Structure, solvation, and dynamics of Mg2+, Ca2+, Sr2+, and Ba2+ complexes with 3-hydroxyflavone and perchlorate anion in acetonitrile medium: A molecular dynamics simulation study

Molecular dynamics simulations of complexes of Mg2+, Ca2+, Sr2+, and Ba2+ with 3-hydroxyflavone (flavonol, 3HF) and ClO 4− in acetonitrile were performed. The united atoms force field model was proposed for the 3HF molecule using the results of DFT quantum chemical calculations. 3HF was interpreted as a rigid molecule with two internal degrees of freedom, i.e., rotation of the phenyl ring and of the OH group with respect to the chromone moiety. The interatomic radial distribution functions showed that interaction of the cations with flavonol occurs via the carbonyl group of 3HF and it is accompanied with substitution of one of the acetonitrile molecules in the cations' first solvation shells. Formation of the cation–3HF complexes does not have significant impact on the rotation of the phenyl ring with respect to the chromone moiety. However, the orientation of the flavonol's OH-group is more sensitive to the interaction with doubly charged cations. When complex with Mg2+ is formed, the OH-group turns out of the plane of the chromone moiety that leads to rupture of intramolecular H-bond in the ligand molecule. Complexation of Ca2+, Sr2+, and BaClO 4+ with 3HF produces two structures with different OH-positions, as in the free flavonol with the intramolecular H-bond and as in the complex with Mg2+ with disrupted H-bonding. It was shown that additional stabilization of the [MgClO4(3HF)]+ and [BaClO4(3HF)]+ complexes is determined by strong affinity of perchlorate anion to interact with flavonol via intracomplex hydrogen bond between an oxygen atom of the anion and the hydrogen atom of the 3-hydroxyl group. Noticeable difference in the values of the self-diffusion coefficients for Kt2+ from one side and ClO 4−, 3HF, and AN in the cations' coordination shell from another side implies quite weak interaction between cation, anion, and ligands in the investigated complexes