(77g) A Speculation of Mechanism of Gate Effect of Molecularly Imprinted Polymer Based On Solution Content and Adsorption

Molecularly imprinted polymer (MIP) is a tailor-made material which has specific binding sites generated by cross-linking of functional monomers self-organizing with the target or template. MIP can be produced easily and economically, then is feasible as a substitute for enzyme or antibody in biosensors. A thin layer of MIP changes its solute diffusive permeability by specific binding with its templates. This phenomenon, termed the "gate effect," is applicable to biomimetic sensors. However, the mechanism of the gate effect is yet to be understood. We have developed a self-supporting membrane of phenylalanine (Phe) imprinted polymer for analysis for the mechanism of gate effect. In this study, we researched the relationship between the gate effect and the influence of template to solution content which is one the most important of the parameters to solute permeability. The self-supporting phenylalanine (Phe) imprinted polymer membrane is formed by copolymerization of methacrylic acid and 2-vinylpyrridine as functional monomers and triethyleneglycol dimethacrylate as a crosslinker in the presence of L- (or D-) phenylalanine as a template. The test solution was L- (or D-) Phe (0 or 5 mM) in mixed solvent of methanol and water (methanol concentration 0 ¨C 50 wt%). The membrane was soaked in the test solution for 48 h to remove the template. The diameter of the soaked membrane was measured by a vernier caliper. The thickness of the MIP membrane was measured by a digimatic micrometer. Then, the observed volume (V) of the membrane was determined. Membrane were placed in a pycnometer with the test solution and the total weight (W1) was measured. The weight of the pycnometer filled with the test solution only (W2) was also measured. After the measurement, the membrane was soaked in a large volume of mixed solvent (50 wt% methanol in water) for > 24 h to extract Phe, and air-dried at room temperature for > 24 h, then the weight of the dried membrane (W3) was measured. The net volume of the membrane (Vm) was determined by Eq. 1. The volumetric solution content Sc% was determined by Eq. 2. The solution content of the membranes increased with methanol concentration in the solvent as shown in Fig.1. The content in the polymer membrane prepared without template (non imprinted polymer ; Non MIP) was insensitive to Phe. The content of the L- (or D-)Phe imprinted membrane increased by the template at the higher methanol concentration (¨R 30 wt%), decreased by the template at the lower methanol concentration (¨Q 20 wt%), however, was almost insensitive to the enantiomer of the template. Then we conclude that solution content of MIP membrane is very important parameter for discussion on the mechanism of the gate effect.