Free metal ion depletion by “good's” buffers: II. N-(2-acetamido)-2-aminoethanesulfonic acid (ACESH): Complexes with Calcium(II), Magnesium(II), Manganese(II), Cobalt(II), Zinc(II), Nickel(II), and Cooper(II)

Potentiometric, visible, and infrared studies of the complexation of N-(2-acetamido)-2-aminoethanesulfonic acid (ACESH) by Ca(II), Mg(II), Mn(II), Co(II), Zn(II), Ni(II), and Cu(II) are reported. Ca(II), Mg(II), and Mn(II) were found not to complex with ACES^?, while Co(II), Zn(II), Ni(II), and Cu(II) were found to form 2:1, ACES^? to M²⁺, complexes, and [Cu(ACES)₂] was found to undergo stepwise deprotonation of the amide groups to form [Cu(H_?1ACES)₂^2?]. Formation (affinity) constants for the various metal complexes are reported, and the probable structures of the various metal chelates in solution are discussed.     

Circular dichroic studies on Cu(II) interactions with a protamine,scylliorhinine Z3

The interaction of Cu(II) with the protamine scylliorhinine Z₃ was studied by means of CD measurements. At a 1:1 molar ratio, three complexes are formed. (1) In the pH range 5–6.5, the results suggest the formation of a five-membered chelate ring through the coordination of two nitrogen atoms, the N-terminal and the contiguous peptide nitrogen. (2) At pH ≥ 6.4, there is involvement of the lateral NH₂ group of Arg; at pH 6.5–8, the formation of a 3N cupric complex is strongly suggested. (3) At pH ≥ 8, results indicate the formation of a 4N complex as a major species in Cu(II)-Z₃ solution. The transformation from a 2N to a 3N complex, and from a 3N to a 4N complex was followed with the help of the σ(αNH₂) → Cu(II) charge-transfer dichroic band transitions. At Cu(II):Z₃ molar ratios ≥ 2 and at pH > 8, a new dichroic band appears, indicating the involvement of the tyrosine residue side chain in metal-ion complexation.     

Decomposition and superoxide dismutase activity of the copper complex of D-penicillamine (Cu(II)6Cu(I)8 (D-penicillamine)12 Cl)5−

The possible time- and/or light-dependent decomposition of the purple Cu(I), Cu(II)-complex of D-penicillamine (Cu(II)₆Cu(I)₈(D-penicillamine)₁₂Cl)^5? was examined. Superoxide dismutase activity of the freshly prepared complex was assayed using the nitroblue tetrazolium assay. The formazan colour formation was inhibited by 50% in the presence of approximately 500 μM copper. Ageing of the copper complex, especially in the light, resulted in a marked increase of EDTA-sensitive activity. Upon gel chromatography of the aged samples the original low inhibitory activity was restored. All EDTA-sensitive inhibitory activity was found in a clearly separated low M_r copper-containing fraction. Aerobic irradiation with a tungsten lamp at 30 °C accelerated the decomposition of (Cu(II)₆Cu(I)₈(D-penicillamine)₁₂Cl)^5?. ?_Cu518 = 1800 M^?1 cm^?1 dropped to ?_Cu640 = 60 M^?1 cm^?1. The photochemical conversion of (Cu(II)_6? Cu(I)₈(D-penicillamine)₁₂Cl)^5? was complete within 48 h. Due to the identical electronic absorption profile of both, the decomposition product and Cu(II) D-penicillamine disulphide the latter complex was assigned to be the unknown low M_r copper-compound. Circular dichroism and electron paramagnetic resonance measurements support this conclusion.     

Investigations of different chemiluminescent peaks in H2O2–SCN−–Cu2+–OH−–luminol flow system

In the H₂O₂–SCN^?–Cu²⁺–OH^?–luminol oscillatory system of chemiluminescence, the effects of the ingredient concentrations, temperature, flow rate and complexing agent on the oscillatory dynamics were investigated in a continuous‐flow stirred tank reactor (CSTR). The dynamical structure of two peaks during a period was discussed in detail. By addition of EDTA to the oscillating system, the peak I height decreased sharply while the peak II height was little affected, and the period kept constant. This may be due to the fast reaction between Cu(II) and EDTA and the highly stable complex Cu(II)–EDTA. From the experimental study and mechanism analysis, the chemiluminescent peak I corresponds to Cu(II) → Cu(I) transformation and the peak II corresponds to the Cu(I) → Cu(II) transformation process. The key species involving in the two‐transformation process are inferred to be superoxide radical and hydroxyl radical. Copyright © 2010 John Wiley & Son, Ltd.     

