Computer-assisted Design For The Preparation Of Molecularly Imprinted Polymers For Pyrethroid Pesticides

In recent years, increasing attention has been paid to the quality and safety (QS) of farm products and foodstuffs, and this issue has already become the top priority for the sake of human being's health all over the world. As a key role for food QS control and environmental monitoring, the determination of pesticide residues becomes a hotspot in the related research field. Molecular imprinting technique (MIT) has proved to be an available and convenient alternative for solving the selectivity or specificity in sample analysis and product separation. Nowadays, it is a rising tide of study on pesticide residue analysis.MIT has been developed very quickly since the end of the last century. However, the efficient synthesis of molecularly imprinted polymer (MIP) is affected by lots of physical and chemical factors, and thus there are only a few kinds of MIPs which have been really developed for the commercial application. A majority of the reported MIPs were only on the laboratorial stage owing to the complexity of molecular imprinting system, especially for the poor functionalized templates. In the present study, a computational approach using Hyperchem(?) 7.5 molecular modelling software was firstly applied to predict the non-covalent interactions between pyrethroid pesticides and functional monomers. The minimum energy conformations of eight commonly used pyrethroid pesticides and thirteen functional monomers were simulated by molecular mechanics (MM) and then refined using PM3 semi-empirical mechanic methods. Afterward, the Amber MM method was used to analyse possible interactions between templates and functional monomers and to calculate their binding energies, so as to select the suitable templates and monomers and thus to design for pyrethroid-MIP development. Results indicated that, generally, in view of functional monomers, complexes of templates with methacrylic acid (MAA) and 2-hydroxyethyl methacrylate (HEMA) gave the relatively higher binding energies than these with other monomers. In terms of the eight pyrethroid pesticides, fenvalerate showed the relatively stronger interactions with MAA and HEMA, but cyhalothrin gave the opposite phenomenon; while other pyrethroids displayed the diverse intensity of interactions with the two monomers; for the same pyrethroid, the more or less variation of the interactions among different isomers was also found.Based on the above research and considering the current pesticide marketing information and the demand for residue monitoring, fenvalerate and cyhalothrin were selected as the typical templates which respectively showed high and low interactions with functional monomers. Using different monomers, cross-linkers, porogenic solvents and polymerization methods, various MIPs for fenvalerate and cyhalothrin were synthesized and screened. Then the appropriate solvent system for the specific rebinding of the MIPs was optimized and the selective recognition of related MIPs to other pyrethroids was also investigated. Results revealed that different rebinding solvents greatly influenced the selective absorption of MIPs to the corresponding pesticides. The cyhalothrin-MIPs prepared with HEMA (as functional monomer),p-divinylbenzene (DVB, as cross-linker) and acetonitrile (as porogen) had the better selectivity in n-hexane system than in other organic solvents, and particularly the MIP microsphere synthesized by precipitation polymerization had the much higher binding capacity. Withal, the HEMA-co-DVB cyhalothrin-MIP also had selective recognition to fenvalerate and deltamethrin, which suggested that this type of MIP could hopefully be applied to multi-residue determination of type II pyrethroids. Besides, fenvalerate-MIP prepared by precipitation polymerization in the mixture solvent of acetonitrile and toluene (3:1, v/v) using MAA (as functional monomer) and DVB (as cross-linker) could specifically recognize its template molecule in n-hexane, with imprinting factor (IF) up to 2.16. Compared with cyhalothrin-MIP, the imprinting efficiency of fenvalerate-MIP was higher. In addition, aimed at achieving higher specificity and efficient recognition of MIPs to pyrethroid pesticides in aqueous media, inclusion interaction was employed to synthesize pyrethroid MIPs withβ-cyclodextrin as functional monomer. And equilibrium rebinding test reflected that the developed MIP would be used as potential high-performance materials for the selective concentration and/or separation of trace pyrethroids from complex sample matrixes under the hydrophilic condition. Overall, it was found that, satisfactorily, the experimental results were in accord with the outcomes from computer simulation.In this study, an elementary research system of computer-assisted design for the preparation of MIPs for pyrethroid pesticides was established. Moreover, the mechanism of MIPs'selective binding to pyrethroid templates was also shallowly probed. It was illuminated that the formation of binding sites not only lied on the interaction between template and functional monomer, but also was tightly related to its stereostructure of template molecule. The present research could provide an academic guidance to the development of MIT for pyrethroid pesticide detection, and offered a useful reference to the preparation of MIPs for other analytes, especially the non-polar compounds.