Electrochemical generation of Cu(I) complexes in aqueous solutions studied by on-line mass spectrometry (original) (raw)
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Electroanalysis, 2018
Bicinchoninic acid (BCA) is widely used for determining the valence state of copper in biological systems and quantification of the total protein concentration (BCA assay). Despite its well-known high selectivity of Cu(I) over Cu(II), the exact formation constants for Cu(I)(BCA) 2 3À and Cu(II)(BCA) 2 2À complexes remain uncertain. These uncertainties, affect the correct interpretations of the roles of copper in biological processes and the BCA assay data. By studying the voltammetric behaviors of Cu(I)(BCA) 2 3À and Cu(II)(BCA) 2 2À , we demonstrate that the apparent lack of redox reaction reversibility is caused by an adsorption wave of Cu(II)(B-CA) 2 2À. With the adsorption wave identified, we found that the Cu(I)/Cu(II) selectivity of BCA is essentially identical to another popular ligand, bathocuproinedisulfonic acid (BCS). Density functional theory calculation on the geometries of Cu(I)(BCA) 2 3À and Cu(II)(BCA) 2 2À rationalizes the preferential Cu(I) binding by BCA and the strong adsorption of the Cu(II)(BCA) 2 2À complex at the glassy carbon electrode. Based on the shift in the standard reduction potential of free Cu(II)/Cu(I) upon binding to BCA, we affirm that the formation constants for Cu(I)(BCA) 2 3À and Cu(II)(BCA) 2 2À are 10 17.2 and 10 8.9 , respectively. Therefore, BCA can be chosen among various ligands for effective and reliable studies of the copper binding affinities of different biomolecules.
Electrochemical Reduction of Copper Complexes with Glycine, Alanine and Valine
Journal of The Electrochemical Society, 2021
Basic electrochemical studies of coordination complexes between cupric ions and simple amino acids as ligands (L), namely glycine, alanine and valine, have been carried out to provide insight in the effect of complexation on Cu2+ discharge electrochemistry. The results show that there are strong differences in their cyclic voltammograms, despite the similarities in coordination equilibrium, central atom d electronic structure and inner sphere coordination distances (verified by chemical equilibrium quantification, UV spectroscopy and EXAFS). Evidence of mass transport limitations by diffusion of the neutral CuL2 complexes in solution, and cuprous species generation on the electrode during copper electrodeposition was found, both of which proved to be the main phenomena accounting for the different electrochemical behaviour previously mentioned. Voltammetric studies also showed that, surprisingly, cuprous species are produced not only at the onset of copper electroreduction but at mo...
Bangladesh Journal of Scientific and Industrial Research, 2011
Complexation and speciation of copper (II) in ppb level with 1,10-phenanthroline (L) in aqueous media have been investigated by differential pulse anodic stripping voltammetry using thin mercury film glassy carbon electrode (TMFGCE). The work was carried out at constant ionic strength of 0.01 mol dm-3 using NaNO3 at ambient temperature. The pH was kept constant at 9.12 ± 0.10 by the addition of borate buffer. Applying the concept of DeFord and Hume, the stability constants of different species of copper with 1,10-phenanthroline were calculated from the variation of peak potential and diffusion current of simple and complexed metal ions under the present experimental conditions. It was found that copper(II) form three complexes (1:1, 1:2 and 1: 3; metal : ligand) with 1,10-phenanthroline. The overall stability constant of copper complexes, MLn can be defined as βMLn= [MLn ]/[M2+][L]n in which M2+ = Cu2+ and L = 1,10-phenanthroline; n is an integer. The values of the stability constan...
Central European Journal of Chemistry, 2013
Electrospray ionization mass spectrometry was used to study the complexes of ligands containing two bipyridine units, namely 3,5-bis(2,2-bipyridin-4-ylethynyl)benzoic acid (1) and its methyl and ethyl esters (2, 3), with copper cation, with CuCl2 as a source of copper. It was found that the type of complexes formed strongly depends on CuCl2 concentration. At lower CuCl2 concentration, the detected complexes were rather simple and some of them were formed upon electrospray ionization conditions e.g. ions [22+Cu2]2+ and [32+Cu2]2+ (complexes ligand-Cu(I) of stoichiometry 2:2) which are analogical to the well known, for quaterpyridine, helical complexes. At higher CuCl2 concentration, the detected complexes were more complicated, and most of them contained copper cations bridged by chlorides. The largest ions were [L2+Cu4Cl6]2+. The CID MS/MS spectra of these ions allowed determination of their mass spectrometric fragmentation pathways and as a consequence their structure elucidation.
