M.Sc Thesis

M.Sc StudentKimhi Ohad
SubjectAdsorption of Amin-Acids on Temperature Sensitive Hydrogel
DepartmentDepartment of Biotechnology
Supervisor PROF. Havazelet Bianco-Peled


poly(N-isopropylacrylamide) (PNIPA) is a thermosensitive hydrogel, that is highly swollen in water at a temperature bellow the lower critical solution temperature (LCST) (ca. 32 oC), and shrinks drasticaly upon heating above it. This volume transition is associated with an increases in the gel hydrophobicity above the LCST. PNIPA-based sorbent have been successfully used in temperature-modulated chromatography of biochemicals, in which the resolution and selectivity are controlled via the column temperature. To obtain further insight into the mechanisms governing this process, we have measured the binding enthalpy between three model amino acids (valine, aspartic acid and phenyl alanin) and PNIPA microgels. Equilibrium binding isotherms of aspartic acid and valin showed enhanced binding with a temperature elevation from 25oC to 37oC. On the other hand, phenyl alanin which is more hydrophobic than valine showed a decrease in binding with a temperature elevation. Isothermal Titration Calorimetry (ITC) measurements showed that the binding of valine and phenyl alanin was endothermic, which implies an entropy-driven binding mechanism. Contrary, the binding of aspartic acid was exothermic, suggesting a mechanism based on interactions such as hydrogen bonding. Differential Scanning Calorimetry (DSC) measurements detected changes in the gel phase transition temperature. Our results show that a direct measurment of the binding enthalpy gives  further insight into the balance of binding mechanisms between biochemicals and PNIPA gel.