Lignite Humic Acids Research Articles

Impact of a Single Lignite Humic Acid Application on Soil Properties and Microbial Dynamics in Aeolian Sandy Soils: A Fourth-Year Study in Semi-Arid Inner Mongolia

Impact of a Single Lignite Humic Acid Application on Soil Properties and Microbial Dynamics in Aeolian Sandy Soils: A Fourth-Year Study in Semi-Arid Inner Mongolia

Хімічні властивості та характеристики поверхневої активності гумінової кислоти з бурого вугілля

The article is devoted to the study of some specific physicochemical properties of humic acids, which are attracting increasing attention due to their potential applications. The unique structural composition, which includes both hydrophilic and hydrophobic sites, makes these materials a versatile agent in various technological processes. It has been shown that humic acid solutions have the properties of surfactants and can serve as a natural alternative to surfactants. The paper presents the results of studies of a sample of humic acid obtained from lignite. Infrared spectroscopy has revealed signs of the aromatic structure of humic acid, the presence of phenolic and other functional groups, such as hydroxyl and nitrile. The presence of carboxylic acids, esters, and complex esters was established. The complex and heterogeneous nature of humic acids has been confirmed, which makes them promising for use as surfactants. No clear evidence of the presence of -NH₂ groups was found in the IR spectrum. This suggests that lignite humic acids generally correspond to the structural formula reported in the literature. The potentiometric titration of the lignite humic acid sample made it possible to determine the dissociation constants of functional groups. The obtained values are close to the calculated dissociation constants of carboxyl groups for the model molecule of lignite humic acid. The analysis of the calculated properties of humic acid based on various structural models showed that lignite is a promising raw material for the production of humic acids with certain surface-active properties. Compared to other structures, humic acid from lignite is more hydrophobic and less soluble in water, which indicates the prospects of its use as a surfactant with better interaction with the oil phase. Keywords: humic acids, lignite, surfactant, infrared spectroscopy, composition, functional groupsб structural model. Corresponding author: Bannikov L.P., e-mail: ukhinbannikov@gmail.com

Modeling of Smart Bio-Medical Active Polymeric Hydrogel Transdermal Materials

In this article, effective 3D printing modeling technology of smart bio-medical polymeric hydrogel transdermal materials based on gelatin and sodium alginate, modified by humic acids, was researched. Such smart biologically active polymeric hydrogel materials showed interesting applicability in tissue engineering fields due to their intrinsic biological compatibility, adaptability, and capacity to replicate the extracellular matrix environment. A literature review was carried out and proved that 3D printing modeling technology is a perspective for the functional effect on the smart bio-medical polymer hydrogel transdermal properties. Smart biomedical polymeric transdermal hydrogel patches were produced using a micromolding technique. A stereolithography (SLA) 3D printer was used to print the master mold. The three-stage technology of lignite humic acids modification of smart biologically active polymeric hydrogel transdermal microneedles patches based on gelatin, hydroxypropyl methylcellulose, and sodium alginate was designed. It was shown that modification of gelatin-sodium alginate and hydroxypropyl methylcellulose-sodium alginate biopolymer hydrogels by humic acids makes it possible to obtain smart biologically active polymeric hydrogel transdermal materials with an increased swelling degree and ability to improve the skin moisture-lipid balance (from the initial moisture 34–36 % and fatness 8–10, they increase to 58–66 % and 52–60 %). Finally, the developed 3D printing modeling technology of smart bio-medical polymeric hydrogel transdermal materials hydrogel based on gelatin sodium alginate, modified by humic acids, is a transdermal material with required properties.

Solid-Phase Extraction at High pH as a Promising Tool for Targeted Isolation of Biologically Active Fractions of Humic Acids.

