Preconcentration of 198Au in a green alga, Rhizoclonium</p> </p>

Summary The bioaccumulation of ¹⁹⁸Au radionuclide, by Rhizoclonium riparium a member of Chlorophyceae has been studied. It has been observed that accumulation of gold on Rhizoclonium is almost pH independent and slightly higher at basic pH. Accumulation of gold was studied with ¹⁹⁸Au radiotracer, 0.1, 1 and 5 ppm concentrations of gold. It has been concluded from the biochemical analysis that the gold accumulation is due to adsorption in the cellulose and not in protein, fat and carbohydrate. Accumulated gold was recovered when washed with conc. HNO₃.</p> </p>     

Radiochemical solvent extraction of Au(III) using thionalide in ethyl methyl ketone/iso buthyl methyl ketone

A radiochemical method for the determination of gold using¹⁹⁸Au, has been developed. It is based on the synergistic extraction of Au(III) with thionalide (TA) in ethyl methyl ketone (EMK) or isobuthyl methyl ketone (IBMK) at pH 5.0.Effect of various parameters such as pH, nature of solvent and interferences due to other radionuclides have been studied. The method can be used up to 25 ng of Au.     

Ultratrace determination of platinum in biological materials via neutron activation and radiochemical separation

A neutron activation analysis scheme based upon a radiochemical separation of the activation products has been developed. The method utilizes the inherent sensitivity of the activation reaction¹⁹⁸Pt(n, γ)¹⁹⁹Pt and counting of the daughter nuclide¹⁹⁹Au. This nuclide is radiochemically separated from interfering activities by homogeneous precipitation as elemental gold. The remaining interference of the secondary reaction¹⁹⁷Au(n,γ)¹⁹⁸ Au(n,γ)¹⁹⁹Au from gold in the samples is quantitatively assessed and corrected. During this process accurate gold concentrations in the samples are obtained at ultratrace levels. The analysis scheme is applied to gold and platinum determinations in biological Standard Reference Materials and human liver specimens. Gold and platinum are determined at concentrations of 5·10^?11 g/g, and at higher levels.     

The express simultaneous neutron activation determination of gold,palladium and platinum

The method of express neutron-activation (NA) determination of Au, Pd and Pt has been developed. The method is based on the quantitative isolation of¹⁹⁸Au+¹⁹⁹Au and¹⁰⁹Pd activities by extraction with organic sulfides. The radiation of¹⁰⁹Pd is measured on a thin NaI(Tl) crystal and that of¹⁹⁸Au and¹⁹⁹Au on a Ge(Li) detector. The calculations of interferences from gold have been performed for various neutron fluxes and various cadmium ratios. Some interferences introduced by other competitive nuclear reactions into the determination of Pt by its daughter isotope¹⁹⁹Au are discussed.     

Synthesis of radioactive gold nanoparticle in surfactant medium

The present study describes the synthesis of radioactive gold nanoparticle in surfactant medium. Proton irradiated stable ¹⁹⁷Au and radioactive ¹⁹⁸Au were simultaneously used for production of radioactive gold nanoparticle. Face centered cubic gold nanoparticles with size of 4–50 nm were found in proton irradiated gold foil. However, the size of nanoparticle varies with pH using both stable and radioactive gold.     

Production of cationic 198Au3+ and nonionic 198Au0 for radionuclide therapy applications via the natAu(n,γ)198Au reaction

