Mitchell R. M. Bruce

Stripping Analyses of Mercury Using Gold Electrodes: Irreversible Adsorption of Mercury

The electrochemical deposition and stripping of mercury on gold surfaces was investigated to assess whether gold electrodes would return to mercury-free states after stripping analyses. X-ray photoelectron spectroscopy studies demonstrate the presence of mercury on gold foil electrodes that have undergone controlled-potential deposition procedures in Hg(2+) solutions (10 nM-0.1 mM) followed by stripping and cleaning in mercury-free electrolyte. Results show that mercury is not completely removed electrochemically from the gold electrodes, even when the oxidizing potential is +2.5 V vs Ag/AgCl. Bulk electrolyses deposition and stripping procedures coupled with cold vapor atomic absorption spectroscopic analyses of solutions after deposition and stripping are also reported. Results suggest that the nature of the gold electrode is fundamentally altered by irreversible adsorption of mercury; that is, mercury is adsorbed during deposition and some of the mercury is retained even after stripping and cleaning. The implications and strategies for using stripping analysis and gold electrodes for the measurement of mercury under the experimental conditions employed in this study are discussed.

Novel metallamacrocyclic gold(I) thiolate cluster complex: structure and luminescence of [Au9(μ-dppm)4(μ-p-tc)6](PF6)3

The structure of a novel metallamacrocyclic phosphine gold(I) thiolate cluster, [Au9(mu-dppm)4(mu-p-tc)6](PF6)3, where dppm = bis(diphenylphosphine)methane and p-tc = p-thiocresolate, is reported and shows AuAu attractions of approximately 3.0 A and gold(I) atoms linked to thiolate and phosphine ligands in distorted trigonal and nearly linear geometries.

Perspectives in Inorganic and Bioinorganic Gold Sulfur Chemistry

A detailed picture of the chemical and electrochemical oxidation of a series of mononuclear and dinuclear phosphine Au(I) thiolates is presented. The medicinal implications of the results are illustrated by redox studies on the anti-rheumatoid drug, auranofin, [(2,3,4,6-tetra-acetyl-1-thio- g -D-glucopyranosato)(triethylphosphine) gold(I)]. The phosphine Au(I) thiolate complexes undergo a broad irreversible oxidation in the range, +0.6 to +1.1 V, and a second irreversible oxidation at more positive potentials from +1.2 to +1.6 V (vs. SCE). Chemical oxidation of the Au(I) thiolate complexes with (Cp 2 Fe)(PF 6 ) results in disulfide and tetragold(I) clusters with bridging thiolate ligands, except for the unusual nine Au(I) atoms cluster obtained by oxidation of [(dppm)Au 2 (p-SC 6 H 4 CH 3 ) 2 ]. Chemical oxidation of auranofin with (Cp 2 Fe)(PF 6 ) results in disulfide and a cationic Au(I) cluster with bridging thiolate ligands, [(Et 3 PAu) 2 ( w -SATg)] 2 2+ , typical of mononuclear gold(I) thiolates. The Au(I) clusters react with disulfide to undergo thiolate/disulfide exchange. Comparative rates show clusters react much faster than the mononuclear complex, Ph 3 PAu(SC 6 H 4 CH 3 ). A mechanism for the oxidation of auranofin and related complexes, and possible biological implications are discussed.

Cyclic Voltammetry of Auranofin

The oxidative behavior of Auranofin, 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranosato- S(triethylphosphine)gold(I), was investigated by using cyclic voltammetry (CV) in 0.1 M Bu4NPF6/CH2Cl2 and 0.1 M Bu4NPF4/CH2Cl2 solutions using Pt working and auxiliary electrodes and a Ag/AgCI reference. CV studies at scan rates from 50-2,000 mV/s and Auranofin concentrations between 1 and 4 mM, show two irreversible oxidation processes occurring at +1.1 V and +1.6 V vs. Ag/AgCl. Ph3 (p-thiocresolate) was also investigated as a reference for comparison of the oxidation processes in Auranofin to that of other phosphine gold thiolate complexes previously reported. The electrochemical response appears to be sensitive to adsorption at the electrode as well as to the nature of the supporting electrolyte solution. Repeated cycling shows a build up of products at the electrode.

Preferential adsorption of mercury(II) ions in water: chelation of mercury, cadmium, and lead ions to silica derivatized with meso-2,3-dimercaptosuccinic acid

Meso-dimercaptosuccinic acid (DMSA) covalently attached to silica gel via amide bond linkages (DMSA-[silica]) was evaluated as a chelate for Hg(II), Cd(II), and Pb(II). All three metal ions are separately chelated by DMSA-[silica]; 95% of Hg(II) is chelated, 81% of Cd(II), and 74% of Pb(II). When equal molar concentrations of the three metals are allowed to react simultaneously with DMSA-[silica] for 2 h, mercury is preferentially bound (99%) compared to cadmium (13%) or lead (0.4%). Attachment of DMSA to silica surfaces via amide bond formation, which increases the thiol to carboxylic acid ratio over free DMSA, is suggested as a factor in enhancing the preference of DMSA-[silica] for mercury.

