Modifications of celluloses and proteins for novel structures and properties.

摘要

This dissertation covers three aspects of my Ph.D. research which involve polymer synthesis and modification for novel structures and properties. The aims of these projects are either to develop advanced materials based on biopolymers, including polysaccharides and proteins; or to apply biotechnology to polymer substrates, such as enzyme-catalyzed reactions and enzyme immobilization; or to develop advanced materials that have important biotechnical applications, such as hydrogels and ultra-thin fibrous membranes. A general overview of the relevant polymers and techniques shown is given in Chapter 1. More specific reviews are covered in the introduction part of each chapter.; Chapter 2 describes the modification of cellulose solids by enzyme-catalyzed transesterification with vinyl esters in anhydrous organic solvents. The protease enzyme, subtilisin Carsberg, was made soluble in organic media through ion-paired enzyme-surfactant complexes, and was found to be catalytic active towards transesterification reaction on cellulose. The reaction regioselectively targets the primary hydroxyl group of cellulose and has the advantage over the existing multi-step chemical reactions. This technique opens up new fields for enzyme applications as biocatalysis.; In Chapter 3, two series of hydrogel-cellulose composites have been prepared by ceric ion initiated grafting of crosslinked poly(N-isopropylacrylamide) on cellulose substrates. The hydrogel-cellulose composites exhibit lower extent of phase transition over a wider temperature range than free PNIPAAm hydrogels. The procedures offer the options to reinforce hydrogels with solid supports, or to prepare cellulose membranes whose pore size can be controlled by the swelling of hydrogel. These materials may find important biomedical applications.; Chapter 4 discusses the processing of natural proteins into ultra-thin fibrous membranes by electrospinning. These membranes have ultra-high surface-to-volume ratios and very fine porous structure, and are expected to be biocompatible and biodegradable. Enzymes encapsulated in these electrospun membranes exhibit higher catalytic activity than in casted membranes.