Zwitterionic structures of selenocysteine-containing dipeptides and their interactions with Cu(II) ions

The molecular structures of a series of selenocysteine-containing dipeptides in their zwitterionic forms were studied using the B3LYP/6-311++G(d,p) level in the aqueous phase. The B3LYP and BH and HLYP functionals in combination with 6-311++G(d,p) and LANL2DZ basis sets were used to investigate the effects of metal coordination on the structural and molecular properties of the dipeptides by complexing them with bivalent copper ions. The results from this DFT study provide valuable insights into the interaction enthalpies (metal ion-binding affinities) and free energies, the influence of the C-terminal moiety on the backbone structural features, the existence of various types of intramolecular H-bond interactions, harmonic vibrational frequencies, along with various other electronic properties pertaining to the zwitterions of the dipeptide molecules as well as their metallic complexes. Metal coordination via the carboxylate groups tends to enhance the planarity of the amide planes. The participations of the N- and C-terminal side-chain moieties in metal-binding markedly enhance the thermodynamic stability of the metalated dipeptides. The theoretical λ_maxvalues, calculated using the TD/DFT level for all the systems, well represent the occurrence of d-d transitions in the Cu-dipeptide complexes.     

Ruthenium(II) complexes of 1,12-diazaperylene and their interactions with DNA

Four complexes of the ligand 1,12-diazaperylene (DAP) have been prepared, [Ru(bpy)n(DAP)(3-n)]2+ where n = 0-2 and [Ru(DAP)3]2+. The [Ru(DAP)3]2+ complex was characterized by X-ray analysis and was found to exhibit the expected propeller-like structure with significant intermolecular pi-stacking interactions. The three Ru(II) complexes showed self-consistent optoelectronic properties with similar ligand-centered pi-pi* absorptions in the range of 333-468 nm and MLCT bands associated with the DAP which increased in intensity and decreased in energy as the number of DAP ligands varied from 1 to 3. Hypochromicity and viscosity changes were observed that were consistent with DAP intercalation into DNA, and binding constants were measured in the range of 1.4-1.6 x 10(6) M(-1) for the mixed ligand complexes. Furthermore, the complex [Ru(bpy)2(DAP)]2+ was found to photocleave plasmid DNA upon irradiation with visible light.     

Electrochemical detection of Cu(I) and Cu(II) in styrene media

A method is described to detect Cu(II) and Cu(I) added as bromide simultaneously in styrene solution containing tetrahexylammoniumperchloraat (THAP) as supporting electrolyte. It was found that Cu(II) and Cu(I) behave similarly in styrene and in aqueous solution. Reduction of Cu(II) and Cu(I) to metallic copper, as well as oxidation of Cu(I) to Cu(II) and the dissolution of a deposited metallic copper layer are observed. Ohmic drop problems were circumvented by adding THAP to the styrene solution and using ultramicro electrodes. The simultaneous detection of Cu(II) and Cu(I) is based on recording a cyclic voltammetric curve in a mixture of these compounds and calculating their concentration from the cathodic limiting current obtained at −0.80 V vs. RE and the anodic stripping peak corresponding to the dissolution of metallic copper. A detection limit of 2.0×10⁻⁴ mol l⁻¹ was obtained for both Cu(II) and Cu(I) and reproducible results were obtained concerning sensitivity and stability of the calibration curves.     

Recognition and detection of oligonucleotides in the presence of chromosomal DNA based on entrapment within conducting-polymer networks

Overlapping voltammetric signals, accrued from redox processes of nucleobases, do not permit discrimination between short oligonucleotides and chromosomal DNA molecules when conventional electrochemical techniques are used. This article describes a new genoelectronic route for discriminating between short oligonucleotides and chromosomal DNA, based on the polypyrrole (PPy) doping process. Such a route relies on the profound effect of short nucleic acid dopants upon the redox activity of PPy, and hence on the square-wave voltammetric signal of the polymer-modified electrode in a blank electrolyte solution. The electropolymeric growth of PPy thus serves for preferential accumulation (by doping) of short oligonucleotides. High selectivity is demonstrated for voltammetric measurements of oligo(dG)₂₀ and oligo(dT)₂₀ in the presence of otherwise interfering ss- and ds-DNA. The signals for the oligonucleotides are also not affected by a large excess of chloride or phosphate ions. The response of the new preconcentration (doping)–medium-exchange–voltammetric protocol is proportional to the concentration of the oligonucleotide dopant. Such a new recognition process, based on the doping of conducting-polymer networks, enhances the scope of electroanalysis of nucleic acids.     

