Sensors chromogenic

This type of chromogenic sensor utilizes the coordination chemistry of transition metal complexes, which have vacant binding sites to bind specific anions or have pendant arms containing anion receptor units. Transition metal complexes already have their own specific colors due to their different electronic structures. Coordinating directly to anions or binding of anions by the pendant arms results in perturbations of their electronic structures and causes color changes. 

Fig. 13 Schematic operation of displacement method for a chromogenic sensor...

Shao and coworkers [61] have demonstrated that a noncovalent charge-transfer complex of calix[4]pyrrole-chloranil can be used as a chromogenic sensor for F and H2POj. Upon addition of calix[4]pyrrole 75 to the solution of chloranil 76 in chloroform, the color changed from pale yellow to blue. This indicated the formation of a charge-transfer complex between calix[4] pyrrole and chloranil in chloroform. The Job s plot analysis showed a 1 1 complex with... 

The transformation of a reactant to another form by changing the pH of the solution can be used as a chromogenic sensor. The 1,3,5-triaryl-1,5-pentane-dione derivative 89 [69] can be readily transformed into the corresponding pyrylium ion, as shown in Fig. 17. Addition of nitric acid to a solution of 89 in... 

The doubly functionalized calix[4]arene 9, bearing two chiral arms , was prepared recently [48]. This neutral system proved not only to be a good receptor for a-phenylglycine anions, it was also found to display good enantioselectivity towards the L-isomer fCa(L)//< l(D) = 4.76. It was thus proposed by the authors, that this presumably preorganized receptor could function as a chromogenic sensor for nonracemic a-phenylglycine anions. 

The crucial recognition events of chemistry, biology, and materials science occur at a molecular level. Information about these events can be conveniently transmitted to us via light signals emitted by purpose-built molecular devices. There are three different families of fluorescent (and chromogenic) sensors (Figure 16.1) [1] ... 

Colorimetric pH sensing has a long tradition and numerous chromogenic sensors such as phenolphthalein, bromothymol blue, methyl red, and many others, have been developed. These indicators are involved in protonation-deprotonation equilibria between two (or more) forms of different spectral properties. Much higher sensitivity can be obtained with fluorescent proton sensors. Furthermore, this technique can be widely used in bioanalytical chemistry, cellular biology, and medicine. Application of fluorescence imaging techniques provides spatial information on pH. 

Recently, Comes et al. developed a versatile strategy to covalently anchor dyes inside siliceous zeolites and demonstrated its potential use as chromogenic sensors for the visual discrimination of closely related molecules by size and polarity. ... 

Chang K-C, Su I-H, Lee G-H, Chung W-S (2007) Triazole- and Azo-coupled Calix[4]arene as a highly sensitive chromogenic sensor for Ca and Pb ions. Tetrahedron Lett 48 7274-7278... 

The majoiity of the various analyte measurements made in automated clinical chemistry analyzers involve optical techniques such as absorbance, reflectance, luminescence, and turbidimetric and nephelometric detection means. Some of these ate illustrated in Figure 3. The measurement of electrolytes such as sodium and potassium have generally been accomphshed by flame photometry or ion-selective electrode sensors (qv). However, the development of chromogenic ionophores permits these measurements to be done by absorbance photometry also. 

Generally, sensors based on chromogenic or fluorogenic indicators are advantageous over sensors based on PSDs or ion-exchange/co-extraction. A... 

Fe(III), Cu(II), Ni(II), and even NH4. The second type of optical sensor can be designed in the same way as the proton sensors if a fluorogenic or chromogenic compound is found to bind with the cation selectively and reversibly, e.g. 

Suksai C, Tuntulani T (2003) Chromogenic anion sensors. Chem Soc Rev 32 192-202... 

Lee DH, Lee KH, Hong JI (2001) An azophenol-based chromogenic anion sensor. Org Lett 3 5-8... 

The combination of dyes with microporous materials opens-up a way to develop selective chemosensors microporous zeolites with an anchored squaraine 27 (Fig. 13) and some other types of dyes can be used as chemosensors for the chromogenic discrimination of amines [75], These dye-zeolite hosts are expected to be promising sensor materials allowing the visible discrimination of selected target guests by size and/or polarity within families or closely related molecules. It was found that the response of the solid to amines was basically governed by the three-dimensional architecture of the solid material. 

Figure 5.16 — Flow-through photometric sensor for the determination of traces of copper based on the immobilization of a chromogenic ligand (PAN) in a special flow-cell coupled on-line with a flow injection (A) or continuous-flow (B) configuration. IV injection valve SV switching valve W waste TGA thioglycollic acid. For details, see text. (Adapted from [42] with permission of Elsevier Science Publishers).

For decades solvatochromism was a phenomenon without any great technical importance in commercial applications, being used largely to characterise solvents or to understand the excitation behaviour of chromogenic solutes, e.g. commercial azo dyes." " However, in the last two decades of the 20th century there was a rapid growth in the use of optical probes and sensors in a range of outlets, and this led to a renewed interest in solvatochromism. 

Polyphenylene and polyfluorene have been extensively used as fluorescence-based sensors, and several chromogenic forms of these polymers have been reported. Incorporation of monomers with additional coordination sites into these polymers has led to the development of a variety of different anion sensors, mostly for halide ions (Lee et al. 2004 Zhou et al. 2005 Vetrichelvan et al. 2006 Kim et al. 2007). Extension of these materials toward recognition of more complex analytes should be possible. 

Keywords Chromogenic anion sensor Colorimetric anion sensor... 

The concept of chromogenic anion sensors is illustrated in Fig. 1. The crystal in the figure can be compared to analytes such as anions, and the cup acts like a receptor that is connected to a light bulb. When the crystal goes into the cup that fits its shape, the electronic part of the light bulb is perturbed, and the light bulb will give a different color. 

These hosts include simple anion sensor systems containing urea, thiourea, amine, amide, alcohol, and pyrrole groups linked to chromophores. Chro-mophores used in this type of chromogenic anion sensors are mainly organic dyes such as azobenzene, nitrobenzene, indoaniline, and anthraquinone or... 

---