Flexibility of DNA and RNA upon Binding to Different Metal Cations. An Investigation of the B to A to Z Conformational Transition by Fourier Transform Infrared Spectroscopy

Abstract

The interaction of DNA and RNA with Cu(II), Mg(II), [Co(NH₃)₆]³⁺ [Co(NH₃)₅Cl]²⁺ chlorides and, cis- and trans-Pt(NH₃)₂Cl₂ (CIS-DDP, trans-DDP) has been studied by Fourier Transform Infrared (FT-IR) spectroscopy and a correlation between metal-base binding and conformational transitions in the sugar pucker has been established. It has been found that RNA did not change from A-form on complexation with metals, whereas DNA exhibited a B to Z transition. The marker bands for the A-form (C′₃-endo-anti conformation) were found to be near 810–816 cm^?1, while the bands at 825 and 690 cm^?1 are marker bands for the B- conformation (C′₂-endo, anti), The B to Z (C₃′-endo, syn conformation) transition is characterized by the shift of the band at 825 cm^?1 to 810–816 cm^?1 and the shift of the guanine band at 690 cm^?1 to about 600–624 cm^?1.     

Effects of chloride depletion on electron donation from the water-oxidizing complex to the photosystem II reaction center as measured by the microsecond rise of chlorophyll fluorescence in isolated pea chloroplasts

The role of Cl^? in the electron transfer reactions of the oxidizing side of Photosystem II (PS II) has been studied by measuring the fluorescence yield changes corresponding to the reduction of P⁺-680, the PS II reaction center chlorophyll, by the secondary PS II donor, Z. In Cl^?-depleted chloroplasts, a rapid rise in fluorescence yield was observed following the first and second flashes, but not during the third or subsequent flashes. These results indicate that there exists an additional endogenous electron donor beyond P-680 and Z in Cl^?-depleted systems. In contrast, the terminal endogenous donor on the oxidizing side of PS II in Tris-washed preparations has previously been shown to be Z, the component giving rise to EPR signals II_f and II_vf. The rate of reduction of P⁺-680 in the Cl^?-depleted chloroplasts was as rapid as that measured in uninhibited systems, within the time resolution of our instrument. Again, this is in contrast to Tris-washed preparations in which a dramatic decrease in the rate if this reaction has been previously reported. We have also carried out a preliminary study on the rate of rereduction of Z⁺ in the Cl^?-depleted system. Under steady-state conditions, the reduction half-time of Z⁺ in uninhibited systems was about 450 μs, while in the Cl^?-depleted chloroplasts, the reduction of Z⁺ was biphasic, one phase with a half-time of about 120 ms, and a slower phase with a half-time of several seconds. The appearance of the quenching state due to P⁺-680 observed following the third flash on excitation of Cl^?-depleted chloroplasts was delayed by two flashed when low concentrations of NH₂OH (20–50 μM) were included in the medium. Hydrazine at somewhat higher concentrations showed the same effect. This is taken to indicate that the reactions leading to PS II oxidation of NH₂OH or NH₂NH₂ are uninhibited by Cl^? depletion. Addition of NH₂OH at low concentrations to Tris-washed chloroplasts did not alter the pattern of the fluorescence yield, indicating that the reactions leading to the NH₂OH oxidation present in Cl^?-depleted systems are absent following Tris inhibition. The results are discussed in terms of an inhibition by Cl^? depletion of the reactions of the oxygen-evolving complex. It is suggested that no intermediary redox couple exists between the oxygen-evolving complex and Z, and that Z⁺ is reduced directly by Mn of the complex. In terms of the S-state model, Cl^? depletion appears to inhibit the advancement of the mechanism beyond S₂, but not to inhibit the transitions from S₀ to S₁, or from S₁ to S₂.     

