Antioxidant properties of brown coal humic substances

Abstract

Humic substances (HS) belong to a fairly common class of organic compounds in nature, which are a component of soils, peat, lignite and sapropels. Some properties of humates (salts of humic acids) make it possible to use them in various fields – crop production, animal production, well drilling and soil structuring. The biological and chemical activity of humic substances is well known. It is caused by the presence of such functional groups as carboxyl, hydroxyl, carbonyl, nitrogen- and sulfur-containing in the composition of GR macromolecules. This fact also serves as a basis for a more extensive study of other properties of GR, namely antioxidant activity. Purpose. Deepening and expanding the understanding of the biological and antioxidant activity of lignite humic (HA) and hymatomelanic (HmA) acids, determining its nature and evaluating the prospects of its use in little-studied processes of oxidation of organic and consumer substances. Methodology. The paper used a photocolorimetric method for determining the antiradical activity (ARA) of two components of humic substances of domestic lignite - humic and hymatomelanic acids. The antioxidant activity (AOA) of humic and hymatomelanic acids from lignite was determined using the gas volumetric method, evaluating the rate of reaction inhibition using the example of the initiated liquid-phase oxidation of cumene with oxygen. Findings. It was established that humic acids exhibit more pronounced antioxidant properties in the processes of radical-chain oxidation of hydrocarbons compared to hymatomelanic acids. The total AOA of HA is 1.68 relative units, which is almost three times higher than this figure for HmA (0.50). On the other hand, it has been experimentally proven that hymatomelanic acids have more pronounced antiradical properties than humic acids. ARA HmA is 0.90 relative units, which is approximately three times more than the similar value for HA (0.57). Originality. Despite the fact that a number of methods for determining the antiradical and antioxidant activity of low-molecular antioxidants and their mixtures have been developed, a method for determining these indicators for high-molecular native compounds has not yet been created. For the first time, a method for determining the antiradical effect of humic substances using the stable 2.2-diphenyl-1-picrylhydrazyl radical (DPPH) was proposed and experimentally tested. A method for determining the antioxidant activity of humic and hymatomelanic acids in hydrocarbon oxidation processes (on the example of cumulus) has been developed. The convenience and satisfactory reproducibility of the developed methods are shown. Practical value. The green-chemistry related development and application of drugs based on native and modified humic substances as polymers with adjustable redox properties (redox polymers) is a relevant direction of sustainable development of society. These substances are the basis for obtaining new medicines, plant protection products, new sorbents, preparations for the reclamation of territories contaminated with radionuclides, heavy metals, organic ecotoxicants, oil products, etc.