Sensors cation

Ajayaghosh A (2005) Chemistry of squaraine-derived materials near-IR dyes, low band gap systems, and cation sensors. Acc Chem Res 38 449 159... 

Nath S, Maitra U (2006) A simple and general strategy for the design of fluorescent cation sensor beads. Org Lett 8 3239-3242... 

Cation sensors require the presence of an additional binding site for the substrate cation. For instance, the Zn2+ sensor (59) acts by incorporation of Zn2+ ions into a separate aminocarbox-ylate binding pocket.164 This perturbs intermolecular PET, and gives rise to enhancement of the luminescence intensity. 

Figure 12 Self assembled monolayer of TTF-based cation sensor on gold substrate (Redrawn from Moore et a/.114)...

Yet the majority of cation sensors are mediator-based sensing. One type of optical sensor is based on the fluorescence quenching of fluor-ophore Rhodamine 6G by transition metals such as Co(II), Cr(III),... 

The fourth type of mediator-based cation optical sensing is using potential sensitive dye and a cation selective ionophore doped in polymer membrane. Strong fluorophores, e.g. Rhodamine-B C-18 ester exhibits differences in fluorescence intensity because of the concentration redistribution in membranes. PVC membranes doped with a potassium ionophore, can selectively extract potassium into the membrane, and therefore produce a potential at the membrane/solu-tion interface. This potential will cause the fluorescent dye to redistribute within the membrane and therefore changes its fluorescence intensity. Here, the ionophore and the fluorescence have no interaction, therefore it can be applied to develop other cation sensors with a selective neutral ionophore. 

An analogous system to the cation sensors is the use of optically nonactive anion ionophores together with a pH-sensitive chromophore for the anion sensing. In this system, simultaneous extraction of H+ and anion X- from the aqueous solution into an organic phase results in protonation of the chromophore anion C, e.g. 

Figure 6.20 Action of a fluorescent PET potassium cation sensor as a molecular switch using a macrocyclic electron donor and anthracene fluorophore...

PET (photoinduced electron transfer) cation sensors 10.3.2.1 Principles... 

Fig. 10.26. Excimer-forming cation sensors (E-1 Bouas-Laurent H. et al. (1986) J. Am. Chem. Soc. 108, 315. Marquis D. and Desvergne J.-P. (1994) Chem. Phys. Lett. 230, 131. E-2 Suzuki...

Water-soluble sensors for transition metals ferrocene polyazamacrocycles 28 Reducible cation sensors 35... 

OXIDIZABLE CATION SENSORS Ferrocene crown ether species... 

It is hence evident that if we would have applied a difference of potential AE between the reference and the working electrodes before the complexation, we would have generated a current due to the oxidation process, Figure 35a. In contrast, upon applying the same potential difference AE after the cation complexation, we do not produce current if we wish to generate current we have to apply an extra potential AE, Figure 35b. The extent of AE is intuitively correlated to the nature of the complexed cation. From here we get the term cationic sensor. 

In fac-(bpy)Re(I) (CO)3-A (where bpy is 2,2 -bipyridine and A is an aromatic amine), the d-7t(Re)—>jr (bpy) MLCT fluorescent excited state is strongly quenched via intramolecular aniline-Re charge transfer leading to a nonfluorescent LLCT state. By incorporating the donor amino group belonging to the A moiety into a crown-macrocycle, Schanze and Mac Queen(137) have provided a new luminescent cation sensor whose quantum yield of fluorescence raises from 0.0017 (without cation) to... 

Ping et al. have fabricated an integrated microsensor array on a silicon wafer for pH imaging [89]. Six different pH-sensitive colorimetric dyes (methyl violet 6B, phenolic red, alizarin complexone, 5-carboxy-fluorescein, alizarin red and methylthymol blue) were used to cover the whole pH range. The dyes were adsorbed on microbeads and placed in etched microwells on the silicon wafer. The indicator array was also used as a cation sensor chip (see Sect. 2.4). 

Section 13) and 64 is successful for Na+.162 All this notwithstanding, several integrated lumophore-receptor systems, e.g. 65,91 have been persuaded to act as cation sensors in physiology with respect to their excitation spectra. The influence of these sensors have been immense and Tsien has been a pioneer in this general area.90,12,163... 

Protons are relatively simple targets for sensor molecules and do not require engineered receptors, however, achievement of selective interactions with other chemical species requires much more elaborate receptors. In the most cases cations are bound via electrostatic or coordinative interactions within the receptors alkali metal cations, which are rather poor central ions and form only very weak coordination bonds, are usually bound within crown ethers, azacrown macrocycles, cryptands, podands, and related types of receptor moieties with oxygen and nitrogen donor atoms [8], Most of the common cation sensors are based on the photoinduced electron transfer (PET) mechanism, so the receptor moiety must have its redox potential (HOMO energy) adjusted to quench luminescence of the fluorophore (Figure 16.3). 

Crowned Spirobenzopyrans as Alkali Metal Cation Sensors.108... 

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