¹⁹⁸Au (??_max?=?0.96?MeV (98.6?%), ??_max?=?0.412?MeV (95.5?%) and T _1/2 ?=?2.7?days) is a radionuclide with very appealing characteristics. ¹⁹⁸Au has been widely used to treat the uterus, bladder, cervix, prostate, melanoma, breast, skin and other cancers. In the present study, cationic ¹⁹⁸Au⁺³ and nonionic ¹⁹⁸Au⁰ are prepared following thermal neutron irradiation of commercially available natural gold compounds in Tehran Research Reactor via the ^natAu(n,??)¹⁹⁸Au reaction. The prospects in the production of pure ¹⁹⁸Au⁰ and ¹⁹⁸Au⁺³ for radionuclide therapy are discussed and effect of reduction on the activity of radioactive gold is evaluated. Au⁰ particles were synthesized via NaBH₄ reduction of aqueous solutions of hydrogen tetrachloroaurate trihydrate. Then two quartz tubes were charged with cationic ¹⁹⁸Au³⁺ and nonionic ¹⁹⁸Au⁰. After irradiation by thermal neutrons, the samples were analyzed for a period of 1?month by liquid scintillation counter and high purity germanium detector. As a result, ^natAu³⁺ reduction process had no significant effect on the activity of the ¹⁹⁸Au sample. In conclusions, natural gold thermal neutron activation cross section is reasonably high for medical application.     

Influence of the Preparation Procedure on the Catalytic Activity of Gold Supported on Diamond Nanoparticles for Phenol Peroxidation

The catalytic activity of diamond‐supported gold nanoparticle (Au/D) samples prepared by the deposition/precipitation method have been correlated as a function of the pH and the reduction treatment. It was found that the most active material is the one prepared at pH 5 followed by subsequent thermal treatment at 300 °C under hydrogen. TEM images show that Au/D prepared under optimal conditions contain very small gold nanoparticles with sizes below 2 nm that are proposed to be responsible for the catalytic activity. Tests of productivity using large phenol (50 g L ^?1) and H₂O₂ excesses (100 g L ^?1) and reuse gives a minimum TON of 458,759 moles of phenol degraded per gold atom. Analysis of the organic compounds extracted from the deactivated solid catalyst indicates that the poisons are mostly hydroxylated dicarboxylic acids arising from the degradative oxidation of the phenyl ring. By determining the efficiency for phenol degradation and the amount of O₂ evolved two different reactions of H₂O₂ decomposition (the Fenton reaction at acidic pH values and spurious O₂ evolution at basic pH values) are proposed for Au/D catalysis. The activation energy of the two processes is very similar (ranging between 30 and 35 kJ mol^?1). By using dimethylsulfoxide as a radical scavenger and N‐tert‐butyl‐α‐phenylnitrone as a spin trap under aerated conditions, the EPR spectrum of the expected PBN? OCH₃ adduct was detected, supporting the generation of HO^., characteristic of Fenton chemistry in the process. Phenol degradation, on the other hand, exhibits the same activation energy as H₂O₂ decomposition at pH 4 (due to the barrierless attack of HO^. to phenol), but increases the activation energy gradually up to about 90 kJ mol^?1 at pH 7 and then undergoes a subsequent reduction as the pH increases reaching another minimum at pH 8.5 (49 kJ mol^?1).     

The extraction of low-concentrations of gold(I) with 198Au as a radiotracer

The solvent extraction of gold from alkaline cyanide solution was studied by using ¹⁹⁸Au as a radiotracer. The influence of several variables on the gold extraction, including the concentration of gold, the molar ratio of extractants to gold(I), the volume percentage of cosolvent and the pH value of the aqueous phase, was investigated. The results indicated that the radioactive tracer technique is a quick, accurate, and convenient tool to investigate the extraction behavior of an element existing in low concentrations. The experimental results indicated that the studied amines, tetradecyldimethylbenzylammonium chloride, N1923 and tri-n-octylamine, could be used as extractants for the recovery of gold from aqueous alkaline cyanide solutions.     

