended to retrace the effect of different gamma irradiation doses on the size of prepared NPs. UV/vis. spectra showed a single peak at 531nm attributed to the surface plasmon resonance (SPR) peak of Au NPs. The blue shift of SPR peak after irradiation process indicated that gamma irradiation could be utilized as size control partner. Transmission electron micrographs (TEM) showed a decrease in the size of Au NPs and a narrow size distribution with an increase in the gamma irradiation dose. Results of TEM were coinciding with those obtained from UV/vis. spectra. Bragg reflections in X-ray diffraction analysis and diffraction pattern of TEM confirmed the presence of face-centered cubic (FCC) Au NPs with (111), (200), (220), and (311) reflection planes. Fourier transform infrared (FT-IR) analysis revealed the physical and chemical complexation of gold with extract. Energy dispersive X-ray spectroscopic analysis (EDAX) confirmed the presence and biosynthesis of Au NPs.

Heteroditopic P,N ligands in gold(I) complexes: Synthesis, structure and cytotoxicity

New heteroditopic, bi- and multidentate imino- and aminophosphine ligands were synthesised and complexed to [AuCl(THT)] (THT=tetrahydrothiophene). X-ray crystallography confirmed Schiff base formation in three products, the successful reduction of the imino-group to the sp3-hybridised amine in several instances, and confirmed the formation of mono-gold(I) imino- and aminophosphine complexes for four Au-complexes. Cytotoxicity studies in cancerous and non-cancerous cell lines showed a marked increase in cytotoxicity upon ligand complexation to gold(I). These findings were supported by results from the 60-cell line fingerprint screen of the Developmental Therapeutics Programme of the National Institutes of Health for two promising compounds. The cytotoxicity of some of these ligands and gold(I)complexes is due to the induction of apoptosis. The ligands and gold(I)complexes demonstrated selective toxicity towards specific cell lines, with Jurkat T cells being more sensitive to the cytotoxic effects of these compounds, while the non-cancerous human cell line KMST6 proved more resistant when compared to the cancerous cell lines. Results from the NIH DTP 60 cell-line fingerprint screen support the observed enhancement of cytotoxicity upon gold(I) complexation. One gold(I)complex induced high levels of apoptosis at concentrations of 50μM in all the cell lines screened in this study, while some of the other compounds selectively induced apoptosis in the cell lines. These results point towards the potential for selective toxicity to cancerous cells through the induction of apoptosis.

DFT study of structure, IR and Raman spectra of dendrimer with P[dbnd]N[sbnd]P[dbnd]S linkages and its complexation with gold

The Fourier transform IR and Raman spectra of the zero generation dendrimer G1 with two PNPS linkages and four terminal aldehyde groups have been recorded. The optimized geometry of low energy isomer of G1 have been calculated by density functional (DFT) method at the PBE/TZ2P level of theory. DFT is used for analyzing the properties of PNPS linkages. DFT results for the structure of G1 are in good agreement with X-ray diffraction measurements. A complete vibrational assignment is proposed for different parts of G1. The global and local reactivity descriptors have been used to characterize the reactivity pattern of the core function and terminal group. Natural bond orbital (NBO) analysis has been applied to comparative study of charge delocalization. Our study reveals that the softness and electrophilicity of sulfur atom in the core of the dendrimer G1 is higher than that of sulfur atoms and of the dendron G2. Thus PNPS linkage has a high electron density on sulfur which allows the regiospecific complexation of gold, whereas the other PS groups do not react this way. This explains why PN bond in PNPS linkage is much more stable than isolated PN bonds, which are easily hydrolyzed.

Analysis of gold(I/III)-complexes by HPLC-ICP-MS demonstrates gold(III) stability in surface waters.

