Cation recognition

In the area of ion sensing, cation recognition by electrodes containing functionalized redox-active polymers has been an area of considerable interest. Fabre and co-workers have reported the development of a boronate-functionalized polypyrrole as a fluoride anion-responsive electroactive polymer film. The electropolymerizable polypyrrole precursor (11) (Fig. 11) was synthesized by the hydroboration reaction of l-(phenylsulfonyl)-3-vinylpyrrole with diisopinocampheylborane followed by treatment with pinacol and the deprotection of the pyrrole ring.33 The same methodology was utilized for the production of several electropolymerizable aromatic compounds (of pyrrole (12) (Fig. 11), thiophene (13 and 14) (Fig. 11), and aniline) bearing boronic acid and boronate substituents as precursors of fluoride- and/or chloride-responsive conjugated polymer.34... 

Valeur B., Leray I., Design principles of fluorescent molecular sensors for cation recognition, Coord. Chem. Rev. 2000 205 3. 

R. Ludwig and N.T.K. Dzung, Calixarene-based molecules for cation recognition. Sensors 2, 397—416... 

Taylor However, there is evidence from us and other groups that the bivalent cation recognition properties of the sites that mediate stimulation and inhibition may be different. 

Aliphatic solvents, alkyllithium compounds and, 14 250-251 Aliphatic sulfonates, 26 145 Aliquot samples, 13 413-415 analysis of, 13 416 Aliskren, 5 158 Alitame, 12 42 24 232 Alite, phase in Portland cement clinker, 5 471, 472t, 473t Alitretinoin, 25 790 Alizarin, color of, 7 331 Alizarin derivatives, 9 337 Alizarin pure Blue B, 4 361t Alkadienes, metathesis of, 26 923 Alkali/alkaline-earth cation recognition,... 

The examples described above illustrate the immense variety of fluoroionophores that have been designed for cation recognition. Emphasis was put on the understanding of cation-induced photophysical changes, which should help the user and the designer of this kind of sensor. 

Valeur B. and Leray I. (2001) PCT (Photo-induced Charge Transfer) Fluorescent Molecular Sensors for Cation Recognition, in Valeur B. and Brochon J. C. (Eds),... 

Electrochemical cationic recognition studies were carried out on [57] using... 

The discovery of crown ethers and cryptands in the late sixties opened new possibilities of cation recognition with improvement of selectivity, especially for alkali metal ions for which there is a lack of selective chelators. Then, the idea of coupling these ionophores to chromophores or fluorophores, leading to so-called chromoionophores and fluoroionophores, respectively, emerged some years later l9) As only fluorescent probes are considered in this chapter, chromoionophores will not be described. 

Figure 2.2. Principle of cation recognition based on cation control of photoinduced electron transfer in nonconjugated donor-acceptor systems. (Example from Ref. 26.)...

At the present time, there is a striking contrast between the extensive development of fluorescent probes for cation recognition and the limited number of available probes for anions notwithstanding the great need for the latter. This is due to the difficulty of the design of selective anion receptors progress made in the relevant field of supra-molecular chemistry will certainly lead in the future to new selective fluorescent signaling receptors of anions. 

The main feature for cation recognition by tetra-bridged phosphorylated cavitands arises from the cooperative effect of the four phosphorus groups and the aromatic molecular cavity. In the phosphorus(IV) cavitands guest binding will be achieved through O (P=0) or S (P=S) coordination with different affinity for hard or soft metal ions. On the other hand, transition metal rim complexes described above can act as host for metal cation. 

In this section, complexes that contain macrocyclic or calix[4]arene recognition domains coupled to bpy ligands are considered. In addition, discussions of calix[4]arene-containing complexes are extended to include a number of species that are of interest other than for anion or cation recognition. Compounds are organized according to the type of species that they bind. 

Figure 7.5.2. C60 derivative monolayer self-assembled as a result of ammonium cation recognition by crown ether moiety.

Since binding in solution results from a compromise between interaction with the ligand and solvation, new insights into the origin of the cation recognition process and of the macrocyclic and cryptate effects can be gained from experimental gas phase studies [2.34, 2.35] as well as from computer modelling calculations in vacuo or in a solvent [1.35b, 1.42, 1.43, 1.45, 2.36, 2.37, A.37]. In particular, molecular dynamics calculations indicate that complementarity is reflected in restricted motion of the ion in the cavity [1.45, 2.36]. 

Moore, A. J., Goldenberg, L. M., Bryce, M. R., etal, New crown annelated tetrathiafulvalenes Synthesis, electrochemistry, self-assembly of thiol derivatives, and metal cation recognition. J. Org. Chem. 2000, 65, 8269-8276. 

TABLE 6. Electrochemical Group I metal cation recognition data3... 

Cation recognition by luminescence sensing has also been reported. As referred to above, release and recapture of alkali and alkaline earth metal ions for [(bpy)Re(CO)3L ]+, where Lj contains an azacrown ether [63] was controlled by light. A sensor for lanthanide ions is shown in Fig. 27. The photoactive center was RcI( bpy ) and its emission was quenched by the lanthanide ion [119]. 

A ditopic receptor 71, comprising a semitubular calix[4]arene system [91] for cation recognition and urea moieties for anion recognition, was reported very recently. The complexation of sodium or potassium cations into the central ethylene glycol cavity invokes substantial enhancement of the binding strength (more than one order of magnitude) towards selected anions (halides, acetate). 

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