Gold 1994

Housecroft, Catherine E.

doi:10.1016/s0010-8545(97)00028-3

Cited by 7 publications

(4 citation statements)

References 77 publications

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“…The Au(1)−S(1) bond is slightly longer than the Au(2)−S(2) bond, which can be attributed to a higher extent of strain in the square environment of Au(1) compared with the linear coordination of Au(2). The Au−Au distance of 2.978(2) Å is comparable with values found in other bi- or multinuclear gold compounds , and is consistent with a bonding “aurophilic” interaction. This is remarkable because Au(1) doubtlessly represents a gold(III) site and both gold atoms are elongated from their ideal coordination environments toward each other.…”

Section: Resultssupporting

confidence: 82%

Gold Complexes with Potentially Tri- and Tetradentate Phosphinothiolate Ligands

Ortner

Zheng

et al. 2000

Inorg. Chem.

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Reactions of [Au(PPh3)Cl], (Bu4N)[AuCl4] and the organometallic gold complex [Au(damp-C1,N)Cl2] (damp- = 2-(N,N-dimethylaminomethyl)phenyl) with the potentially tri- and tetradentate proligands PhP(C6H3-SH-2-R-3)2 (H2L1a, R = SiMe3; H2L1b, R = H) and P(C6H4-SH-2)3 (H3L2) result in the formation of mono- or dinuclear gold complexes depending on the precursor used. Monomeric complexes of the type [AuL1Cl] are formed upon the reaction with [Au(damp-C1,N)Cl2], but small amounts of dinuclear [AuL1]2 complexes with gold in two different oxidation states, +1 and +3, have been isolated as side-products. The dinuclear compounds are obtained in better yields from [AuCl4]-. A dinuclear complex having two Au(III) centers can be isolated from the reaction of [Au(PPh3)Cl] with H3L2, whereas from the reaction with H2L1b the mononuclear [Au(Ph3P)HL1b] is obtained, which contains a three-coordinate gold atom. Comparatively short gold-gold distances have been found in the dinuclear complexes (2.978(2) and 3.434(1) A). They are indicative of weak gold-gold interactions, which is unusual for gold(III).

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Section: Resultssupporting

confidence: 82%

Gold Complexes with Potentially Tri- and Tetradentate Phosphinothiolate Ligands

Ortner

Zheng

et al. 2000

Inorg. Chem.

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“…However, in other experiments native gold was not oxidized and the formation of gold colloids and sols from gold(I/III) complexes was promoted (Fetzer, 1934(Fetzer, , 1946Ong and Swanson, 1969;Fisher et al, 1974;Gray et al, 1998). The interaction of gold and organic matter involves mostly electron donor elements, such as N, O or S, rather than C (Housecroft, 1993(Housecroft, , 1997a. Vlassopoulos et al (1990b) showed that gold binds preferentially to organic S under reducing conditions, whereas under oxidizing conditions it binds mostly to organic N and C. Organo-gold complexes can be present in aqueous solution as gold(I) cyanide complexes (Housecroft, 1993(Housecroft, , 1997a.…”

Section: The Geochemical Characteristics Of Goldmentioning

confidence: 99%

“…The interaction of gold and organic matter involves mostly electron donor elements, such as N, O or S, rather than C (Housecroft, 1993(Housecroft, , 1997a. Vlassopoulos et al (1990b) showed that gold binds preferentially to organic S under reducing conditions, whereas under oxidizing conditions it binds mostly to organic N and C. Organo-gold complexes can be present in aqueous solution as gold(I) cyanide complexes (Housecroft, 1993(Housecroft, , 1997a. Gold(I) forms a strong complex with cyanide [Au(CN) 2 À ] that is stable over a wide range of Eh-pH conditions (Boyle, 1979;Gray, 1998).…”

