(317g) Responsive Membranes for Hydrophobic Interaction Chromatography: The Effect of Salt Ions

Responsive membranes for hydrophobic interaction chromatography:  The effect of salt ions

Ranil
Wickramasinghe, Zizhao Liu,
Xianghong Qian

            The use of
environmentally responsive membranes for hydrophobic interaction chromatography
(HIC) enables high recovery and high resolution during protein purification.  Further the possibility of protein
fractionation also exists.  Here poly N-vinylcaprolactam (PVCL) has been grafted from the surface
of commercially available regenerated cellulose membranes (0.45 μm pore size) via atom transfer radical polymerization.
PVCL displays a lower critical solution temperature (LCST) at around 32 °C in
DI water.  The observed LCST of PVCL is a
strong function of solution ionic strength and type of salt ion present.  Increasing ionic strength leads to a decrease
in the LCST.  Above the LCST the grafted
polymer chains collapse, dehydrate and appear more hydrophobic promoting
protein adsorption.  Below the LCST the
grafted chains swell, hydrate and promote protein desorption.

Optimization of this novel system
requires a systematic investigation of different salt types and concentrations.  Here dynamic binding capacities of our PVCL
modified membranes were determined at different pH, salt type and concentration
at room temperature with two model proteins, a human immunoglobulin₄,
IgG₄, and bovine serum albumin (BSA). In addition, BSA adsorption isotherms
in the presence of monovalent (Na⁺, NH₄⁺),
divalent (Mg²⁺, Zn²⁺) and trivalent (Al³⁺)
sulfate solutions were compared in order to investigate the effect of the cation). Selected BSA binding capacity data (left hand side
y-axis) and recovery data (right hand side y-axis) are given in the figure
below.  As can be seen the ionic strength
and type of salt not only affect the binding capacity, but also the recovery
during elution.  Finally, the
responsiveness of the PVCL ligand synthesized in solution as well as grafted on
silicon wafers was investigated. Molecular dynamics simulations were also
conducted to elucidate the salt effect on the PVCL ligand.