Isolation and sulfation of galactoglucomannan from larch wood (Larix sibirica)

The synthesis of galactoglucomannan sulfates using a sulfamic acid/urea mixture in 1,4-dioxane was studied for the first time. The effect of the galactoglucomannan sulfation time and temperature on the sulfur content in the galactoglucomannan sulfates was investigated. The introduction of sulfate groups into the galactoglucomannan structure was confirmed by the elemental analysis and Fourier transform infrared spectroscopy. The initial and sulfated galactoglucomannans were identified by X-ray diffraction, electron microscopy, and gel permeation chromatography. The thermal analysis has shown that sulfated galactoglucomannan, after the endothermic peak related to the moisture removal, yields a pronounced high-intensity exothermic peak with a maximum at 216 °C, and above 230 °C, the heat absorption effect (endothermic peak) characteristic of decomposition of the parent substance in the range of 230–335 °C is observed. According to the scanning electron microscopy data, the initial galactoglucomannan consists of irregular asymmetric particles with an average size from 400 to 900 µm, and the sulfated galactoglucomannan ammonium salt consists of particles 200–500 µm in size with different shapes. It was shown by gel permeation chromatography that, after the sulfation process, the main galactoglucomannan peak shifts toward higher molecular masses (from 24 to 26 kDa).