Effect Of Surface Properties Of Nano - Zeolite On Protein Adsorption

The increasing applications of protein adsorption in the fields of biosensor, drug delivery and imaging have raised necessity of research into the protein adsorption process and reasonable design of biomaterials. Nanozeolite materials are possessed with large external surface areas and tunable surface properties (e.g., surface charge, hydrophobicity/hydrophilicity, ion-exchangeability), which make nanozeolites an ideal immobilization carrier for biomolecules such as enzymes and polypeptides. In our previous studies, we have successfully achieved bio-applications of nanozeolites in the fields of protein digestion, bio-detection, biosensor and biocatalysis. In these studies, nanozeolite particles displayed a fast protein adsorption process, amazing adsorption capacities and high retention of enzyme activities. Different nanozeolite materials also showed different adsorption capacities and bio-performance due to their various surface characteristics. The promising prospect of nanozeolites in bio-applications evokes our interest to do more fundamental and systematical research into their interactions with biomolecules. In this thesis, the influence of surface properties of nanozeolites on protein adsorption behavior is systematically investigated. This study not only provides a novel view for interactions between proteins and microporous materials, but also assists in strategically engineering nanozeolites and other porous materials for bio-applications.Firstly, various kinds of nanozeolites were synthesized and their surface properties were modulated by microwave-assisted hydrothermal procedure in Chapter II. Nanozeolites silicalite-1, Beta, SOD and LTL with varying surface micropore structures, surface hydrophobicity, surface curvature and morphology were prepared. The surface and textural properties of as-prepared nanozeolites were comprehensively analyzed by multi-characterization methods. These materials laid a solid foundation for the research on protein adsorption.Abundant exposed microporous arrays are the primary characteristic of nanozeolites different from other nanocrystals. Therefore, our study focused on the influence of surface micropores of nanozeolites on protein adsorption behavior in Chapter III. Cytochrome c (Cyto-c) and Candida antarctica Lipase B (CALB) were employed as model proteins to evaluate their adsorption amounts, adsorption strength, protein conformations and bio-activities on porous and non-porous nanozeolites. It was found that abundant exposed pore openings on the surface of nanozeolites remarkably determined protein-nanozeolite interaction despite their smaller pore sizes compared to protein dimensions. Both Cyto-c and CALB showed stronger affinity to porous nanozeolites than to non-porous ones, which resulted in greater protein conformational changes on porous surfaces. Larger extent of protein unfolding induced by porous nanozeolites was positive for the enzyme activity of Cyto-c while negative for that of CALB. The seemingly opposite catalytic performance of two proteins virtually demonstrates the same nature of interaction. That is, proteins have stronger affinity to nanozeolites with abundant pore openings on the surface. What’s more, high protein adsorption amounts and adsorption strength observed on the (001) crystal plane of nanozeolite LTL as well as similar adsorption behavior of proteins adsorbed on small-pore sized nanozeolites SOD before and after detemplation provided indirect evidence for the pore opening effect. The strong interaction between proteins and porous nanozeolites was assigned to the recognition of certain amino acid residues or size-matching secondary structures by pore openings, which induced penetration of protein residues into the pore mouth and reduced adsorption free energy. What’s more, it turned out that protein surface coverage could pronouncedly affect protein conformations and bioactivities, indicating that to increase protein loading may help to narrow the gap or even reverse the trend of protein activity on porous and non-porous surfaces.Besides surface micropores, the effect of surface hydrophobicity/hydrophilicity and surface curvature of nanozeolites on protein adsorption behavior was also preliminarily studied in Chapter IV. It was found that surface hydrophobicity had little impact on the adsorption behavior of Cyto-c and hemoglobin (Hb), but it pronouncedly influenced the catalytic performance of CALB whose enzyme activity was doubled on the hydrophobic surface. On nanozeolites with different surface curvature, small proteins (Cyto-c and CALB) and large protein Hb displayed opposite performance, which indicated the importantce of the size of supporting materials and protein dimensions in the research of curvature effect to achieve reasonable results.