Er for critically reading the manuscript. Conflicts of Interest: The Daunorubicin site authors declare no conflict of interest.
Copyright: 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is definitely an open access report distributed beneath the terms and circumstances on the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).The antioxidant properties of all-natural humic substances (HS) attract substantial consideration due to their significance for each the biological activity of HS as well as the mediating effects in microbial and photochemical reactions [1]. In the benchmark publication by Aeschbacher et al. [4], the authors applied electrochemical method for the direct measurement of each the donor- and accepting capacities of HS [4]. The systematic electrochemical measurements undertaken on regular samples on the International Humic Substances Society (IHSS) isolated from leonardite, soil, peat, and freshwater, enabled assessment of theAgronomy 2021, 11, 2047. https://doi.org/10.3390/agronomyhttps://www.mdpi.com/journal/agronomyAgronomy 2021, 11,2 ofnatural variation array of donor and acceptor capacities of HS: the highest donor capacity was observed for freshwater HS, the lowest one–for the leonardite HA [5,6]. In the similar time, the leonardite HA had been characterized together with the highest acceptor capacity [5,6]. The obtained information have been important not just for understanding the organic variations in donor and accepting capacity of HS. They enabled structure–redox properties and mechanistic research on organic HS. As a result, photo-oxidation was associated with the modifications in electrochemical properties of HS [7], the molecular basis of natural polyphenolic antioxidants was proposed [8], biogeochemical redox transformations of natural organic matter (NOM) and HS too as iron cycling have been explained [93] and substantial progress was achieved in understanding contaminants’ biotransformation [14,15]. The dominant role of aromatic structural units, nominally, titratable phenols, was unambiguously demonstrated [7], providing strong experimental proof for the long-stated hypothesis on quinonoid moieties as carriers of redox activity of HS [16]. The obtained structure-property relationships are of distinct worth for mechanistic understanding of redox-behavior of HS inside the environment. They enabled predictions around the fate of redox-sensitive contaminants (e.g., Hg(II), Cr(VI), Pu(V, VI), diazo dyes, and other individuals) in the organic-rich environments [7,179]. Offered the critical part of biocatalytic cycles within the redox transformations of contaminants inside the atmosphere, the information and facts on redox mediating capacity of HS is of indispensable worth [14,17]. Methodical electrochemical approaches for the assessment of mediating properties of HS were developed in a different set of publications by Aeschbacher et al. [5,20], who’ve demonstrated that HS could effectively function as an extracellular electron shuttle enhancing the accessibility of insoluble substrates for microbial redox transformations. In our earlier perform [21], we applied phenol formaldehyde condensation for incorporation of quinonoid centers into HS backbone aimed at controlling the redox properties of humic materials. The big drawback of this strategy is actually a use of toxic formaldehyde, which prevents its broad application for agricultural and environmental applications. This study is devoted to development of an option “green” Resazurin site synthesis of the quinonoidenriched derivatives.