A search for novel sources of biologically active compounds is at the top of the agenda for biomedical technologies. Natural humic substances (HSs) contain a large variety of different chemotypes, such as condensed tannins, hydrolyzable tannins, terpenoids, lignins, etc. The goal of this work was to develop an efficient separation technique based on solid-phase extraction (SPE) for the isolation of narrow fractions of HS with higher biological activity compared to the initial material. We used lignite humic acid as the parent humic material, which showed moderate inhibition activity toward beta-lactamase TEM 1 and antioxidant activity. We applied two different SPE techniques: the first one was based on a gradient elution with water/methanol mixtures of the humic material sorbed at pH 2, and the second one implied separation by a difference in the pKa value by the use of sequential sorption of HS at pH from 8 to 3. SPE cartridges Bond Elute PPL (Agilent) were used in the fractionation experiments. The first and second techniques yielded 9 and 7 fractions, respectively. All fractions were characterized using high-resolution mass spectrometry and biological assays, including the determination of beta-lactamase (TEM 1) inhibition activity and antioxidant activity. The acidity-based separation technique demonstrated substantial advantages: it enabled the isolation of components, outcompeting the initial material at the first step of separation (sorption at pH 8). It showed moderate orthogonality in separation with regard to the polarity-based technique. Good perspectives are shown for developing a 2D separation scheme using a combination of polarity and acidity-based approaches to reduce structural heterogeneity of the narrow fractions of HS.

Base-Catalyzed Polymerization of a Substituted Methylenebicyclo[3.3.1]nonane

Lignite humic acid on reaction with formaldehyde and aqueous alkali led to a polybicyclo[3.3.1]nonane. This was characterized spectroscopically using mass spectrometry, FT-IR, powder X-ray diffraction, TEM, and NMR studies (1H-NMR, CP-MAS-SS-NMR) which though challenging were useful for confirming the structure of the BCN polymer. The product showed an envelope peak in its MALDI-MS spectrum, based on which M ̅ n , M ̅ w , and polydispersity index have been calculated. Based on the NMR spectrum of intermediate, the presence of the N-formyl group has been shown in it. The new polymer could be useful in agriculture in water-deficient areas. Most papers on humic acids include only broad and general information like elemental analysis (occasionally TEM, SEM, TGA, DSC, etc.). Very complicated structures have been proposed by scientists earlier. Only in very recent years, it has been recognized that these are relatively small molecules which masquerade as supramolecular structures. It is pointed out that most papers do not put down the structure of the compound and provide no concrete proof for proposing such structures. The novelty of our work is that we have characterized the precise molecular weights based on mass spectrometry and NMR spectroscopy along with a well-defined structure. This is not the case in most other publications.

From feedstock to digestion: Unraveling the impact of humic acid composition on anaerobic digestion

In the anaerobic digestion (AD) process, the effects of humic acid (HA) derived from different feedstocks on AD are influenced by the variations in their structural composition and oxygen-containing functional groups. Thus, clarifying the structural differences of HA obtained from different feedstocks is crucial for understanding their impact on AD. In this study, the structure of five humic acids (HAs) derived from liquid digestate, food waste, silage corn straw, lignite and commercial HA, and their effects on AD were investigated. The study found that HA from food waste had more carboxyl groups, while straw-derived HA had more phenolic hydroxyl groups. Both types of HA had higher aromaticity and humification degree and showed significant inhibition effect on AD. HA from food waste had an average methanogenic inhibition rate of 43.5 % with 1 g/L HA added. In addition, commercial HA and HA derived from lignite had similar functional group types and aromaticity, with an average methanogenic inhibition rate of about 20 %. The study revealed that HAs with more carboxyl groups exhibited greater effectiveness in inhibiting AD, thereby confirming the influence of HA structures derived from different feedstocks on AD. In conclusion, this study provides valuable insights into the mechanism of HA effect on AD and offers guidance for future research focused on enhancing AD efficiency.

