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Sulfation of wheat straw soda lignin by the sulfamic acid–urea mixture in different solvents has been investigated for the first time. The effect of a catalyst used in the lignin sulfation process on the yield of the lignin sulfates and sulfur content in them has been explored. It has been found that the optimal medium for the lignin sulfation with sulfamic acid is dioxane and, in the presence of a catalyst, urea. Although the sulfated lignins obtained using the reaction in dimethyl sulfoxide and diglyme have the maximum sulfur contents (11.2% and 9.9%, respectively), these products are difficult to isolate and purify, which complicates the use of these solvents. Sulfated lignin obtained in the dioxane medium has a high (10.1%) sulfur content and is easy to isolate and purify. The incorporation of sulfate groups into the lignin structure has been confirmed by the infrared and nuclear magnetic resonance spectroscopy investigations. In the infrared spectra of sulfated lignin, characteristic absorption bands at 800–860 and 1260–1200 cm−1 appear. The dominant substitution of aliphatic hydroxyl groups has been confirmed by the nuclear magnetic resonance spectroscopy study. It has been found that, during the modification and purification of lignin, the latter is fractionated, which results in the redistribution of molecular weights toward the high molecular-weight region, as well as the removal of some low-molecular-weight components, which is reflected in a decrease in the number of signals in the nuclear magnetic resonance spectra.

A comparison of IR spectra and molecular weight distribution of arabinogalactan sulfates as sodium and ammonium salts obtained using various sulfating reagents was performed. According to the data, sulfated derivatives of arabinogalactan differ from each other in the nature of hydrogen bonds and molecular weight distribution. Using coagulological tests during activation of coagulation of platelet-poor human plasma in vitro, the anticoagulant properties of sulfated arabinogalactan derivatives in various salt forms differing in the preparation method, sulfation degree, and molecular weight were studied. It was found that the sample in the form of the sodium salt of sulfated arabinogalactan (SAG 1) with a sulfur content of 13.2 wt % and a polydispersity degree of 1.52 exhibited twofold greater anticoagulant activity than the sample in the form of the ammonium salt of sulfated arabinogalactan (SAG 2) with a sulfur content of 6.6 wt % and a polydispersity degree of 1.30. The antithrombin (aIIa) activity of the samples obtained by sulfation with a complex of pyridine and sulfuric anhydride (SAG 1) and a complex of sulfamic acid (SAG 2) was 23.42 ± 1.86 and 10.20 ± 1.50 U/mg, respectively; the value of the antifactor Xa activity of SAG 1 and SAG 2 was 2.13 ± 0.42 and 0.37 ± 0.08 U/mg; the aIIa/aXa ratio for SAG 1 and SAG 2 was 11 and 28, respectively. The antifactor Xa (aXa) activity of SAG, which is lower than that of unfractionated heparin (UFH), and a high aIIa/aXa activity ratio may contribute to less provocation of bleeding by SAG samples compared to UFH.

Interpolymer complexes based on chitosan and arabinogalactan with a different degree of sulfation (7.7–40.8%) stable for 30 days are synthesized. The resulting complexes are characterized by scanning electron microscopy, IR spectroscopy, dynamic light scattering, and ζ-potential electrophoretic measurements. The main mechanism of complex formation is considered in terms of the electrostatic bonding of polyions. New complexes show promise as biosorbents and drug delivery systems.

The sulfation of ethanol lignin of abies wood by sulfamic acid–urea mixture in N,N-dimethylformamide (DMF) medium was studied for the first time. The effect of the duration of lignin sulfation process on the yield and sulfur content in resulted lignin sulfates was studied. It was shown that the reaction of ethanol lignin sulfation begins and ends in a homogeneous medium. At temperature 100 °C, the sulfur content in lignin varies from 5.4 to 6.8% mass, depending on the process time. The introduction of sulfate groups into the lignin structure was confirmed by FTIR and 2D NMR spectroscopy. It was found that both alcohol and phenolic hydroxyl groups of lignin enter the sulfation reaction. The molecular weight distribution of sulfated ethanol lignin was determined by gel permeation chromatography. The optimized method of synthesis allows to obtain sulfated ethanol lignin with low polydispersity (1.31) and narrow molecular weight distribution (3.25–3.75 kDa).

