Copper complexes electrodes

Neutralization to phenolphthalein is satisfactory, but a glass electrode might give better results. Hydroxyurea is decomposed very rapidly in aqueous acidic medium, whereas its metallic salts (sodium or the copper complex salts) are stable. 

Shuman and Michael [10] applied a rotating disk electrode to the measurement of copper complex dissociation rate constants in marine coastal waters. An operational definition for labile and non-labile metal complexes was established on kinetic criteria. Samples collected off the mid-Atlantic coast of USA showed varying degrees of copper chelation. It is suggested that the technique should be useful for metal toxicity studies because of its ability to measure both equilibrium concentrations and kinetic availability of soluble metal. 

With the exception of Elder et. al., who used EXAFS to look at redox properties of copper complexes diffused in Nafion film modified electrodes (21), no in-situ studies have been reported on modified electrodes using EXAFS. 

An appropriate ion-specific electrode was found to provide a convenient, precise and relatively inexpensive method for potentiometry of copper(II) ion in copper-complex azo or formazan dyes. Copper(II) ion in copper phthalocyanine dyes can be quantified after anion exchange. Twelve commercial premetallised dyes evaluated using this technique contained copper(II) ion concentrations in the range 0.007 to 0.2%. Thus many copper-complex direct or reactive dyes are likely to contribute low but possibly significant amounts of ionic copper to textile dyeing effluents [52]. 

The insolubility of the Cu(I) halide salts, as well as the possibility of /x-halo-bridge formation between two copper atoms (as discussed later) or between the copper complex and the electrode surface, suggests that the presence of hahdes may alter the electrochemical properties observed for copper-containing solutions. 

The occurrence of the redox-driven reversible assembling-disassembling process involving copper complexes of 16 has been verified through cyclic voltammetry experiments at a platinum electrode in a MeCN solution. Figure 2.17 shows the CV profile obtained with a solution of the double-strand helicate complex [ Cu 21 (16)212 +. 

The Ni(II) complex of the hexaaza macrocyclic ligand 1 is reported to show a high activity for the electrocatalytic reduction of C02 to CO when a rotating copper disc electrode is used (85). In addition, water-soluble Niu-azacyclam complexes, 3a-3g, where R = carboxamide or sulfonamide, either aliphatic or aromatic, are found to be active in the electrocatalytic reduction of C02 at a mercury cathode. The efficiency is comparable to that of [Ni(cyclam)]2+ (14). 

Table 13.2 shows the concentrations of Cu2+ in tap water and lake water determined by the MPA-Gly-Gly-His modified electrode and compared with those of inductively coupled plasma mass spectrometry (ICP-MS). The measured concentration of Cu2+ in tap water when dilutions were accounted for using the MPA-Gly-Gly-His modified electrode was 0.55 +0.08 pM (95% confidence interval). This value is much lower than the copper concentration measured by ICP-MS of 1.70+0.15 pM (95% confidence interval). The peptide-modified electrode measures free Cu2+ or weakly bound copper complexes rather than the total metal-ion concentration measured by ICP-MS. Hence the use of peptides has the ability to measure metal-ion bioavailability for specific species. The results are consistent with others who have also shown that the labile fraction of copper is much less than the total copper [7]. 

The analytical application of MPA-Gly-Gly-His modified electrodes was also demonstrated in the determination of Cu2+ in lake water. The concentration of Cu2+ in lake water, after dilutions were accounted for, was ll+4nM (95% confidence interval). The analytical result obtained is significantly lower than that measured by ICP-MS of 925 + 22nM (95% confidence interval). This difference is more pronounced in lake water compared to tap water presumably due to greater presence of copper complexes in lake water which are not measured by the MPA-Gly-Gly-His sensor. 

Shuman, M.S. and Michael, L.C., 1978. Application of the rotated disk electrode to measurement of copper complex dissociation rate constants in marine coastal samples. Environm. Sci. Technol., 12 1069-1072. 

Figure 3. Cyclic voltammograms of bis-chelate copper complexes (a) [Cu(phen)2] and (b) [Cu(dmbp)2] in CH3CN- n-C4H9)4NC104 (0.1 M), and (c) of copper-catenate Cu.5 in CH3CN for oxidation, in DMF for reduction. Oxidation on Pt, reduction on the hanging mereury electrode.

Reactions of copper complexes show these ligand effects. Table 12-18 lists some of these reactions and their electrode potentials. If the reactions of the aquated Cu(II)... 

