Gold Fragments Research Articles

Sterically Crowded Gold Germylene Compounds with Methyl and Hydride Substituents

AbstractThis work explores the combination of sterically crowded low‐valent germanium compounds bearing one or two terphenyl (C6H3‐2,6‐Ar2) substituents with gold fragments, the latter stabilized by crowded phosphines also containing a terphenyl moiety. The steric protection of these motifs has allowed to examine a series of unusual gold‐germylene compounds featuring small hydride and methyl substituents at the germanium site. A gold‐germylene dicationic structure is also reported. The bonding in this series is investigated by computational means, providing understanding for the two‐way transfer of electrons from germanium to gold and vice versa.

A Cavity-Shaped Gold(I) Fragment Enables CO2 Insertion into Au-OH and Au-NH Bonds.

A cavity-shaped linear gold(I) hydroxide complex acts as a platform to access unusual gold monomeric species. Notably, this sterically crowded gold fragment enables the trapping of CO2 via insertion into Au-OH and Au-NH bonds to form unprecedented monomeric gold(I) carbonate and carbamate complexes. In addition, we succeeded in the identification of the first gold(I) terminal hydride bearing a phosphine ligand. The basic nature of the Au(I)-hydroxide moiety is also explored through the reactivity toward other molecules containing acidic protons such as trifluoromethanesulfonic acid and terminal alkynes.

Anti-Tumoural [NHC(thiolato)] Gold(I) Complexes Derived from HIF-1α Inhibitor AC1-004 Target the Mitochondrial Redox System and Show Antiangiogenic Effects in vivo.

AC1-004 is a potent inhibitor of the hypoxia-inducible factor alpha (HIF-1α) pathway, essential for tumour growth, angiogenesis and metastasis. We modelled a series of gold(I) complexes on AC1-004, retaining its 5-carboalkoxybenzimidazole as an NHC ligand while replacing its 2-aryloxymethyl residue with modified thiolato gold(I) fragments. The intention was to augment a potential HIF-1α inhibition by conducive effects typical of NHC gold complexes, such as an inhibition of tumoural thioredoxin reductase (TrxR), an increase in reactive oxygen species (ROS), and cytotoxic and antiangiogenic effects. We report on the synthesis and biological effects of twelve such N,N'-dialkylbenzimidazol-2-ylidene gold(I) complexes, obtained in average yields of 65 % for the thiophenolato and 45 % for the novel 4-(adamant-2-yl)benzenethiol complexes. The structure of one complex was validated via single-crystal X-ray diffraction. Structure-activity relationships (SAR) were derived by variation of the N-substituents (Me, Et, iPr, pentyl, Bn) and the thiolato ligand. Their cytotoxicity against various human cancer cell lines of different entities reached IC50 values in the single-digit micromolar range. The complexes were also assayed for the induction of tumour cell apoptosis (activation of caspase-3/7), TrxR inhibition and antiangiogenic effects in zebrafish. Cyclopropene-bearing congeners were employed in click reactions to examine the subcellular accumulation of the complexes.

Polarized Au(I)/Rh(I) bimetallic pairs cooperatively trigger ligand non-innocence and bond activation.

The combination of molecular metallic fragments of contrasting Lewis character offers many possibilities for cooperative bond activation and for the disclosure of unusual reactivity. Here we provide a systematic investigation on the partnership of Lewis basic Rh(I) compounds of type [(η5-L)Rh(PR3)2] (η5-L = (C5Me5)- or (C9H7)-) with highly congested Lewis acidic Au(I) species. For the cyclopentadienyl Rh(I) compounds, we demonstrate the non-innocent role of the typically robust (C5Me5)- ligand through migration of a hydride to the Rh site and provide evidence for the direct implication of the gold fragment in this unusual bimetallic ligand activation event. This process competes with the formation of dinuclear Lewis adducts defined by a dative Rh → Au bond, with selectivity being under kinetic control and tunable by modifying the stereoelectronic and chelating properties of the phosphine ligands bound to the two metals. We provide a thorough computational study on the unusual Cp* non-innocent behavior and the divergent bimetallic pathways observed. The cooperative FLP-type reactivity of all bimetallic pairs has been investigated and computationally examined for the case of N-H bond activation in ammonia.

