Simultaneous with solute recognition

While detection of cations via porphyrin-ba.sed materials has been explored less than anion sensing, the ability of a porphyrin to coordinate different metals and the unique spectral signatures that result form the basis for metal ion detection. Use of free-base porphyrins in polymer matrices has allowed for the detection of heavy metal ions by Ache et Immobilization of 5,10,15,20-tetrakis(4-N-methylpyridyOporphyrin on Nafion membranes pennitted detection of cadmium and mercury in solution with detection limits of 5 X 10 M and 2 x 10 M, respectively over a 20-minute measuring period. The method is subject to interferences from other metal ions, but the researchers were able to detect several ions simultaneously using pattern-recognition techniques such as principal component analysis. Sol-gel films doped with 5,l0,l5,20-tetra(p-sulfonatophenyDporphyrin have also been used by Ache and coworkers for the fluorimetric determination of mercury in solution, with a detection limit of approximately 7 X 10... 

In contrast, the three ligands 96 are designed for the simultaneous recognition of a 4f-3d metal ion pair (96a) (Piguet et al., 1996), a homopair of 4f ions (H296b) (Elhabiri et al., 1999), or a heteropair of 4f ions (96c) (Andre et al., 2002). For instance, under stoichiometric conditions, [M Ln (96a)3] is the only species formed out of a potential mixture of at least six species (three and two Ln -containing complexes were identified in solutions with... 

The unit operation of erystallization is governed by some very complex interacting variables. It is a simultaneous heat and mass transfer process with a strong dependence on fluid and particle mechanics. It takes place in a multiphase, multicomponent system. It is concerned with particulate solids whose size and size distribution, both incapable of unique definition, vary with time. The solids are suspended in a solution which can fluctuate between a so-called metastable equilibrium and a labile state, and the solution composition can also vary with time. The nucleation and growth kinetics, the governing processes in this operation, can often be profoundly influenced by mere traces of impurity in the system a few parts per million may alter the crystalline product beyond all recognition. 

The power of array sensing is most apparent when discriminating multianalyte solutions. In such solutions, multiple compounds (possibly hundreds or even thousands) make up each mixture. Array sensing is ideal for such a situation, with its inherent ability to detect multiple analytes simultaneously using various differential sensors, especially in circumstances where the multianalyte solutions have only subtle differences in chemical compositions. The resultant fingerprint response achieved for each solution allows discrimination through pattern recognition. 

Fabbrizzi developed receptor 45 that is able to bind L-His, with log K = 5.5, in aqueous solution, and rationalized this behavior by the simultaneous coordination of the imidazole of L-His to both Cu(II) centers of the receptor. A further development was reported by the same group two years later with the synthesis of a binuclear Zn complex of an anthracenic ligand (46) for the recognition of L-His (log K = 2.92) (Figure 19). This receptor is also a fluorescent chemosensor for this amino acid, provided the imidazole ring acts both as a coordinating bridge between two zinc centers and as a quencher of the anthracenic fluorescence (via PET). 

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