Reducible cation sensors

Quinone- and anthraquinone-containing species have also been utilized as electrochemical sensor species in another area of this chemistry pioneered by Gokel and co-workers (Gustowski et al., 1986 Delgado et al., 1988). These systems have been reviewed elsewhere (Kaifer and Echegoyen, 1990). 

Direct coordination between the redox centre and guest leads to generally large perturbations in the electrochemical behaviour of the host. A particularly elegant example of this type redox/coordination coupling is given by the quinone crown ether species synthesized by Cooper and co-workers (Wolf and Cooper, 1984 Delgado et al., 1992) (Fig. 24). 

A number of differently sized crown ethers were synthesized and the shift of the first reduction potential was found for each compound in the presence of excess alkali metal tosylate. The shifts were all between 60 and 70 mV for compound [50] but the larger crowns displayed larger shifts (Table 10). In contrast to the expected order of the magnitudes of the shifts from ion pairing effects alone, K+ with compound [51] yields the largest potential shift followed by Rb+ Na+ Cs+ Li+. 

By oxidizing the free phenolic rings of various calixarenes it is pos- 

The p-t-butylcalix[4]arenediquinone-bis(methylether) [56], which had previously been synthesized by Gutsche and co-workers, was used as a model compound in these studies. The receptors [54] and [55] have been shown by nmr titration techniques to form 1 1 solution state complexes with group 1 and 2 metal, ammonium and alkylammonium guest species. 

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Water-soluble sensors for transition metals ferrocene polyazamacrocycles 28 Reducible cation sensors 35... 

The design of an OR molecule demands that the PET quenching be eliminated through addition of either stimulus. This need is reflected in the anthracene derivative 3, in which the tricarboxylate Group II cation sensor also contains a tertiary amine. Thus, if compound 3 is buffered at pH 7.3, with no metal cations present, the system will not fluoresce, as a consequence of PET from the tertiary amine to the anthracene. If the pH is reduced, the... 

Because Nafion film can preconcentrate organic cations at a substrate electrode surface, Nafion-coated electrodes can be used as sensitive and selective sensors for electroactive organic cations. The film-entrapped ion is then either oxidized or reduced and the resulting current is recorded and related to the concentration of ions in the aqueous solution (qualitatively similar to anodic stripping voltammetry). It was shown that ion-exchange voltammetric determination of the dication methyl viologen at a Nafion-film-coated electrode results in an improvement of three orders of magnitude in detection limit relative to an uncoated electrode.46... 

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