The Raman Spectroscopy, XRD, SEM, and AFM Study of Arabinogalactan Sulfates Obtained Using Sulfamic Acid

Abstract

The structure of sodium salts of arabinogalactan (AG) sulfates obtained by sulfating AG of larch wood with a sulfamic acid–urea mixture in 1,4-dioxane was studied by the methods of Raman spectroscopy, X-ray diffraction (XRD) phase analysis, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The introduction of sulfate groups into the structure of arabinogalactan was confirmed by the appearance in the Raman spectra of new absorption bands related to the deformation vibrations δ (SO₃) at 420 cm^–1 and δ (О=S=O) at 588 cm^–1, stretching vibrations ν (C–O–S) at 822 cm^–1, symmetrical stretching vibrations ν_s (O=S=O) at 1076 cm^–1, and asymmetric stretching vibrations of ν_as (O=S=O) at 1269 cm^–1. According to the XRD data, the amorphization of arabinogalactan structure occurs during the sulfation process. The SEM method revealed a significant difference in the morphology of the sulfated and starting arabinogalactan. The starting AG consists of particles of predominantly globular shape with a size of 10 to 90 μm; arabinogalactan sulfates, of particles of various shapes with sizes of 1–8 μm. According to the AFM, the surface of sulfated arabinogalactan film consists of rather homogeneous spherical particles about 70 nm in size. The root-mean-square value of the surface roughness is 33 nm. The surface of sulfated AG film does not contain impurities.