Determination of the Distribution of Substituent Groups in Sodium Cellulose Sulfate: Assignment of 1H and 13C NMR Peaks by Two-Dimensional COSY and CH-COSY Methods

Abstract

ABSTRACT:An attempt was made to give full assignment to the 1 H and 13 C NMR spectra of sodium cellulose sulfate (NaCS) dissolved in D 20 and to determine the molar fractions of all possible 8 kinds of anhydroglucopyranose (AHG) units constituting NaCS molecule. For this purpose five NaCS samples with the total degree of substitution ranging from 0.61 to 2.42 were synthesized by three different methods. Using a NaCS sample 1 H and 13 C peaks for 2,3,6-trisubstituted AHG were reasonably assigned by two-dimensional (2D) homonuclear 1 H correlation spectroscopy (COSY) and heteronuclear 1 H-13 C correlation spectroscopy (CH-COSY) techniques. In the same manner, 1 H and 13 C NMR peaks originating from unsubstituted AHG were assigned by analysis on NaCS with Chemical shifts (o) of protons and carbons in monosubstituted and disubstituted AHG units were calculated using shift factors empirically estimated from the observed o values of trisubstituted and unsubstituted AHG units. The assignments on 1 H NMR peaks for NaCS previously made by Kamide and Okajima [Polym. J., 13, 163 (1981)] on the basis of the peak assignment of cellulose acetate were found to be partly incorrect. The average degree of substitution for each three hydroxyl groups attached to C2, C 3 , and C 6 carbon positions (k=2, 3, and 6) was estimated based on the assignment made here and a relation > > was obtained for the NaCS samples synthesized here.

Spectroscopic study of natural and synthetic polysaccharide sulfate structures

“…Therefore, the progress of the sulfation reactions can be estimated by comparing the chemical shifts of the reaction product and the native polysaccharide. Detailed structural analysis, such as the confirmation of the positions of the substituents in the sugar units, requires the utilization of homo‐ and/or heteronuclear correlation techniques . However, 1‐D 1 H and 13 C NMR techniques are often used in the routine structural confirmation of both carrageenans and synthetic polysaccharide sulfates .…”

“…Sulfate groups, which are attached to the sugar backbones of polysaccharides, usually make the compounds water‐soluble. Hence, D 2 O can frequently be used as the NMR solvent . Polysaccharide sulfate samples are often repeatedly freeze‐dried from D 2 O before the preparation of the actual sample solution .…”

“…Due to these properties, the preparation of various synthetic polysaccharide sulfates has generated interest along with the utilization of natural compounds. Sulfate derivatives have been prepared from many starch species , cellulose , dextran , pullulan , curdlan , chitin , chitosan , pectin , and alginate . Furthermore, sulfation reactions have also been carried out on natural polysaccharide sulfates .…”

“…The number of sulfate substituents attached to a repeating unit of a polysaccharide has an impact on the chemical, physical, and biological properties of polysaccharide sulfates. Thus the determination of the degree of substitution (DS) or the sulfate content usually forms an essential part of the analysis of synthetically prepared polysaccharide sulfates . DS is also determined routinely for commercial carrageenans due to the limits imposed by the European Commission for the sulfate content of carrageenans used as food additives (15–40%) .…”

“…Synthetic polysaccharide sulfates can be analyzed in a similar fashion as carrageenans. NMR and IR spectroscopy and HPLC are frequently used techniques. Structural analyses are used on one hand to confirm the attachment of sulfate groups to the polysaccharide chain, and on the other hand to study the possible side effects the reactions may have had on the structure of the compounds.…”