Characterisation of regioselectively functionalized 2,3-O-carboxymethyl cellulose by enzymatic and chemical methods

The determination of the molecular structure of 2,3-O-carboxymethyl cellulose (2,3-O-CMC), prepared via 6-O-(4-monomethoxy)triphenylmethyl cellulose, was carried out in detail by means of enzymatic and chemical methods. The 2,3-O-CMCs had degrees of substitution (DS) in the range of 0.5–1.2 showing a narrow molar mass distribution as revealed by SEC. As a result of an endoglucanase treatment, an intensive depolymerization of the samples occurred which was more pronounced for 2,3-O-CMC with comparatively low DS. All degraded samples could be separated into 18 fractions by preparative SEC and the proportion of each individual repeat unit was analysed by anion exchange chromatography (AEC) following complete hydrolytic chain degradation. The results indicated a homogeneous distribution of the functional groups within the polymer chain. Moreover, it became obvious that a preferred carboxymethylation of O-2 compared with O-3 occurred and that a preferred functionalization of already carboxymethylated units occurred as the reaction progressed. AEC with pulsed amperometric detection, which was used to separate and analyse the differently functionalized repeating units as well as glucose, had to be calibrated. Therefore, a method to determine the response factors of the individual carboxymethylated glucose units was developed using ¹³C NMR spectroscopic measurements (inverse gated decoupling) of depolymerised 2,3-O-CMC.