Screening of molecularly imprinted pre-assembly system for detection of deltamethrin pesticide residues and its specific adsorption properties

Abstract: To efficiently prepare decamethrin molecular (DM) imprinted polymers, the molecular dynamics simulation and ultraviolet spectrum were involved to study the preassembled system of DM and functional monomers in this paper. The binding energy (?E) between DM and three different functional monomers (acrylic acid, AA; acrylamide, AM; methacrylic acid, MAA) in different solvents (n-hexane, chloroform, acetone and acetonitrile) were calculated by molecular dynamics simulation. Results showed that the AM monomer and acetonitrile solvent had the highest stabilization energy for the pre-polymerization adducts. Additionally, the polymer obtained from the molar ratio of DM to AM at 1:4 to 1:6 may be more stable. Ultraviolet spectrum analysis results showed that there was strong interaction between DM and AM, the red shift degree of ultraviolet spectrum maximum absorption peak followed the order: AM > AA = MAA, and then indicated that AM was most suitable monomers for DM molecular imprinted polymers, which was consistent with the predictions based on the computer simulation. Differential ultraviolet spectrum showed that when acetonitrile used as solvent, one DM molecule could be combined with AA monomer in the ratio of 1:3 or AM monomer in the ratio of 1:4. However, it was difficult for DM to form stable complex with MAA because the fitting correlation coefficient of the equation was less than 0.86. Best performance was observed when chemical coordination ratio (n) between DM and AM was equal to 4, at this time, the fitting correlation coefficient of the equation was 0.997 3, and the binding constant K was 6.614×105. Based on the above computer simulation and ultraviolet spectrum analysis results, the molecularly imprinted polymers of DM were synthesized by the precipitation polymerization method with the AM as the functional monomer, and its synthetic formula was optimized through orthogonal experiment design. Then, the optimum imprinting conditions were established: 1 mmol DM as the template molecule, 4 mmol AM as the functional monomers, 40 mL acetonitrile as the solvent, 20 mmol ethylene dimethacrylate (EGDMA) as the cross-linker. Using these conditions, the DM molecular imprinted polymers had bigger saturated adsorption capacity of 68.61 mg/g than other conditions. The prepared molecular imprinted polymers were characterized by scanning electron microscopy (SEM), brunauer-emmett-teller (BET) and Fourier transform infrared spectroscopy (FTIR). SEM demonstrates that the DM molecular imprinted polymers formed staggered porous structure. The data of BET revealed that the DM molecular imprinted polymers had smaller pore size (15.83 nm) than non-imprinted polymers (18.84 nm), but with a larger specific surface area (95.58 m2/g) and pore volume (0.578 5 cm3/g). The FTIR results confirmed the successful preparation of the DM molecular imprinted polymers. And then the adsorption selectivity of prepared polymers on deltamethrin and its analogues cypermethrin, lambda-cyhalothrin and bifenthrin were studied. The experimental results showed that the static equilibrium adsorption capacity and static distribution coefficient of DM was much higher than that of other analogues. Its imprinting factor (IF) was 2.269, and the corresponding separation factor α was more than 3.2, which has exhibited obvious specific identification. All above results showed that computer simulation and ultraviolet spectrum analysis could help to design the better performance molecular imprinted polymers.