Understanding the form in which gold is transported in surface- and groundwaters underpins our understanding of gold dispersion and (bio)geochemical cycling. Yet, to date, there are no direct techniques capable of identifying the oxidation state and complexation of gold in natural waters. We present a reversed phase ion-pairing HPLC-ICP-MS method for the separation and determination of aqueous gold(III)-chloro-hydroxyl, gold(III)-bromo-hydroxyl, gold(I)-thiosulfate, and gold(I)-cyanide complexes. Detection limits for the gold species range from 0.05 to 0.30 μg L(-1). The [Au(CN)2](-) gold cyanide complex was detected in five of six waters from tailings and adjacent monitoring bores of working gold mines. Contrary to thermodynamic predictions, evidence was obtained for the existence of Au(III)-complexes in circumneutral, hypersaline waters of a natural lake overlying a gold deposit in Western Australia. This first direct evidence for the existence and stability of Au(III)-complexes in natural surface waters suggests that Au(III)-complexes may be important for the transport and biogeochemical cycling of gold in surface environments. Overall, these results show that near-μg L(-1) enrichments of Au in environmental waters result from metastable ligands (e.g., CN(-)) as well as kinetically controlled redox processes leading to the stability of highly soluble Au(III)-complexes.

Gold nanoparticle formation via microbial metallophore chemistries

Microbes are evolved to live in almost every environment and often produce small molecules to protect themselves, communicate, and sequester nutrients and minerals from their surroundings. Our recent discovery that the gold-associated microbe, Delftia acidovorans, overcomes Au3+ toxicity through complexation and precipitation of soluble gold by the nonribosomal peptide metallophore, delftibactin, revealed a new mechanism for gold biomineralization and a possible industrial application for gold sequestration. In this work, we have sought to define more the scope of nanoparticle formation by other microbial metallophores and the physical properties of gold nanoparticles created by microbial natural products (hydroxamates, catechols, citrates, mixed ligands) and synthetics.

Determination of Gold by Flame Atomic Absorption Spectrometry with Hollow Fiber Liquid Phase Microextraction Using Room Temperature Ionic Liquids

A novel method to preconcentrate gold was developed employing a synergistic enhancement of a room temperature ionic liquid combined with hollow fiber liquid phase micro-extraction with flame atomic absorption spectrometry detection. The method is based on the complexation of gold with dithizone. The formed hydrophobic complex was subsequently extracted into the lumen of a hollow fiber. The organic phase was siphoned into FAAS for the determination. A room temperature ionic liquid and dithizone were used the enhancement reagent and chelating reagent, respectively. The addition of a room temperature ionic liquid led to a five-fold improvement in the extraction of gold. The 1-octanol was immobilized in the pores of the polypropylene hollow fiber as the liquid membrane and was also used as the acceptor solution. Some parameters that influenced extraction and determination were evaluated in detail, such as concentrations of the ionic liquid and dithizone, pH of samples, stirring rates, extraction time, and interferences. Under optimized conditions, a detection limit of 0.9 ng mL−1 and an enrichment factor of 130 were achieved. The relative standard deviation (RSD) was 3.7% for Au (40 ng mL−1, n = 5). The proposed method was successfully applied to the determination of gold in certified reference environmental samples and ore samples with satisfactory results.

Complexation of gold in S3−-rich hydrothermal fluids: Evidence from ab-initio molecular dynamics simulations

Recent Raman spectroscopic studies suggest that S3− is an important sulfur species in magmatic hydrothermal and metamorphic fluids at P>0.5GPa and T>250°C, and may be an important ligand for metal transport (Pokrovski and Dubrovinsky, 2011). Based on static Density Functional Theory calculations, Tossell (2012) confirmed the stability of the S3− ion, and suggested some possible Cu–S3 complexes in the ideal gas phase and in aqueous solution. We investigated the complexation of Au and S3− in aqueous fluids by ab-initio molecular dynamics (MD) simulations. We performed ab-initio MD simulations in aqueous solution at 300°C, 0.5 and 2GPa to investigate the competition among the S3−, HS−, H2S(aq), OH− and H2O ligands for Au+, aiming at evaluating the significance of the ‘exotic’ S3− ligand for Au metallogenesis. The results indicate that, in contrast to results of static calculations that show a symmetric Au–S3 complex with bidentate structure, Au+ forms linear complexes with S3−. The stoichiometry of these complexes depends on pH and fluid composition (e.g., Au(H2O)S3(aq); Au(HS)S3−; Au(OH)S3−; Au(S3)2−). The S3− and bisulfide (HS−) ions are ligands of similar strength for Au+; this confirms Pokrovski and Dubrovinsky's (2011) assumption that such ‘exotic’ ligands may play a major role in promoting Au mobility in magmatic and metamorphic environments.