Many examples are given within the electron transfer (ET)-based series involving copper complexes (Table 3). In some cases (see for example entry 3 in Table 3), the supporting electrolyte consists of a mixture of a copper salt and of a salt containing the ligand concerned. In that case, the [Cu(L2)] anions only form within the solution and react with oxidized ET on the electrode. Moreover, note (see Table 3) that different modifications of the same compound may be obtained depending on the electrochemical conditions. 

Because the mercury chelate is more stable than the corresponding complexes of such cations as calcium, zinc, lead, or copper, complexation of these ions occurs only after the ligand has been freed by the electrode process. 

P. W. Alexander, P. R. Haddad, and M. Trojanowicz, Potentiometric Flow Injection Determination of Copper Complexing Inorganic Anions with a Copper Wire Indicator Electrode. Anal. Chem., 56 (1984) 2417. 

Soares, H.M.V.M., Vasconcelos, M.T.S.D., 1995. Application of potentiometric stripping analysis for speciation of copper complexes with adsorbable ligands on the mercury electrode. Anal. Chim. Acta 314, 241-249. 

Copper complexes adsorbed (167-169) and covalently (170) bound to electrode siufaces were shown to be good electrocatalysts for the four-electron reduction of dioxygen. The results indicate that a CU2O2L2 (L = phenantroline) intermediate is formed dining the reduction. 

As described above, the self-assembly of Cys promotes the electron transfer between SOD and the Au electrode. This Cys-promoted rapid and direct electron transfer of SOD and its relevance to the redox reaction of the copper complex moiety in SOD formed a strong basis for the development of a SOD-based third-generation biosensor for 02 because the copper complex moiety has been well documented as the active site for the catalytic dismutation of O2 [128]. Figure 10-39 shows CVs at the bare Au, Cys/Au and SOD/Cys/ Au electrodes in PBS (O2 saturated) containing 0.002 unit of XOD and 50 pM xanthine, i.e. in the presence of O2. Both cathodic and anodic peak currents corresponding to the redox reaction of the SOD confined on the electrode are significantly increased, compared with those in the absence of O2 (Fig. 10-36a) [133—135]. Such a redox response was not... 

Application of ion-selective electrodes to determine copper by standard addition method in nickel plating bath was suggested by Frant. Later Hulanicki et al." using a copper ion-selective electrode proposed a method based on multiple standard addition in presence of a copper complexing agent to prevent a harmful influence of chloride ions. In this work a similar method is used to determine copper also in zinc and cobalt baths. 

In the interpretations of the mechanism of detection, as presented up to date the equilibrium between metallic copper and more or less complexed copper ions in solution was considered. A voltammetric study with a metallic copper disc electrode in neutral phosphate buffer solution, used frequently as eluent in chromatographic detection, shows formation of an oxide layer on the copper surface. Its thickness and stoichiometric composition distinctly depends on the electrode pretreatment. 

Rotating-copper-disk electrode techniques have been used to evaluate the efficiency of the nickel macrocycle catalyst for the reduction of CO2 to Studies have been performed using Ni(diazacyclam) + (diazacyclam = 3,10-dimethyl-1,3,5,8,10,12-hexaazacyclophane) (5.6), a complex derived from cy-clam, which appears to be more active than [Ni(cyclam)2] " under the same conditions (see Figure 5.70) . These results are consistent with a mechanism proposed by other authors - . ... 

In the presence of A and adenosine, the copper(II)/copper(Hg) couple split to the copper(II)/copper(I) and copper(I)/copper(Hg) couples [179, 180]. Sparingly soluble compounds of copper(I) with A and its ribonucleoside were accumulated on the electrode, either by reduction of the Cu(II) ions or by oxidation of the copper amalgam electrode. The copper(I) A deposit was stripped either cathodically or anodically. The stripping peaks obtained for copper complexes had higher detection limits, but appeared over a wider range of pH and at more negative potentials than the peaks related to mercury compounds [161]. It was shown that in addition to A, other purine bases, such as G, hypoxanthine, xanthine, and their nucleosides (guanosine and inosine) [181-183],... 

Fig. 8). A deep degradation of DNA due to acid hydrolysis [248] or oxidative damage mediated by copper complexes [306] was required to observe increased intensity of DNA signals on carbon electrodes. 

By using a copper amalgam electrode, which in effect is a copper(I)- and copper(II)-aqua ion electrode, and a pure mercury electrode, which is a redox electrode, IB remeasured and confirmed the gross complexity constant Pa and the fifth consecutive constant for the copper(II)-ammine system and provided, in addition to a number of standard redox potentials, the two step constants of the copper(I)... 

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