Metals in biology: Electronic structure,properties and charge transfer for copper complexes of glyoxal and dithiene

Summary In an attempt to study the role of metals in biologyab initio SCF calculations have been performed on a model complex simulating the binding between metals and biological materials. There is a certain distinction between the copper complexes compared to the other transition metals and in many cases the copper complexes are more similar to the Li and Be complexes than to other transition metal complexes. One special feature of the copper complexes is their strong ability for an easy transfer between the Cu(I) and Cu(II) states, allowing for a very flexible charge transfer with small energies required for the redox processes. These processes have been described in terms of orbital energies and Mulliken populations.Dedicated to Professor Inga Fischer-Hjalmars on the occasion of her 75th birthday     

Redox-driven transport of copper ions in an emulsion liquid membrane system

A new redox-driven type of emulsion liquid membrane separation is described. Milligram amounts of copper(II) in 0.2 M hydrochloric acid were reduced to copper(I) in the presence of ascorbic acid (1 M≡1 mol l⁻¹). The copper solution was emulsified with a (1+4) mixture of toluene and n-heptane using Span-80 (sorbitan monooleate) as an emusifier. The resulting water-in-oil emulsion was dispersed in 0.2 M hydrochloric acid containing hydrogen peroxide and neocuproine (2,9-dimethyl-1,10-phenanthroline) by stirring for 10 min. The copper in the internal aqueous phase was selectively transported to the external one, leaving other heavy metals (e.g., Mn, Co, Ni, Cd and Pb) in the internal aqueous phase. After collecting the dispersed emulsion globules, they were demulsified by heating and the metals in the segregated aqueous phase were determined by graphite-furnace atomic absorption spectrometry (GFAAS). The selective transport of copper offered the multielement separation of trace heavy metals from a copper matrix, allowing the GFAAS determination of impurities at the 0.01% level in copper metal.     

Size fractionation of metals in wine using ultrafiltration

Ultrafiltration has been used to examine the size fractionation of lead, copper, iron, aluminium, calcium, potassium and sodium in white and red wines. Fractionation patterns demonstrated that the behaviour of lead is significantly diferent to the other metals considered. In red wine, there was a sudden decrease for lead between 100 000 and 30 000 nominal molecular weight cut off (NMWCO) and in white wine, a gradual decrease in the lead concentration was observed from 100 000 NMWCO. Iron was the only other metal which showed, for red wine, a size distribution pattern with a reduction in the iron concentration between 30 and 50% from 100 000 to 1000 NMWCO. Potential binding agents for lead and iron are discussed. The absence of any fractionation pattern for the other metals examined has been interpreted in terms of the metals existing as aquated cations (potassium and sodium), metal tartrate complexes (aluminium, copper and calcium) and either tartrate or phosphate for iron in white wine. The possibility of ultrafiltration disturbing kinetically facile processes, particularly for copper and calcium, is identified.     

Redox active metal-induced oxidative stress in biological systems

A number of studies performed on biological systems have shown that redox-active metals such as iron and copper as well as other transition metals can undergo redox cycling reactions and produce reactive free radicals termed also reactive oxygen species (ROS) or reactive nitrogen species (RNS). The most representative examples of ROS and RNS are the superoxide anion radical and nitric oxide, respectively, both playing a dual role in biological systems. At low/moderate concentrations of ROS and RNS, they can be involved in many physiological roles such as defense against infectious agents, involvement in a number of cellular signaling pathways and other important biological processes. On the other hand, at high concentrations, ROS and RNS can be important mediators of damage to biomolecules involving DNA, membrane lipids, and proteins. One of the most damaging ROS occurring in biological systems is the hydroxyl radical formed via the decomposition of hydrogen peroxide catalyzed by traces of iron, copper and other metals (the Fenton reaction). The hydroxyl radical is known to react with the DNA molecule, forming 8-OH-Guanine adduct, which is a good biomarker of oxidative stress of an organism and a potential biomarker of carcinogenesis. This review discusses the role of iron and copper in uncontrolled formation of ROS leading to various human diseases such as cancer, cardiovascular disease, and neurological disorders (Alzheimer’s disease and Parkinson’s disease). A discussion is devoted to the various protective antioxidant networks against the deleterious action of free radicals. Metal-chelation therapy, which is a modern pharmacotherapy used to chelate redox-active metals and remove toxic metals from living systems to avoid metal poisoning, is also discussed.     