The solubility of gold in H 2O–H 2S vapour at elevated temperature and pressure

This experimental study sheds light on the complexation of gold in reduced sulphur-bearing vapour, specifically, in H 2O–H 2S gas mixtures. The solubility of gold was determined in experiments at temperatures of 300, 350 and 365 °C and reached 2.2, 6.6 and 6.3 μg/kg, respectively. The density of the vapour varied from 0.02 to 0.22 g/cm 3, the mole fraction of H 2S varied from 0.03 to 0.96, and the pressure in the cell reached 263 bar. Statistically significant correlations of the amount of gold dissolved in the fluid with the fugacity of H 2O and H 2S permit the experimental data to be fitted to a solvation/hydration model. According to this model, the solubility of gold in H 2O–H 2S gas mixtures is controlled by the formation of sulphide or bisulphide species solvated by H 2S or H 2O molecules. Formation of gold sulphide species is favoured statistically over gold bisulphide species and thus the gold is interpreted to dissolve according to reactions of the form: (A1) Au(s) + ( n + 1 ) H 2 S ( g ) = AuS · ( H 2 S ) n ( g ) + H 2 ( g ) (A2) Au(s) + H 2 S ( g ) + m H 2 O ( g ) = AuS · ( H 2 O ) m ( g ) + H 2 ( g ) Equilibrium constants for Reaction (A1) and the corresponding solvation numbers ( K A 1 and n) were evaluated from the study of Zezin et al. (2007). The equilibrium constants as well as the hydration numbers for Reaction (A2) ( K A 2 and m) were adjusted simultaneously by a custom-designed optimization algorithm and were tested statistically. The resulting values of log K A 2 and m are −15.3 and 2.3 at 300 and 350 °C and −15.1 and 2.2 at 365 °C, respectively. Using the calculated stoichiometry and stability of Reactions (A1) and (A2), it is now possible to quantitatively evaluate the contribution of reduced sulphur species to the transport of gold in aqueous vapour at temperatures up to 365 °C. This information will find application in modelling gold ore-forming processes in vapour-bearing magmatic hydrothermal systems, notably those of epithermal environments.

New bis(thiosemicarbazonate) gold(III) complexes inhibit HIV replication at cytostatic concentrations: Potential for incorporation into virostatic cocktails

Four bis(thiosemicarbazonate)gold(III) complexes (1–4) with a general formula [Au(L)]Cl {L = L1, glyoxal-bis(N 4-methylthiosemicarbazone); L2, glyoxal-bis(N 4-ethylthiosemicarbazone); L3, diacetyl-bis(N 4-methylthiosemicarbazone); L4, diacetyl-bis(N 4-ethylthiosemicarbazone)} were synthesised and screened for activity against the human immunodeficiency virus (HIV). Complexes 1–4 were characterised using 1H-NMR and IR spectroscopy; and their purity established by micronanalysis. Complex 3 inhibited viral infection of TZM-bl cells by 98% (IC 50 = 6.8 ± 0.6 μM) at a non toxic concentration of 12.5 μM while complex 4 inhibited infection of these cells by 72 and 98% (IC 50 = 5.3 ± 0.4 μM) at concentrations of 6.25 and 12.5 μM respectively. The mechanism of inhibition of infection in TZM-bl cells is presumably as a result of the cytostatic or anti-proliferative activity that was observed for complex 4 in real time cell electronic sensing (RT-CES) and carboxyflourescein succinimidyl ester (CFSE) analysis. Treatment of T lymphocytes from HIV infected individuals with 4 decreased CD4+ T cell expression (p = 0.0049) as demonstrated by multi-parametric flow cytometry without suppressing cytokine production. None of the ligands (L1–L4) demonstrated anti-viral activity, supporting the importance of metal (gold) complexation in these potential drugs. Complexes 3 and 4 were shown to have ideal lipophilicity values that were similar when shake flask (0.97 ± 0.5 and 2.42 ± 0.6) and in silico prediction (0.8 and 1.5) methods were compared. The activity and drug-like properties of complexes 3 and 4 suggests that these novel metal-based compounds could be combined with virus inhibitory drugs to work as cytostatic agents in the emerging class of anti-HIV drugs known as virostatics.

