Adsorption of proteins on zeolite FAU

A highly dealuminated form of zeolite FAU, ultra-stable zeolite Y (USY), was used as an adsorbent matrix in the purification of proteins. Undesired proteins were removed from a crude preparation by adsorption on USY, increasing the purity of an unadsorbed protein (horse radish peroxidase), or the protein of interest was adsorbed on the zeolite and subsequently eluted through changes in the solution conditions (hen egg lysozyme, mouse-immunoglobulin G).

The adsorption of proteins on USY in single protein solutions was found to be dependent on both the pH and the ionic strength of the solution. The most pronounced adsorption was obtained at or close to the isoelectric point (IEP) of the protein. The adsorption is believed to be predominantly mediated through the interaction of protein in an aggregated form and the zeolite surface. This conclusion was supported by cryo-transmission electron microscopy (cryo-TEM) studies of vitrified specimens containing both USY crystallites and proteins.

Sintered USY pellets were fractionated and sieved and then employed in either batch or column flow systems. The addition of kaolinite as a binder resulted in a change in the mesopore size distribution and possibly also in the macropore range. The addition of blowing agents to the zeolite powder prior to sintering caused a reduction in the bulk density of the material but did not affect the porosity at pore diameters of less than 100 nm. Both treatments resulted in an increase in the availability of absorption sites, as shown by the increase in the rate of adsorption of Triton X-100 micelles on size fractionated particles.

The difference in surface properties between the so-called hydrophobic USY and its hydrophilic counterpart, NaY, was indicated by cryo-TEM studies of the adsorption of ferritin under otherwise identical conditions. Structural information, e.g. unit cell parameters, concerning the solid material present in vitrified solutions was also obtained.