Fluorescent sensors cations

Benzimidazolium is one of the typical scaffolds of the hemicyanine group, and cationic hemicyanine derivatives can be assumed as potential fluorescent sensors due to their electrostatic interactions. Based on this assumption, Chang and... 

Pu KY, Pan SYH, Liu B (2008) Optimization of interactions between a cationic conjugated polymer and chromophore-labeled DNA for optical amplification of fluorescent sensors. J Phys Chem B 112 9295-9300... 

The design of fluorescent sensors is of major importance because of the high demand in analytical chemistry, clinical biochemistry, medicine, the environment, etc. Numerous chemical and biochemical analytes can be detected by fluorescence methods cations (H+, Li+, Na+, K+, Ca2+, Mg2+, Zn2+, Pb2+, Al3+, Cd2+, etc.), anions (halide ions, citrates, carboxylates, phosphates, ATP, etc.), neutral molecules (sugars, e.g. glucose, etc.) and gases (O2, CO2, NO, etc.). There is already a wide choice of fluorescent molecular sensors for particular applications and many of them are commercially available. However, there is still a need for sensors with improved selectivity and minimum perturbation of the microenvironment to be probed. Moreover, there is the potential for progress in the development of fluorescent sensors for biochemical analytes (amino acids, coenzymes, carbohydrates, nucleosides, nucleotides, etc.). 

PET fluorescent sensors for cations have been highly developed (Bissell et al., 1993). The principle is the same as for PET pH indicators, described in Section 10.2.2.5. 

Most PET fluorescent sensors for cations are based on the principle displayed in Figure 10.7, but other photoinduced electron transfer mechanisms can take place with transition metal ions (Fabbrizzi et al., 1996 Bergonzi et al., 1998). In fact, 3d metals exhibit redox activity and electron transfer can occur from the fluorophore... 

E-3 (Figure 10.26) is the first example of an ionophoric calixarene with appended fluorophores, demonstrating the interest in this new class of fluorescent sensors. The lower rim contains two pyrene units that can form excimers in the absence of cation. Addition of alkali metal ions affects the monomer versus excimer emission. According to the same principle, E-4 was designed for the recognition of Na+ the Na+/K+ selectivity, as measured by the ratio of stability constants of the complexes, was indeed found to be 154, while the affinity for Li+ was too low to be determined. 

A distinct advantage of PET sensors is the very large change in fluorescence intensity usually observed upon cation binding, so that the expressions off-on and on-off fluorescent sensors are often used. Another characteristic is the absence of shift of the fluorescence or excitation spectra, which precludes the possibility of intensity-ratio measurements at two wavelengths. Furthermore, PET often arises from a tertiary amine whose pH sensitivity may affect the response to cations. 

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. 

The development of fluorescent probes for anion recognition has been very limited so far in comparison with those for cations. Most of the presently available methods of detection of anions based on fluorescence involve quenching, redox reactions, substitution reactions, ternary complex formation(15) and thus cannot be considered as recognition methods. For instance, the fluorescent sensors that are used for the determination of chloride anions in living cells are based on collisional quenching of a dye by halide ions 6-methoxy-iV-(sulfopropyl)quinoliniuni and... 

J. R. Lakowicz, H. Szmacinski and K. W. Berndt, Fluorescence lifetime-based sensing of blood gases and cations, in Fiber Optic Medical and Fluorescent Sensors and Applications (J. R. Lakowicz, ed.), Proc. SPIE. 1648, 150-163 (1992). 

This receptor shows a remarkable selectivity for Mg2+ over Ca2+ under physiological conditions and has found applications in 19F NMR probes and ratiometric fluorescent sensors based on wavelength shifts.[62] In high concentrations, however, both Ca2+ and Mg2+ can be bound. The similarity of fluorescence enhancements with both ions is the result of essentially identical conformational changes produced upon complexation. Each ion-bound state effectively decouples the amine substituent from the oxybenzene unit, so that PET is similarly suppressed. This means that the charge density difference between the two cations is of secondary importance in these conformationally switchable systems. 

Aminoalkyl anthracene derivatives have already featured prominently in this discussion with regard to their proton responsive fluorescence. Some of these in their protonated form also appear in a fluorescent signalling role in association with macromolecular species which is however unconnected with PET action. These mono- or oligocations bind to polyanions such as DNA and heparin [87, 88]. On one hand, this can lead to excited state association between two sensor cations residing on the same polyanionic strand. Acridine orange with its cationic jr-system also exhibits a related behaviour which has been... 

The macrocyclic revolution in metal ion coordination chemistry [115] soon had repercussions on the design of fluorescent sensors for alkali cations. Before the advent of PET sensors, the first examinations of crown ether receptors with adjacent n-eleetron systems such as naphtho- and benzo crown ethers (50) [116] and (51) [117, 118] showed small but significant alkali cation induced fluore-... 

Fluorescent Sensors for Alkaline Earth Metal Cations.112... 

Interestingly, if the same titration experiment is performed in presence of any other 3d divalent cation (Mn Fe, Co, Zn ), no fluorescence quenching is observed over the entire 2-12 pH interval. In this connection, it must be noted that deprotonation of the amide groups of the dioxocyclam subunit is an especially endothermic process, which can take place only if the unfavorable heat effect is compensated by the exothermic formation of strong metal-ligand bonds. This situation occurs only with metal ions late in the 3d series, e.g., Ni and Cu , but not with cations earlier in the same series. Thus, the anthracene functionalized dioxocyclam system represents a selective fluorescent sensor for Cu" and Ni , whose signal transduction mechanism is an electron transfer process [13]. 

Fluorescent molecular sensors of cations 313 10.3.5.2 Further calixarene-based fluorescent sensors... 

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