A Theoretical Study on Interaction of Small Gold Clusters Aun (n = 4, 6, 8) with xDNA Base Pairs

xDNA constitutes a novel class of size expanded synthetic nucleic acids in which one of the bases of the base pairs is larger than the natural DNA bases. These expanded bases are called x-bases. In this paper, we investigate the hydrogen bonding characteristics and relevant molecular properties of model complexes (xA…T)-Aun, (xT…A)-Aun, (xG…C)-Aun, and (xC…G)-Aun (n = 4, 6, 8) consisting of xDNA base pairs and gold clusters, in order to study the nature of gold-xDNA binding. We offer detailed characterization of their different aspects, viz., structural, electronic and spectroscopic, effect of gold cluster size, aromaticity, and planarity using quantum mechanics based density functional theory (DFT). Significant charge transfer is seen between the gold clusters and x-base pairs. Gold complexation is found to affect the interbase hydrogen bonding in these complexes. In addition to anchor bonds, X-H…Au type of hydrogen bonding interactions are also found to contribute to the gold-base pair binding in these complexes.

Au(I)-Catalyzed cycloisomerizations terminated by sp(3) C-H bond insertion.

The gold(I)-catalyzed cycloisomerization of 1,5-enynes and 1,4-allylallenes to tetracyclododecane and tetracyclotridecane derivatives, respectively, is reported. Complexation of the cationic gold(I) complex to either the alkyne or allene moiety induces an intramolecular addition of the alkene, leading to a gold(I)-stabilized carbenoid intermediate. This intermediate undergoes a formal sp(3) C-H insertion to generate the tetracyclic adduct. A series of deuterium labeling experiments showed that the C-H functionalization step proceeds with an inverse kinetic isotope effect.

Binding of Gold Nanoclusters with Size-Expanded DNA Bases: A Computational Study of Structural and Electronic Properties.

Binding of gold nanoclusters with size-expanded DNA bases, xA, xC, xG, and xT, is studied using quantum chemical methods. Geometries of the neutral xA-Au6, xC-Au6, xG-Au6, and xT-Au6 complexes were fully optimized using the B3LYP density functional method (DFT). The gold clusters around xA and xT adopt triangular geometries, whereas irregular structures are obtained in the case of gold clusters complexed around xC and xG. The lengths of the bonds between atoms in the x-bases increase on gold complexation. The aromatic character of the x-bases also increases on gold complexation except for the five-member rings. A significant charge transfer from the x-base to gold atoms is seen in these complexes. Second-order interactions are observed in addition to direct covalent bonds between gold atoms and x-bases.

Introduction of Phosphine-Gold(I) Precursors into a Cys-modified Enkephalin Neuropeptide as Part of Solid Phase Peptide Synthesis

The synthesis and full characterization of a series of (triphenylphosphine)gold complexes with thiol-containing amino acids and peptides is reported. Boc-Cys-Au(PPh3) was prepared in solution by reaction of Boc-Cys-OH with (Ph3P)AuCl. The related Ac-Cys-Au(PPh3) and an Au derivative of the cysteine-modified neuropeptide enkephalin (Enk), [Cys]5-Au(PPh3)-Enk, were prepared on the resin, using the orthogonal trityl-protecting group on Cys. For comparison, the metal-free [Cys]5-Enk and an S-tert-butyl-protected [Cys]5-Enk were also prepared. Most noteworthy, gold complexation works best when carried out on the resin, and the gold thiolate survives cleavage from the resin under optimized conditions. The new conjugates were comprehensively characterized, including 1D and 2D NMR spectroscopy, and mass spectrometry. Along with characteristic changes in the 1H and 13C NMR spectra, 31P NMR spectra reveal a characteristic downfield shift of ca. 5 ppm upon complexation of the Au(PPh3)-fragment to Cys, which is also pertinent in the Au-labelled [Cys]5-Enk.

