Light scattering and ultracentrifugation studies of hemicelluloses
Authors: Swenson Harold A. , Morak Alfred J. , Kurath Sheldon 
Published: April 2003

AbstractLight scattering, ultracentrifuge, and intrinsic viscosity analyses were made on a glucomannan from black spruce, a galactoglucomannan from southern pine, and on mixtures of araboglucuronoxylan, arabogalactan, and galactoglucomannan obtained by alkaline extraction of black spruce and slash pine. The extract from black spruce made with 16.770 KOH gave the following residues: xylose I6.4%, mannose 34.3%, uronic anhydride 1.0%, glucose 14.%, galactose 25.5%, and arabinose 8.8%. This analysis indicates that arabogalactan and galactoglucomannan were the predominant hemicelluloses, araboglucuronoxylan being present in lesser amount. The molecular weight by light‐scattering was 41,500; by ultracentrifuge (Archibald method) at 12,590 rpm., 42,400. Both measurements were made in 2% KOH. A small amount of rapidly sedinienting material was not recorded. The bulk of the sample sedimented as a single peak. The intrinsic viscosity in cupriethylenediamine was 0.52 dl./g. The slash pine hemicellulose was obtained by extraction of the chlorite holocellulose with 10% KOH. The component sugar percentages were xylose 50.1, uronic acid anhydride 10.8, mannose 19.7, glucosr 7.3, arabinose 7.4, and galactose 4.7, indicating a predominance of araboglucnronoxylan and lesser quantities of galactoglucomannan and arabogalactan. The rednced viscosity curve in water was typical of a polyelectrolyte. Light scattering measurements done in 2% KOH and in 0.5M NaCl gave molecular weights of 260,000 and ca. 250,000 respectively. Ultracentrifuge analysis (Archibald method) showed a small proportion of heavy material in the sample. The remaining portion had a molecular weight of 63,700 a t the top meniscus and 16,300 at the bottom meniscus, reversing the usual order and revealing marked polydispersity. Under the assumption that crosslinking might have occurred through the nronide carboxyls because of calcium and magnesium in the ash, light scattering was done in 0.25M Nac1–0.5% Calgon and 0.5M NaCl–0.5% Versene; no reduction in the apparent molecular weight occurred. Alkaline sodium borate, 2M NaOH–1M H3BO3, (pH 12.2), was then fonnd to be an effective solvent. When used on the slash pine hemicellulose, a molecular weight of 67,000 given by light scattering, indicated the ability of the solvent to disperse the heavy material in the sample. Intrinsic viscosities of the hemicellulose in 0.5M NaCl, in alkaline borate, and in cupriethylenediamine were 0.79, 0.61, and 0.55 dl./g. respectively. The glucomannan obtained from black spruce sulfite pulp, by extraction with KBO2 following several extractions with KOH, had the following sugar percentages: glucose 23.4, mannose 75.2, and xylose 1.4; it is thus nearly a pure glucomannan. The light scattering molecular weight in the alkaline borate solvent was 66,300. The intrinsic viscosity in borate solvent was 0.23; in cupriethylenediamine, 0.25. A single peak and no evidence of rapidly sedimenting material were found by ultracentrifuge in the borate solvent. The galactoglucomannan from southern pine had a molar ratio of 1:1:3 galactose glucose mannose. Light, scattering and intrinsic viscosity measurements were made in water and in alkaline borate. The molecular weight and viscosity in water were 63,800 and 0.48 dl./g., and in borate solvent, 27,600 and 0.27 dl./g., respectively, indicating that aggregation is present in water. The cupriethylenediamine intrinsic viscosity was 0.29, again nearly identical with that in the borate. The similarity of viscosities in the two solvents was true as well of the other hemicelluloses. Light. scattering depolarixation corrections in the measurements were appreciable, but greater at 436 mμ than a t 546 mμ. Fluorescence was negligible a t the former and absent at the latter wavelength. Dissymmetry ratios between 1.5 and 2.0 were fonnd in the determinations. No Pθ correction factors were, however, applied.