Selective separation of gold from iron ore samples using ion exchange resin

Gold in iron ore samples is separated from iron (major matrix cation), antimony and vanadium using anion exchange resin in (0.2 M) HBr, potassium peroxodisulfate and acetone:water:nitric acid media. The exchangeable anion Cl⁻ of the ion exchanger Dowex 1X 4 is replaced by Br⁻ using (6 M) HBr solution. Certified reference material DGP-M1, spiked ferric magnetic oxide, gold radioactive tracer ¹⁹⁸Au and gold standard solutions are used to study the adsorption efficiency and the yield recovery of tetrabromoaurate AuBr₄⁻ from the resin. Ten eluents have been tried to elute gold from the column, and it has been found that a 10 ml potassium peroxodisulfate and 240 ml acetone:water:nitric acid [125:5:5] solution fulfills the objective. The set up of the separation procedure allows quantitative adsorption of gold by the resin, while the major matrix cation (Fe) and others (Cd, Ag, Cu, V, Sb, Ti) have been passed through the column with the feeding solution (0.2 M) HBr. The resin selectivity coefficient (K) of separating Au from Fe has been found to be K_Fe^Au≈6.4×10¹¹. The eluted Au is treated with K₂S₂O₈ and H₂O₂ for spectrophotometric determination as rhodamine-B complex at 555.6 nm. The linearity, detection limit, precision, and accuracy of the determination method have been found to be up to 2.0 μg g⁻¹, 0.018 μg g⁻¹, 0.009 μg g⁻¹ and 3%, respectively.     

Gold(III) amine complexes in aqueous alkali solutions

The gold(III) 1,3-diaminopropane complex [Au(1,3-pn)(1,3-pn-H)]Cl₂ has been synthesized. Its dissociation constant has been determined: Au(1,3-pn)₂³⁺ = Au(1,3-pn-H)²⁺ + H⁺, logK _a1 = −7.03 ± 0.05 (I = 0.1 mol/L NaClO₄). Considerable spectral changes are observed for strong alkali solutions (pH 11–14) containing the monoamido forms of the gold(III) ethylenediamine, 1,3-diaminopropane, and diethylenetriamine complexes (Au(en)(en-H)²⁺, Au(1,3-pn)(1,3-pn-H)²⁺, Au(dien-H)OH⁺). These changes are attributed to the formation of the diamido species Au(en-H)₂⁺, Au(1,3-pn-H)₂⁺, and Au(dien-2H)OH⁰. The dissociation constants of the monoamido complexes have been determined: Au(en)(en-H)²⁺ (logK _a2 = −10.9 ± 0.1 at I = 0.001–0.01 mol/L NaCl); Au(1,3-pn)(1,3-pn-H)²⁺ (logK _a2 = −11.3 ± 0.1 at I = 0.1 mol/L NaCl); Au(dien-H)OH⁺ (logK _a2 = −12.4 ± 0.1 at I = 0.1 mol/L NaCl).     

Zinc Oxide Modified Au Electrode as Sensor for an Efficient Detection of Hydrazine

ZnO nanoparticles (ZnO NPs) prepared by microwave heating technique are used to modify a gold electrode (ZnO/Au) for the hydrazine detection study. The synthesized product is well characterized by various techniques. Detailed electrochemical investigation of the oxidation of hydrazine on the ZnO/Au electrode in 0.02 M phosphate buffer solution (PBS) of pH 7.4 was carried out. A very low detection limit of 66 nM (S/N=4) and a wide linearity in current for a concentration range from 66.0×10^?3 to 415 µM was achieved by amperometry. The electrode was found to be stable for over a month when preserved in PBS.     

Synthesis of Au/Al2O3 Nanocatalyst and its Application in the Reduction of p‐Nitrophenol

Gold (Au) nanoparticles supported on alumina (Al₂O₃) were prepared at several pH levels via the deposition‐precipitation (DP) method. The effects of pH at below and above the isoelectric point (IEP) of Al₂O₃ as well as the pH adjustment before and after the addition of the support into the gold chloride solution were investigated. The results revealed the formation of cationic, clusters and metallic Au on alumina. The catalytic activity of these species was tested in the reduction of p‐nitrophenol (p‐NP) using hydrazine as a reductant. The catalytic reaction was monitored spectrophotometerically and the highest rate constant (k‐) achieved based on pseudo first order kinetic model was 12.7 × 10^‐3 s^‐1. Structural and elemental characterizations of the supported gold nanoparticles were carried out using X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy‐dispersive X‐rays (EDX), atomic absorption spectrometry (AAS), and ultraviolet‐visible spectroscopy (UV‐Vis).     

