Adsorption Mechanism of Bilirubin on Aminated Crosslinking Microspheres of PGMA

The crosslinking microspheres of poly (glycidyl methacrylate) (PGMA) were modified chemically with aminating agents, hexanediamine and three kinds of multi-ethylene multi-amine. The effects of various factors, such as the chemical structures of the aminating agents, pH values of the medium, ionic strength, and temperature, on the adsorption property of the functional microsphers for bilirubin were examined. The adsorption mechanism of the aminated microspheres towards bilirubin was studied deeply. The experimental results showed that the aminated microspheres had strong adsorption ability for bilirubin and the adsorption capacity could reach 17.80 mg·g -1; the isotherm adsorption could be fitted by Freundlich equation satisfactorily. There were three acting forces between the aminated microspheres and bilirubin molecules, i.e., electrostatic, hydrogen bonding and hydrophobic interactions. Among them, the electrostatic interaction was dominative, and the latter two kinds exert cooperating action. As pH=6, there was the strongest electrostatic interaction between the aminated microspheres and bilirubin molecules, leading to the highest adsorption capacity. The higher ionic strength was disadvantageous to the electrostatic interaction, and salinity conduces to the weakening of the electrostatic interaction and the decreasing of the adsorption capacity. The rising of temperature was advantageous to the hydrophobic interaction, whereas unfavorable to hydrogen bonding, and the predominated one of themdominates the effect of temperature on the adsorption capacity. The adsorption ability of the aminated microspheres modified with hexanediamine was stronger than that of those aminated microspheres modified with multi-ethylene multi-amine owing to enhancement of the hydrophobic interaction and smaller steric hindrance which came fromlonger spacer arm.