Early Medieval burial complex of the burial mound of Maslennikovo I in the Samara Volga region

This paper is devoted to the publication of materials obtained during the study of the burial of the early Middle Ages in the burial mound Maslennikovo I. This necropolis is located in the steppe southwestern part of the Samara Trans-Volga region. The excavated mound 1 was built in the Bronze Age in the process of making eight burials of this time. Burial 2, admitted into the floor of the embankment in its southern part, dates back to the Middle Ages. The burial was made in a grave pit in the shape of an elongated oval and oriented with its long axis along the NW-SE line. The buried man lay stretched out on his back with his head to the northwest. The bone of a horses leg lay at his head. Gold foil fragments, which may have been the remains of a symbolic death mask, and earrings were also found in the area of the head. The remains of a wooden object with silver plates at the edges, probably of a quiver on the chest of a deceased burial were found. The remains of a scabbard, which also had silver plates there were in the region of the pelvis and between the thigh bones. Seven silver sewn-on plaques with embossed ornaments and several poorly preserved iron objects were found in the grave. The peculiarities of the funeral rite and accompanying implements make it possible to include this complex in the number of burials attributed by researchers as Magyar (proto-Magyar, Hungarian) and to consider it as the burial of an individual integrated into the ethnocultural environment of the Hungarians of the Middle Volga region of the 9th-10th centuries.

From Thioureas to Thioquinolines through Isolated Benzothiazines by Gold Catalysis.

New benzothiazine heterocycles have been formed from thiourea derivatives by using different gold catalysts. The catalyst and the conditions were optimised towards the selective synthesis of six‐membered benzothiazine heterocycles, characterised by X‐ray diffraction. Interestingly, these organic compounds evolved under gold catalysis in basic medium to achieve the formation of amino thioquinolines through an unprecedented aromatisation process of the heterocycle. The reaction was also carried out stoichiometrically by reaction with gold complexes to afford thioquinolines coordinated to the gold fragment. Benzothiazine, amino thioquinoline heterocycles and gold‐derived species have a great potential for biological applications.

Vittae Auratae:Interpreting the History and Technology of a Group of Roman Gold Textile Fragments

Fifty-six gold fragments—forty-nine pieces of woven textile and seven of twisted cord—from the collection of the J. Paul Getty Museum were the subject of an art historical and scientific study to ascertain their original form, function, and method of manufacture. The fragments were examined through the use of noninvasive technologies, including digital microscopy, X-radiography, scanning electron microscopy with energy dispersive spectroscopic (SEM-EDS) analysis, and scanning macro-X-ray fluorescence (MA-XRF) spectroscopy. By these means, it was possible to determine the chemical composition of the gold threads and details of the ancient weave, which enabled the authors to digitally reconstruct the original form of the more well-preserved fragments. Historical research supports the interpretation of the reconstructed sections, suggesting that the original artifact closely resembles ribbons of woven gold (vittae) found in Italy and dating to the late Hellenistic through the early Imperial Roman periods (ca. 100 BCE–200 CE).

Høj Stene – en monumental skibssætning ved Gudenåen

Høj Stene – en monumental skibssætning ved Gudenåen

Monitoring of the Pre-Equilibrium Step in the Alkyne Hydration Reaction Catalyzed by Au(III) Complexes: A Computational Study Based on Experimental Evidences.

The coordination ability of the [(ppy)Au(IPr)]2+ fragment [ppy = 2-phenylpyridine, IPr = 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene] towards different anionic and neutral X ligands (X = Cl−, BF4−, OTf−, H2O, 2-butyne, 3-hexyne) commonly involved in the crucial pre-equilibrium step of the alkyne hydration reaction is computationally investigated to shed light on unexpected experimental observations on its catalytic activity. Experiment reveals that BF4− and OTf− have very similar coordination ability towards [(ppy)Au(IPr)]2+ and slightly less than water, whereas the alkyne complex could not be observed in solution at least at the NMR sensitivity. Due to the steric hindrance/dispersion interaction balance between X and IPr, the [(ppy)Au(IPr)]2+ fragment is computationally found to be much less selective than a model [(ppy)Au(NHC)]2+ (NHC = 1,3-dimethylimidazol-2-ylidene) fragment towards the different ligands, in particular OTf− and BF4−, in agreement with experiment. Effect of the ancillary ligand substitution demonstrates that the coordination ability of Au(III) is quantitatively strongly affected by the nature of the ligands (even more than the net charge of the complex) and that all the investigated gold fragments coordinate to alkynes more strongly than H2O. Remarkably, a stabilization of the water-coordinating species with respect to the alkyne-coordinating one can only be achieved within a microsolvation model, which reconciles theory with experiment. All the results reported here suggest that both the Au(III) fragment coordination ability and its proper computational modelling in the experimental conditions are fundamental issues for the design of efficient catalysts.