The influence of Cu(II), Mg(II) on the binding of adriamycin with DNA and the study on their interaction mechanism

Cu(II) and Mg(II) have different binding capacity with daunomycin, and have different combination mode with DNA. Selecting these two different metal ions, the influence of them on the binding constant of adriamycin with DNA and the related mechanism has been studied by using absorption and fluorescence spectroscopy. The result showed that Mg(II) has weaker binding capacity with the drug comparing Cu(II), but both Mg(II) and Cu(II) can obviously reduce the binding constant of DNA with the drug. Addition of Cu(II) to the drug-DNA binary system can cause the reduction of fluorescence in the system, but addition of Mg(II) to it can cause the enhancement of fluorescence in some conditions. This show that the influence of Cu(II) and Mg(II) on the binding of the drug with DNA may be by a different mechanism. According to the main function of Mg(II) to bind with the phosphate groups on DNA, it can be deduced that for the interaction of the aglycon portion of the drug into the base pairs of DNA, the electrostatic binding between amine group of the drug with the phosphate group on DNA is a prerequisite.     

Catalytic determination of Pb(II) in the presence of Cu(II)

A kinetic method is presented to determine micro-molar amounts of Pb(II) from various river and wastewater samples, in the presence of trace copper. The procedure is based on the catalytic effect of both species on the oxidation of mercaptosuccinic acid by chromate in acidic media. The extent of the reaction is followed spectrophotometrically at 420 nm and pseudo-first-order rate coefficients of the rate-determining step are determined as a function of catalyst concentrations. The optimum operating conditions (ionic strength, temperature, and concentration of reagents) regarding sensitivity towards lead were established. Interference by several ionic species has been studied. The effect of Fe(III), the only severe interferent, is suppressed by complexation with 1,10-phenantroline. The bi-component calibration model employs an artificial neural network to compute the Pb(II) concentration from a k(obsd) value and the a priori-known Cu(II) concentration of the sample. Working concentration ranges are 20-2160 micro g L(-1) for Pb(II) and 80-650 micro g L(-1) for Cu(II), respectively. Detection limits are 20 micro g L(-1) Pb(II) and 80 micro g L(-1) Cu(II), respectively. The relative standard deviations (3 measurements) for four different testing points are lower than 2.5%. The method was applied to samples of river and wastewater of the mining region of Baia-Mare, Northern Romania. The results were compared to those obtained by an officially standardized AAS method. Good agreement was achieved. The method is inexpensive, fairly rapid, and sensitive. Its working range covers the exact range of concentrations usually encountered in the mentioned geographic area.     

Potentiometric study of Cd(II) and Pb(II) complexation with two high molecular weight poly(acrylic acids); comparison with Cu(II) and Ni(II)

The cadmium (II) or lead (II) complex formation with two poly(acrylic acids) of high molecular weight (Mw=2.5×10⁵ and 3×10⁶) was investigated in dilute aqueous solution (NaNO₃ 0.1 mol l⁻¹; 25°C). Potentiometric titrations were carried out to determine the stability constants of the MA and MA₂ complex species formed. Bjerrum’s method, modified by Gregor et al. (J. Phys. Chem. 59 (1955) 34–39), for the study of polymeric acids was used. The results were compared to those previously obtained in the same conditions with copper (II) and nickel (II) . It appeared that the two polymers under study present similar binding properties and that the stability constants of the complex species formed increased in the following order, depending on the metal ion: Ni(II)β₁₀₂ was found to be close to 7.0) and allowed the formation of the predominant PbA₂ species in a quite large pH domain. Finally, the greater stability of PAA complexes compared to those of their monomeric analogs, glutaric and acetic acids, was confirmed.     

Potentiometric study of Cu(II) and Ni(II) complexation with two high molecular weight poly(acrylic acids)

The copper (II) or nickel (II) complex formation with two poly(acrylic acids) of high molecular weight (Mw=2.5×10⁵ and 3×10⁶) was investigated in aqueous dilute solution (NaNO₃ 0.1 mol l⁻¹; 25°C). Potentiometric titrations were carried out, first to precise the acid-base properties of the two polymers, and secondly to determine the stability constants of the MA and MA₂ complex species formed. The Bjerrum's method, modified by Gregor et al. (J. Phys. Chem., 59 (1955) 34–39), for the study of polymeric acids was used. The results obtained showed that both polymers present very similar properties. As expected, copper (II) is more readily bound to poly(acrylic acids). CuA₂ was the predominant observed species; the global stability constant log β₁₀₂ was found to be close to 6.6. With nickel (II), none of the complex species MA or MA₂ becomes predominant (log β₁₀₂=5.5). Finally, the PAA complexes present a greater stability compared with that of monomeric analogs.     

