Chiral Electrochemical Sensors

chiral analysis is progressively becoming an organic part of the pharmaceutical analysis, where MIPs may play an important part. 

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Chiral Electrochemical Sensors Based on Molecularly Imprinted Polymers with Pharmaceutical Applications... 

In this chapter, we present the evolution in the development of MlP-based chiral electrochemical sensors and also discuss the impediments encountered in the imprinting process of one of the enantiomers in the polymer. The nature of the polymers and their electrical properties are also addressed. An important part of the chapter is dedicated to the analytical applications of these sensors. 

In order to really prove the versatility and real analytical potentials of MIP-based chiral electrochemical sensors, in the near future their performance also toward more complex chiral molecules ought to be demonstrated so they could overcome the laboratory scale barrier. 

A chiral electrochemical sensor for propranolol based on multi-walled carbon nanotubes/ionic liquids nanocomposite, 105,... 

Lower rim derivatization is far easier to effect and examples include alkyl-, ester-, amide-[4], pyridyl- [5] and pyrene-appended [6] systems, not to mention the more exotic species that bind gallium [7] or give a colorimetric response when complexing chiral guests [8] as shown in Figure 3.19. Further examples include oxacalix[3]arenes that form capsules [9,10], palladium cross-linked dimers [11-13] and 2 1 inclusion complexes with C6o [14,15]. Oxacalixarenes with lower rim substituents have even been incorporated into electrochemical sensors for... 

Since in most cases only one enantiomer possesses a desired pharmacological activity, it is necessary to construct enantioselective sensors to improve the quality of analysis due to the high uncertainty obtained in chiral separation by chromatographic techniques.315 For this purpose, enantioselective amperometric biosensors and potentiometric, enantioselective membrane electrodes have been proposed.264 The selection of one sensor from among the electrochemical sensor categories for clinical analysis depends on the complexity of the matrix because the complexity of different biological fluids is not the same. For example, for the determination of T3 and T4 thyroid hormones an amperometric biosensor and two immunosensors have been proposed. The immu-nosensors are more suitable (uncertainty has the minimum value) for direct determination of T3 and T4 thyroid hormones in thyroid than are amperometric biosensors. For the analysis of the same hormones in pharmaceutical products, the uncertainty values are comparable. 

The design and development of effective chiral separation and recognition of enantiomers is the key point of the chiral technique. Many technologies have been developed for chiral recognition and separation of amino acids and their derivatives including HPLC, CE and electrochemical sensors. However, they are expensive techniques in terms of time and reagent consumption. Accordingly, there is considerable interest in the development of simple, rapid and economical methods that will afford the analysis of enantiomeric species. 

Is represented by synthetic chemical compounds able to interact by nonselective chemical bonds with the anal)d e of interest but also with chemical compounds that possess same chemical functionalities as the analyte. An alternative increasingly employed In electrochemistry is represented by a class of materials whose selectivity can be directed in the fabrication process toward the target molecule. These materials, molecularly imprinted polymers (MlPs), although they were exploited in electrochemistry for quite some time, only recently have begun to be used as the recognition element in the electrochemical sensors for the chiral discrimination of racemic compounds. 

As it has been shown, basically all chiral MIP-based electrochemical sensors were developed up till now for amino acids or monosaccharides. However, chiral pharmaceuticals present more complex structures compared to the already mentioned molecules thus, their efficient molecular imprint is considered to be more difficult. Moreover, in the case of amino acids, the asymmetric carbon is at the molecule s extremity carrying two functional groups (-NH2 and -COOH) strongly interacting with the used common functional monomers, thus easily leading to highly enantiospecific imprinted cavities. 

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