Silver-silver nitrate couple as reference electrode in acetonitrile

Properties of relatively new polymeric materials are capitalized upon to address a relatively old problem in electrochemistry, the comparison of electrode potentials measured in different solvents. In particular, electrode potentials measured in acetonitrile and in water are compared at voltammetrically relevant concentrations. Activity coefficients are measured for silver perchlorate in acetonitrile using the isopiestic technique. These results are used to interpret the influence of silver perchlorate activity on apparent formal potentials measured in acetonitrile for an electrochemically polymerized redox polymer. Similar measurements are made on the same redox polymer in water, and in both solvents the cell potentials are Nernstian for a simple ionic stoichiometry. The cell potentials measured in acetonitrile are +0.244 V of those measured in water. This difference is consistent with the difference expected from estimates of the free energy of transfer of silver perchlorate. It is also consistent with predictions based on certain extrathermodynamic assumptions concerning the free energies of transfer of the single ions. The results reported here suggest that the free energy for transferring silver perchlorate from water to acetonitrile is -21.9 ( 0.9 kJ/mol and that the potential of the Ag|a(AgClO 4 ) CH3CN ) 1 couple is -0.227 ( 0.009 V of the Ag|a(AgClO 4 ) H2O ) 1 couple. The influence of electrolyte activity on formal potentials measured for redox couples dissolved in acetonitrile is also investigated. Our results demonstrate that internal reference couples such as ferrocene/ferrocenium should be used with caution. Over certain concentration ranges, ion pairing may play an important role in determining formal potentials measured for dissolved reference compounds. To provide a reliable set of values to which subsequent comparisons can be made in acetonitrile, we report apparent formal potentials as a function of electrolyte activity for several popular internal reference couples.In this paper we describe our efforts to measure activity coefficients in acetonitrile, to compare the potential for the Ag|X M AgClO 4 couple in water with that of the Ag|X M AgClO 4 couple in acetonitrile, and to measure formal potentials for a series of redox couples as a function of AgClO 4 activity in acetonitrile. These efforts were initiated due to dissatisfaction with our limited ability to interpret cell potentials in solvents other than water. Unfortunately, there is no completely unambiguous way of interpreting potentials in many nonaqueous solvents. Much of this ambiguity stems from the lack of suitable reference half-cells. Three major problems plague reference half-cells in nonaqueous solvents: (1) unknown liquid junction potentials, (2) questionable extrathermodynamic assumptions concerning internal reference couples, and (3) unknown activity coefficients for the reference couple. Our efforts to overcome these obstacles have enabled us to make a series of measurements in acetonitrile that are similar to the classical ...

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“…Suppose that the Pt|Ox n+ , Red (n-1)+ , X M AgClO 4 ||X M AgClO 4 |Ag (13) Ox n+ + e -) Red (n-1) (14)…”

Section: Resultsmentioning

confidence: 99%

Influence of Electrolyte Activity on Apparent Formal Potentials Measured for Redox Probes in Water and Acetonitrile

and

Mechalke

1997

Anal. Chem.

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“…A platinum disc or glassy carbon working electrode and a platinum wire auxiliary electrode were employed for these measurements versus an Ag/AgNO 3 reference electrode (E°= 0.503 V versus NHE). 26 Unless mentioned, all the electrochemical measurements were performed under argon atmosphere. Spectro-electrochemical behaviour was monitored with a combined Hewlett-Packard model 8452A diode array spectrophotometer and a PARC potentiostat model 173.…”

Section: Methods and Instrumentsmentioning

confidence: 99%

Di-imine copper(II) complexes as redox mediator and modulator in 2-deoxy-D-ribose oxidative damage

Azzellini

Bagatin²,

Ferreira³

2006

Redox Rep.

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Redox properties of copper complexes are important for their catalytic functions in vitro and in biological systems, and can contribute to their reactivity toward selected targets. In order to evaluate the influence of different ligands on the reactivity of copper ions, comparative studies were carried out with some copper(II) complexes containing a tridentate imine, or a tetradentate di-Schiff base ligand with a mixed pyridine, pyrazine, or imidazole donor set, acting as catalysts in the oxidation of 2-deoxy-D-ribose. Addition of the reducing agent glutathione (gamma-glutamylcysteinylglycine; GSH), which can also act as a good ligand for copper(I), mediated the oxidation of the substrate. For some of these compounds, a reductive activation followed by competition for the metal ion was verified, with formation of copper(I)-glutathione complex monitored by fluorescence measurements. For others, however, the reduction of the metal by the glutathione seems to not occur. In the presence of hydrogen peroxide, the oxidative damage is significantly enhanced for all the complexes tested. Redox potential measurements by cyclic voltammetry corroborated partially these results, indicating that the most reactive complexes are those with more positive redox potential. Evidence for site-specific attack to 2-deoxy-D-ribose was also observed, consistent with the intermediary formation of a copper-hydroxyl species, [LCu(II)(*OH)], rather than 'free' hydroxyl radical.

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“…The experiments were performed in acetonitrile using an Ag/Ag 0.01 M (TEAClO 4 0.1 M) reference electrode. All potentials were corrected to SHE by adding 0.503 V as reported in the literature [37].…”

Section: Methodsmentioning

confidence: 99%

Synthesis and Characterization of a Novel Dodecanuclear Porphyrin Ruthenium Cluster

Toma

Araki

Silva

1998

Monatshefte fuer Chemie

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A new symmetric dodecanuclear complex constituted by a 5,10,15,20-tetra pyridyl porphyrin centre coordinated to four triangular "-oxo-ruthenium acetate clusters, [Ru 3 O (Ac) 6 (py) 2 ] ( py pyridine), is reported. Its electrochemical and spectroelectrochemical behaviour involves ®ve accessible oxidation states of the cluster unities, in addition to the porphyrin oxidation and reduction waves, in the range of À1.5 to 2.4 V. The cluster porphyrin species associates very strongly with tetrasulfonate phthalocyaninatecopper (II), forming electrostatically assembled stacked compounds both in dimethylsulfoxide solution and in the solid state.

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Silver-silver nitrate couple as reference electrode in acetonitrile

Cited by 72 publications

References 18 publications

Influence of Electrolyte Activity on Apparent Formal Potentials Measured for Redox Probes in Water and Acetonitrile

Influence of Electrolyte Activity on Apparent Formal Potentials Measured for Redox Probes in Water and Acetonitrile

Di-imine copper(II) complexes as redox mediator and modulator in 2-deoxy-D-ribose oxidative damage

Synthesis and Characterization of a Novel Dodecanuclear Porphyrin Ruthenium Cluster

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