Lysozyme Adsorption onto Mesoporous Materials: Effect of Pore Geometry and Stability of Adsorbents

In this paper, adsorption of lysozyme onto two kinds of mesoporous adsorbents (KIT-5 and AlSBA-15)has been investigated and the results on the effects of pore geometry and stability of the adsorbents are also discussed. The KIT-5 mesoporous silica materials possess cage-type pore geometry while the AlSBA-15 adsorbent has mesopores of cylindrical type with rather large diameter (9.7 nm). Adsorption of lysozyme onto AlSBA-15 aluminosilicate obeys a Langmuir isotherm, resulting in pore occupation of 25 to 30%. In contrast, the KIT-5 adsorbents showed very small adsorption capacities for the lysozyme adsorption, typically falling in 6 to 13% of pore occupation. The cage-type KIT-5 adsorbents have narrow channel (4 to 6 nm)where penetration of the lysozyme (3 × 3 × 4.5 nm) might be restricted. The KIT-5 adsorbent tends to collapse after long-time immersion in water, as indicated by XRD patterns, while the AlSBA-15 adsorbent retains its regular structure even after immersion in basic water for 4 days. These facts confirm superiority of the AlSBA-15 as an adsorbent as compared with the KIT-5 mesoporous silicates. This research strikingly demonstrates the selection of mesoporous materials is crucial to achieve efficient immobilization of biomaterials in aqueous environment.