Quantum chemical calculations on the interaction between flavonol and functional monomers (methacrylic acid and 4-vinylpyridine) in molecularly imprinted polymers

Abstract

Quantum chemical calculations were performed to characterize the interaction of the flavonol molecule (FL) with methacrylic acid (MAA) and 4-vinylpyridine (4VPy) in the formation of imprinted polymers. The polarizable continuum model (PCM) was used to gain insight on the type of interaction between the reactant molecules under vacuum conditions and in the presence of different solvents. The effect of solvent on the pre-polymerization complex formation was evaluated through the stability energy, in which chloroform behaves as the best solvent for the synthesis of the imprinted polymers since it facilitates the reaction by lowering its degree of stabilization. The reactivity was analyzed in terms of the electrostatic surface potential (ESP) and Mulliken charge. By means of these results, it has been possible to determine two potential recognition sites for the interaction of the MAA monomer and one for the 4VPy in relation to the strength of interaction with FL. In this concern, the interaction of the system FL-MAA is stronger than FL-4VPy.

Figure 1

Torsion angles ф₁ and ф₂. (a) Flavonol (FL), (b) methacrylic acid (MAA) and (c) 4-vinylpyridine (4VPy).

Figure 2

Graphical representation of the PES for flavonol molecule, for the dihedral angles torsion (ф₁ and ф₂), see Figure 1 (a). The corresponding selected geometry structure is in Table 1.

Figure 3

Graphical representation of the PES for methacrylic acid, MAA, for the dihedral angles torsion (ф₁ and ф₂), see Figure 1 (b). The corresponding selected geometry structure is in Table 1.

Figure 4

Graphical representation of the PES for 4-vinylpyridine, 4VPy, for the dihedral angles torsion (ф₁), see Figure 1 (c). The corresponding selected geometry structure is in Table 1.

Figure 5

Pre-polymerization complexes proposed in a FL-MAA molecular ratio 1:1.

Figure 6

Optimized structure of FL-MAA complex. The Figure shows the two recognitions sites.

Figure 7

Geometrically optimized structure of FL-4VPy complex. The figure shows one recognition site.

Figure 8

¹³C-NMR experimental spectrum of flavonol in CDCl₃. The numbering that appears on each signal is relative to carbon atoms.

Figure 9

¹³C-NMR experimental spectrum of the complex FL-MAA 1:1 in CDCl₃. The numbering that appears on each signal is relative to carbon atoms.

Figure 10

¹³C-NMR experimental spectrum of the complex FL-4VPy 1:1 in CDCl₃. The numbering that appears on each signal is relative to carbon atoms.