Synthesis of Three-dimensionally Continuous Nanoporous Membranes from Molecular Network/Polymer Mixtures, and Study on Biocatalysis by the Enzymes Distributed inside their Pores

Abstract

The thesis investigates the synthesis of bicontinuous nanoporous structures from the mixtures of polymers/urea-linked molecular network sol, and application of the continuous nanopore for ultrafiltration and enzymatic biocatalysis. We experimentally revealed the nanostructure-forming principle and important experimental parameters for generating nanostructure from polymer/UN sol mixtures. A structure-forming mechanism was proposed for the polymer/UN blend system, in addition to developing an empirical descriptor devised to correlate the morphology and polymer characteristics. Based on the knowledge about the structure-forming principles, we show that appropriate polymer species allow facile preparation of NCF with short extraction time for polymer removal and pore size distribution easily controlled by blending composition. Application of the nanoporous membrane for ultrafiltration of sub-10 nm molecular solutes are demonstrated in both aqueous and organic media. The following study reveals the effect of nanocaging enzyme in the nanoporous membrane by employing several enzymes. We first focused on stabilization and size-selective protection of the embedded enzyme under various environmental conditions detrimental to free enzymes. Moreover, macro-structuring in the presence of enzyme and compartmentalization was demonstrated, which was not available for powdery medium for enzyme immobilization. Taking advantage of the robust nature of the nanoporous membrane with tunable pore sizes, we explored continuous flow reaction with the enzymes entrapped in the continuous nanopore. The entrapped or nanocaged enzyme exhibited long-term stability for enzymatic kinetic resolution of secondary alcohol under flow reaction mode. The different reaction kinetics coming from the reaction modes are compared in various aspects such as loading amount and substrate concentrations. The activity enhancement effect of confining enzyme in nanopore is also revealed by controlling the pore size distribution of the membrane. The overall results show the potential of continuous nanoporous membrane built from molecular networks as a useful platform for studying catalytic flow reaction through nanopore, and as a scalable film-type reactor for organic synthesis.