ABSTRACT: Whole-genome expression microarray experiments were conducted to assess the response of C. metallidurans CH34 to aqueous Au(III)-chloride and identify possible biochemical pathways for Au detoxification. Four microarray experiments were conducted to assess gold response at low, medium and high Au(III)-chloride concentrations (i.e., 10, 50 and 100 µM Au(III)-chloride) and different induction times (10 and 30 minutes with 50 µM Au(III)-chloride). Based on these arrays, the differentially expressed genes upon gold-exposure can be identified. Overall design: The four microarray experiments (10, 50 and 100 µM Au(III)-chloride at 10 minutes and 50 µM Au(III)-chloride at 30 minutes) were all performed in biological triplicate and containing three (in-slide) technical repeats. For all conditions, the metal-induced sample (Cy5) was compared with the non-induced sample (Cy5) to identify those genes that were differentially expressed upon gold exposure.
Project description:Whole-genome expression microarray experiments were conducted to assess the response of C. metallidurans CH34 to aqueous Au(III)-chloride and identify possible biochemical pathways for Au detoxification. Four microarray experiments were conducted to assess gold response at low, medium and high Au(III)-chloride concentrations (i.e., 10, 50 and 100 µM Au(III)-chloride) and different induction times (10 and 30 minutes with 50 µM Au(III)-chloride). Based on these arrays, the differentially expressed genes upon gold-exposure can be identified. The four microarray experiments (10, 50 and 100 µM Au(III)-chloride at 10 minutes and 50 µM Au(III)-chloride at 30 minutes) were all performed in biological triplicate and containing three (in-slide) technical repeats. For all conditions, the metal-induced sample (Cy5) was compared with the non-induced sample (Cy5) to identify those genes that were differentially expressed upon gold exposure.
Project description:Cupriavidus metallidurans is associated with gold grains and may be involved in their formation. Gold(III) complexes influence the transcriptome of C. metallidurans (F. Reith et al., Proc. Natl. Acad. Sci. U. S. A. 106:17757-17762, 2009), leading to the upregulation of genes involved in the detoxification of reactive oxygen species and metal ions. In a systematic study, the involvement of these systems in gold transformation was investigated. Treatment of C. metallidurans cells with Au(I) complexes, which occur in this organism's natural environment, led to the upregulation of genes similar to those observed for treatment with Au(III) complexes. The two indigenous plasmids of C. metallidurans, which harbor several transition metal resistance determinants, were not involved in resistance to Au(I/III) complexes nor in their transformation to metallic nanoparticles. Upregulation of a cupA-lacZ fusion by the MerR-type regulator CupR with increasing Au(III) concentrations indicated the presence of gold ions in the cytoplasm. A hypothesis stating that the Gig system detoxifies gold complexes by the uptake and reduction of Au(III) to Au(I) or Au(0) reminiscent to detoxification of Hg(II) was disproven. ZupT and other secondary uptake systems for transition metal cations influenced Au(III) resistance but not the upregulation of the cupA-lacZ fusion. The two copper-exporting P-type ATPases CupA and CopF were also not essential for gold resistance. The copABCD determinant on chromosome 2, which encodes periplasmic proteins involved in copper resistance, was required for full gold resistance in C. metallidurans. In conclusion, biomineralization of gold particles via the reduction of mobile Au(I/III) complexes in C. metallidurans appears to primarily occur in the periplasmic space via copper-handling systems.
Project description:Iron core-gold shell (Fe@Au) nanoparticles are prominent for their magnetic and optical properties, which are especially beneficial for biomedical uses. Some experiments were carried out to produce Fe@Au particles with a one-step synthesis method, Ultrasonic Spray Pyrolysis (USP), which is able to produce the particles in a continuous process. The Fe@Au particles were produced with USP from a precursor solution with dissolved Iron (III) chloride and Gold (III) chloride, with Fe/Au concentration ratios ranging from 0.1 to 4. The resulting products are larger Fe oxide particles (mostly maghemite Fe2O3), with mean sizes of about 260-390 nm, decorated with Au nanoparticles (AuNPs) with mean sizes of around 24-67 nm. The Fe oxide core particles are mostly spherical in all of the experiments, while the AuNPs become increasingly irregular and more heavily agglomerated with lower Fe/Au concentration ratios in the precursor solution. The resulting particle morphology from these experiments is caused by surface chemistry and particle to solvent interactions during particle formation inside the USP system.
