Selective Adsorption of Biopolymers on Zeolites

Zeolites adsorb biopolymers on their surface and may be suitable as a new type of chromatographic carrier material for proteins, nucleic acids, and their conjugates. We report here various parameters that influence the adsorption of biopolymers on synthesized zeolites with regard to the Si/Al2 ratio and three‐dimensional structure. There are three physicochemical principles that may underly the adsorption: 1) below the isoelectric point (pI), mainly Coulombic attraction similar to ion‐exchange chromatography; 2) at pI, hydrophobic interactions (a kind of van der Waals attraction) plus the three‐dimensional mesopore structure; and 3) above pI, the sum of the Coulombic repulsion and attraction forces, such as the hydrophobic interaction, and also substitution reaction of water on the Al molecule with a protein amino‐base. At high Si/Al2 ratio in the presence of a small amount of Al and with mesopores between the zeolite particles, maximal adsorption was seen at pI and was suggested to be dependent on the number of hydrophobic interaction points on the mesopores, and their morphology. The application of zeolites to biochemistry and biotechnology is also discussed. The peculiar pore structure of zeolites and the pH conditions of the solution leads to selective adsorbtion of biopolymers through Coulombic and hydrophobic interactions. Generally, zeolites that have high hydrophobicity and mesopores of 10 to 40 nm in diameter tend to adsorb biopolymers very well over a wide pH range. In our case, USY with a Si/Al2 ratio and mesopore size of 13.7 and about 30 nm, respectively, has proven to be the best adsorbent for biopolymers.