Enzyme Hydrolysis of Cellulose Derivatives. Active Site Studies and Polymer Characterisation

Abstract: Soluble derivatives of cellulose have become increasingly important in industrial products e.g. in pharmaceutical applications and in technical dispersions. The polymer characteristics of modified celluloses are to a high degree determined by the substituent distribution along the polymeric backbone. The distribution will be more or less heterogeneous both due to the fact that polymers from renewable resources are not homogenous, and due to the manufacturing process that is performed in heterogeneous conditions. Both these factors induce variation in substitution pattern and thus in the polymer behaviour. The available analytical techniques based on acid depolymerisation, are not sufficient to explain the variation in behaviour, thus an approach using selective cellulose degrading enzymes is attractive. Due to the enzymes different selectivity they will give rise to specific degradation pattern, which will reflect both the enzymes capability to cope with substituents and the polymer characteristics, i.e. how evenly the substituents are distributed. In this thesis, several pure endoglucanases ability to depolymerise cellulose ethers (MC, CMC, HPC and HPMC) has been studied. The formed products were analysed using SEC-MALS-RI, ESI-MS and MALDI-TOFMS. The MS analysis gave detailed knowledge about the enzyme specificity towards substituents. This information could then be related to enzyme active site structures, explaining the differences in degradation pattern. From NMR and chromatographic analysis, knowledge about the substituent distribution could be elucidated. This could then be related to the observed clouding behaviour of the polymer.