TECHNOLOGY OF HYBRID MODIFICATION WITH HUMIC ACIDS OF BROWN COAL HYDROXYPROPYLMETHYL CELLULOSE FILMS

The peculiarities of the technology of hybrid modification of lignite humic acids of biodegradable films based on hydroxypropylmethylcellulose are considered. As a result of the conducted research, hybrid biodegradable films with antibacterial properties were obtained for the first time. Hydroxypropylmethylcellulose of the Walocel brand was used for the production of biodegradable films, and citric acid (99.88%) according to GOST 3652 is used as a catalyst for crosslinking biodegradable polymer films. As part of the research, the hybrid structures of hydroxypropylmethylcellulose modified with different types of humic acids were actually determined by IR spectroscopy. As a result of the study, the regularities of changes in the time of appearance of mold of films within the framework of the technology of hybrid modification with lignite humic acids were established. It was also established that the technology of hybrid modification of hydroxypropylmethylcellulose films with humic acids of lignite and giving them antibacterial properties allows to preserve the properties of biodegradation. It was established that the technology of hybrid modification of hydroxypropylmethylcellulose with lignite humic acids of biodegradable hydroxypropylmethylcellulose films with different types of humic acids, while giving them antibacterial properties, allows the biodegradation of films based on them to be at least 91% within 6 months with an optimal humic acid content of 10% by mass. Biodegradable films with bactericidal properties based on hydroxypropylmethylcellulose, obtained according to the technology of hybrid modification with humic acids of lignite, in terms of their operational characteristics, are superior to known similar biodegradable films based on natural biopolymers and can be recommended for the manufacture of packaging of dry food products (bread, cereals, nuts, etc.) with an extended storage period.

Study of lignite humic acids hybrid modification technology of biodegradable films based on polyvinyl alcohol

Object of article study is lignite humic acids hybrid modification technology of biodegradable films based on polyvinyl alcohol. The possibility of increasing the strength and operational properties of biodegradable polymeric materials based on polyvinyl alcohol by using its modification with the different types of humic acids from lignite is considered. Lignite humic acids hybrid modification films with antibacterial properties were obtained. The two-stage technology of lignite humic acids hybrid modification of biodegradable films based on polyvinyl alcohol was formalized. At the first stage of lignite humic acids hybrid modification technologies for hybrid-modified biodegradable materials production, lignite humic acids are received. At the second stage, hybrid modification of lignite humic acids (that are part of biodegradable polyvinyl alcohol films), which are received by watering from a solution, takes place. It has been conducted a study on determining the effect of lignite humic acids hybrid modification on the most important operational properties of biodegradable film based on polyvinyl alcohol, i. e., tensile strength, relative elongation at break and time of mold appearance. Changes in tensile strength, relative elongation at break and time of mold appearance for the lignite humic acids hybrid modified biodegradable polymeric materials based on polyvinyl alcohol were revealed depending on the content of the different types of lignite humic acids. It was also shown that the lignite humic acids hybrid modification of polyvinyl alcohol with the different types of humic acids allows preserving the biodegradability of the films along with imparting the antibacterial properties. The developed lignite humic acids hybrid modified biodegradable polyvinyl alcohol films with antibacterial properties, in terms of their operational characteristics, are superior to the known similar biodegradable films based on natural biopolymers.

Дослідження хімічно-фізичних особливостей похідних бурого вугілля для оцінки потенціалу їх гібридної функціональності

STUDY OF CHEMICAL AND PHYSICAL FEATURES OF LIGNITE DERIVATIVES FOR EVALUATION OF THEIR HYBRID FUNCTIONALITY POTENTIAL © V.V. Lebedev, PhD in technical sciences, D.V. Miroshnichenko, Doctor of Technical Sciences, D.O. Savchenko, E.I. Lytvynenko, PhD in technical sciences (National Technical University «Kharkiv Polytechnic Institute», 2 Kyrpychova Str., Kharkiv, 61002, Ukraine)) The article shows that despite the existence of studies on the modification of various types of polymeric materials with lignite and its derivatives (in particular, it has been proven that the addition of lignite to polymers can affect their biodegradation), there is a further need to study the physicochemical features of the hybrid functionality of these materials in relation to a wide range of materials. The paper analyzes lignite and its derivatives in the form of humic acids in terms of their use for hybrid modification of multifunctional materials. The subject of the study is related to the non-energy and non-fuel use of fossil coal. This area is one of the most promising, as it allows to obtain marketable products of high demand, the cost of which is much higher than the cost of the raw materials. By performing qualitative, quantitative, and spectroscopic analyses of humic acids of different types of lignite, it has been proved that they have a significant hybrid functionality due to the presence of a large number of different functional groups in their composition. It has been shown that the most characteristic functional groups of lignite humic acids include phenolic hydroxyl -OH groups, carboxyl COO-, NH2 deformation groups, aliphatic CO groups, etc. This determines the ability of lignite humic acids to act as hybrid modifiers in relation to a wide range of substances through the following mechanisms: chemical interaction, dipole-dipole interaction in the form of hydrogen bond systems, and configuration changes in the structure of various materials and substances. It has also been found that the high hybrid functionality of lignite humic acids is determined by their polarity, which significantly increases the reactivity of active peripheral groups. Keywords: coal, humic acids, hybrid functionality, modification, properties. Corresponding author Denys V. Miroshnychenko, e-mail: dvmir79@gmail.com