Chromogenic and fluorogenic sensing of Cu based on coumarin

A new highly selective, reversible, chromogenic, and fluorogenic chemosensor (4) based on thiazole-coumarin moieties for quantification of copper ions in aqueous-DMSO was designed and synthesized. The mechanism of fluorescence was based on ICT, which was modified by the introduction of an electron-donating diethylamino group making it chromogenic and increasing the binding affinity. The selectivity toward copper ions was not affected by the presence of representative alkali metals, alkali earth metals, or other transition metals.     

6-Methyl-2-pyridinecarboxamide oxime, a reagent for copper

6-Methyl-2-pyridinecarboxamide oxime (R) forms a yellow compound with copper(I), the molar absorptivity being 7.2 x 10(3) at the wavelength of maximum absorption, 405 nm. The copper compound, CuR(2), forms completely over the pH range 4.5-7 and is easily extracted into isoamyl alcohol. R is highly specific for copper, the methyl group neighbouring the ring nitrogen atom preventing reaction with iron and other metals.     

Ratiometric fluorescent sensor proteins with subnanomolar affinity for Zn(II) based on copper chaperone domains

The ability to image the concentration of transition metals in living cells in real time is important for further understanding of transition metal homeostasis and its involvement in diseases. The goal of this study was to develop a genetically encoded FRET-based sensor for copper(I) based on the copper-induced dimerization of two copper binding domains involved in human copper homeostasis, Atox1 and the fourth domain of ATP7B (WD4). A sensor has been constructed by linking these copper binding domains to donor and acceptor fluorescent protein domains. Energy transfer is observed in the presence of Cu(I), but the Cu(I)-bridged complex is easily disrupted by low molecular weight thiols such as DTT and glutathione. To our surprise, energy transfer is also observed in the presence of very low concentrations of Zn(II) (10(-)(10) M), even in the presence of DTT. Zn(II) is able to form a stable complex by binding to the cysteines present in the conserved MXCXXC motif of the two copper binding domains. Co(II), Cd(II), and Pb(II) also induce an increase in FRET, but other, physiologically relevant metals are not able to mediate an interaction. The Zn(II) binding properties have been tuned by mutation of the copper-binding motif to the zinc-binding consensus sequence MDCXXC found in the zinc transporter ZntA. The present system allows the molecular mechanism of copper and zinc homeostasis to be studied under carefully controlled conditions in solution. It also provides an attractive platform for the further development of genetically encoded FRET-based sensors for Zn(II) and other transition metal ions.     

Copper-promoted enantioselective Reformatsky-type reaction with ketones

Controlled living polymerization of a broad range of monomers is a radical process known as ATRP (atom transfer radical polymerization) and is mediated by a variety of metals. A complex of copper has been found to be the most efficient catalyst, with a copper(I)/copper(II) catalytic cycle. The radical, enantioselective catalytic Reformatsky reaction mediated by Me₂Zn can be efficiently promoted by copper(I) complexes avoiding the use of other promoters such as air and oxidant, giving more reproducible and affordable conditions. The CuCN-mediated enantioselective addition of ethyliodoacetate to functionalized ketones is described in this paper.     