The new process of abies ethanol lignin sulfation by a low-toxic mixture of sulfamic acid and urea in 1,4-dioxane medium was optimized, and the structure of sulfated ethanol lignin was studied. The process of lignin sulfation is described by a first-order equation in the temperature range 70–100 °C. The value of the rate constants is weakly dependent on the ratios of lignin and sulfating complex (sulfamic acid–urea mixture). The activation energy of the sulfation process decreases from 11.5 to 7.5 kJ/mol with an increase in the content of the sulfating complex (SC). The optimal conditions for sulfation of abies ethanol lignin with a high yield of water-soluble sulfated lignin [(100% of mass) with sulfur content of 7.9%] were found: temperature 95–100 °C, L/SC ratio 1:2.3–1:2.9, time 2 h. The composition and structure of water-soluble sulfated ethanol lignin were determined by elemental analysis, FTIR spectroscopy, two-dimensional NMR spectroscopy and gel permeation chromatography. It was shown that only alcoholic OH groups of ethanol lignin react with sulfamic acid. Sulfated ethanol lignin has a higher molecular weight and a lower degree of polydispersity compared to the initial ethanol lignin.

Sulfation of larch wood arabinogalactan (AG) with sulfamic acid in dimethylsulfoxide (DMSO) medium in the presence of urea was studied for the first time. The use of DMSO as a solvent instead of more toxic 1,4-dioxane allows to sulfate AG under homogeneous conditions. The sulfated AG with a high sulfur content (12.0-12.5 wt %) was produced by sulfation at a temperature of 85-90 °C, the molar ratio of AG / sulfating agent equal to 1:0.85 during 2-3 h. The introduction of sulfate groups into the structure of arabinogalactan was confirmed by the appearance of new absorption bands in FTIR and FT Raman spectra, characteristic for the vibrations of the sulfate groups. It was proved by 13C NMR spectroscopy that the predominant substitution of the primary hydroxyl groups at C6 carbon atoms of the terminal galactose units of main and side chains of arabinogalactan takes place. Simultaneously, the hydroxyl groups associated with C2 and C4 carbon atoms of galactose unit of the main chain are only partially sulfated. According to results of GPC study, the sulfated AG is characterized by a narrow molecular weight distribution with an average molecular weight of 18.8 kDa and a polydispersity of 1.3. Supplementary information The online version contains supplementary material available at 10.1007/s00226-021-01341-2.

Sulfated polysaccharides, due to the presence of anionic groups, are able to form complexes with positively charged molecules. This work presents the results of obtaining complexes of the sulfated polysaccharide arabinogalactan with tetramethylammonium bromide. The resulting complex was shown to be soluble in water and methylene chloride. The introduction of tetramethylammonium bromide into the molecule of sulfated arabinogalactan has been proven by elemental analysis and FTIR spectroscopy.

The process of sulphation of potato starch with a deep eutectic solvent, a mixture of sulfamic acid: urea, was optimized. The influence of varying factors was established - the ratio of sulfamic acid: urea (SAA: U), the ratio of starch: sulfating complex (St: SC) and the duration of the process on the sulfur content (wt.%) in the obtained starch sulfate. The data of analysis of variance for the obtained mathematical models indicate good prognostic properties. The optimal conditions for starch sulfation, which provide water-soluble sulfated starch with a high (up to 11.2% wt.) sulfur content, have been established. The optimal conditions for the process of sulfation of potato starch are the ratio SAA: U 1: 2.0-1: 2.2, the ratio St: SC 1: 3.5-1: 4.0 and the duration of the process is 118-120 minutes.

In this paper, a new method for the synthesis of the sulfated starch-casein complex is proposed. The resulting new complex was characterized by FTIR and UV-spectroscopy. It has been shown by FTIR spectroscopy that both nitrogen atoms and the carboxyl group of amino acid residues are protonated in casein. The sulfated starch-casein complex obtained in this work may have biological activity, as well as its analogues isolated from plants, fungi, and microorganisms, as well as synthesized in laboratory conditions.

The guar gum was sulfated for the first time with a deep eutectic solvent, a sulfamic acid / urea mixture at a ratio of (1:1). The optimal conditions of the process are shown to ensure the production of guar gum sulfate with a maximum sulfur content (16.1% wt.). The introduction of a sulfate group into a guar gum molecule is proved by elemental analysis. A mathematical model of the process of sulfation of guar gum is calculated. It is shown that the resulting model has high predictive properties. The developed method is environmentally safer due to the fact that it eliminates the use of toxic solvents.