Abstract
In this paper, the main work was to study the theoretical self-assembly process of thermosensitive molecularly imprinted polymers (MIPs) for α-lipoic acid and to investigate thermosensitive functional monomers through density functional theory calculations (DFT) and intermolecular weak interaction analysis. The M06-2X/6-311+G (d, p) level was used to study the structural parameters, bonding sites, natural population analysis, binding energies ( Δ E ), atom in molecules (AIM), independent gradient model (IGM), and imprinted molar ratio. The results revealed that α-lipoic acid mainly interacted with N-vinyl caprolactam (NVCL) by weak hydrogen bonds, and the best conditions for MIP synthesis were an optimum molar ratio of 1 : 4 (α-lipoic acid/NVCL). The thermosensitive properties showed that the highest adsorption was at 40°C and the lowest adsorption was at 20°C; also, the MIPs released the intercepted α-lipoic acid inside polymers, and the lower critical solution temperatures (LCST) of MIPs and nonimprinted polymers (NIPs) are 25.7°C and 19.4°C, respectively. In this study, the thermosensitive MIPs displayed a different adsorption capacity towards NVCL, which could be applied for controlled separation and release of α-lipoic acid in different temperatures in a complex matrix.
Highlights
It is well known that α-lipoic acid (ALA) is a multifunctional therapeutic compound that exists mainly in the liver tissue of animals and plants and shows activity in both vitro and vivo experimental studies [1, 2]
For the synthesis of molecularly imprinted polymers (MIPs), the following reagents were employed: N-vinyl caprolactam (NVCL, functional monomers), α-lipoic acid (ALA, template), ethylene glycol dimethacrylate (EGDMA, 98%, cross-linking agent), dihydrolipoic acid (DHLA), 3phenylbutanoic acid (PBA), and 2,2-azobisisobutyronitrile (AIBN, radical initiator) were obtained from Sigma-Aldrich which were of reagent grade
We investigated the nature of imprinted polymers and recognition mechanism through theoretically calculating the structural parameters, binding energies, and potential active sites of ALA and NVCL in different molar ratios at M06-2X/6-311+G (d, p) level
Summary
It is well known that α-lipoic acid (ALA) is a multifunctional therapeutic compound that exists mainly in the liver tissue of animals and plants and shows activity in both vitro and vivo experimental studies [1, 2]. The stimulus-responsive technology has been applied in imprinted polymers including but not limited to responding to chemical (pH) and physical condition (temperature) [18, 19] This kind of polymer has been applied to controlled drug release, tissue engineering, and gene transfection. The choice of calculated methods has a significant influence on the accuracy of the calculated results, and it has been deployed in the previous investigations on MIPs. To be specific, Khan et al built a computational model to understand the nature of weak interactions between the template molecule and the functional monomers using the B3LYP method, which is the most comprehensively utilized in the studies so far [23]. To further investigate the thermosensitive property of the MIPs, the effects of different temperatures on the adsorption selectivity were studied
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