Cations chemosensors

One of the first alkali metal cation chemosensors was based on the molecular architecture of the anthracene derivative (Figure 16.2c) [9]. Substitution of the simple tertiary amino group with an azacrown macrocycle resulted in fluorescence of the chemosensor responding to protons and potassium cations (Figure 16.5a). Further increase in selectivity of the sensor can be achieved via reduction of Brpnsted s basicity of the macrocycle. On the other hand, this modification must retain the electron donor character of the receptor in order to preserve the PET mode of... 

Valeur B., Badaoui F., Bardez E., Bourson J., Boutin P., Chatelain A., Devol I., Larrey B., Lefevre J. P. and Soulet A. (1997) Cation-Responsive Fluorescent Sensors. Understanding of Structural and Environmental Effects, in Desvergne J.-P. and Czarnik A. W. (Eds), Chemosensors of Ion and Molecule Recognition, NATO ASI Series, Kluwer Academic Publishers, Dordrecht, pp. 195-220. 

Fluorescent Chemosensors for Cations, Anions, and Neutral Analytes... 

Ho HA, Leclerc M. New colorimetric and fluorometric chemosensor based on a cationic polythiophene derivative for iodide-specific detection. J Am Chem Soc 2003 125 4412-4413. 

Fig. 8.16 Chemosensor with cation-selective benzo[l 5]crown-5 entities...

Calixarenes modified with a reporter site are equally competent chemosen-sors for the detection of a variety of analytes according to Scheme 6, especially when the analyte is cationic. The tt-cavity of a tetraanionic resorcin[4]arene readily binds cationic guests, a feature that Inouye et al. have exploited in the development of an acetylcholine chemosensor [358], The fluorescence from a pyrene-modified N-alkylpyridinium is strongly quenched upon its association with the tetraphenolate form of resorcin[4]arene (24). This quenching is consis-... 

It is believed that two crowns bind a K+ ion, thus leading to loosely preassembled bis-pyrene subunits. When the metal ion recognition event occurs in the presence of y-CD, dramatic enhancements of excimer emission are observed, thus providing a method to selectively detect K+ ion in aqueous solution. This ability to sense an ionic analyte is unusual for CD chemosensors. Modification of 28 with other ion binding sites should provide a general method for cation detection. 

Many chemosensors designed by Shinkai and coworkers are based on modification of the lower rim of a calix[4]arene with a fluorophore, whose emission properties change upon association of alkali metal cations. Fluorescence from the biphenyl subunit of 42 increases markedly upon the association of Na+... 

Cyclenes are a useful component of metal sensor molecules. The common structure of such chemosensor is fluorophore - linker - sensor. Various fluorophores were connected to the cyclene which ensured the detection of the desired cation. These molecules were often water soluble and worked under physiological conditions what made them interesting from the biomedical point of view. 

One constant problem for crown ether based sensors in vivo is the ubiquitous presence of chemical species that will compete with the target analyte for the sensor binding site. For sensors incorporating [18]crown-6 this especially problematic as sodium, potassium, ammonium and hydronium (H30+) cations are all attracted to the threefold symmetry of the crown s cavity. Protonated terminal amines, including amino acids and peptides, can also interfere with analyte detection. It is therefore all the more pleasing when a crown ether based sensor is developed that does not bind to biologically common cations. This is the case for a saxitoxin chemosensor reported by Gawley, LeBlanc and co-workers [24],... 

Figure 16.3 Principle of the PET (photoinduced electron transfer) chemosensor. (a) The HOMO level of the unbound receptor acts as an electron donor and effectively quenches the fluorescence of the sensor, (b) Upon coordination of the substrate, the energy of the HOMO level of the receptor is decreased due to electrostatic or coordinative interaction with cationic species and PET quenching is no longer possible...

Chang JH, Jeong Y, Shin Y-K. Selective photoinduced electron transfer-based cyanoan-thryl fluorescent chemosensors for paramagnetic metal cations. Bull Korean Chem Soc 2003 24 119-22. 

The great impact in metal-ion coordination chemistry caused by the discovery of the macrocyclic polyethers31 has led to new designs of chemosensors for the alkali cations. Application of a supramolecular receptor to fluorescence sensing was first... 

In this section, the sensing properties of the cryptand and bibrachial lariat-type crowned spirobenzopyrans were presented. In the spirobenzopyrans, coloration was efficiently induced in the presence of the alkaline earth metal cations. The cryptand and bibrachial lariat-type crowned spirobenzopyrans represent highly sensitive and selective chemosensors for alkaline earth metal cations. 

Cram, Czech et al. [2] reported the development of chemosensors 1-4 (Figure 1) for commercial use as Na" and assays in serum and other solutions. When a cation binds to the crown portion of these compounds, the complexation is coupled to an increase in acidity of the conjugated aniline NH deprotonation at constant pH... 

Rare Earth Complexes as Luminescent Chemosensors for Cations... 

A typical example of a cation-selective chemosensor based on a ianthanide compiex was reported by Nagano and coworkers. Based on Zn " " induced switch-on of absorption-energy transfer-emission (A-ET-E), a Tb " " compiex Tb-13 (Figure 13.8) was developed to serve as a sensitive luminescent sensor for Zn " " [35]. For Tb-13, a diethyienetriaminepentaacetic acid (DTPA)-bisamide moiety was used as the coordination ligand of Tb " ", and two di-(2-pyridinylmethyi)amine groups were designed as both sensitizers of Tb " " and binding sites of... 

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