Influence of organic matter removal on competitive and noncompetitive adsorption of copper and zinc in acid soils

We studied competitive and noncompetitive adsorption of copper and zinc in four acid soils, and compared the behavior of the two metals in untreated samples and samples treated with hydrogen peroxide to remove organic matter in the soil. Copper exhibited stronger competitive adsorption than zinc in the untreated samples. However, removal of organic matter reduced copper adsorption to a greater extent than zinc adsorption, the two metals exhibiting a more similar adsorption pattern than the untreated samples. The presence of copper dramatically reduced zinc competitive adsorption in untreated samples; on the other hand, that of zinc only resulted in slightly reduced competitive adsorption of copper. The hydrogen peroxide treatment decreased competitive adsorption in both metals; however, copper continued to be more efficient than zinc in competing for binding sites on adsorbing surfaces. Desorption of Cu occurred much less readily than desorption of Zn and hysteresis is apparent especially for Cu.     

N-Heterocyclic Carbenes Reduce and Functionalize Copper Oxide Surfaces in One Pot

Benzimidazolium hydrogen carbonate salts have been shown to act as N-heterocyclic carbene precursors, which can remove oxide from copper oxide surfaces and functionalize the resulting metallic surfaces in a single pot. Both the surfaces and the etching products were fully characterized by spectroscopic methods. Analysis of surfaces before and after NHC treatment by X-ray photoelectron spectroscopy demonstrates the complete removal of copper(II) oxide. By using ¹³C-labelling, we determined that the products of this transformation include a cyclic urea, a ring-opened formamide and a bis-carbene copper(I) complex. These results illustrate the potential of NHCs to functionalize a much broader class of metals, including those prone to oxidation, greatly facilitating the preparation of NHC-based films on metals other than gold.     

Distribution of Copper,Nickel, Cobalt and Iron between Products of Smelting of Copper Concentrate Obtained by Flotation of Converter Matte

An experimental study of the equilibrium between the bottom phase (sulfide melt or copper) and slag in neutral and oxidizing atmospheres yielded dependences of the content of dissolved copper, nickel, and cobalt in the slag on that of sulfur in the sulfide melt and also the dependence of the content of dissolved copper and nickel on that of nickel in the metallic melt. The distribution coefficients of the metals between copper and slag were determined and compared with the results of other investigations.     

Unusual properties of tetraphenylporphyrin copper complex

5,10,15,20-Tetraphenylporphyrin reacted with copper powder in boiling xylene on exposure to air (but not in an inert atmosphere) to give bright red copper complex which differed in properties from the initial porphyrin and its complexes with other metals. The copper complex was stable to oxidation with Cu²⁺ ions (during chromatography), and it readily underwent demetalation by the action of LiAlH₄ in tetrahydrofuran.     

Biosorption of Copper and Cadmium in Packed Bed Columns with Live Immobilized Fungal Biomass of <Emphasis Type="Italic">Phanerochaete chrysosporium</Emphasis>

Biosorption of copper (II) and cadmium (II) by live Phanerochaete chrysosporium immobilized by growing onto polyurethane foam material in individual packed bed columns over two successive cycles of sorption–desorption were investigated in this study. Initial pH and concentrations of the metals in their respective solutions were set optimum to each of those: 4.6 and 35 mg·l⁻¹ in case of copper and 5.3 and 11 mg·l⁻¹ for cadmium. The breakthrough curves obtained for the two metals during sorption in both the cycles exhibited a constant pattern at various bed depths in the columns. The maximum yield of the columns in removing these metals were found to be, respectively, 57% and 43% for copper and cadmium indicating that copper biosorption by the immobilized fungus in its column was better than for cadmium. Recovery values of the sorbed copper and cadmium metals from the respective loaded columns by using 0.1 N HCl as eluant was observed to be quite high at more than 65% and 75%, respectively, at the end of desorption in both the cycles. Breakthrough models of bed-depth service time, Adams–Bohart, Wolborska, and Clark were fitted to the experimental data on sorption of copper and cadmium in the columns, and only the Clark model could fit the sorption performance of the columns well over the entire range of ratios of concentrations of effluent to influent, i.e., C/C ₀ for both copper and cadmium biosorption. The kinetic coefficients of mass transfer and other suitable parameters in the system were determined by applying the experimental data at C/C ₀ ratios lower than 0.5 to the other three models.     

