Metal ion-sensing systems

Rapid Time-Response of Metal ion-Sensing Systems... 

In this chapter, we will concentrate on the development of macrocycle-based fluorescent chemosensors for metal ions. Some examples from our laboratory will be discussed in detail. We have also inserted a few paragraphs dealing with the crowned spirobenzopyran ion-sensing systems since this new type of chemosensor has been developed only recently. 

In this section, various crowned spirobenzopyrans for use as alkali metal cation receptors have been presented. This new type of chromoionphore is conceptually different from the crown ether dyes because, in the case of the crown ether dyes, the absorption bands of the chromophones are shifted by complexation of cations. Crowned spirobenzopyrans might provide sophisticated ion-sensing systems such as ion sensors whose ion selectivity can be photochemically switched between cations and anions.104... 

There are a munber of reports of potentiometric membranes based on Schiff bases that have been applied to the problem of lanthanide and actinide metal ion sensing. The ionophores that underlie the success of these systems may be divided into two classes, specifically symmetric and asymmetric. To date, most symmetric Schiff bases used for ISE production have consisted of tetra- or hexadentate Ugands... 

Table 5.1 Metal ion-sensing assays and sensing performance of monolithic cage nanosenors during the recognition of Hg, Sb, Cd and analyte ions at pH 9, 3, 9.5 and 7, respectively. The sensor amount, total volumes and temperature of the sensing systems were maintained at4mg, 20cm and 25°C, respectively.

In the Pb ion-sensing system, the HOM-DZ sensor at 596 run exhibited a blue shift to 501 nm after the addition of Pb ions. These results indicated the formation of charge-transfer complexes between the metal ions and the probes (as shown in Schemes 5.1-5.4). 

Rates of Reaction. The rates of formation and dissociation of displacement reactions are important in the practical appHcations of chelation. Complexation of many metal ions, particulady the divalent ones, is almost instantaneous, but reaction rates of many higher valence ions are slow enough to measure by ordinary kinetic techniques. Rates with some ions, notably Cr(III) and Co (III), maybe very slow. Systems that equiUbrate rapidly are termed kinetically labile, and those that are slow are called kinetically inert. Inertness may give the appearance of stabiUty, but a complex that is apparentiy stable because of kinetic inertness maybe unstable in the thermodynamic equihbrium sense. 

Other detection methods have been used in optical MIP sensing systems. An MIP-based chemiluminescent flow-through sensor was developed for the detection of 1,10-phenanthroline (Lin and Yamada 2001). A metal complex was used to catalyze the decomposition of hydrogen peroxide and form the superoxide radical ion that can... 

As pointed out already, free NH-sulfoximines were considered to be the most useful synthetically, because they allowed a variety of post-modifications at the sulfoximine nitrogen. Although at the outset of our studies the binding site of metals (in the sense of metal ions, metal complexes, and suchlike) was uncertain and it was difficult to predict which heteroatom of the sulfoximine (or even both) would coordinate [38, 39], we expected the sulfoximine nitrogen to play an important role in the activity and the stereoselectivity of a given catalytic system. 

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