| dc.description.abstract | The characteristics of preventing nonspecific adsorption of protein has lead to extensive usage of PEG and its derivatives for biomedical applications. We consider that the interaction of water with the PEG is a major determinant of preventing protein adsorption. However, the thermodynamics aspect of the mechanism has not been well addressed. Therefore, in this study, we described the hydration behavior of PEG by measuring the dilution heat of PEG with various salt concentration, types of salt ions, temperature and molecular weight of PEG. In addition, we measured the isotherms and the interaction enthalpy between protein and Ether-650S with various salt concentrations, salt types and temperature by batch isotherms and ITC.
From the results of dilution heat, we observed that all the dilution heat are exothermic at all condition (i.e. salt conc. and types, temperature, PEG MW). It indicated that the PEG molecule is prefer to hydrate with water than aggregation in the conditions investigated. At high salt concentration, temperature and molecular weight of PEG, the dilution heat of PEG is less exothermic due to the poor hydration of PEG. In thermodynamics, the dilution of PEG is more energy unfavorable at high salt concentration, temperature and molecular weight of PEG. And the extent of salt ions which affect the hydration of PEG is consistent with the Hofmeister series. Besides, we also observed that all the values of Flory-Huggins parameter(χ) are negative at each condition. It also indicated that all the solvent which we used are good solvent for PEG.
From the results of isotherm, the amount of lysozyme adsorb on Ether-650 will decrease with increase the salt concentration. We considered that both of hydrophobic and electrostatic interaction affect the binding affinity of lysozyme.
The enthalpy of lysozyme adsorbed on Ether-650S are almost endothermic. It indicated that the hydrophobic force is the driving force during the adsorption process. However, the enthalpy of adsorption is exothermic at 1M KCl. This lead to the suggestion that the adsorption of lysozyme with the Ether-650 is of the “nonclassical” hydrophobic type interaction at 1M KCl. In this study, we also calculated the number of water molecules released during the adsorption by preferential interaction model. From the results of P.I Model, we can conclude : (1) when we adding
ammonium chloride to the solution, the system released more water molecules than add that of potassium chloride during the binding process.(2)compare with literature data, PEG ligand have stronger capability of hydration than other hydrophobic ligands. | en_US |