Mechanism Of Copper Research Articles

The interpretation of cyclic creep deformation mechanism of copper in terms of the anelastic recovery

The cyclic creep deformation behaviour of copper has been studied in the temperature range of 0.4 to 0.5T m and under the constant stress range of (σ/E)=4×10−4 to 10×10−4. To see the effect of cyclic stress frequency, stress amplitude and the duration of the unloading time in a fixed frequency on cyclic creep behaviour, static and cyclic creep tests were conducted under the conditions mentioned above. The measured activation energies for static and cyclic creep were analysed in terms of the various experimental parameters. Anelastic behaviour during the unloading period was also studied to find out the possible assistance for the positive creep deformation in cyclic creep. Using the concept of anelastic recovery and the activation energy for the anelastic it is hypothesized that the accelerated cyclic creep deformation is controlled by the anelastic recovery during the unloading period.

Kinetics and Mechanism of Copper(II), Zinc(II), and Cadmium(II) Incorporation into 5,10,15,20-Tetraphenylporphine and N-Methyl-5,10,15,20-tetraphenylporphine in N,N-Dimethylformamide

Abstract The kinetics of reactions of 5,10,15,20-tetraphenylporphine (H2(tpp)) and N-methyl-5,10,15,20-tetraphenylporphine (H(metpp)) with CuII, ZnII, and CdII ions was studied spectrophotometrically in N,N-dimethylformamide. The rate of incorporation of metal ions (M2+ : Cu2+, Zn2+, Cd2+) into H(metpp) is first order with respect to both H(metpp) and metal ion: d[M(metpp)+]/dt=[k[H(metpp)][M2+] with k(25 °C)=11.5±0.5 mol−1 dm3 s−1 for Zn2+ and (5.8±0.8)×102 mol−1 dm3 s−1 for Cd2+. The rate of incorporation of copper and zinc into H2(tpp) is first order in H2(tpp) and the conditional first-order rate constants are expressed as follows: k0(M)=K[M2+](1+K[M2+])−1(k1+k2[M2+]) where for Cu2+ and Zn2+ K/mol−1 dm3, k1/s−1, and k2/mol−1dm3 s−1 at 25°C are (1.6±0.2)×104 and (7.2±1.5)×102, (1.2±0.1)×10−4 and (3.5±0.7)×10−5, and (5.2±0.2)×10−2 and (8.6±0.2)×10−4, respectively. Metal ion incorporation into H2(tpp) proceeds through the formation of intermediates prior the rate-limiting step. For the H(metpp) system, the methyl group on the pyrrole in H(metpp) prevents the formation of such an intermediate. On the other hand, the rate of cadmium incorporation into H2(tpp) is first order with respect to Cd2+ and H2(tpp) and its second order rate constant k is (6.5±1.0)×10−3 mol−1 dm3 s−1. The large cadmium(II) ion can not fit into the porphyrin nucleus and its reaction proceeds through a pathway involving a mononuclear activated complex.

Structure and mechanism of copper, zinc superoxide dismutase

Copper, zinc superoxide dismutase (SOD) catalyses the very rapid two-step dismutation of the toxic superoxide radical (O-2) to molecular oxygen and hydrogen peroxide through the alternate reduction and oxidation of the active-site copper. We report here that after refitting and further refinement of the previous 2 A structure of SOD2, analysis of the new model and its calculated molecular surface shows an extensive surface topography of sequence-conserved residues stabilized by underlying tight packing and H-bonding. There is a single, highly complementary position for O-2 to bind to both the Cu(II) and activity-important Arg 141 with correct geometry; two water molecules form a ghost of the superoxide in this position. The geometry and molecular surface of the active site, together with biochemical data, suggest a specific model for the enzyme mechanism.

