Miniaturization of Anthracene-Containing Nonapeptides for Selective Precipitation/Recovery of Metallic Gold from Aqueous Solutions Containing Gold and Platinum Ions

The separation and recovery of noble metals is increasingly of interest, in particular the recovery of gold nanocrystals, which have applications in medicine and industry. Typically, metal recovery is performed using liquid–liquid extraction or electrowinning. However, it is necessary to develop noble metal recovery systems providing high selectivity in conjunction with a one-pot setup, ready product recovery, and the use of dilute aqueous solutions. In prior work, our group developed a selective gold recovery process using peptides. This previous research showed that RU065, a nonapeptide containing an anthracene moiety (at a concentration of 2.0 × 10−4 M), is capable of selective reduction of HAuCl4 to recover gold from a solution of HAuCl4 and H2PtCl6, each at 5.0 × 10−5 M. However, peptide molecules are generally costly to synthesize, and therefore it is important to determine the minimum required structural features to design non-peptide anthracene derivatives that could reduce operational costs. In this study, we used RU065 together with 23 of its fragment peptides and investigated the selective precipitation/recovery of metallic gold. RU0654–8, a fragment peptide comprising five amino acid residues (having two lysine, one L-isoleusine, and one L-alanine residue (representing six amide groups) along with an L-2-anthrylalanine residue) provided an Au/Pt atomic ratio of approximately 8, which was comparable to that for the full-length original RU065. The structural features identified in this study are expected to contribute to the design of non-peptide anthracene derivatives for low-cost, one-pot selective gold recovery.

Entrapment of glucose oxidase within gold converts it to a general monosaccharide-oxidase

We report that entrapping glucose oxidase (GOx) within metallic gold, expands its activity to become an oxidase for monosaccharides that do not have a natural enzyme with that activity—fructose and xylose—and that this entrapment also removes the enantioselectivity, rendering this enzyme capable of oxidizing the “wrong” l-enantiomer of glucose. These observations suggest that in this biomaterial adsorptive interactions of the outer regions of the protein with the gold cage, pull apart and widen the tunnel between the two monomeric units of GOx, to a degree that its stereoselectivity is compromised; then, the active sites which are more versatile than currently attributed to, are free and capable of acting on the foreign sugars. To test this proposition, we entrapped in gold l-asparaginase, which is also a dimeric enzyme (a dimer of tight dimers), and found, again, that this metallic biomaterial widens the activity of that enzyme, to include the D-amino acid counter enantiomer as well. Detailed kinetic analyses for all substrates are provided for the gold bio-composites, including determination of the difference between the activation energies towards two opposite enantiomers.

Surface structure of Amur region high grade native gold

The purpose of the research is to study the surface structure of high grade gold. The subject of research is gold ore fields in the Amur region. The object of the study is samples of native high grade gold grains from these fields. The study uses the methods of thermodynamics and X-ray electron microscopy. The study results in revealing a multilayer structure of the surface of high grade minerals of the Amur region native gold with the following levels: a boundary layer with zero oxidation degree Au0 in the form of yellow metallic gold; an oxide layer with the oxidation degree Au+1 in the form of purple Au2O; an oxide layer with the oxidation degree Au+3 in the form of a yellow-brown Au2O3; a hydrated oxide layer with the oxidation degree Au+3 in the form of a red-yellow-brown Au(OH)3. The methods of electron microscopy have allowed to identify external surface structures – dense oxide layers of the form of Au2O3 and loose hydrated layers of the form of Au(OH)3, whereas the inner layers of metallic and monovalent gold are not visible. Important thermodynamic characteristics of the presented levels are the values of standard oxidation-reduction potentials (E°), which determine their physicochemical properties: for metallic gold E° = +1.68 V; for the oxide layer with the oxidation degree Au+1 in the form of Au2O – E° = +0.32 V; for the oxide layer with the oxidation degree Au+3 in the form of Au2O3 – E° = +1.36 V; for the hydrated oxide layer with the oxidation degree Au+3 in the form of Au(OH)3 – E° = +0.7 V. The results of the conducted studies indicate that the surface structure has several layers that lower the oxidation-reduction potential, which explains the generation and formation of migratory forms of gold in humid hypergene conditions of natural environment.

Enzymes in a golden cage

We describe a general method for the entrapment of enzymes within bulk metallic gold.

Catalytic activity of nanosized Au/CeO2 catalyst towards H2O2 decomposition and the role of cationic/metallic ratio in its activity

The catalytic decomposition of H2O2 on differently pre-treated Au/CeO2 catalyst was studied by kinetic measurements at 20-50 °C. The prepared catalyst was subjected to pre-treatment by heating either in oxidative (10% O2/N2) or inert (pure N2)atmosphere at 400 °C. The different oxidation states of gold were determined by X-ray photoelectron spectroscopy measurements. The Au/CeO2 catalyst exhibited an excellent catalytic activity towards H2O2 decomposition. The catalytic activity of oxygen pre-treated sample was about twice higher than that measured for nitrogen pre-treated sample. This finding ran parallel to the amount of Aun+ as determined by XPS, indicating the role played by Aun+ species as the most active catalyst’s constituent. However, one cannot overlook the role of metallic gold in catalyzing the H2O2, decomposition showing small activity compared to that of cationic gold. The average crystallites size of metallic gold particles was found to be 7±0.5 nm independent of the pre-treatment conditions. The apparent activation energy of the catalyzed reaction was found to be 46.5 and 47.8 kJ/mol for oxygen and nitrogen pre-treatment, respectively.