Application of carbon nitride nanosheets for adsorption of various humic substances from aqueous solutions

Humic substances (HSs) cause serious problems such as membrane fouling and disinfection by-products. Particularly, HSs as the main UV-quenching substances in landfill leachate pose great challenges. In this study, we evaluated the application of carbon nitride nanosheets (CN-Ns) for adsorption of various HSs, as well as leachate nanofiltration concentrates (LNCs). The characterization revealed that as increasing thermal oxidation temperature, the properties of CN-Ns were affected, such as morphology, porosity, and crystallinity. The surface area of CN-N at 575 °C (CN-N-575) was 145.3 m2·g−1, resulting in an enhanced adsorption performance. The adsorption capacity of CN-N-575 for lignite humic acid (LHA) and soil fulvic acid (SFA) was considerably greater than that of bulk CN; the maximum adsorption amounts of LHA and SFA were 143.11 and 63.27 mg C·g−1, respectively. Upon adsorption, the removal rate of LHA and Elliott soil humic acid was about 90 %. Among HSs and LNCs, the humic-like components showed superior affinity; in some cases, the removal rate reached 100 %. The adsorption preference of aromatic compounds in HSs and LNCs was ascribed to π-electron interactions. The adsorption of LHA was more pH-dependent than that of SFA, attributed to the interactions (electrostatic, hydrogen bonding, and complexation) along with a specific conformation effect. The findings proved the great potential of CN-Ns in HSs adsorption, especially in the treatment of landfill leachate.

Effects of Different Organic Amendments on Soil Improvement, Bacterial Composition, and Functional Diversity in Saline–Sodic Soil

The agricultural productivity of farmland in Northeast China’s Liaohe Plain is restricted by the salinity and sodicity of the soils, which have additionally low organic matter content. In order to improve saline–sodic soils, organic amendments are frequently applied. Our objective was to clarify how different organic amendments affect the diversity and composition of soil microbes, as well as how these factors are related to crop yield. In 2020–2021, we conducted an experiment with different organic amendments. The treatments included the application of crop residue incorporation (SR), lignite humic acid (LHA; 6 ton/ha), or cow manure (FM; 30 ton/ha), and a control (CK). The results show that, compared with CK, the content of SOM in soil treated with organic amendments increased by 5.3–7.4 g/kg; the available potassium (AK) of the LHA treatment was significantly higher than that of the FM and SR treatments by 32.17 and 42.79 mg/kg, respectively; and the available phosphorus (AP) of the LHA treatment was significantly higher than that of the SR treatment by 7.19 mg/kg. The pH and EC1:5 values of the LHA treatment were significantly lower than those of CK by 1.36 units and 0.2 mS/cm, respectively. The application of organic amendments and changes in environmental conditions also significantly affected community structure and increased soil microbial richness and diversity. SR treatment increased the abundance of Acidobacteria. Further FAPROTAX (Functional Annotation of Prokaryotic Taxa) analysis showed that organic amendments can increase the abundance of microbes involved in the carbon and nitrogen cycle processes, such as aerobic_ammonia_oxidation, aerobic_chemoheterotrophy, nitrification, etc., which increases the kernel number per row and increases crop yield. LHA can increase the microbial abundance of the nitrogen cycle and reduce soil carbon mineralization, while also increasing soil nutrients and crop yield. This study provides a comprehensive understanding of the application of organic amendments in saline–sodic cultivated land.

