Electrochemical Recognition of Cations

Group IA, IIA Metal Cations by Organic Redox-Active Macrocycles 

Electrochemical Group IA Metal Cation Dependence of Quinone and Nitroaromatic Crown Ether Macrocycles 

Compound Group IA metal cation (1 equivalent added) AE (V)° ( complex fn ) Binding enhancement (KrfKi) calculated from Eq. (1)  

0 Shift in reduction potential produced by presence of metal cation. b Can be calculated only in two-wave case, see Ref. (34). r Two-wave situation. 

Redox-Active Macrocycles Containing Transition Metal Organometallic Redox Centers 

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Electrochemical recognition of cationic guest species by redox-active... 

Beer, P. D. Gale, P. A. Chen. G. Z. Mechanisms of electrochemical recognition of cations, anions and neutral guest species by redox-active receptor molecules, Coord. Chem. Rev. 1999, 185-186, 3-36. 

Supramolecules containing metal-polypyridine units, especially the Ru(dpp)-based dendrimers, could be used as electron reservoirs or components of molecular-electronic devices. Supramolecules in which an electroactive M(N,N) group is attached to a receptor capable of molecular recognition (crown ethers, calixarenes, cryptands etc.) can work as electrochemical sensors. Electrochemical recognition of cations as well as anions has been reported [33-35, 257, 263]. 

Nevertheless, as the cyclic voltammograms were stabilized only after a very large number of scans, poty(13a) was not suitable for the electrochemical recognition of cations in real time. 

D. Electrochemical Recognition of Transition Metal Guest Cations by Ferrocene Aza-, Thia-Donor Macrocyclic Ligands... 

Electrochemical methods have played an important role in the recognition of cation radicals as intermediates in organic chemistry and in the study of their properties. An electrode is fundamentally an electron-transfer agent so that, given the proper solvent system, anodic oxidation allows formation of the cation radical without any associated proton or other atom transfer and without the formation of a reduced form in the immediate vicinity of the cation radical. Moreover, because the potential of the electrode can be adjusted precisely, its oxidizing power can be controlled, and further oxidation of the cation radical can often be avoided. Finally, the electrochemical experiment can involve both production of the cation radical and an analysis of its behavior, so that information about the thermodynamics of its formation and the kinetics of its reaction can be obtained, even if the cation radical lifetime is as short as a few milliseconds. There are some limitations, however, in the anodic production of cation radicals. The choice of solvent is limited to those that show reasonable conductivity with a supporting electrolyte (e.g. tetra-n-butylammonium perchlorate, TBAP). Acetonitrile, methylene chloride and nitrobenzene have been employed as solvents, but other favorites, such as benzene and cyclohexane, cannot be used. The relatively high dielectric constant of the suitable... 

In contrast to the recognition of cations or anions, the electrochemical sensing of neutral molecules by redox-active receptors is relatively rare, with few systems undergoing a significant electrochemical response to complexation. Some ferrocene compounds that electrochemically respond to neutral molecules and charge-neutral species are shown in Figure 4. 

A. C. Ion, J. -C. Moutet, A. Pailleret, A. Popescu, E. Saint-Aman, E. Siebert, E. M. Un-gureanu. Electrochemical recognition of metal cations by polylcrown ether ferrocene) films investigated by cyclic voltammetry and electrochemical impedance spectroscopy, J. Electroanal. Chem., 1999,464, pp. 24-30. 

J.-J. Xu, H.-Q. Fang, and H.-Y. Chen, The electrochemical characteristics of an inorganic monolayer film modified gold electrode and its molecular recognition of alkali metal cation. J. Electroanal. Chem. 426,139-143 (1997). 

The electrochemical properties of ferrocene have been utilized by many workers in the field of electrochemical molecular recognition. Saji (1986) showed that the previously synthesized (Biernat and Wilczewski, 1980) ferrocene crown ether molecule (Fig. 3 [1]), whose binding properties had previously been studied only by nmr and UV/Vis techniques (Akabori et al., 1983), could be used as an electrochemical sensor for alkali metal cations involving a combination of through-space and through-bond interactions. 

Electrochemical recognition experiments with Co(Et2NCS2)3 revealed no evidence of interactions with Group I metal cations. 

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