Reactions of Medicinal Gold(III) Compounds With Proteins and Peptides Explored by Electrospray Ionization Mass Spectrometry and Complementary Biophysical Methods.

Electrospray ionization mass spectrometry (ESI MS) is a powerful investigative tool to analyze the reactions of metallodrugs with proteins and peptides and characterize the resulting adducts. Here, we have applied this type of approach to four experimental anticancer gold(III) compounds for which extensive biological and mechanistic data had previously been gathered, namely, Auoxo6, Au2phen, AuL12, and Aubipyc. These gold(III) compounds were reacted with two representative proteins, i.e., human serum albumin (HSA) and human carbonic anhydrase I (hCA I), and with the C-terminal dodecapeptide of thioredoxin reductase. ESI MS analysis allowed us to elucidate the nature of the resulting metal–protein adducts from which the main features of the occurring metallodrug–protein reactions can be inferred. In selected cases, MS data were integrated and supported by independent 1HNMR and UV–Vis absorption measurements to gain an overall description of the occurring processes. From data analysis, it emerges that most of the investigated gold(III) complexes, endowed with an appreciable oxidizing character, undergo quite facile reduction to gold(I); the resulting gold(I) species tightly associate with the above proteins/peptides with a remarkable selectivity for free cysteine residues. In contrast, in the case of the less-oxidizing Aubipyc complex, the gold(III) oxidation state is conserved, and a gold(III) fragment still containing the original ligand is found to be associated with the target proteins. It is notable that the C-terminal dodecapeptide of thioredoxin reductase containing the characteristic –Gly–Cys–Sec–Gly metal-binding motif is able in all cases to trigger gold(III)-to-gold(I) reduction. Our investigation allowed us to identify in detail the nature of the gold fragments that ultimately bind the protein targets and determine the exact binding stoichiometry; some insight on the reaction kinetics was also gained. Notably, a few clear correlations could be established between the structure of the metal complexes and the nature of the resulting protein adducts. The mechanistic implications of these findings are analyzed and thoroughly discussed. Overall, the present results set the stage to better understand the real target biomolecules of these gold compounds and elucidate at the atomic level their interaction modes with proteins and peptides.

Luminescent Bimetallic IrIII/AuI Peptide Bioconjugates as Potential Theranostic Agents

Invited for the cover of this issue are Vanesa Fernández-Moreira, Nils Metzler-Nolte, M. Concepción Gimeno and co-workers at Universidad de Zaragoza and Ruhr-Universität Bochum. The image depicts the reported bimetallic bioconjugates as planes directing the gold fragment towards the target (lysosomes). Read the full text of the article at 10.1002/chem.202002067.

Tuning Activity and Selectivity during Alkyne Activation by Gold(I)/Platinum(0) Frustrated Lewis Pairs.

Introducing transition metals into frustrated Lewis pair systems has attracted considerable attention in recent years. Here we report a selection of three metal-only frustrated systems based on Au(I)/Pt(0) combinations and their reactivity toward alkynes. We have inspected the activation of acetylene and phenylacetylene. The gold(I) fragments are stabilized by three bulky phosphines bearing terphenyl groups. We have observed that subtle modifications on the substituents of these ligands proved critical in controlling the regioselectivity of acetylene activation and the product distribution resulting from C(sp)–H cleavage of phenylacetylene. A mechanistic picture based on experimental observations and computational analysis is provided. As a result of the cooperative action of the two metals of the frustrated pairs, several uncommon heterobimetallic structures have been characterized.

Luminescent Re(I)/Au(I) Species As Selective Anticancer Agents for HeLa Cells.