Study on the interaction of a copper(II) complex containing the artificial sweetener aspartame with human serum albumin

A copper(II) complex containing aspartame (APM) as ligand, Cu(APM)₂Cl₂·2H₂O, was synthesized and characterized. In vitro binding interaction of this complex with human serum albumin (HSA) was studied at physiological pH. Binding studies of this complex with HSA are useful for understanding the Cu(APM)₂Cl₂·2H₂O–HSA interaction mechanism and providing guidance for the application and design of new and more efficient artificial sweeteners drive. The interaction was investigated by spectrophotometric, spectrofluorometric, competition experiment and circular dichroism. Hyperchromicity observed in UV absorption band of Cu(APM)₂Cl₂·2H₂O. A strong fluorescence quenching reaction of HSA to Cu(APM)₂Cl₂·2H₂O was observed and the binding constant (K_f) and corresponding numbers of binding sites (n) were calculated at different temperatures. Thermodynamic parameters, enthalpy change (?H) and entropy change (?S) were calculated to be ?458.67 kJ mol^?1 and ?1,339 J mol^?1 K^?1 respectively. According to the van’t Hoff equation, the reaction is predominantly enthalpically driven. In conformity with experimental results, we suggest that Cu(APM)₂Cl₂·2H₂O interacts with HSA. In comparison with previous study, it is found that the Cu(II) complex binds stronger than aspartame.     

Inhibition of bovine plasma amine oxidase by superoxide dismutase active Cu(II) complexes

Aqueous Cu²⁺ and Cu(II) complexes of salicylate, lysine, and tyrosine decrease the rate of benzylamine oxidation by bovine plasma amine oxidase. Bissalicylato Cu(II) and Cu²⁺ inhibit non-competitively with respect to benzylamine. Lysine, tyrosine, Cu(EDTA)^2?, Zn²⁺, and Co²⁺ do not inhibit, and erythrocyte Cu, Zn superoxide dismutase shows only slight inhibition of the amine oxidase. The data are most consistent with an inhibitory mechanism involving dismutation of O₂^? by the Cu(II) complexes within a site relatively inaccessible to the enzyme superoxide dismutase. Excess lysine significantly decreases inhibition by the bis-lysine complex of Cu(II).     

Change of speciation of Cu(II) in growth medium due to uptake of ammonia byPseudomonas testosteroni during growth

Growth ofPseudomonas testosteroni in a medium containing 1mm Cu(II) causes a color change from blue to green. The spectrum of the supernatant solution from the blue culture shows an absorption at 660 nm, identical to that of 1mm [Cu(II)] in the medium. The green supernatant solution shows a UV absorption, which tails into the visible and so is responsible for the green color, and ad-d absorption at 720 nm. The absorption at 660 nm for the blue supernatant solution is probably due to [Cu(NH₃)₃(H₂O)₃]²⁺. Growth of the organism causes loss of ammonia and a speciation change to [Cu(NH₃)₂(H₂O)₄]²⁺, with a shift in absorption maximum from 660 to 720 nm. These conclusions are based upon the spectra of known aquaammine complexes of Cu(II) and calculations of the speciation of Cu(II) before and after growth. Change in metal speciation owing to nutrient uptake by an organism does not appear to have been recognized previously.     

Synthesis and crystal structure of a highly selective colorimetric and fluorometric sensor for hydrogen sulfide

A novel Cu(II) complex chemosensor for hydrogen sulfide with azo as the colorimetric group has been synthesized. The complex and ligand crystals were obtained and the molecular structures were characterized by X‐ray diffraction and Electrospray ionization High resolution mass spectrometer (ESI‐HRMS). The photophysical and recognition properties were examined. The complex can recognize S^2?, with an obvious color change from yellow to red based on a copper ion complex displacement mechanism. By contrast, no obvious changes were observed in the presence of other anions (AcO^?, H₂PO₄^?, F^?, Cl^?, Br^? and I^?). We present a simple, easily prepared, yet efficient, inorganic reaction‐based sensor for the detection of S^2?. The complex should have many chemical and analytical applications in the sensing of hydrogen sulfide.     