STUDY OF BIODEGRADABLE FILMS BASED ON CELLULOSE ETHERS WITH BACTERICIDAL PROPERTIES

The article shows research on the development of the latest biodegradable films with bactericidal properties based on hydroxypropylmethylcellulose modified with brown coal humic acids. Hybrid biodegradable films with bactericidal properties were obtained by pouring solutions of hydroxypropylmethylcellulose with a concentration of 2 wt.%, to which different amounts of humic acid were added. When obtaining biodegradable films with bactericidal properties, hydroxypropylmethylcellulose of the Walocel™ brand manufactured by Dow Corning (USA) was used. As hybrid modifiers, humic acids were used, obtained by extraction of brown coal with an alkaline solution of sodium pyrophosphate, followed by extraction with a 1% sodium hydroxide solution and precipitation with mineral acid. Determination of water absorption of samples of biodegradable films in cold water was carried out according to ISO 62:2008, tensile strength properties of biodegradable films were determined according to ISO 527-2:2021, to measure the gas permeability of biodegradable films, the differential pressure method and a vacuum tester VAC-V1 were used. The effect of the hybrid modification of hydroxypropylmethylcellulose with lignite humic acids in terms of the studied performance characteristics increased in the direction of lignite humic acid types No. 3> No. 2> No. 1. It has been shown that hybrid modification by the mechanism of matrix synthesis of biodegradable films with bactericidal properties based on hydroxypropylmethylcellulose with brown coal humic acids makes it possible to reduce their water absorption, increase the basic strength characteristics and impart antibacterial properties to them, which is confirmed by the data on the time of mold appearance. Optimum in terms of strength and performance characteristics are biodegradable films with bactericidal properties at a content of 10% wt. humic acids No. 3. In general, it has been established that hybrid modification with humic acids according to the mechanism of matrix synthesis of biodegradable films based on hydroxypropylmethylcellulose makes it possible to obtain durable water-soluble films with antibacterial properties for use as packaging for dry food products (bread, cereals, nuts, etc.) with an extended shelf life. storage.

Surface complexation modeling of the effects of dissolved inorganic carbon on adsorption of U(VI) onto Fe3O4 nanoparticles coated with lignite humic acid

Abstract Lignite humic acid (LHA) surface-functionalized magnetite nanoparticles (NPs) represent a promising sorbent for removal of U(VI) from industrial waste streams and contaminated environmental waters, but the effects of dissolved inorganic carbon (DIC) on the adsorption mechanisms and efficiency are poorly constrained. We measured the adsorption of U(VI) onto LHA-coated Fe3O4 NPs as a function of pH, ionic strength, adsorbent concentration, DIC concentration and dissolved calcium concentration. The observed U(VI) adsorption onto LHA-coated Fe3O4 NPs is ionic strength independent, and below pH 5, the extent of U(VI) adsorption increases with increasing pH and adsorbent concentration. The extent of U(VI) adsorption decreases dramatically with increasing concentration of added NaHCO3 and CaCl2 above pH 5 and pH 6 respectively. The adsorption data were modeled using a non-electrostatic surface complexation modeling approach to determine the identities and thermodynamic stabilities of possible uranyl complexes on the LHA-coated Fe3O4 NP surfaces. The modeling results indicate that L1-(UO2)+, >L2-UO2(OH), >L2-(UO2)3(OH)5, >L2-UO2(CO3)-, >L3-(UO2)2(CO3)(OH)32-, >L4-UO2(CO3)23- and >L4-(UO2)3(OH)72- are involved in the adsorption under different pH (3.0–9.5) and DIC (0–25 mM) concentration conditions. The log stability constant values (±2σ) of these uranyl surface complexes are calculated as 4.59(±0.12), 6.59(±0.14), 6.33(±0.13), 6.08(±0.18), 6.16(±0.06), 7.07(±0.19) and6.13(±0.15). The model can be applied to predict the distribution of U(VI) in complex LHA-coated Fe3O4 NP-bearing systems under a wide range of pH, ionic strength, DIC, and solute: sorbent conditions.

Characterization of humic acids produced from fungal liquefaction of low-grade Thar coal