Determination and distribution of gold in Greek bauxites of the Parnassos-Ghiona area by gamma-spectroscopy after ion exchange separation

For the determination of gold in Greek bauxites from the Parnassos-Ghiona area, an analytical technique was used based on the selective adsorption of gold on SRAFION NMRR chelating anion exchanger resin, after leaching the bauxites with aqua regia in a teflon-autoclave at 120 °C, and the determination of the retained gold directly on the resin by instrumental neutron activation analysis (INAA), using the 411.8 keV line of the ¹⁹⁸Au isotope. The procedure allowed to determine Au in concentrations down to ng/g. The obtained data were used to examine the distribution of Au in the profiles of a group of different bauxites from the upper or the called third bauxitic horizon of the Parnassos-Ghiona area in Greece. Especially in the basement of some bauxite deposits unexpected high concentrations of Au up to 2 mg/g have been found. Furthermore, the correlation of Au with other trace elements, found in the bauxitic samples, was investigated.     

Interactions between an amphipathic di‐histidine peptide and a metal affinity chromatographic resin derived from a bis(tacn)butane chelating ligand

The interactive behavior of an amphipathic peptide with the Cu²⁺, Ni²⁺, and Zn²⁺ complexes of 1,4‐bis(triazacyclonon‐1‐yl)butane), bis(tacn)^but, immobilized onto Sepharose CL‐4B, has been investigated. The effects of incubation time, as well as the incubation buffer pH and ionic strength, have been examined. The binding data have been interrogated using Langmuir, Langmuir‐Freundlich, bi‐Langmuir, and Temkin isothermal models and Scatchard plots. These results confirm that this amphipathic peptide binds with relatively high capacities to the immobilized Cu²⁺‐ and Ni²⁺‐1,4‐bis(triazacyclonon‐1‐yl)butane)‐Sepharose CL‐4B sorbents via at least two discrete sites. However, the corresponding immobilized Zn²⁺‐sorbent had low binding capacity. Moreover, the magnitude of the binding capacities of these sorbents was dependent on the pH and ionic strength of the incubation buffer. These results are relevant to the isolation of E. coli expressed recombinant proteins that incorporate this and related amphipathic peptide tags, containing two or more histidine residues, located at the N‐ or C‐terminus of the recombinant protein, and the co‐purification of low abundance host cell proteins of diverse structure, by immobilized metal ion affinity chromatographic methods.     

Al Electrode Modified by Au Atoms as a Novel Electrode for Electrocatalytic Oxidation of Thiosulfate

An aluminum electrode modified with gold atoms was introduced as a novel electrode. Gold atoms were deposited both chemically and electrochemically onto the aluminum electrode to make an aluminum/gold (Al/Au) modified electrode (ME). The experimental results showed that the Al/Au modified electrode prepared by chemical deposition, exhibits much more current than the electrochemical deposition method. The electrochemical behavior of the Al/Au modified electrode was studied by cyclic voltammometry. This modified electrode showed two pairs of peaks, a₁c₁ and a₂c₂, with surface‐confined characteristics in a 0.5 M phosphate buffer. The dependence of E_pa of the second peak (a₂c₂) on pH shows a Nernestian behavior with a slope of 55 mV per unit pH. The effect of different supporting electrolytes, solution's pH and different scan rates on electrochemical behavior of Al/Au modified electrode was studied. Au deposited electrochemically on a Pt electrode (Pt/Au) was also used as another modified electrode. A comparative study of electrochemical behavior of bare Al, Pt/Au and Al/Au modified electrodes showed that both Pt/Au and Al/Au electrodes have the ability of electrocatalytic oxidation of S₂O₃^2?, but the electrocatalytic oxidation on the latter was better than the former. The kinetics of the catalytic reaction was investigated by using cyclic voltammetry and chronoamperometry techniques. The average value of the rate constant for the catalytic reaction and the diffusion coefficient were evaluated by means of chronoamperometry technique.     