Polarographic investigation of the Cu(II) complex with ampicillin

The complex of Cu(II) ion and ampicillin is investigated polarographically in aqueous medium, at pH = 6, an ionic strength = 0.2, and room temperature. The stoichiometric ratio of Cu(II) and ampicillin in the complex, and the stability constant, logK = 5.1, were determined by Lingane's method.     

Synthesis and characterisation of Cu(II), Ni(II), and Zn(II) complexes of furfural derived from aroylhydrazones bearing aliphatic groups and their interactions with DNA

Two new Schiff base-hydrazones bearing furan ring, (Z)-4-butoxy-N′-(furan-2-ylmethylene)benzohydrazide (IV) and (Z)-N′-(furan-2-ylmethylene)-4-(hexyloxy)benzohydrazide (V), as well as their Cu(II), Ni(II), and Zn(II) complexes have been synthesised and characterised. The DNA-binding and DNA-cleavage activities of both aroylhydrazone ligands and their transition metal complexes were examined using UV-VIS titration and agarose gel electrophoresis in the presence of an oxidative agent (H₂O₂). The results indicate that the copper complexes bind significantly to calf thymus DNA and effectively cleave pBR322 DNA whereas the nickel and zinc complexes interact slightly with DNA.     

Electrochemical studies of nitroprusside in the presence of copper(II): formation of Cu(I) reduced nitroprusside species

Cu²⁺ is reduced in the presence of nitroprusside to form two Cu(I) reduced nitroprusside species at about +0.050 V (pH 7.6). These species are reduced further at about −0.60 V. The two species are formed by an EC mechanism, and the species are believed to be [Cu^IFe(CN)₄NO]⁻, which predominates in acidic solution, and [Cu^IFe(CN)₅NO]²⁻, which predominates in alkaline solution. These conclusions are supported by cyclic voltammetric and bulk electrolysis/coulometric experiments.     

Mixed metal hydroxycarboxylic acid complexes. Spectrophotometric study of complexes of U(VI) with In(III), Cu(II), Zn(II) and Cd(II)

The formation of mixed metal complexes between uranium (VI), as the central metal ion, and aluminium (III), indium (III), copper (II), zinc (II) and cadmium (II), as the additional metal ions, with a hydroxycarboxylic acid chosen between citric, tartaric or malic, has been studied using spectrophotometric methods.The effect of pH has been examined, and the results show that at pH=4 stable complexes are formed for most of the systems. At this pH the method of mole ratio and Job's method of continuous variations, were employed to determine the stoichiometry of the mixed metal complexes. Al(III), In(III) and Cu(II) showed a high tendency to form mixed metal complexes with U(VI), while the formation of complexes is uncertain for Cd(II) and Zn(II). The ratio of the ligand to the total metal ion has been found to be 21 and metal:metal ratios of 11 and 12 have been observed.Represents part of the Ph.D. thesis submitted by Emanuel Manzurola to Ben Gurion University of the Negev.     

Electrochemical study of quercetin-DNA interactions: part II. In situ sensing with DNA biosensors

Quercetin interaction with dsDNA was investigated electrochemically using two types of DNA biosensor in order to evaluate the occurrence of DNA damage caused by oxidized quercetin. The results showed that quercetin binds to dsDNA where it can undergo oxidation. The radicals formed during quercetin oxidation cause breaks of the hydrogen bonds in the dsDNA finally giving rise to 8-oxoguanine since the DNA guanosine and adenosine nucleotides in contact with the electrode surface can easily be oxidized. A mechanism for oxidized quercetin-induced damage to dsDNA immobilized onto a glassy carbon electrode surface is proposed and the formation of 8-oxoguanine is explained. The importance of DNA-electrochemical biosensors in the determination of the interaction mechanism between DNA and quercetin is clearly demonstrated.     

Kinetics and mechanism of piperidine carbonylation in the presence of Cu(I) and Cu(II) complexes

The kinetics of piperidine carbonylation to bispentamethylenurea in the presence of Cu(I) and Cu(II) complexes has been studied. An adequate mechanism of the process is proposed and the constant of the rate-determining step has been calculated.

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(I, II) -. .