Project description:Carbon-supported gold catalysts have the potential to replace the toxic mercuric chloride-based system applied industrially for acetylene hydrochlorination, a key technology for the manufacture of polyvinyl chloride. However, the design of an optimal catalyst is essentially hindered by the difficulties in assessing the nature of the active site. Herein, we present a platform of carbon supported gold nanostructures at a fixed metal loading, ranging from single atoms of tunable oxidation state and coordination to metallic nanoparticles, by varying the structure of functionalised carbons and use of thermal activation. While on activated carbon particle aggregation occurs progressively above 473 K, on nitrogen-doped carbon gold single atoms exhibit outstanding stability up to temperatures of 1073 K and under reaction conditions. By combining steady-state experiments, density functional theory, and transient mechanistic studies, we assess the relation between the metal speciation, electronic properties, and catalytic activity. The results indicate that the activity of gold-based catalysts correlates with the population of Au(i)Cl single atoms and the reaction follows a Langmuir-Hinshelwood mechanism. Strong interaction with HCl and thermodynamically favoured acetylene activation were identified as the key features of the Au(i)Cl sites that endow their superior catalytic performance in comparison to N-stabilised Au(iii) counterparts and gold nanoparticles. Finally, we show that the carrier (activated carbon versus nitrogen-doped carbon) does not affect the catalytic response, but determines the deactivation mechanism (gold particle aggregation and pore blockage, respectively), which opens up different options for the development of stable, high-performance hydrochlorination catalysts.
Project description:This paper illustrates the effect of substrate topography on morphology evolution in nanoporous gold (np-Au) thin films. One micron-high silicon ridges with widths varying between 150 nm to 50 µm were fabricated and coated with 500 nm-thick np-Au films obtained by dealloying sputtered gold-silver alloy films. Analysis of scanning electron micrographs of the np-Au films following dealloying and thermal annealing revealed two distinct regimes where the ratio of film thickness to ridge width determines the morphological evolution of np-Au films.
Project description:Geochemical exploration for gold (Au) is becoming increasingly important to the mining industry. Current processes for Au analyses require sampling materials to be taken from often remote localities. Samples are then transported to a laboratory equipped with suitable analytical facilities, such as Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) or Instrumental Neutron Activation Analysis (INAA). Determining the concentration of Au in samples may take several weeks, leading to long delays in exploration campaigns. Hence, a method for the on-site analysis of Au, such as a biosensor, will greatly benefit the exploration industry. The golTSB genes from Salmonella enterica serovar typhimurium are selectively induced by Au(I/III)-complexes. In the present study, the golTSB operon with a reporter gene, lacZ, was introduced into Escherichia coli. The induction of golTSB::lacZ with Au(I/III)-complexes was tested using a colorimetric ?-galactosidase and an electrochemical assay. Measurements of the ?-galactosidase activity for concentrations of both Au(I)- and Au(III)-complexes ranging from 0.1 to 5 µM (equivalent to 20 to 1000 ng g(-1) or parts-per-billion (ppb)) were accurately quantified. When testing the ability of the biosensor to detect Au(I/III)-complexes(aq) in the presence of other metal ions (Ag(I), Cu(II), Fe(III), Ni(II), Co(II), Zn, As(III), Pb(II), Sb(III) or Bi(III)), cross-reactivity was observed, i.e. the amount of Au measured was either under- or over-estimated. To assess if the biosensor would work with natural samples, soils with different physiochemical properties were spiked with Au-complexes. Subsequently, a selective extraction using 1 M thiosulfate was applied to extract the Au. The results showed that Au could be measured in these extracts with the same accuracy as ICP-MS (P<0.05). This demonstrates that by combining selective extraction with the biosensor system the concentration of Au can be accurately measured, down to a quantification limit of 20 ppb (0.1 µM) and a detection limit of 2 ppb (0.01 µM).