A series of neutral and cationic heterotrimetallic complexes of the type fac-[Re(CO)3(bipy(CC)2-(AuL)2)X]n, where bipy(CC)2 is 4,4'-alkynyl-2,2'-bipyridine; L is either triphenylphosphine (PPh3), [1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene] (IPr), or tert-butyl isocyanide (CNtBu); and X is a chloride (n = 0) or acetonitrile (n = 1), were synthesized and characterized together with their Re(I) precursors, i.e., fac-[Re(CO)3(bipy(CC)2)X]n. X-ray diffraction of complexes 1, 3, and 6 corroborated the expected octahedral and linear distribution of the ligands along the Re(I) and Au(I) centers, respectively. Luminescent studies showed that all the complexes displayed a broad emission band centered between 565 and 680 nm, corresponding to a 3MLCT from the Re(I) to the diimine derivative. The presence of the gold fragment coordinated to the diimine ligand shifted in all cases the emission maxima toward higher energies. Such an emission difference could be potentially used for assessing the precise moment of interaction of the probe with the biological target if the gold fragment is implicated. Antiproliferative studies in cancer cells, A549 (lung cancer) and HeLa (cervix cancer), showed a generalized selectivity toward HeLa cells for those heterotrimetallic species incubated at longer times (72 vs 24 h). ICP-MS spectrometry revealed the greater cell internalization of cationic vs neutral species. Preliminary fluorescence microscopy experiments showed a different behavior of the complexes in HeLa and A549 cell lines. Whereas the complexes in A549 were randomly distributed in the outside of the cell, those incubated with HeLa cells were located close to the cellular membrane, suggesting some type of interaction, and possibly explaining their cellular selectivity when it comes to the antiproliferative activity displayed in the different cell lines.

Versatile coordinative abilities of perhalophenyl-gold(I) fragments to Xantphos: Influence on the emissive properties

Reaction of perhalophenylgold(I) complexes [AuR(tht)] (R = C6Cl2F3, C6Cl5; tht = tetrahydrothiophene) with different number of equivalents of Xantphos (4,5-Bis(diphenylphosphino)-9,9-dimethylxanthene) leads to discrete complexes in which the metal atom displays very different coordination environments. Thus, the ionic complex [Au(Xantphos)2][Au(C6Cl2F3)2] (1) or the neutral [Au(C6Cl5)(Xantphos)] (2) one are obtained when a 1:1 (Au:Xantphos) stoichiometry is used. However, similar compounds [Au2R2(μ-Xantphos)] (R = C6Cl2F3 (3); C6Cl5 (4)) are synthesized when the amount of gold is increased to a 2:1 ratio. The use of diphosphine Xantphos, which can act as bridging, chelate or even as mono-dentate ligand, together with the use of different perhalophenyl groups bonded to the gold(I) centres, allows the synthesis of cationic tetracoordinate gold(I) fragments (1), mononuclear (2) or dinuclear (3–4) dicoordinated gold(I) complexes. This structural diversity in the coordination arrangements as well as the different aryl groups present in the molecules directly affect their photophysical properties, giving rise to different luminescent emission energies ranging from 470 to 580 nm, and also to a different origin for the electronic transitions related to them such as 3IL (3) to 3MLCT (4) and also a mixture of them 3MLCT/3IL (1 and 2). The experimental photophysical results obtained for these gold(I) complexes were supported by DFT and TD-DFT calculations. On the other hand, the behaviour of these complexes in solution is different, losing their emissive properties for all complexes or displaying the co-existence of different structural arrangements in the case of complexes 1 and 2, as observed through variable-temperature 31P{1H} NMR experiments.

The 2-isocyanoazulene-gold(I) fragment as a versatile element for organometallic dyes and liquid crystals

This manuscript reports the synthesis and liquid crystal behavior of isocyanoazulene gold(I) complexes [AuX (CN-Az)] (Az = azulene; X = halide, perhalophenyl or alkynyl) and [μ-4,4′-C6F4C6F4{Au(CN-Az)}2]. The comparison of the X-ray structures of homologous compounds, reveals that the introduction of a long substituent in the system produces a loss of molecular planarity that induces a decrease in the melting temperatures. The free 2-isocyanoazulene is not a liquid crystal itself, but its gold complexes bearing a C10 hydrocarbon chain display a SmA mesophase, whose formation is driven by nanosegregation between molten chains and aromatic parts. The free isocyanide is strongly colored and displays fluorescence in solution associated with the azulene fragment, which is largely diminished upon coordination to the gold fragment.

Aurophilicity in action: stepwise formation of dinuclear Au(i) macrocycles with rigid 1,8-dialkynylanthracenes.

Two phosphane-gold(i) functions (with tri(para-tolyl)- or tri-n-butylphosphane) were attached to a 1,8-diethynylanthracene backbone. The ligand size prevents direct interaction between the gold atoms, but the initial products rearrange to form macrocyclic anions comprising two 1,8-diethynylanthracene and two gold units, linked to cationic gold(i) fragments by maximising aurophilic interactions.

"Doping" of Polyyne with an Organometallic Fragment Leads to Highly Conductive Metallapolyyne Molecular Wire.

