Adsorption behaviors and mechanisms of bilirubin onto charged amorphous carbon surface with and without water by a molecular dynamics simulation

The adsorption of bilirubin onto a carbon surface holds pivotal significance in enhancing bilirubin clearance efficiency within artificial liver devices. We performed molecular dynamics simulations to reveal the adsorption behaviors and mechanisms of bilirubin onto a charged amorphous carbon surface. The hydrogen atoms are used as binding sites facilitating the adsorption of bilirubin molecules onto the uncharged amorphous carbon surface. Conversely, the oxygen atoms are used as binding sites, enhancing bilirubin adsorption on charged amorphous carbon surfaces due to their higher electronegativity. The bilirubin adsorption rate, the mean-squared displacements of bilirubin, and the interaction energy between bilirubin and amorphous carbon increase as the surface charge increases, and the adsorption amount reaches an asymptotic value as the surface charge approaches a certain threshold. In the presence of water, the competitive adsorption between bilirubin and water would occur. The hydration layer formed on charged amorphous carbon surface and the electrostatic and nearwall hydrogen-bond interactions emerge as two pivotal factors influencing bilirubin adsorption. The structured arrangement of hydration water can hinder the bilirubin adsorption, whereas the electrostatic interaction and near-wall hydrogen-bond interaction promote it. The whole competitive adsorption process unfolded in distinct stages of bilirubin adsorption and desorption, and a critical value of surface charge exists for the complete desorption of bilirubin.