Location of sulfate groups on sulfoacetate derivatives of cellulose

Abstract

A water-soluble cellulose acetate sulfate (CAS) with a degree of acetylation (DS Ac) 2.4 and a degree of sulfation (DS Sulf) of 0.3 was obtained by direct acetylation of cellulose using sulfuric acid as catalyst. Using methylation analysis, IR and NMR spectroscopy, sulfate groups have been located on primary alcohol function of glucose residues. The distribution of the sulfate groups along the cellulose chain has been investigated using enzymatic hydrolysis. CAS was first de-acetylated under mild hydrolysis conditions (NaOH 0.25 mol/L at room temperature), and then cellulose sulfate was hydrolyzed by a cellulolytic complex (Celluclast 1.5L). Reaction products were separated by ion exchange chromatography on a DEAE Sepharose CL6B column into five fractions F 1, F 2, F 3, F 4 and F 5, which were analyzed for their chemical composition. F 1 was glucose and represented the main product of reaction (∼50% of the initial glucose), F 2 was a dimer (∼30%) with a ratio Sulfates–Glucose of 0.41 (about one sulfate group for two glucose units), F 3 a trimer (∼10%) with a ratio Sulfates–Glucose of 0.62 (about two sulfate groups for three glucose units), and F 4 a tetramer (∼5%) with a ratio Sulfates–Glucose of 0.69. The structure of the oligomers was established using 1H and 13C NMR. The observed proportion of the different blocks of sulfate groups was in good agreement with computed random distribution.