Complexation of (trimethylphosphine)gold(I) with Selenones

Mixed ligand complexes of gold(I) with various selenones and Me3P, [Me3PAuSe=C C=Se mode of selenones upon complexation is indicative of selenone binding to gold(I) via a selenone group. An upfield shift in 13C-n.m.r. for the >C=Se resonance of selenones and downfield shifts in 31P-n.m.r. for Me3P moiety are consistent with the selenium coordination to gold(I). The steric effect as well as the basicity of Me3PAu+ plays a significant role in bonding with Se-containing ligands compared to the Et3PAu+ and Ph3PAu+ complexes.

Complexation of gold and silver nanoparticles with radiolytically-generated radicals

The reactivity of (SCN)˙−2, Br˙−2 and phenoxyl radicals in aqueous solution, generated by pulse radiolysis, was studied on gold and silver nanoparticle surfaces. The spectral changes associated with chemical interaction of radicals with metal nanoparticles were elucidated using time-resolved absorption spectroscopy. The resultant complexes of (SCN)˙−2 and Br˙−2 with Au nanoparticles have shown a strong absorption band at 390 nm and 260 nm, respectively. The stability of the particles after adsorption of SCN−, Br− and phenols was measured by steady-state absorption. It has been shown that the concentration of CTAB plays a significant role in the stabilization of particles in the presence of an adsorbate.

Preparation, Structure and Gold(I) Complexation of p-Xylylene-1,4-diphosphines

1,4-Dimethyl-2,5-di(phosphinyl)benzene (1) was prepared in high yield in a four-step synthesis from 1,4-dibromo-2,5-dimethyl-benzene. The intermediates with (Et2N)2P and Cl2P groups (2, 3) with the corresponding substitution pattern have been isolated and structurally characterized. All three compounds (1 - 3) adopt a centrosymmetrical conformation with one of the P-X bonds of each X2P group located in the ring plane while the other reaches out from this plane in a roughly perpendicular orientation. Distortions of the ring and its substituents from a standard planar hexagonal geometry are readily explained by invoking steric and inductive effects. The crystal structure of 1,4-dibromo-2,5-dimethyl-benzene has also been determined for reference purposes. Compound 1 was employed as a substrate for auration by tri(gold)oxonium salts of the type {[(R3P)Au]3O}BF4. Hexanuclear complex salts of the type {[(R3P)Au]3P(C6H2Me2)P[Au(PR3)]3}(BF4)2 were obtained in almost quantitative yield with R3P = tBu3P (4) and Ph3P (5). The former (4) has the higher thermal stability, it could be crystallized and its structure determined. It features a conformation in which the xylene plane bisects one of the Au-P-Au angles at both tetrahedrally coordinated central phosphorus atoms placing its methyl groups in sterically least hindered positions. Compound 5 is labile in solution and shows rapid ligand exchange on the NMR time scale. The limited stability has also been confirmed by mass spectrometry. Similar structural details and differences in stability were observed in the related trinuclear gold complexes based on 1-naphthyl-phosphine, which were prepared as reference materials using the same preparative procedure. Of the two compounds {(1-C10H7)- P[Au(PR3)]3}BF4, with R3P = tBu3P (6) and Ph3P (7), the former is the more stable species. In the solid state the cation approaches mirror symmetry in a conformation comparable to that of 4. Compound 7 is thermally labile and shows a rapid ligand exchange in solution.

Complexation and Reduction of Gold (III) During Extraction from HCl by Calix[4,6]arenes Upper‐Rim Functionalized with Alkyl‐ or Tolylthiamethyl Groups

Gold (III) extraction from hydrochloric media by solutions of new sulphur‐containing calix[4]arenes (L) bearing alkyl(tolyl)thiamethyl groups at the upper rim was investigated. Interphase equilibria were quantitatively described and conditional constants (Kln) of gold extraction in form (AuCl3)nL (n=1–4) were defined. Influence of CHCl and diluent properties (CCl4, toluene, benzene, 1,2‐dichloroethane) on gold extraction was clarified. Among investigated extractants the most effective ones are calixarenes with CH2SAlk groups (Alk=CH3, n‐C4H9), which exceeds monodentate thioethers on extraction properties. It was shown that the redox process following extraction includes intra‐ or intermolecular reduction of gold (III) by free SR‐groups. The rate of the first process depends equally on steric and donor properties of the substituent at the sulphur atom, while the rate of the second process is mainly determined by steric properties.