Chemical shift assignment of the complicated monomers comprising cellulose acetate by two-dimensional NMR spectroscopy

Abstract

(1)H and (13)C chemical shift assignment of the anhydroglucose units (AGUs) that comprise cellulose acetate with the total degree of substitution of 2.33 was performed by a combination of two-dimensional NMR spectra obtained from COSY, TOCSY, HSQC-TOCSY, and HSQC experiments. In the TOCSY spectra, there are 13 kinds of correlation networks for the H1 to H6' atoms of AGU; each (1)H resonance of the 13 AGUs was assigned from the changes in the intensities of the (1)H resonances with TOCSY spin-lock time during the TOCSY experiments. The ring (13)C resonances were assigned via analysis of HSQC spectra. Comparison of the shift data enabled the assignment of the 13 AGUs as three types of 2,3,6-tri-acetylated, one type of 2-mono-, 3-mono-, 6-mono-, 2,3-di-, 2,6-di-, and 3,6-di-acetylated AGU, and unsubstituted AGU, and three types of AGUs located in end units. These shift data will be useful for characterizing the molecular structures of cellulose derivatives as well as cellulose acetate (CA).