     

Interaction of antitumor flavonoids with dsDNA in the absence and presence of Cu(II)

The binding of antitumor flavonoids, namely 3-hydroxyflavone (3HF) and hesperidin (Hesp) with dsDNA was investigated in the absence and presence of Cu(II) using cyclic voltammetry and square wave voltammetry at the hanging mercury drop electrode. The reduction currents of 3HF, 3HF-Cu complex, and the 3HF-β-cyclodextrin inclusion complex decreased after intercalation into dsDNA. The intercalation of Hesp into dsDNA is weak. dsDNA is reduced at a potential of ?1.48 V overlaying the reduction of Hesp. In contrast, in the presence of Cu(II), the interaction of Hesp with dsDNA leads to a much stronger intercalation. The binding constants of the flavonoid-Cu complex with dsDNA were evaluated and calibration graphs for the determination of dsDNA were obtained from the decrease in the peak current in the cyclic voltammograms of 3HF in the presence of dsDNA. The proposed method exhibited good recovery and reproducibility for indirect determination of dsDNA.     

Interaction of Cu(II) and Cd(II) ions with DNA from Spirulina platensis

Equilibrium dialysis and atomic absorption analysis were used to obtain adsorption isotherms and determine the stoichiometric binding constants of Cu(II) and Cd(II) ions to DNA from Spirulina platensis in solutions. The stoichiometric constants of Cu(II) and Cd(II) ions with DNA from S. platensis in 3 mM NaCI are 15.56⋅10⁴ and 14.40⋅10⁴, respectively. Effect of ionic strength and DNA GC content on binding constants of Cu(II)- and Cd(II)-DNA complexes were studied out. It was showed that the binding constants of Cu(II)- and Cd(II)-DNA complexes decrease with increase of ionic strength. The empirical dependences of logK on the GC content has been derived for Cd(II)- and Cu(II)-DNA complexes.     

Photolysis of oxygen saturated ethers in the presence of Sn(Ⅱ) or Cu(Ⅱ) salts

Photolysis of diethyl ether-oxygen charge transfer complex in the presence of Sn(Ⅱ)or Cu(Ⅱ)salts gave higher yields of the oxidation products,ethyl acetate,acetaldehyde,ethanol,ethyl formate and methanol compared with those without the salts.In addition,the photolysis of an oxygen saturated te-trahydrofuran(THF)or dibutyl ether solution gave y-butyro-lactone or butanol and butyl butyrate as major products with small amounts of undetermined compounds,respectively.Their yields were also affected by the addition of Cu(Ⅱ)or Sn(Ⅱ)salts.     

Applications of electron paramagnetic resonance spectroscopy to study interactions of metalloenzymes with Cu(II) ions

In the past, the method of reconstitution was used to investigate the interaction between metalloenzymes (containing Zn(II)) and metal ions. In this paper, electron paramagnetic resonance (EPR) has been employed to firstly study the direct interactions between Bacillus subtilis neutral proteinase (BSNP), nuclease P1 and Cu(II) ions added in aqueous solution, respectively. These results show that a dynamic equilibrium exists between the Zn(II) in the active site of native enzymes and the added Cu(II), the added Cu(II) partly replaces the Zn(II), forming Cu(II)-enzyme derivatives. As a result, the activity of the native enzymes is influenced. The influences of pH value on this kind of interaction have also been investigated, and the results demonstrate that the change of pH value has little influence on the system of nuclease P1, but has remarkable influence on BSNP. We firstly obtained the EPR spectra for Cu(II)-enzyme derivatives. In addition, the derivative of Cu(II)-BSNP exists in the solution with two different conformations (I type g(parallel)=2.34, A(parallel) (mT)=13.4; II type g(parallel)=2.25, A(parallel) (mT)=16.1), and this two conformations exchanged each other depending on pH.     

Influence of Cu(II) on the interaction of sulfite with DNA

The quantitative influence of Cu(II) on the interaction of eukaryotic DNA with sulfite (SO(3)(2-)), which is a derivative of sulfur dioxide in the human body, was studied using ultraviolet (UV) absorption spectrometry. The results showed that under physiological pH conditions, SO(3)(2-) reacted weakly with DNA at concentrations of up to 10(-1)M, at which point a rapid increase in the reaction constant and the reaction number of SO(3)(2-) with DNA was observed. The addition of Cu(II) at concentrations ranging from 6.67 x 10(-4) to 3.33 x 10(-3)M to DNA-SO(3)(2-) binary systems increased the reaction constant of SO(3)(2-) with DNA 41- to 115-fold at a low concentration of SO(3)(2-) (10(-3)M), and 4- to 84-fold at an intermediate concentration of SO(3)(2-) (10(-2)M), but had little influence on the reaction number of SO(3)(2-) with DNA compared with the absence of Cu(II). When the concentration of SO(3)(2-) reached 10(-1)M, the presence of Cu(II) reduced the reaction number but had no effect on the reaction constant of SO(3)(2-) with DNA. These results show that the efficiency of SO(3)(2-) is increased in the presence of Cu(II) at high concentrations of SO(3)(2-).