Fungal liquefaction of coal is a promising technology to convert low rank coal into value-added products such as humic acids (HAs) that are extensively used as fertilizer. Use of Pakistani Thar lignite for humic acid extraction can promote agriculture industry in Pakistan. In this study, fifty-five fungal strains were isolated from Thar lignite and screened for their lignite solubilization efficiency. Isolates M13 and MI exhibited highest capacity for lignite solubilization and HA was extracted with 67.4 ± 4.3 percent (w/w) yield. Elemental analysis showed increased nitrogen (0.72–1.39 percent) and oxygen (41.7–48 percent), and decreased carbon (51.8–46.1 percent) and sulphur (1.18–0.73 percent) contents in bio-extracted HA (bHA) compared to chemically extracted HA (cHA). UV/Vis spectroscopy showed increased E4/E6 value from 5.6 ± 0.39 (cHA) to 6.28 ± 0.35 (bHA) indicating reduced molecular mass and aromaticity and increased bioactivity of molecule. FTIR analysis also confirmed these results. HPLC analysis of bHA and cHA showed typical choromatogram of humic acids. Enzyme activity staining indicated the presence of fungal cellulase and xylanase on SDS-PAGE gel. The degradation of lignite macromolecules by lignin degrading fungi is a complex process dependent on alkaline substances, chelators, surfactants and extracellular fungal enzymes.

U(VI) adsorption to Fe3O4 nanoparticles coated with lignite humic acid: Experimental measurements and surface complexation modeling

Lignite humic acid-coated Fe3O4 nanoparticles (LHA-coated Fe3O4 NPs) with different extents of LHA coating were synthesized and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transformed infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and potentiometric titration. The results of characterization revealed that LHA-coated Fe3O4 NPs contained plentiful oxygen-containing groups. Batch adsorption measurements show that U(VI) adsorption is pH dependent, with an optimum pH range of 5.0–8.0. The removal kinetics of U(VI) can be well fitted by the pseudo-second-order model. The maximum adsorption capacities at 298 K were 42.5, 55.6, and 68.7 mg g−1 on 0.5, 1.5, and 2.5 LHA-coated Fe3O4 NPs, respectively. The regeneration experiment showed that LHA-coated Fe3O4 NPs exhibited good recoverability for U(VI) adsorption. The adsorption mechanism of U(VI) on LHA-coated Fe3O4 NPs revealed by XPS and surface complexation model. XPS results indicate that both > Fe surface sites and oxygen-containing groups are involved in U(VI) adsorption. Moreover, no significant U(VI) reduction occurs on the surfaces of the LHA-coated Fe3O4 NPs, possibly because of the insulating properties of the LHA coating. Surface complexation modeling further demonstrated that U(VI) adsorption onto the Fe3O4 NPs with the highest extents of LHA coating is dominated by binding onto the LHA-associated binding sites (e.g., carboxyl sites), whereas > Fe surface sites are also involved in U(VI) adsorption onto Fe3O4 NPs with the lowest extent of LHA coating. LHA-coated Fe3O4 NPs represents a cost-efficient and good stability adsorbent for the effective removal of U(VI) from aqueous solutions, and our results provide the means for modeling the adsorption behavior as a function of the pH and extent of LHA coating.

The NMR and spectral study on the structure of molecular size-fractionated lignite humic acid

In this study, high pure humic acid (HA) extracted from lignite was fractionated into four fractions according to their molecular weights by the ultrafiltration method. The structural characteristics of various HA fractions were investigated by UV–Vis,FTIR, and 3D fluorescence spectra and 13 C/ 1 H-NMR tests. The experiment results showed that the HA fractions with the molecular weight ＞50 KDa are major, containing 70.89%. The active hydrogen proportion declined from 43.96% to 21.27% with the increase of HA molecular weight, meaning the decrease of the large HA molecules’ acidic group content. On the other hand, 80.93% of the aromatic nucleus content and 12.5% of the alkyl carbon (aliphatic structure) were observed in the large HA molecules that are much higher than those in the small HA molecules. The NMR and spectra studies indicated that the small HA molecules have more acidic groups such as hydroxy, carboxyl. Meanwhile, the large HA molecules have more aromatic and aliphatic structures. The above research indicated that the HA fractions with low molecular weight could provide more active sites for the interaction between HA and iron minerals. Moreover, the carbon chain and aromatic nucleus in the high molecular weight HA fractions could keep the space structure of HA stable. • High pure lignite humic acid was fractionated successfully by ultrafiltration. • The differences of composition and structure of various HA fractions were investigated. • The structure proportion of HA was quantized by integral and PARAFAC method. • The smaller HA molecular had more abundant oxygen-bearing groups. • The larger HA molecular had more aromatic structures.

