Molecular investigation of interplay mechanism between polydopamine and graphene oxide: The effect of oxidation degree on the adsorption behavior of polydopamine

The interfacial behaviors taking place between polydopamine (PDA) and graphene oxide (GO), two types of biocompatible functional nanomaterials popular in drug delivery and cancer therapy, were investigated by classical molecular dynamics (MD) simulations. The analysis of the self-assembly of PDA on the GO surface indicated that the rise in oxidation degree of PDA (signifying the increase of the carbon-to-hydrogen ratio and intramolecular cyclization) enhanced the adsorption capacity of GO to PDA, as a result of the impact of resonance effect of substituents on the polarity of functional groups. The inter-/intramolecular hydrogen bonds were proved to play a crucial role in mediating the adsorption of PDA. The non-amine-participating hydrogen bonds can promote the adsorption of PDA, whereas the amine-participating hydrogen bonds only have limited benefits to the adsorption, meanwhile, consume or preempt the hydrogen-bond sites on GO surface. Moreover, the hydrophobicity of functional groups in PDA was proved to be an important driving force to determine the adsorption affinity between PDA and GO, relying on the estimations of solvent accessible surface area and hydrogen bonding interaction with water molecules. The present computational study provides insights into the intrinsic mechanisms of the functional modification of carbon-based nanomaterials by the organic coatings.