Design And Preparation Of Enzyme Carriers Based On Metal-organic Coordination

Based on the ubiquitous metal-organic coordination coupling with the multifunctionality of polyphenols, several kinds of immobilized carriers were prepared to endow the immobilized enzyme with high activity and excellent stability. This study investigated the role of metal-organic coordination in the formation of carriers as well as its effect on structures and properties of carriers.The details in this study were summarized as follows:Firstly, hydrogel beads were prepared by two kinds of coordination interaction, catechol and Ti4+, alginate and Ca2+. The as-synthesized catechol modified alginate(AlgDA) could chelate Ti4+ and Ca2+ simultaneously. The titanium(IV) coordination resulted in a more compact network structure with a decreased segmental mobility of polymers chains. The swelling of hydrogel beads was inhibited and the mechanical properties were obviously enhanced. Therefore, storage and recycling stabilities of the immobilized enzyme were all improved.Secondly, metal-organic coordination enabled LbL self-assembly to prepare hybrid microcapsules. The shell thickness and mechanical/thermal stability of the microcapsules could be easily controlled by the graft ratio of AlgDA and the number of deposited layers. Enzyme can be either entrapped in the lumen or covalently attached in the surface of microcapsules. Compared with free enzyme, the immobilized enzyme exhibited desirable pH and thermal stability.Thirdly, enzyme microcapsules were prepared through template-mediated interfacial reaction coupling with coordination interaction between alginate and Ca2+. Enzyme was the formation constituent of microcapsules with biocatalytic activity. CaCO3 template was coated with AlgDA via the coordination interaction. The pressure change trends inside the microcapsules were investigated during the removal of template. The structures and properties of microcapsules prepared with different amount of enzyme were analyzed. Enzyme microcapsules retained high bioactivity, were stable over wide pH and temperatures range, and long-time storage.Fourthly, a dual hard-template approach coupling with coordination interaction between TA and Zn2+ was exploited to prepare ultrathin titania microcapsules with rough surface. ZIF-8 and CaCO3 were utilized to mediate the formation of microcapsules shell and lumen. The coordination interaction between TA and Zn2+ exposed on the surface of ZIF-8 insured the deposition of ZIF-8. The rough surface of microcapsules facilitated the contact of substrates with enzyme molecules, insured the affinity of immobilized enzyme toward substrates. The titania microcapsules(100 nm) with enhanced mechanical stability, thus kept a spherical shape upon drying, endowed the immobilized enzyme with good reusability and long-term storage stability.Finally, an multienzyme system based on catechol modified gelatin(GelC) was constructed for converting CO2 to methanol. Three enzymes were respectively, entrapped in the lumen, covalently attached onto GelC layer, and entrapped in the silica layer. GelC enabled(1) the regulation of the amount of individual enzyme according to activity;(2) the ordered assembly of enzymes within nanometer distances to facilitate substrate channeling without equilibrating with the bulk fluid;(3) the formation of pore size to avoid the leakage of enzyme and acquire low mass transfer resistance for the intermediates. Hence, the multienzyme system displayed much higher methanol yield and selectivity than that of multienzyme in free form. Moreover, the microcapsules displayed high mechanical stability, which rendered the multienzyme system with good recyclability.