1H and 13C chemical shift assignment of the monomers that comprise carboxymethyl cellulose

Abstract

1H and 13C chemical shift assignment of the anhydroglucose units (AGUs) that comprise sodium carboxymethyl cellulose (CMC) with a degree of substitution (DS) of 0.70 was performed using 2D NMR spectra obtained from COSY, TOCSY, HSQC, and HSQC–TOCSY experiments. In the 2D COSY and TOCSY spectra, there are eight correlation networks for the H1 to H6′ atoms of AGU; each 1H resonance of the eight AGUs was assigned from the changes in the intensities of the resonances with mixing times during the TOCSY experiments. The ring 13C resonances were assigned via analysis of HSQC–TOCSY spectra and confirmed via the HSQC spectra. Comparison of the shift data enabled the assignment of the eight AGUs as two types of both 2,3,6-tri-O- and 3,6-di-O-carboxymethylated, one type each of 2,6-di-O-, 2-mono-O-, and 6-mono-O-carboxymethylated AGU, and unsubstituted AGU. The obtained shift data will also be useful for characterization of the substitution distribution of other cellulose derivatives.