Thermotropic liquid crystals based on ferrocenylbiphenyl and ferrocenylterphenyl

4′‐Ferrocenyl‐1,1′‐biphenyl‐4‐yl 4‐alkoxybenzoates Fc–(C6H4)2–OC(O)–C6H4–O–C n H2n+1 (n = 8, 10, 12) (3a–c), representing a new class of ferrocene‐containing thermotropic mesogens with nematogenic properties, were prepared. Two approaches were used for the construction of these mesogens: (i) reaction of 4′‐ferrocenyl‐1,1′‐biphenyl‐4‐ol with 4‐alkoxybenzoylchlorides, and (ii) crosscoupling of tris(4‐ferrocenylphenyl)boroxine with the corresponding halobenzenes. Crosscoupling was also applied for the synthesis of terphenyl‐containing mesogens Fc–(C6H4)3–OC(O)–C6H4–O–C n H2n+1 (n = 10, 12) (6a,b) and (RC5H4)Fe‐[C5H4–(C6H4)3–OC(O)–C6H4–O–C10H21] (11a, R = Et; 11b, R = n−Bu). The latter compounds also form nematic phases. Mesogens 6a,b form mesophases with wider temperature ranges than their biphenyl‐containing counterparts 3b,c. The most pronounced mesomorphism was displayed by compounds 11a and 11b, which have mesophases in the ranges 141–253°C and 120–238°C, respectively. The purity of compounds was established by 1H NMR spectra and elemental analysis. Mesophases were identified by polarizing optical microscopy and differential scanning calorimetry.

Redox chemistry of gold(i) phosphine thiolates: sulfur-based oxidation.

The redox chemistry of mononuclear and dinuclear gold(I) phosphine arylthiolate complexes was recently investigated by using electrochemical, chemical, and photochemical techniques. We now report the redox chemistry of dinuclear gold(I) phosphine complexes containing aliphatic dithiolate ligands. These molecules differ from previously studied gold(I) phosphine thiolate complexes in that they are cyclic and contain aliphatic thiolates. Cyclic voltammetry experiments of Au2 (LL)(pdt) [pdt = propanedithiol; LL = 1,2-bis(diphenylphosphino)-ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), 1,4-bis(diphenylphosphino)butane (dppb), 1,5-bis(diphenylphosphino)pentane (dpppn)] in 0.1 M TBAH/CH3CN or CH2Cl2 solutions at 50 to 500 mV/sec using glassy carbon or platinum electrodes, show two irreversible anodic processes at ca. +0.6 and +1.1 V (vs. SCE). Bulk electrolyses at +0.9 V and +1.4 V result in n values of 0.95 and 3.7, respectively. Chemical oxidation of Au2(dppp)(pdt) using one equivalent of Br2 (2 oxidizing equivalents) yields 1,2-dithiolane and Au2(dppp)Br2. The reactivity seen upon mild oxidation ≤ +1.0 V is consistent with formal oxidation of a thiolate ligand, followed by a fast chemical reaction that results in cleavage of a second gold-sulfur bond. Oxidation at higher potentials (≥ +1.3 V) is consistent with oxidation of gold(I) to gold(III). Structural and electrochemical differences between gold(I) aromatic and aliphatic thiolate oxidation processes are discussed.

Reactions of Organic Disulfides and Gold(I) Complexes

Gold-thiolate/disulfide exchange reactions of (p-SC6H4Cl)2 with Ph3PAu(SC6H4CH3), dppm(AuSC6H4CH3)2, and dppe(AuSC6H4CH3) 2 were investigated. The rate of reactivity of the gold-thiolate complexes with (p-SC6H4Cl)2 is: dppm(AuSC6H4CH3)2>> dppe(AuSC6H4CH3)2>Ph2PAu (SC6H4CH3). This order correlates with conductivity measurements and two ionic mechanisms have been evaluated. 1H NMR experiments demonstrate that in the reaction of dppm(AuSC6H4CH3)2 with (p-SC6H4Cl)2, the mixed disulfide, ClC6H4SSC6H4CH3, forms first, followed by the formation of (p-SC6H4CH3)2. The rate law is first order in (pp-SC6H 4Cl)2 and partial order in dppm(AuSC6H4CH3)2. Results from electrochemical and chemical reactivity studies suggest that free thiolate is not involved in the gold-thiolate/disulfide exchange reaction. A more likely source of ions is the dissociation of a proton from the methylene backbone of the dppm ligand which has been shown to exchange with D2O. The implications of this are discussed in terms of a possible mechanism for the gold-thiolate/disulfide exchange reaction.

Heavy metal detection combining stripping electrochemistry and piezoelectric sensor technology

Mercury and other toxic, heavy metals must be detected at part per billion levels in drinking water and environmental monitoring applications. No portable technology is presently capable of providing the required sensitivity, simplicity or reliability. Piezoelectric sensor technology and electrochemical technology have both offered sound approaches to the detection of these pollutants. Both exhibit limitations which prevent their widespread acceptance in water quality assurance and in environmental remediation.

Identification of dimethyl sulfide in dimethyl sulfoxide and implications for metal-thiolate disulfide exchange reactions

The concentration of dimethyl sulfide (DMS) in seven different samples of research grade dimethyl sulfoxide (DMSO), including one deuterated sample, was measured by GC-MS. The average concentration of DMS is 0.48 ± 0.14 mM (range: 0.44–0.55 mM) and ca. 0.35 mM in DMSO-d6. The presence of DMS in DMSO is potentially problematic for compounds that are susceptible to reaction with DMS and are present at μM–mM concentrations. Standard methods of purification of DMSO were unsuccessful in removing all traces of DMS.