This research was carried out to studied the electrochemical behavior of metals Cu(II) with Lysine (Lys) by Cyclic voltammetry (CV), Chronamperometry (CA), UV-Vis and FTIR spectroscopic techniques. Electrochemical and spectroscopic techniques reveal the interaction of Cu(II), with the ligands (Lys) that may be formed of metal-ligand complexes. Electrochemical studies have been carried out in variation of metal ion concentration, ligand concentration, buffer solution of different pH and different scan rate. In this study all the experiment is carried out only in aqueous buffer solution; KCl or other conventional supporting electrolytes are not used in the solution. The effect of pH of Cu(II)-Lys was studied by varying pH from 3.0 to 9.0. The maximum peak current was obtained at pH 4. This shows that the electrochemical oxidation of Cu(II)-is facilitated in acid media and consequently the rate of electron transfer is quicker. The slopes of the plots of E p against pH of Cu-Lys metal ligand system was determined graphically as anodic peak 21-31 mV/pH at 0.1V/s, which is close to the theoretical value of 30 mV which indicates that the oxidation of all the studied metal-ligand systems proceeded via the 2e − /2H + processes. During the bulk electrolysis the electrosynthesized metal-ligand products were generated. UV-Vis and FTIR techniques were also used to confirm the interaction of Cu(II) with Lys.
Electrochemical studies of a dinuclear copper complex with imidazole derivative ligand H 3bphenim
Journal of Electroanalytical Chemistry, 2005
A new polynucleating ligand 4,5-bis(phenylalanyl-N-methyl)-2-methylimidazole (H 3 bphenim) has been synthesized and characterized. H 3 bphenim produces the crystalline dinuclear copper compound, [(Cu 2 bphenim)(H 2 O) 4 ]NO 3 the structure of which includes an imidazolato bridge between the two Cu(II) ions. Electrochemical and spectrophotometric evidence is produced for the cleavage of this imidazolato bridge when the complex is dissolved. The absence of the 375 nm band in the UV-Vis spectrum, known to be characteristic for such imidazolato-bridged Cu(II) compounds as well as the presence of two irreversible Cu II ! Cu I peaks in the cyclic voltammogram (CV), corroborate the formation of the asymmetric Cu A bphenimCu B ðCu II A LCu II B Þ where each copper coordination sphere is identified by spectroelectrochemical procedures. The key role of the solvent was demonstrated when mixtures of variable CH 3 CN:H 2 O ratio were studied and the corresponding voltammograms compared. CV studies also confirm the formation of a copper(I) solvated species after Cu A (I) decoordination. Potential step procedures were applied to elucidate the mechanisms of two coupled homogeneous reactions: the decoordination and subsequent solvation of Cu A (I) and the reproportionation reaction between Cu II A LCu II B and Cu I A LCu I B formed during electrolysis. The mechanisms proposed from the electrochemical behavior are verified by the low catalytic activity shown by the complex in the 3,5-di-tert-butylcatechol oxidation, when it is compared with similar compounds having the imidazolato-bridged Cu(II) structure.
Journal of The Electrochemical Society, 2003
The charge-transfer reaction between copper͑II͒ and copper electrodes is studied in electrolytes that are similar to galvanic copper baths, 2.2 M H 2 SO 4 ϩ 0.3 M CuSO 4 ϩ chloride ions (c Cl р 1 ϫ 10 Ϫ2 M͒, and polyethyleneglycol 1500 ͑PEG, c PEG р 4 ϫ 10 Ϫ3 M͒. Electrochemical quartz crystal microbalance ͑EQCM͒ measurements are conducted, mainly under conditions of cyclic voltammetry. The formation and dissolution of CuCl on the electrode surface at c Cl у 2 mM is demonstrated, a notable shift of the pseudo-equilibrium potential associated with CuCl deposition is analyzed, and the inhibition of the charge-transfer reaction by the PEG/Cl Ϫ surface layer is characterized. It is shown that the inhibiting layer forms by reaction between the adsorbate-covered copper electrode and PEG, i.e., neither Cu ϩ nor Cu ϩϩ from the electrolyte are required. Numerical simulations of the processes as well as parallel experiments conducted with electrolytes not containing Cu͑II͒ support the proposed mechanisms, in particular the role of the intermediate Cu ϩ .
Analytica Chimica Acta, 1999
The complexes formed from copper(II) and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP or HL) in aqueous methanol solution was studied by electrospray ionization mass spectrometry. The solution of a 1:1 complex of Cu(II) with 5-Br-PADAP showed ®ve peaks assignable to a binuclear complex [Cu 2 L 2 (AcO)] and mononuclear complexes [CuL] , [CuL(H 2 O)] , [CuL(AcOH)] and [CuL(HL)] (AcOacetate). Collision activated dissociation revealed the relative order of bonding strengths; Cu±L>Cu±HL>CuL±AcOH>CuL±H 2 O. The peak intensities of the binuclear complex showed secondorder dependency on those of the mono complex. As for the solution of Ni(II)±5-Br-PADAP, no binuclear complex was observed in the mass spectra. Thus, it was suggested that [Cu 2 L 2 (AcO)] was formed by the fast gas phase reaction: 2[CuL] AcO À @[Cu 2 L 2 (AcO)] .