The Mechanism of Copper(II) Binding by Humic Acid: An Electron Spin Resonance Study of a Copper(II)—Humic Acid Complex and Some Adducts with Nitrogen Donors

AbstractElectron spin resonance (ESR) spectroscopy was used to study the mechanism of Cu2+ binding by humic acid (HA) extracted from a Chalmers silt loam soil. The Cu‐HA complex and some adducts with nitrogen donors were examined. The ESR data presented showed that the addition of pyridine (py) and 1,10‐phenanthroline (phen) to the Cu‐HA complex resulted in the substitution of coordinated H2O ligands by the nitrogen donor ligands without displacement of HA oxygen donor ligands also coordinated to the Cu2+ center. The addition of a more basic nitrogen donor, ethylenediamine (en), resulted in the displacement from Cu2+ of both coordinated H2O ligands and HA oxygen donors, forming Cu(en)22+. The g‖ and A‖ values obtained for the py and phen adducts revealed that there were two HA oxygen donors coordinated equatorially to the Cu2+ center in the original Cu‐HA complex. The characterization of the adducts with phen and en was consistent with the formation of a Cu2+ chelate in the original Cu‐HA complex, where the two equatorial Cu‐HA oxygen bonds would occupy cis‐ positions. The crystal field strength of HA oxygen donor ligands coordinated to the Cu2+ center was stronger than that of H2O.

The sensitivity of hexaploid and octoploid triticales and their parent species to copper deficiency

The tolerance of two triticales to soil of low copper status was determined in deep pots in a glasshouse experiment, and compared with the tolerance of their wheat and rye parent types. Both tetraploid and hexaploid wheats were extremely sensitive to copper deficiency, producing no grain without copper added to the soil. In contrast, rye and the hexaploid triticale were completely tolerant of the copper-deficient soil, producing as much grain without added copper as at the highest rate of copper supply. The octoploid triticale produced about 60% of maximum grain yield in the unamended soil, a performance intermediate between its rye and hexaploid-wheat parents. The cause of grain failure in the wheats was pollen sterility induced by copper deficiency, and this was related to low uptake of copper into the shoot and heads of wheat from the unamended soil. The pattern of uptake of zinc was quite different from that of copper in these plants, which suggests that a specific uptake mechanism for copper exists in rye which is genetically controlled and transferable to triticale, its hybrid with wheat. The copper efficiency so conferred on triticale would appear to be adequate for most field situations where copper deficiency exists.

Copper(I) nitrile complexes, part IV. Mechanism of copper(II) acetate and trifluoroacetate reduction by copper in acetonitrile in the presence of free carboxylic acid

Copper(II) carboxylates, Cu(O2CR)2, R = Me or CF3, in acetonitrile are reduced to copper(I) complexes by copper metal in the presence of RCO2H. No reduction however, was observed in the absence of the acid. The CuO2CMe, Cu(O2CCF3)(MeCN) and Cu(O2CCF3)(CF3CO2H)2(MeCN)4, complexes were isolated from the reaction mixture. Copper(I) species are stabilized by coordination of diacetamide or isoamide, a reaction product of the free acid and nitrite. Copper(I) carboxylate is obtained after decomposition of the coordinated species to the original acid and nitrite.

Mechanism of suppressive effect of basic cupric acetate on rat liver carcinogenesis by ethionine.

The rate of ethylation of t-RNA in vivo by L-ethionine[ethyl-1-14C] markedly lowered in the liver of rats fed a diet containing copper than that of control. In corporation of the labeled compound into the t-RNA of liver by a single injection. of L-ethionine[ethyl-1-14C] was inhibited as much as 50% by the preceding concurrent administration of copper and ethionine added in the diet to rats. Direct interaction of copper ion with ethylation by ethione in the specific t-RNA of the rat liver was examined as an important biochemical explanation in molecular level for the inhibitory mechanism of copper on rat liver carcinogenesis by ethionine. Profiles of normal t-RNA on methylated albumin-kieselguhr column chromatography revealed three components for leucine, two of which were found at the tube number 40 to 50 and disappeared in the leucyl t-RNA treated with ethionine. The components for leucine that disappeared were normalized in the liver of rats by the concurrent administration of copper.

