Atrazine-imprinted polymers preparation

Matsui, J., Dobihoff-Dier, O., and Takeuchi, T., Atrazine-selective polymer prepared by molecular imprinting technique, Chem. Lett., 24, 489-496, 1995. 

Takeuchi et al. reported the preparation of an imprinted polymer for the conversion of the herbicide atrazine (100) in atraton (101), a less toxic compound, by conversion of an atrazine chloride into methoxy [59, 60]. After polymerisation and removal of the template, analysis of the imprinted polymer showed saturation kinetics, suggesting an enzyme-like behaviour of the polymer. 

High selectivity can be obtained by imprinting polymers with neutral molecules.80 In this process, a cross-linked polymer is prepared in the presence of a template. Then the template is removed by solvent extraction. The extracted polymer is then used to pick up the template molecules from other sources. Among the examples in the literature are some that deal with atrazine (an herbicide), cholesterol, other sterols, dipeptides, TV-acetyltryptophane resolution (L-isomer favored by a factor of 6), adenine, and barbiturates.81 The polymerizations in the first two examples, are shown in (7.16) (The cross-linking comonomer with the cholesterol-containing monomer was ethylenebis-methacrylate. The cholesterol was cleaved from the polymer with sodium hydroxide in methanol.)... 

The polymer prepared as in Example 6.1 was ground in a mortar and dried in vacuo. Then the polymer particles were passed through a sieve (mesh size 32-65 pm) and suspended in acetonitrile. Too small particles were removed by decantation. The particles thus obtained were slurried and packed in a stainless-steel column-tube using an HPLC pump. In order to wash out the atrazine (used as the template for the molecular imprinting) from the column, AcOH/MeOH solution was caused to flow until a stable baseline was obtained (monitored by UV detector). The column was now available for HPLC analysis. 

Imprinted polymer membranes are prepared using atrazine as the template, methacrylic acid as a functional monomer, and tri(ethylene glycol) dimethacrylate (TEDMA) as a cross-linker. The molar ratio of the functional monomer to the template is 5 1. This ratio has to be optimized for each template. In order to obtain thin, flexible and mechanically stable membranes, oligourethane acrylate (molecular mass 2600) is added to the monomer mixture. Preparation of the molecularly imprinted polymer membrane is done as follows. Atrazine (20 mg) is mixed with methacrylic acid (40 mg), TEDMA (289 mg), oligourethane acrylate (51 mg), AIBN (2 mg) and 30% v/v of chloroform. Then a 60-120 pm gap between two quartz slides is filled with the monomer mixture. To initiate polymerization, the slides with the mixture are exposed to UV radiation (365 nm, intensity 20 W m ) for 30 min. After polymerization, atrazine is extracted with ethanol in a Soxhlet apparatus for 2h. This should not cause any visible changes in the MIP membrane. A membrane for control experiments can be prepared similarly except that no atrazine is added to the monomer mixture. 

Another nice example of nanostructuring an MIP layer is the work published by Wu et al. [138, 139] who developed a label-free optical sensor based on molecularly imprinted photonic polymers. Photonic crystals were prepared by self-assembly of silica nanospheres. The space between the spheres was then filled with MIP precursor solution. After polymerization, the silica was dissolved, leaving an MIP in the form of a 3D-ordered interconnected macroporous inverse polymer opal (Fig. 15). The authors were able to detect traces of the herbicide atrazine at low concentrations in aqueous solution [139]. Analyte adsorption into the binding sites resulted in a change in Bragg diffraction of the polymer characterized by a color modification (Fig. 15). 

In this chapter, all the processes of the molecular imprinting reaction (from the design of reaction systems to the analysis of resultant polymers) are described, so that the reader can form a clear and comprehensive mental picture of this elegant method. Non-covalent imprinting for the preparation of polymeric receptors towards atrazine (a herbicide) is taken as a typical example (Fig. 6.1). 

Fig. 38 (a) Schematic illustration of the procedure used fm the preparation of the molecularly imprinted photonic polymer (MIPP). (b) Color change induced by exposure to atrazine at different concentrations. Reproduced with permission from [116]... 

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