Cu2+ activities

Trace element speciation in soil solution is affected by total metal concentrations in soils. Free Cu2+ activity increases with total Cu content in soils from Quebec and New York (Sauve et al., 1997). Total free Cu activity in soils could be predicted from total Cu content and soil pH ... 

The type of the oxidation product on galena is independent of the chemical environment during preparation. Rao152) measured the adsorption heat of K amyl xanthate (KAX) on unactivated and Cu2+-activated pyrrhotite (FeS) and compared his results with heats of the reaction between KAX and Fe2+ or Cu2+ salts. With the unactivated mineral, the interaction involves a chemical reaction of xanthate with Fe2+ salts present at the interface (i.e. not bound to the crystal surface). The adsorption enthalpy is identical with the formation of Fe2+ amyl xanthate FeS04 + 2 KAX —> FeX2 + K2S04, and -AH = 97.45 kJ/mol Fe2+). As revealed from the enthalpy values and the analysis of anions released into the solution, the interaction of xanthate with Cu2+-activated pyrrhotite consists of xanthate adsorption by exchange for sulfate ions (formed by an oxidation of sulfides) at isolated patches (active spots), and by further multilayer formation of xanthate. The adsorption heat of KAX on pyrrhotite at the initial pH 4.5 was - AH (FeS unactivated) = 93.55 kJ/mol Fe2+ and - AH (FeS activated) = 70.03 kJ/mol Cu2+. 

Figure 2. Effect of polymer concentration on Cu(II)-induced changes in rotation of single-stranded poly(A) and poly(C) at pH 6 in 0.1M NaClOji and 0.01 M caco-dylate. 6r is fractional change in rotation = [a] — [aj/ [a](j — [a]0 where [a] = rotation at given Cu2+ activity, [aj = rotation in the absence of Cu2+, and [ad] = rotation of fully disordered structure. A poly(A), B poly(C). Concentrations (A) 5 X I0"4M 5 X 10 5M (Oj5 X...

The effect of polymer concentration on the disordering provides an additional clue to its mechanism. Figure 2 shows that the higher the polymer concentration, the lower the Cu2+ activity required for the tran-... 

An iron penknife blade may be copper plated in CuS04 solution, by displacement of Cu2+ ions with Fe2+ ions. Assuming that enough penknife blades are available, how-low can the Cu2+ activity be taken at 25°C if the initial activity is one ... 

The activity recovery in dry NO-gas after removal of water vapor is shown in Fi e 4. The Mg(52)/Cu(66)-ZSM-5 ually restored some of its activity to ca 45% of its original value. However, no recovery was found for the Cu(72)-ZSM-5 catalyst. For the over- exchanged Cu(141)-ZSM-5, 30% of its original dry gas activity was recovered after removal of water vapor. The cocation (Mg +, Ba " ", y3+ and Ce " ") modified Cu-ZSM-5 catalysts recovered a larger fraction of their original catalytic activity than Cu(141)-ZSM-5. Among these cations, Ce + cations displayed the most pronounced positive effect on the wet gas-Cu2+ activity as well as on dry gas-activity recovery (more than 66%). The Ce/Cu-ZSM-5 catalyst was, thus, chosen for additional testing. 

It is also of interest to note that Wranglen considers that the decrease in the corrosion rate of steel in the atmosphere and the pitting rate in acid and neutral solution brought about by small alloying additions of copper is due to the formation of CU2S, which reduces the activity of the HS and Scions to a very low value so that they do not catalyse anodic dissolution, and a similar mechanism was put forward by Fyfe etal. to explain the corrosion resistance of copper-containing steels when exposed to industrial atmospheres. 

Murakami et al. reported that a cyclophane 27 having two imidazole groups is activated by Cu2+ ions in the hydrolysis of p-nitrophenyl dodecanoate 25,26), although the activation seemed to be small. 

Luciferase-catalyzed luminescence of luciferin. Odontosyllis luciferin emits light in the presence of Mg2+, molecular oxygen and luciferase. The relationship between the luminescence intensity and the pH of the medium shows a broad optimum (Fig. 7.2.8). The luminescence reaction requires a divalent alkaline earth ion, of which Mg2+ is most effective (optimum concentration 30 mM). Monovalent cations such as Na+, K+, and NH have little effect, and many heavy metal ions, such as Hg2+, Cu2+, Co2+ and Zn2+, are generally inhibitory. The activity of crude preparations of luciferase progressively decreases by repeated dialysis and also by concentrating the solutions under reduced pressure. However, the decreased luciferase activity can be completely restored to the original activity by the addition of 1 mM HCN (added as KCN). The relationship between the concentration of HCN and the luciferase activity is shown in Fig. 7.2.9. Low concentrations of h and K3Fe(CN)6 also enhance luminescence, but their effects are only transient. 

Consequently, the antioxidant activity of GA in biological systems is still an unresolved issue, and therefore it requires a more direct knowledge of the antioxidant capacity of GA that can be obtained by in vitro experiments against different types of oxidant species. The total antioxidant activity of a compound or substance is associated with several processes that include the scavenging of free radical species (eg. HO, ROO ), ability to quench reactive excited states (triplet excited states and/ or oxygen singlet molecular 1O2), and/or sequester of metal ions (Fe2+, Cu2+) to avoid the formation of HO by Fenton type reactions. In the following sections, we will discuss the in vitro antioxidant capacity of GA for some of these processes. 

