Theoretical design and preparation research of molecularly imprinted polymers for steviol glycosides

In this paper, a novel molecularly imprinted polymer (MIP) for specific adsorption of steviol glycosides was designed, and the imprinting mechanism of self-assembly system between template and monomers was clearly explored. Firstly, steviol (STE) was chosen as dummy template, and the density functional theory (DFT) at B3LYP/6-31 + G (d, p) level was used to select monomers, imprinting molar ratios, solvents, and cross-linking agents. The selectivity to five steviol glycosides was also calculated. Importantly, reduced density gradient (RDG) theory combined with atom in molecules (AIM) and infrared spectrum (IR) was applied to investigate the bonding situation and the nature of noncovalent interaction in self-assembly system. The theoretical designed results showed that the template which interacts with acrylic acid (AA) has the minimum binding energy, and the complex with the molar ratio of 1 : 4 has the most stable structure. Toluene (TL) and ethylene glycol dimethacrylate (EGDMA) were chosen as the optimal solvent and cross-linking agent, respectively. Five hydrogen bonds formed in the self-assembly system are the key forces at the adsorption sites of MIPs through the RDG and AIM analyses. The MIPs were synthesized by theoretical predictions, and the results showed that the maximum adsorption capacity towards dulcoside A is 26.17 mg/g. This work provided a theoretical direction and experimental validation for deeper researches of the MIPs for steviol glycosides. In addition, the method of RDG theory coupled with AIM and IR also could be used to analyze other imprinting formation mechanisms systematically.