Radiation and Temper Embrittlement Processes in Advanced Reactor Weld Metals

Experimental weld filler metals having high resistance to radiation embrittlement at ≃550 F (288 C) have been developed for quenched and tempered A543 and A542 steel. The filler metals are from a special 2-1/4 Cr-1 Mo-0.40Si-0.10C composition series formulated to study the effects of variable copper, nickel, and manganese contents on weld performance. This report presents an advanced evaluation of weld deposit performance based on new Charpy-V (Cv) and tension data and an analysis of temper embrittlement and radiation embrittlement processes. High fluence assessments confirm the high resistance to radiation embrittlement of the low copper content filler metal group. A 530 F (277 C) irradiation of one typical submerged arc weld deposit to a fluence of 3.8 × 1020 n/cm2 > 1 MeV did not elevate its Cv 30 ft-lb transition temperature to above 275 F (135 C) or reduce its Cv shelf energy level to below 50 ft-lb. Radiation embrittlement saturation was not evident. Temper embrittlement and radiation embrittlement development and the probable mechanisms of copper and phosphorus influences on radiation embrittlement sensitivity are analyzed with the aid of experimental data for the weld metals and A543 plate. Temper embrittlement and radiation embrittlement are shown to be additive effects which can occur simultaneously or sequentially. A separate component of irradiation effects, manifested as a strength increase without embrittlement, is revealed. The enhancement of radiation sensitivity by high copper content (≧0.16–0.27 percent Cu) is related to a copper influence on the radiation elevation of yield strength; the enhancement of radiation sensitivity of phosphorus is ascribed to a detrimental effect similar to that of temper embrittlement. It is proposed that copper acts to pin radiation-induced defect aggregates and dislocation arrays in the matrix and that phosphorus segregates during irradiation to weaken the interface of ferrite platelets and carbides.

Mechanism of copper(II) oxidation of reducing sugars. I. Kinetics and mechanism of oxidation of D-xylose, L-arabinose, D-glucose, D-fructose, D-mannose, D-galactose, L-sorbose, lactose, maltose, cellobiose, and melibiose by copper(II) in alkaline medium

Mechanism of copper(II) oxidation of reducing sugars. I. Kinetics and mechanism of oxidation of D-xylose, L-arabinose, D-glucose, D-fructose, D-mannose, D-galactose, L-sorbose, lactose, maltose, cellobiose, and melibiose by copper(II) in alkaline medium

Varietal Differences in the Kinetics of Iron Uptake by Excised Rice Roots

Iron uptake by excised rice roots can be described in kinetic terms of active absorption and the formation of ion-carrier complexes. Conventional interpreta tion indicates two carriers, one of which is responsible for iron absorption at low concentrations, with the second primarily functioning at high iron levels. The maximum absorption of both carriers varies greatly between varieties, the variety Pebifun having much greater absorptive capacity than either Siam-29 or Paldal. Varietal differences in uptake capacity primarily depend on total carrier concentration, 0 93, 0-40, and 0-31 p. moles per g roots of Pebifun, Siam-29, and Paldal respectively. Although the kinetic treatment suggests two carriers, the chromatographic evidence indicates the presence of the iron primarily in one major initial complex, with suggestions of accumulation rather than turnover. An alternative to the carrier hypothesis is therefore put forward which regards the accumulation of iron as binding initially on to one or several closely related sub stances, followed by incorporation into secondary products when a critical level of the initial product is exceeded. Manganese was found to competitively inhibit iron uptake by rice roots. Inhibition was more severe in Siam-29 than in Paldal and can be explained on the basis of carrier concentration and competition for the same carrier site. Copper was found not to be competitive for the iron absorption sites. The effect of copper was not significant with the low levels of iron but only with the 5 X io~4 M Fe level. The effect varied between varieties, in Pebifun both 5 X i o ~5 and S X io-6 M Cu inhibited iron uptake compared with the control. In the case of Siam-29 both copper levels accelerated iron uptake, 5 X io-5 M Cu giving the greatest uptake. With 5 X io-5 M Cu Pebifun took up much less iron than Siam-29. The mechanism of copper inhibition/stimulation is highly speculative.

Infrared Absorption Evidence on Exchange Reaction Mechanism of Copper and Zinc with Layer Silicate Clays and Peat

The degree to which cations which form weak bases are sorbed in excess of cations which form strong bases is shown to be about 10% in montmorillonite and 40% in peat. These excesses were accounted for by a special reaction mechanism which was revealed when layer silicate clays or peat fractions were examined by an infrared absorption technique. Copper and zinc saturation decreased the 2.8 micron hydroxyl absorption intensity of montmorillonite, vermiculite, and kaolinite, indicating a reaction with octahedral OH in the layer silicates. The larger OH peak of kaolinite at 2.7 microns was not affected. Also, the copper treatment yielded an additional pair of absorption peaks at 6.4 and 7.0 microns. Aluminum and iron treatment tended to increase the 2.8 micron peak slightly. Copper and zinc saturation of peat fractions resulted in numerous shifts in the double bond region of the spectrum, which were indicative of chelation with C = O and N = O groups.