Modeling of butyric acid recognition by molecular imprinted polyimide

The constitutional repeating unit structures of poly(pyromellitic dianhydride-co-4,4'-oxydianiline) or polyamiс acid, butyric acid and complexes between butyric acid and one, two or three units of polyamiс acid were calculated using the density functional theory method (DFT B3LYP) on a 6-31G(d,p) basis with the basis set superposition error (BSSE) correction in the program Gaussian 09. The optimised structures of the template and polyamiс acid allowed to establish intermolecular non-covalent interactions during imprinting and, based on the results, develop a method of polyimide-based molecularly imprinted polymer preparation using butyric acid as template. It was shown that the optimum molar ratio of reagents used for the synthesis of molecularly imprinted polymer is 1:1 (interaction energy ∆E = 43.2 kJ/mol). In the presence of a large number of polyamic acid units in prepolymerisation complexes, the self-association of polyamic acid and the steric hindrance, which reduce the stability of the complexes, occur. The simulation results are in good agreement with experimental data. When analysing the energy values and parameters of bonds of the complexes, it was shown that butyric acid interacts with carboxyl groups from units of polyamiс acid via hydrogen bonding of moderate strength. The IR spectra of a complex between structural unit of polyamic acid and butyric acid were also obtained in order to understand the intermolecular interactions responsible for the molecular recognition. According to the IR spectra, it was shown that the vibrations of the C=O and O-H groups of butyric acid and polyamic acid participating in the interaction are weakened; their vibration frequencies are reduced. The polyimide structure was also constructed in the work. It was shown that two polyimide chains interact with each other due to hydrogen bonds between the hydrogen atoms of the benzene rings and the oxygen of the imide groups.