Copper(I)-incorporation into spinach apoplastocyanin

Spinach plastocyanin was converted into the apoprotein. CuSO₄ and oxidized Cu(II)- thionein reacted with the apoprotein to Cu(II) plastocyanin. Cu(I) transfer from Cu(I)0-thionein was only 15%. The structural analogue of the copper thiolate chromophore [Cu(I)(thiourea)₃]Cl as well as [Cu(CH₃CN)₄]ClO₄ successfully formed the Cu(I)- holoprotein. Characteristic circular dichroism bands at θ₂₈₄ (?5300 deg·cm²·dmol^?1 and θ₃₁₀ (+3300 deg·cm²·dmol^?1) were seen. Upon oxidation with ferricyanide and dialysis against phosphate buffer the correct Cu(II) binding into the active centre of Cu(II) plastocyanin was confirmed by EPR-measurements. The use of [Cu(I)(thiourea)₃] Cl as a convenient Cu(I) source for reconstitution studies on copper proteins is highly recommended.     

The amylin peptide implicated in type 2 diabetes stimulates copper-mediated carbonyl group and ascorbate radical formation

Human amylin (hA), which is toxic to islet β-cells, can self-generate H₂O₂, and this process is greatly enhanced in the presence of Cu(II) ions. Here we show that carbonyl groups, a marker of oxidative modification, were formed in hA incubated in the presence of Cu(II) ions or Cu(II) ions plus H₂O₂, but not in the presence of H₂O₂ alone. Furthermore, under similar conditions (i.e., in the presence of both Cu(II) ions and H₂O₂), hA also stimulated ascorbate radical formation. The same observations concerning carbonyl group formation were made when the histidine residue (at position 18) in hA was replaced by alanine, indicating that this residue does not play a key role. In complete contrast to hA, rodent amylin, which is nontoxic, does not generate H₂O₂, and binds Cu(II) ions only weakly, showed none of these properties. We conclude that the hA-Cu(II)/Cu(I) complex is redox active, with electron donation from the peptide reducing the oxidation state of the copper ions. The complex is capable of forming H₂O₂ from O₂ and can also generate ^•OH via Fenton chemistry. These redox properties of hA can explain its ability to stimulate copper-mediated carbonyl group and ascorbate radical formation. The formation of reactive oxygen species from hA in this way could hold the key to a better understanding of the damaging consequences of amyloid formation within the pancreatic islets of patients with type 2 diabetes mellitus.     

Specific platinum chelation by the guanines of the deoxyhexanucleotide d(T-G-G-C-C-A) upon reaction with cis-[Pt(NH3)2(H2O)2](NO3)2

The stoichiometric reaction between d-TpGpGpCpCpA (d(T-G-G-C-C-A)) and $\text{cis}$-[Pt(NH₃)₂(H₂O)₂](NO₃)₂ (8.4 × 10^?6 to 1.3 × 10^?4M in water at pH 5.5–6) gives a single complex. High pressure gel permeation chromatography and pH-dependent ¹H NMR analyses of the nonexchangeable base protons, show that it is a platinum chelate with the $\text{cis}$-Pt^II(NH₃)₂ moiety bound to the two N7 atoms of the adjacent guanines. A 3 × 10^?3M reaction gives the same platinum chelate, via the formation of intermediate complexes, together with unsoluble adducts.     

Mechanistic flexibility in the reduction of copper(II) complexes of aliphatic polyamines by mercapto amino acids