Gamma-ray spectrometric analysis of neutron irradiated golden sands

A nondestructive method has been used for the qualitative and quantitative determination of elements such as Au, Cu, Ag in minerals and especially in golden sand. The induced radioactivity has been analyzed with a high resolution gamma spectrometer containing a Ge(Li) semiconductor detector type and a multichannel analyzer. The samples have been collected from the alluvia of the Mure? and Some?ul Mic river basins, proving the presence of gold and copper in small concentrations. These results have been correlated to previous data showing the existence of some gold mines in these zones. This nondestructive, rapid and highly sensitive method can be used for industrial processes [1] control and prospections. The use of a NaI(Tl) scintillation crystal for routine measurements of the ¹⁹⁸Au radioisotope type and the interferences by copper, silver and indium in the irradiated samples are discussed.     

Immunosensors Based on Layer‐by‐Layer Self‐Assembled Au Colloidal Electrode for the Electrochemical Detection of Antigen

Colloidal Au particles have been deposited on the gold electrode through layer‐by‐layer self‐assembly using cysteamine as cross‐linkers. Self‐assembly of colloidal Au on the gold electrode resulted in an easier attachment of antibody, larger electrode surface and ideal electrode behavior. The redox reactions of [Fe(CN)₆]^4?/[Fe(CN)₆]^3? on the gold surface were blocked due to antibody immobilization, which were investigated by cyclic voltammetry and impedance spectroscopy. The interaction of antigen with grafted antibody recognition layers was carried out by soaking the modified electrode into a phosphate buffer at pH 7.0 with various concentrations of antigen at 37 °C for 30 min. Further, an amplification strategy to use biotin conjugated antibody was introduced for improving the sensitivity of impedance measurements. Thus, the sensor based on this immobilization method exhibits a large linear dynamic range, from 5–400 μg/L for detection of Human IgG. The detection limit is about 0.5 μg/L.     

Electrochemical and ESR studies of au-protein from Micrococcus luteus

Au-protein from Micrococcus luteus, with and without Au inactive center, and chloroauric acid (HAu ^IIICl₄·4H₂O) with the addition of rutin, catechol, and riboflavin have been studied by means of electrochemistry and ESR. The redox potentials for Au-protein, as well as for the complexes Au-rutin and Au-catechol, have been measured, and ESR spectra of complexes Au-rutin and Au-catechol have been recorded. It has been shown that the Au atom binds to Au-protein via OH-groups of rutin. Flavin does not participatein gold binding. Au-protein is characterized by two peaks of cyclic voltammogram, −0.37 and −0.54 V. Au-protein with these potentials is able to function in the electron-transport chain of membranes between flavoproteins and quinones.     

Kinetics and mechanism of the reduction of gold(III) by glycine in acetate buffer

The kinetics of reduction of tetrachloroaurate(III) by glycine has been spectrophotometrically studied in NaOAc–AcOH buffer in the pH range 3.73–4.77. The reaction is first order with respect to both Au(III) and glycine. Both H⁺ and Cl⁻ ions have inhibiting effects on the reaction rate. The rate decreases with a decrease in the dielectric constant of the medium. AuCl₄⁻ and AuCl₃(OH)⁻ are presumed to be the predominant oxidizing species under the conditions of the experiment. The reaction of gold(III) and zwitterionic species of glycine proceeds with the intermediate formation of gold(I) and iminic cation and the latter subsequently hydrolyses in a fast step to produce formaldehyde and ammonium ion. Formaldehyde was identified as the only organic product by ¹H NMR spectroscopy.     

Cross sections and isomeric ratios in197Au(α, 2pn)198(m,g)Au reactions

Excitation functions for the production of^198mAu,¹⁹⁸Au,^198(m+g)Au, by (, 2pn) reactions on gold and isomeric ratios for¹⁹⁸Au were determined experimentally. The method of activation of metallic foils was employed. The irradiations were performed in the isochronous cyclotron at Karlsruhe (Germany) with -particles at 90 MeV. Gamma-spectrometry by means of an intrinsic Ge detector was used to determine the nuclides produced. In addition, a comparison between the cross sections obtained and a calculation using the hybrid model of pre-equilibrium reactions, in combination with the statistical model development by ERNST is presented.