Catalytically active species derived from 4. Spectrophotometric titration of the backbone ligand of the sngar discriminating dinuclear copper(ll) complex N, N-bis[(2-pyridylmethyl)-l,3-diaminopropan-2-olato] (//-acetato) dicoppeftll) perchlorate (Cu2(bpdpo), 4) in the presence of two equivalents of copper(ll) ions with sodium hydroxide indicates successive replacement of the bridging acetate anion bound in the sohd state with two hydroxyl ions and two water molecnles in alkaline aqneons solntion (eqs. 2 and 3) (20-22). Two species, [Cu2(L h)(OH)] (4a) and [Cn2(L h)(OH)2] (4b), are thus observed in a pH-dependent equihbrium (20). 

Activators are those reagents which act in a manner converse to the action of depressants, i.e., they render those minerals floatable which either have been temporarily depressed or would not float without their assistance. They are generally soluble salts which ionize in the aqueous medium. The ions then react with the mineral surface, providing a monomolecular coating and thereby making the mineral surface favourably disposed to the collectors. Sphalerite (ZnS) is essentially not floatable with common collectors. The addition of Cu2+ to the solution, however, alters the mineral surface to CuS, which can adsorb collector. This feature is described elaborately in a later section. 

The mineral, sphalerite, on account of its resistance to oxidation, contributes very little of Zn2+ through dissolution. In this case, zinc sulfate is added and the reaction, which is shown in the parenthesis, is pressed into proceeding from right to left (i.e., PhS + Zn2+ —> ZnS +Pb2+). This is equivalent to saying deactivation of sphalerite. Besides Pb2+, Cu2+ is also known to give rise to activation. In this case, cyanide ions are introduced into the system. The stability of Cu(CN)2, relative to Zn(CN)2- results in ratios of dissolved Cu to Zn such that activation cannot occur. 

Thus, if Cu2+ and H+ are existing at unit activity, the reduction of Cu2+ is easier than the reduction of H+, and Cu2+ ions must be discharged in preference to H+, until the Cu2+ concentration has dropped to such a point that the E for its half-cell reaction is less then that for the H+ H2 half-cell. 

The replacement of vanadia-based catalysts in the reduction of NOx with ammonia is of interest due to the toxicity of vanadium. Tentative investigations on the use of noble metals in the NO + NH3 reaction have been nicely reviewed by Bosch and Janssen [85], More recently, Seker et al. [86] did not completely succeed on Pt/Al203 with a significant formation of N20 according to the temperature and the water composition. Moreover, 25 ppm S02 has a detrimental effect on the selectivity with selectivity towards the oxidation of NH3 into NO enhanced above 300°C. Supported copper-based catalysts have shown to exhibit excellent activity for NOx abatement. Recently Suarez et al and Blanco et al. [87,88] reported high performances of Cu0/Ni0-Al203 monolithic catalysts with NO/NOz = 1 at low temperature. Different oxidic copper species have been previously identified in those catalytic systems with Cu2+, copper aluminate and CuO species [89], Subsequent additions of Ni2+ in octahedral sites of subsurface layers induce a redistribution of Cu2+ with a surface copper enrichment. Such redistribution... 

ESEEM measurements of perdeuterated all-trany-p-carotene imbedded in activated Cu-substituted MCM-41 molecular sieve revealed (Gao et al. 2005) that two deuterons of the carotenoid interact with the Cu2+ at a distance of 3.3 A. Possible double bonds of P-carotene with one deuterium at each carbon that could interact with Cu are C7=C8, CH-C12, 05=05, 02 - C1T, and C8 =C7. 

They have further confirmed the role of sonication and consequently the production of OH/H2O2 species to facilitate the formation of CuBr by decreasing the ultrasound power from 50 to 35 and finally to 15 W and found an increase in the amount of Cu particles, clearly enough due to poor concentration of active species. The mechanism for the action of H202 with Cu2+ ions in aqueous solution could therefore be proposed as under ... 

Hiratsuka et al102 used water-soluble tetrasulfonated Co and Ni phthalocyanines (M-TSP) as homogeneous catalysts for C02 reduction to formic acid at an amalgamated platinum electrode. The current-potential and capacitance-potential curves showed that the reduction potential of C02 was reduced by ca. 0.2 to 0.4 V at 1 mA/cm2 in Clark-Lubs buffer solutions in the presence of catalysts compared to catalyst-free solutions. The authors suggested that a two-step mechanism for C02 reduction in which a C02-M-TSP complex was formed at ca. —0.8 V versus SCE, the first reduction wave of M-TSP, and then the reduction of C02-M-TSP took place at ca. -1.2 V versus SCE, the second reduction wave. Recently, metal phthalocyanines deposited on carbon electrodes have been used127 for electroreduction of C02 in aqueous solutions. The catalytic activity of the catalysts depended on the central metal ions and the relative order Co2+ > Ni2+ Fe2+ = Cu2+ > Cr3+, Sn2+ was obtained. On electrolysis at a potential between -1.2 and -1.4V (versus SCE), formic acid was the product with a current efficiency of ca. 60% in solutions of pH greater than 5, while at lower pH... 

The Fur protein from E. coli was isolated in one step due to its high affinity for metal-chelate columns loaded with zinc. In DNase footprinting experiments, the Fur protein was shown to bind DNA in the promoter region of several iron-regulated genes. The consensus sequence, called the Fur box, is GATAATGATAATCATT ATC. In vitro binding is dependent on the divalent cations Co2+ Mn2+ /s Cd2+ Cu2+ at 150 iM, while Fe2+ seemed to be less active at this concentration, probably due to oxidation to Fe3+ (De Lorenzo et al., 1987). The unspecificity for divalent metals observed in vitro shows that the cells have to select the ions transported carefully and have to balance their active concentrations. In addition, it is a caveat for the experimenter to test a hypothesis on metal-ion specificity not only in vitro, but also in vivo. 

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