Project description:Gold(iii) complexes are garnering increasing interest for opto-electronic, therapeutic and catalytic applications. But so far, very little is known about the factors controlling their reactivity and the very influence of the ancillary ligand. This article reports the first comprehensive study on this topic. The reactivity of a cationic (N,C) gold(iii) complex, namely 1A, towards ethylene has been thoroughly studied and compared with that of the related (P,C) complex 1C. A cationic gold(iii) complex 5A resulting from double insertion of ethylene was selectively obtained. Complex 5A was found to be remarkably stable. It was trapped with chloride and fully characterized. In marked contrast to that observed with 1C, no ?-H elimination or linear-to-branched rearrangement of the alkyl chain occurred with 1A. The energy profile for the reactions of 1A with ethylene has been comprehensively investigated computationally, and the influence of the ancillary ligand has been precisely delineated. Because nitrogen is a weaker donor than carbon (and phosphorus), the (N,C) ligand is very electronically dissymmetric, much more than the (P,C) ligand. This makes the two reactive sites at gold quite different, which noticeably influences the competition between migratory insertion and ?-H elimination, and actually changes the outcome of the olefin insertion at gold. This study provides valuable insight into the influence of ancillary ligands on gold(iii) reactivity, something critical to further develop Au(iii) and Au(i)/Au(iii) catalysis.
Project description:The synthesis of new families of stable or at least spectroscopically observable gold(III) hydride complexes is reported, including anionic cis-hydrido chloride, hydrido aryl, and cis-dihydride complexes. Reactions between (C^C)AuCl(PR3) and LiHBEt3 afford the first examples of gold(III) phosphino hydrides (C^C)AuH(PR3) (R = Me, Ph, p-tolyl; C^C = 4,4'-di- tert-butylbiphenyl-2,2'-diyl). The X-ray structure of (C^C)AuH(PMe3) was determined. LiHBEt3 reacts with (C^C)AuCl(py) to give [(C^C)Au(H)Cl]-, whereas (C^C)AuH(PR3) undergoes phosphine displacement, generating the dihydride [(C^C)AuH2]-. Monohydrido complexes hydroaurate dimethylacetylene dicarboxylate to give Z-vinyls. (C^N^C)Au pincer complexes give the first examples of gold(III) bridging hydrides. Stability, reactivity and bonding characteristics of Au(III)-H complexes crucially depend on the interplay between cis and trans-influence. Remarkably, these new gold(III) hydrides extend the range of observed NMR hydride shifts from ? -8.5 to +7 ppm. Relativistic DFT calculations show that the origin of this wide chemical shift variability as a function of the ligands depends on the different ordering and energy gap between "shielding" Au(d?)-based orbitals and "deshielding" ?(Au-H)-type MOs, which are mixed to some extent upon inclusion of spin-orbit (SO) coupling. The resulting 1H hydride shifts correlate linearly with the DFT optimized Au-H distances and Au-H bond covalency. The effect of cis ligands follows a nearly inverse ordering to that of trans ligands. This study appears to be the first systematic delineation of cis ligand influence on M-H NMR shifts and provides the experimental evidence for the dramatic change of the 1H hydride shifts, including the sign change, upon mutual cis and trans ligand alternation.
Project description:Aquaporins (AQPs) are membrane channels that conduct water and small solutes such as glycerol and are involved in many physiological functions. Aquaporin-based modulator drugs are predicted to be of broad potential utility in the treatment of several diseases. Until today few AQP inhibitors have been described as suitable candidates for clinical development. Here we report on the potent inhibition of AQP3 channels by gold(III) complexes screened on human red blood cells (hRBC) and AQP3-transfected PC12 cells by a stopped-flow method. Among the various metal compounds tested, Auphen is the most active on AQP3 (IC(50)?=?0.8±0.08 µM in hRBC). Interestingly, the compound poorly affects the water permeability of AQP1. The mechanism of gold inhibition is related to the ability of Au(III) to interact with sulphydryls groups of proteins such as the thiolates of cysteine residues. Additional DFT and modeling studies on possible gold compound/AQP adducts provide a tentative description of the system at a molecular level. The mapping of the periplasmic surface of an homology model of human AQP3 evidenced the thiol group of Cys40 as a likely candidate for binding to gold(III) complexes. Moreover, the investigation of non-covalent binding of Au complexes by docking approaches revealed their preferential binding to AQP3 with respect to AQP1. The high selectivity and low concentration dependent inhibitory effect of Auphen (in the nanomolar range) together with its high water solubility makes the compound a suitable drug lead for future in vivo studies. These results may present novel metal-based scaffolds for AQP drug development.
Project description:Response of Cupriavidus metallidurans CH34 to cisplatin, Pt(IV)chloride and Au-NP In this study 7 different treatments were performed (first 2 as 3 replicates) to acquire expression profiles of the total genome of Cupriavidus metallidurans