Section: The Geochemical Characteristics Of Goldmentioning

confidence: 99%

The geomicrobiology of gold

et al. 2007

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Microorganisms capable of actively solubilizing and precipitating gold appear to play a larger role in the biogeochemical cycling of gold than previously believed. Recent research suggests that bacteria and archaea are involved in every step of the biogeochemical cycle of gold, from the formation of primary mineralization in hydrothermal and deep subsurface systems to its solubilization, dispersion and re-concentration as secondary gold under surface conditions. Enzymatically catalysed precipitation of gold has been observed in thermophilic and hyperthermophilic bacteria and archaea (for example, Thermotoga maritime, Pyrobaculum islandicum), and their activity led to the formation of gold-and silver-bearing sinters in New Zealand's hot spring systems. Sulphatereducing bacteria (SRB), for example, Desulfovibrio sp., may be involved in the formation of goldbearing sulphide minerals in deep subsurface environments; over geological timescales this may contribute to the formation of economic deposits. Iron-and sulphur-oxidizing bacteria (for example, Acidothiobacillus ferrooxidans, A. thiooxidans) are known to breakdown gold-hosting sulphide minerals in zones of primary mineralization, and release associated gold in the process. These and other bacteria (for example, actinobacteria) produce thiosulphate, which is known to oxidize gold and form stable, transportable complexes. Other microbial processes, for example, excretion of amino acids and cyanide, may control gold solubilization in auriferous top-and rhizosphere soils. A number of bacteria and archaea are capable of actively catalysing the precipitation of toxic gold(I/ III) complexes. Reductive precipitation of these complexes may improve survival rates of bacterial populations that are capable of (1) detoxifying the immediate cell environment by detecting, excreting and reducing gold complexes, possibly using P-type ATPase efflux pumps as well as membrane vesicles (for example, Salmonella enterica, Cupriavidus (Ralstonia) metallidurans, Plectonema boryanum); (2) gaining metabolic energy by utilizing gold-complexing ligands (for example, thiosulphate by A. ferrooxidans) or (3) using gold as metal centre in enzymes (Micrococcus luteus). C. metallidurans containing biofilms were detected on gold grains from two Australian sites, indicating that gold bioaccumulation may lead to gold biomineralization by forming secondary 'bacterioform' gold. Formation of secondary octahedral gold crystals from gold(III) chloride solution, was promoted by a cyanobacterium (P. boryanum) via an amorphous gold(I) sulphide intermediate. 'Bacterioform' gold and secondary gold crystals are common in quartz pebble conglomerates (QPC), where they are often associated with bituminous organic matter possibly derived from cyanobacteria. This may suggest that cyanobacteria have played a role in the formation of the Witwatersrand QPC, the world's largest gold deposit.

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“…In recent years, gold has been shown to display rich cluster and coordination chemistry 1–10, and gold nanoparticles 11, 12 and nanoelectrodes 13 (containing hundreds of gold atoms) are becoming very important in molecular electronics applications in which molecules are chemically bound to them. Computational approaches to the structural and electronic properties of these systems are typically based either on Hückel (tight binding) theory or on density‐functional calculations.…”

Section: Introductionmentioning

confidence: 99%

Estimating functions for evaluating treatment effects in cluster‐randomized longitudinal studies in the presence of drop‐out and non‐compliance

Cook

Chen

2010

Can J Statistics

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We describe methods for analyzing longitudinal binary data from cluster‐randomized trials in which responses are incompletely observed and subjects may not be fully compliant with the prescribed treatment regimen. The method is based on a marginal regression model for the response where parameter estimates are obtained from generalized estimating equations. Estimating equations are also employed to estimate parameters of the missing data process which are used to compute inverse probability weights. A model is specified for the compliance process which facilitates estimating the expectation of the contributions to the estimating function for the response parameters among individuals without compliance data, which occurs when the control treatment involves no intervention. The approach is robust in the sense that semi‐parametric models are used for the response and the missing data processes and robust variance estimates are advocated. The proposed method is shown to perform well in simulation studies, and data from a randomized trial of patients with depression are analyzed for illustration. The Canadian Journal of Statistics 38: 232–255; 2010 © 2010 Statistical Society of Canada

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Gold 1994

Cited by 7 publications

References 77 publications

Gold Complexes with Potentially Tri- and Tetradentate Phosphinothiolate Ligands

Gold Complexes with Potentially Tri- and Tetradentate Phosphinothiolate Ligands

The geomicrobiology of gold

Estimating functions for evaluating treatment effects in cluster‐randomized longitudinal studies in the presence of drop‐out and non‐compliance

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