Exploration of highly conductive molecules is essential to achieve single-molecule electronic devices. The present paper describes the results on single-molecule conductance study of polyyne wires doped with the organometallic Ru(dppe)2 fragment, X-(C≡C) n-Ru(dppe)2-(C≡C) n-X. The metallapolyyne wires end-capped with the gold fragments (X = AuL) are subjected to single-molecule conductance measurements with the STM break junction technique, which reveal the high conductance (10-3-10-2 G0; n = 2-4) with the low attenuation factor (0.25 Å-1) and the low contact resistance (33 kΩ). A unique "'doping'" effect of Ru(dppe)2 fragment was found to lead to the high performance as suggested by the hybrid density functional theory-nonequilibrium green function calculation.

A fabrication method of gold coated colloidosomes and their application as targeted drug carriers.

Colloidosomes have attracted considerable attention in recent years because of their potential applications in a range of industries, such as food, bioreactors and medicine. However, traditional polymer shell colloidosomes leak low molecular weight encapsulated materials due to their intrinsic shell permeability. Here, we report aqueous core colloidosomes coated with a gold shell, which make the capsules impermeable. The shells can be ruptured using ultrasound. The gold coated colloidosomes are prepared by making an aqueous core capsule with a polymer shell and then adding HAuCl4, surfactant and l-ascorbic acid to form a second shell. We propose to use the capsules as drug carriers. The gold coated colloidosomes demonstrate a low cytotoxicity and after triggering, both encapsulated doxorubicin and broken gold fragments kill cancer cells. In addition, we set up a targeting model by modifying the gold shell colloidosomes using 4,4'-dithiodibutyric acid and crosslinking them with proteins-rabbit immunoglobulin G (IgG). Label-free surface plasmon resonance was used to test the specific targeting of the functional gold shells with rabbit antigen. The results demonstrate that a new type of functional gold coated colloidosome with non-permeability, ultrasound sensitivity and immunoassay targeting could be applied to many medical applications.

Potential importance of ultra-deep penetration for operation of IFE power plants

Possibility of damage of inertial fusion energy power plants caused by ultra-deep penetration of fragments of targets with hohlraums and/or cones for fast ignition has been investigated in this study. Some issues related to the formation of high-velocity solid and liquid fragments of targets and their deceleration and heating in the reaction chamber filled with low-density Xe gas have been studied. It was found that with a Xe gas mass density of approximately 6μg/cm3 and reaction chamber internal radius of 6m, a liquid spherical gold fragment with a radius of 5–7μm could reach the chamber wall with a velocity >1km/s.

Electronic interactions in gold(I) complexes of 2,5-diferrocenyl-1-phenyl-1H-phosphole

The synthesis of gold(I) complexes of 2,5-diferrocenyl-1-phenyl-1H-phosphole (1) is presented. Chloro(2,5-diferrocenyl-1-phenyl-1H-phosphole)gold (3) has successfully been prepared by the reaction of 1 with AuCl(SMe2) (2). Treatment of 2 with arylethyne (aryl = ferrocenyl, phenyl) using catalytical amounts of [CuI] and 1 equiv. of 1 gave arylethynyl-(2,5-diferrocenyl-1-phenyl-1H-phosphole)gold 4a and 4b (aryl: a = ferrocenyl; b = phenyl). Compound [μ-(1,4-phenylenedi-2,1-ethynediyl)]bis(2,5-diferrocenyl-1-phenyl-1H-phosphole)digold (5) could be synthesized by a similar procedure using 0.5 equiv. of 1,4-diethynylbenzene. The electrochemical properties of 3, 4a,b and 5 were investigated by cyclic and square wave voltammetry. In 3, 4a and 4b each ferrocenyl unit shows one reversible redox event with redox separations of the ferrocenyl moieties in 2,5 position of approximately 260 mV. In 5 two redox events for the four ferrocenyl groups were observed. Spectroelectrochemical measurements of 3, 4a and 4b reveal IVCT absorptions with intensities of 1100–1300 L mol−1 cm−1 and a full-width-at-half-height of ≈3650 cm−1. In 5 two mixed-valent units are present per molecule and therefore, the intensity of the IVCT band is increased to 2700 L mol−1 cm−1. Compounds 3, 4a,b and 5 can be classified as moderately coupled class II systems according to Robin and Day. The complexation of the gold(I) fragment by the phosphorus atom leads to a decreased metal–metal interaction when compared to 1.