Towards understanding the interaction of quercetin with chitosan-phytate complex: An experimental and computational investigation

[Display omitted] •H bonds in the precursor system determine the quercetin retention in nanoparticles.•Phytate anion influences the free energy of quercetin binding to chitosan network.•The morphology of the loaded nanoparticles depended on chitosan-phytate mass ratio. Spectroscopic and structural properties of quercetin (QE) encapsulated in chitosan-phytate anion (CT-PA) nanoparticles were investigated, and an all-atom model was employed for molecular dynamics simulations to broaden the perspective on the conformational and energetics aspects regarding the quercetin-chitosan complexation. Quercetin binding to the free chitosan chains and its encapsulation in the nanoparticle obtained in the presence of the phytate anion was confirmed using dynamic light scattering and Fourier-transform infrared spectroscopy, and a considerably hindered rotational motion of the probe bound to the chitosan strand was demonstrated by the steady-state and anisotropy fluorescence measurements. While morphologies ranging from nearly spherical nanoparticles to nanofibrils were observed through atomic force microscopy upon increasing the chitosan content, a high encapsulation efficiency of QE, weakly dependent on the size and shape of CT-PA nanoparticles, was found. Simulation-based structural and energetics predictions indicated a similar H bond pattern for the QE binding to the chitosan strands, either in a free state or reticulated with the aid of the phytic anion. Additional crosslinker-assisted retention of quercetin in the chitosan network, as well as an enhanced electrostatic contribution to the binding free energy obtained at encapsulation, were derived from molecular dynamics simulations.