Fluorescence molecular sensors

Zinc carboxylate interactions have been exploited as part of a fluorescent molecular sensor for uronic acids. The sensors feature two interactions coordination of the carboxylate to the zinc and a boronic acid diol interaction.389 Photoluminescent coordination polymers from hydrothermal syntheses containing Zn40 or Zn4(OH)2 cores with isophthalate or fumarate and 4,4 -bipyridine form two- and three-dimensional structures. Single X-ray diffraction of both dicarboxylates identified the network structure.373... 

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

Kovalchuk A, Bricks JL, Reck G et al (2004) A charge transfer-type fluorescent molecular sensor that lights up in the visible upon hydrogen bond-assisted complexation of anions. Chem Commun 1946-1947... 

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.). 

In fluorescent molecular sensors, the fluorophore is the signaling species, i.e. it acts as a signal transducer that converts the information (presence of an analyte) into an optical signal expressed as the changes in the photophysical characteristics of the fluorophore. In contrast, in an electrochemical sensor, the information is converted into an electrical signal. 

The present chapter is restricted to fluorescent molecular sensors, for which three classes can be distinguished (Figure 10.1) ... 

CEF Chelation or Complexation Enhancement of Fluorescence CEQ Chelation or Complexation Enhancement of Quenching Fig. 10.1. Main classes of fluorescent molecular sensors of ions or molecules. 

Several books and many reviews have been devoted to fluorescent molecular sensors (see Bibliography at the end of this chapter). This chapter will present only selected examples to help the reader understand the fundamental aspects and the principles. 

The fluorescent molecular sensors will be presented with a classification according to the nature of the photoinduced process (mainly photoinduced electron or charge transfer, and excimer formation) that is responsible for photophysical changes upon cation binding. Such a classification should help the reader to understand the various effects of cation binding on the fluorescence characteristics reported in many papers. In most of these papers, little attention is often paid to the origin of cation-induced photophysical changes. 

Box 10.2 Calixarene-based fluorescent molecular sensors for sodium ions... 

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