Radiation-Chemical Reduction of Cd<Superscript>2+</Superscript> Ions in Aqueous Solution

Formation of the metal is observed under irradiation of methanol-containing aqueous solutions of cadmium salts with accelerated electrons. The process of precipitation of the metal and its properties was examined. The radiation-chemical yield is (1.7 ± 0.2) × 10^–2 g kGy. The efficiency of the radiation-induced reduction of a number of other metals in aqueous media: copper, lead, and thallium, was substantiated. The method may be promising for obtaining deposits of pure and amorphous metals from aqueous solutions of their salts and for purification of aqueous effluents containing these toxic metals.     

Extraction of Copper from Sulfate Solutions with Hydrazides of Versatic Higher Acids in the Presence of Accompanying Metals

Fundamental aspects of the extractive recovery of copper(II) in the presence of accompanying metals from sulfuric acid solutions with hydrazides of Versatic (GVIK 509) α-branched tertiary carboxylic acids in kerosene or its mixture with modifying agents: 2-ethylhexanol or alkylphenol. The selective extraction of copper(II) in the presence of nickel(II), cobalt(II), zinc(II), and iron(III) with hydrazides in kerosene is possible at pH 0.1–0.6. The separation coefficients of element pairs were calculated. It was found that the modifiers have no effect on the quantitative extraction of copper(II), but strongly change the extraction pattern of the metals under study. It was shown that the re-extraction of copper(II) with sulfuric acid solutions is in principle possible.     

Application of radioisotopes in column chromatography on substituted celluloses. part V. : The separation of arsenic from copper and other metals

The Chromatographic behaviour of arsenic and copper was studied with radio-isotopes on natural cellulose, cellobiose and seven substituted celluloses in ethyl ether. Arsenic was not adsorbed; copper was retained and eluted quantitatively. For preparative purposes, one gram of arsenic trioxide was purified from nanograms of copper on natural and diethylaminoethyl celluloses. The possibility of purifying arsenic from several other metals, and gold and mercury from copper is indicated.     

On anodic dissolution of silver coatings deposited on base metals

Potentiodynamic polarization and potentiostatic electrolysis techniques were employed to study the anodic oxidation of silver and a number of other metals (copper, iron, nickel, and tin) in sulfite media, both individually and in Ag-M binary electrodes. The conditions in which silver is dissolved with a nearly 100% current efficiency were found.     

Determination of Some Transition Metals by Atomic Absorption Spectroscopy after Extraction with Pyridine-2-aldehyde-2-quinolylhydrazone

The extraction of pyridine-2-aldehyde-2-quinolylhydrazone chelates of cadmium, cobalt, copper, nickel, and zinc into isoamyl alcohol (IAOL) and methylisobutyl ketone (MIBK) has been investigated as a basis for the determination of these metals. Below pH 6 the extraction is enhanced by the addition of perchlorate, suggesting that charged complexes are being extracted by ion-pair formation. Sensitivities (1% absorption) are reported for IAOL and MIBK solutions of the metals sprayed into an air-acetylene flame. A procedure for the determination of the above metals by atomic absorption spectroscopy after extraction is given. The procedure is applied to the analysis of tap water for cadmium, copper, and zinc.     

Amperometric complex-formation titrations of traces of copper

Copper has been determined in the submicrogram range by means of a eomplexometric titration with triethylenetetramine (TRIEN), the end-point being detected by following the anodic wave of the chelating agent at a rotating mercury electrode. The influence of the presence of other metals has been investigated both from the theoretical and the experimental point of view. Because of its higher selectivity TRIEN is preferred to other reagents of the EDTA group. The results show that copper can be determined in the presence of large amounts of most other metals.