Molecularly Imprinted Membranes Having Amphiphilic Scaffold Media for Target Molecule Recognition
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CH-CH 2) x (CH-CH 2) y CN
-
Cl CH2 + CH2 CH3 -N- CH2 CH2 CH2 CH2 CH2 CH2 CH3 CH3
P(AN-co-OMA)
H 3C O
O
H N
N CH3
N
N
THO
Scheme Chemical structure of P(AN-co-OMA) and THO The PAN copolymer (Scheme) was prepared by conventional radical polymerization in the presence of 2,2'-azobis(isobutyronitrile): Copolymerization of acrylonitrile and OMA was carried out at 60 °C for 6 h under nitrogen atmosphere [12]. The amount of fixed charge of the membrane was determined from acid-base titration according to the literature [11] and was evaluated for 0.23 mmol/g. Phase inversion imprinting process for THO target was carried out according to our previous reports [4,5, 8]. Both THO template and P(AN-coOMA) were dissolved into DMSO in 5wt% and 10wt% concentration, respectively. The DMSO cast solution was well mixed at 50°C for 20 h. The solution was cast on a glass plate warmed at 50°C and coagulated in water at 25°C. Then, resultant polymers were rinsed with a large excess of water to remove DMSO and the template. Binding capacity of THO imprinted P(AN-co-OMA) was measured after THO extraction. The maximum absorption band of THO at 272 nm (ε=9700 M/cm in water) was monitored as a function of time by using (A)
(B)
150 nm
110nm 0
2 µm Figure 1 AFM image of surface for THO imprinted P(AN-co-OMA). spectrophotometer (V570, JEOL) in heterogeneous batch experiments. AFM was used to observe surface topology of resultant membrane. The AFM measurement was conducted using a Nanopics 100 (Seiko instruments Inc). All imaging was performed in tapping mode using silicon tips. Image analysis was performed with the supplied software Nanopics 1000 data analysis program, three dimension version 1.2). Sample was carefully lyophilized before the measurements. The SEM pictures were measured with JSM-5310 LVB (JEOL) for gold spattered imprinted membranes. DISCUSSION Figure 1 shows AFM image of membrane surface prepared with phase inversion imprinting 2 for P(AN-co-OMA). As seen by 4x4 µm x150 nm (A), grain like structure can be observed in the image of the surface. Apparently the image has bulges and the grain, indicating porous topology (B) with mean surface roughness Ra =16.1 nm in the surface. For comparison, we also measured AFM image of P(AN-co-OMA) membrane prepared without THO template. The topological difference was not observed without and with the imprinting in the view scale. In SEM images of the imprinted membranes (Figs. 2), the imprinted membrane had
sponge-like cross section having about 70 µm thickness and the pore size of the membrane was less than 0.2 µm diameter. These morphological views of the non-imprinted membrane were same as those of imprinted one. In much wide view, which was magnified 750x, the surface of the imprinted membrane (C) contains many depression places, which look like craters with about 40 µm diameter, while no observation was for the non-imprinted membrane (D). This difference suggests that the presence of the template molecule influences the solidification process of the P(AN-co-OMA) in water. (A
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