Molecular dynamics assisted analysis on improved free radical removal ability of fullerene(C60)-curcumin aggregate

Abstract The self-aggregation of curcumin (Cur) on the surface of fullerene (C60) was induced by ultrasonic solvent exchange method. Associating the characterization results of infrared spectrum, X-ray diffraction, and scanning electron microscopy, the molecular structure and morphology of two components in the aggregate (C60/Cur) were determined unchanged essentially. By analyzing the dependence of related cosmetic effects on the aggregating ratio of C60 and Cur, the monolayer saturation was found advantageous to improve the amphiphilicity and oxidation resistance. Especially, C60/Cur showed a better performance to eliminate free radicals compared to counterpart of simply mixing C60 and curcumin. Based on molecular dynamics simulations of the Forte module, the self-aggregation is proposed occurring through π-π stacking interactions between the benzene ring from curcumin and the spherical π bond of C60, and a molecular configuration was offered for displaying the optimal spatial arrangement of C60/Cur. Furthermore, the Mulliken charges on the phenolic hydroxyl groups of the curcumin molecules with original and aggregated state were calculated respectively using Gaussian software, and the charge values were found to transfer from negative to positive due to the aggregating. The dispersion of the electron cloud on the benzene ring was recognized responsible to enhance the electron absorption capacity of the phenolic hydroxyl group, thereby improving free radical removal ability of C60/Cur.