Reduced catalytic activity of an exogenous extracellular β-D-glucosidase due to adsorption on a model humic-clay complex and different soils under wetting and drying cycles

To ascertain the role of extracellular enzymes in soil biochemical reactions, we followed the changes in catalytic activity of an exogenous β-glucosidase (GLU) enzyme after its adsorption on a synthetic model humic-clay complex, composed by a lignite humic acid coupled by Al bridges to a Ca-montmorillonite (HM), and on three sterilised soils (DS, ISC and IST) with different properties. Either HM or the selected soils enabled a stable GLU adsorption that induced a significant decrease of GLU activity. In the case of soils, both the largest GLU adsorption and reduction of catalytic activity was observed for the clayey and organic matter-rich ISC soil. When the GLU-soil adducts were subjected to wetting and drying (W/D) cycles for 3 and 6 weeks, the enzyme activity was further largely reduced after the first 3 weeks of W/D, while the decrease progressed more slowly during the following 3 weeks. This was attributed to the increasing modification of the enzyme conformational structure due to formation of dispersive and hydrogen bonds with the inorganic and organic components of HM and soils. Our results showed that an exogenous extracellular enzyme, such as GLU, is quantitatively immobilised on model and real soil aggregates, and that the catalytic activity is significantly and progressively reduced by soil physical-chemical changes, thereby implying that soil biochemical transformations are to be accounted more to intracellular than extracellular enzymes.

Influence of Chemical Modification on the Structure, Composition, and Properties of Lignite Humic Acids

The influence of chemical modification on the functional–group composition of humic acids derived from Tisul’sk lignite (Kansko-Achinsk Basin) is studied. The structural changes of the humic acids as a result of destructive alkylation of n-butanol and oxidation of hydrogen peroxide are compared, by means of IR, Raman, ESR, and NMR spectroscopy. Alkylation of the humic acids changes the composition and content of the aliphatic fragments in their structure. Oxidation by hydrogen peroxide increases the content of acid-bearing groups.

Fungistatic Activity of Multiorigin Humic Acids in Relation to Their Chemical Structure.

Humic acid (HA) has an inhibitory effect on phytopathogenic fungi, but the structure-activity relationship remains unclear. HAs were extracted from 14 different materials, and their fungistatic activities and elemental C, N, S, and O contents were measured. Cross-polarization magic-angle spinning 13C nuclear magnetic resonance (CPMAS 13C NMR) was used to measure the organic carbon composition. The results showed that all HAs suppressed phytopathogenic fungi growth, with Yunnan lignite HAs showing the highest inhibition (85.3%) against Physalospora piricola. The soil and compost HA aromaticity (ARO) was <50%, except for black soil HAs, while the ARO of all coal HAs was >60%. The ARO of meadow and moss peat HAs was <50%, while the ARO of woody peat HAs was 50.61%. Mantel test and redundancy analysis (RDA) were applied to evaluate the structure-activity relationship. The Mantel test revealed that the N, S, O, N/O, carbonyl C, aromatic C-O, and anomeric C contents were significantly correlated with fungistatic activity. The RDA analysis showed that the S content was positively correlated with fungistatic activity, while the O content was negatively correlated. The carbonyl C content had a positive correlation with fungistatic activity, while the anomeric C and aromatic C-O content had a negative correlation. A high S content and an active composition (carbonyl C) in HAs would lead to a high degree of fungistatic activity. Phytotoxicity test indicated all HAs were beneficial to plant growth. This work identified the basic properties of HAs from various raw materials that control their fungistatic activities.

Bioconversion of lignite humic acid by white-rot fungi and characterization of products.

Lignite humic acids (LHAs) were sequentially separated from lignite with aqueous NaOH and HCl and biotreated by an isolated fungus WF8. The liquid product (LP), residues (RS) and LHAs were analyzed using a Fourier transform infrared spectrometer (FTIR) and a proton nuclear magnetic resonance (1H NMR). Three main enzymes in WF8 (i.e., lignin peroxidase, manganese peroxidase and laccase) were also measured and analyzed with and without LHAs. The results show that LHAs can induce the ligninolytic enzymes. The oxidation and hydrogenation reactions proceeded to some extent, aromaticity in LHAs and carboxyl in LP decreased, and LHAs were converted into simpler LP via biochemical reactions by WF8.