The reactions of copper(II)-ahphatic polyamine complexes with cysteine, cysteine methyl ester, penicillamine. and glutathione have been investigated, with the goal of understanding the relationship between RS^?-Cu(II) adduct structure and preferred redox decay pathway. Considerable mechanistic flexibility exists within this class of mercapto ammo acid oxidations, as changes in the rate law could be induced by modest variations in reductant concentration (at fixed [Cu(II)]_o), pH, and the structure of the redox partners. With excess cysteine present at 25°C, pH 5 0, I = 0 2 M (NaOAc), decay of 1:1 cys-S^?-Cu(II) transient adducts was found to be first order in both cys-SH and transient. Second-order rate constants characteristic of Cu(dien)²⁺ (6 1 × 10³M^?1sec^?1), Cu(Me₅dien)²⁺ (2.7 × 10³M^?1 sec^?1), Cu(en)₂²⁺ (2.1 × 10³M^?1 sec^?1), and Cu(dien)₂²⁺ (4.7 × 10³ M^?1 sec ^?1) are remarkably similar, considering substantial differences in the composition and geometry of the oxidant first coordination sphere. A mechanism involving attack of cysteine on the coordinated sulfur atom of the transient, giving a disulfide anion radical intermediate, is proposed to account for these results Moderate reactivity decreases in the cysteine-Cu(dien)²⁺, Cu(Me₅dien)²⁺ reactions with increasing [H⁺] (pH 4–6) reflect partial protonation of the polyamine ligands. A very different rate law, second order in the RS^?-Cu(II) transient and approximately zeroth order in mercaptan, applies in the pH 5.0 oxidations of cysteine methyl ester, penicillamine, and glutathione by Cu(dien)²⁺ and Cu(Me₅dien)²⁺. This behavior suggests the mtermediacy of di-μ-mercapto-bridged binuclear Cu(II) species, in which a concerted two-electron change yields the disulfide and Cu(I) products. Similar hydroxo-bridged intermediates are proposed to account for the transition from first- to second-order transient dependence in cysteine oxidations by Cu(dien)²⁺ and Cu(Me₅dien)²⁺ as the pH is increased from 5 to 7. Yet another rate law, second order in transient and first order in cysteine, applies in the pH 5.0 oxidation of cysteine by Cu(Me₆tren)²⁺ (k(25°C) 7.5 × 10⁷ M^?2 sec^?1, I = 0.2 M). Steric rigidity of this trigonal bipyramidal oxidant evidently protects the coordinated sulfur atom from attack in a RSSR^?-forming pathway. Formation of a coordinated disulfide in the rate-determining step is purposed, coupled with attack of a noncoordinated cysteine molecule on a vacated coordination position to stabilize the (Me₆(tren)Cu(I) product.     

Theoretical studies on densities, stability and detonation properties of 2D polymeric complexes Cu(DAT)2Cl2 and its new analogues Zn(DAT)2Cl2

A novel environmentally friendly octahedrally coordinated 2D polymeric complexes bis(1,5-diaminotetrazole) -dichlorozinc(II) (Zn(DAT)₂Cl₂) was first designed based on the the crystal data of bis(1,5-diaminotetrazole)- dichlorocopper(II) (Cu(DAT)₂Cl₂). Density functional theory (DFT) was used to predict the optimized geometries at TPSSTPSS/6-311G(d, p) level. Densities and detonation properties were evaluated using the electron cloud enclosed volume and VLW equation of state (VLW EOS), respectively. Calculation results show that the density of Zn(DAT)₂Cl₂ (2.117 g?·?cm^?1) is a bit more than that of Cu(DAT)₂Cl₂ (2.106 g?·?cm^?1). The calculated high positive heat of formation (HOF) predicts that the stabilities of the title compounds decrease in the order Zn(DAT)₂Cl₂ > Cu(DAT)₂Cl₂, which agrees with the result of bond dissociation energies (BDE). Even though they have the same molecule structures, their first scission steps are different. Furthermore, the title two compounds show good detonation velocities and pressures compared with that of bis-(5-nitro-2H-tetrazolato-N ²) tetraamminecobalt(III) perchlorates (BNCP), and they are potential candidates for high-energy-density materials (HEDM).     

The copper-molybdenum antagonism in ruminants. III. Reaction of copper(II) with tetrathiomolybdate(VI)

The stoichiometry of the reaction between Cu(II) and MoS₄²⁻ in neutral aqueous solution was observed to proceed with a 1.5:1 Cu:Mo ratio. The reaction results in the reduction of Cu(II) and the quantitative formation of an insoluble solid. The results contrast with an earlier report of a 1:1 stoichiometric ratio, this latter ratio was, however, observed with Cu^II(albumin) as reactant, in this case no precipitate was observed. The insoluble products were examined by a number of spectroscopic techniques and by X-ray power diffraction and elemental analysis. Two products were identified. Solid A is isostructural with the known (NH₄)Cu^IMoV^VIS₄, i.e. has the composition M^ICuMoS₄, M^I= NH₄⁺, Na⁺ or Et₄N⁺. Solid B has the approximate composition CuMoS₄O_x, x=2−3 and contains Cu(I) and Mo(V) centres. Formation of compound B therefore involves an unusual internal two-electron redox process. The reaction and products are of particular biological significance.     

Synthesis,DNA Binding,and Photonuclease Activity of New Tetraaza Macrocyclic Constrained Isoxazole Rings as Subunit in Metal Complexes

The DNA-binding and photonuclease activity of newly synthesized tetra-azamacrocyclic ligand L (C₃₂H₃₂N₈O₄) and its complexes of type [MLCl₂] and [ML]Cl₂ (where M = Co(II), Fe(II) and Cu(II); L = N,N′-[3-(4-{5-[(2-amino-ethylamino)-methyl]-isoxazol-3yl}-phenyl)-isoxazol-5-yl methyl-ethane-1,2-diamine] are specified. An octahedral geometry has been proposed for Fe(II) and Co(II) complexes, while the Cu(II) complex has a square planar environment. The absorption spectral results indicate that the complexes bind with the base pairs of DNA, with an intrinsic binding constant K_b of Fe(II), Co(II), and Cu(II) complexes found to be 3.2 × 10⁴ M^?1, 5.3 × 10⁴ M^?1, and 4.2 × 10⁴ M^?1, respectively, in 5 mM Tris-HCl/50 mM NaCl buffer at pH 7.2. The large enhancement in the relative viscosity of DNA on binding to the complexes supports the proposed DNA binding modes. The viscosity and thermal denaturation studies sustain the effective intercalation with DNA. The DNA photocleavage studies demonstrated that compounds exhibit significant photonuclease activity by a concentration dependent on singlet oxygen mediated mechanism.     

Theoretical guidance and experimental confirmation on catalytic tendency of M-CeO2 (M = Zr,Mn, Ru or Cu) for NH3-SCR of NO

Abstract

Herein, we demonstrate that the degrees of catalytic performance of M-CeO₂-based catalysts (M=Mn, Cu, Ru or Zr) for an ammonia selective catalytic reduction (NH₃-SCR) of nitric-oxide (NO) can be estimated using three theoretical terms; (i) an oxygen vacancy formation energy of a catalyst, (ii) an adsorption energy of NO and (iii) an adsorption energy of NH₃. Those terms predict the trend of the catalytic performance as the order; Mn–CeO₂ > Cu–CeO₂ > Ru–CeO₂ > Zr–CeO₂ > CeO₂. To verify the theoretical prediction, the catalysts were synthesized and tested their performances on the NH₃-SCR of NO reaction. The normalized NO conversion rates at low temperatures (100–200 °C) were measured for Mn–CeO₂, Cu–CeO₂, Ru–CeO₂, Zr–CeO₂ and CeO₂ as 2.61–7.46, 1.30–6.82, 0.73–3.02, 0.81–3.31 and 1.55–2.33 mol s^?1 m^?2, respectively. In addition, a concept of a structure-activity relationship analysis shows a strong relationship between theoretical and experimental results. Consequently, an application of predicting the catalytic performance of catalysts from theoretical calculations prior the catalyst synthesis is useful in catalyst design and screening that can reduce time and cost.     

Efficient Photocatalytic Nitrogen Fixation over Cuδ+‐Modified Defective ZnAl‐Layered Double Hydroxide Nanosheets

The photocatalytic reduction of nitrogen (N₂) with water (H₂O) as the reducing agent holds great promise as a sustainable future technology for the synthesis of ammonia (NH₃). Herein, the effect of oxygen vacancies and electron‐rich Cu^δ+ on the performance of zinc‐aluminium layered double hydroxide (ZnAl‐LDH) nanosheet photocatalysts for N₂ reduction to NH₃ under UV–vis excitation is systematically explored. Results show that a 0.5%‐ZnAl‐LDH nanosheet photocatalyst (containing 0.5 mol% Cu by metal basis) affords a remarkable NH₃ production rate of 110 µmol g^?1 h^?1 and excellent stability in pure water. The X‐ray absorption spectroscopy, electron paramagnetic resonance, and density functional theory calculations reveal that Cu addition imparts oxygen vacancies and coordinatively unsaturated Cu^δ+ (δ < 2) with electron‐rich property in the ZnAl‐LDH nanosheets, both of which readily contribute to efficient separation and transfer of photogenerated electrons and holes and promote N₂ adsorption, thereby both activating N₂ and facilitating its multielectrons reduction to NH₃.