Humic acid reactions with amino acids

Reactions between five humic acids extracted from soils with widely differing pedological histories and 17 amino acids commonly occurring in proteins were investigated in aqueous solutions at pH 3.0 and 6.5. The reactions were affected by: (a) nature of the humic acid: (b) pH of the system: and (c) length of contact. The principal reaction appeared to be the microbiological oxidative degradation of the amino acids leading to the formation of substantial amounts of ammonium. While there was no evidence that the humic acids per se interacted with the amino acids, they did not appear to interfere with the microbiological degradation of the amino acids.     

Formation of humic acids during plant residue humification and their nature

The process of humic acid formation during humification of plant residues (clover leaves and roots as well as timothy roots) was studied. According to some characteristics (elementary composition, IR-spectra, the content of COOH-groups) the newly-formed humic acids may be defined as “young forms”. The comparison of the new forms with more mature soil humic acids revealed the following specific features of the latter: (a) a higher degree of aromatic nuclei condensation; (b) a higher content of carboxyl groups; and (c) a more uniform structure.The authors discuss some defects of the methods used for extraction of humic acids from fresh and slightly humified plant residues by alkaline solutions. An artificial formation of humus-like substances and their extraction as admixtures together with true humic acids are inevitable with these methods. This should be taken into account in studying and systematizing such forms of humic acids.     

On artificial humic acids

I. Absorption Spectra of Some Artificial Humic Acids

It is a well known fact that numerous dark brown or black and amorphous substances cap be produced from organic compounds by purely chemical processes. Some of them are called artificial humic acids, and have been used as a model of soil humic acids by many workers. But it is doubtful whether such artificial humic acids are considered to be a model of soil humic acids, even if there can be found any similarities in their properties. However it may be an useful method for the study of humus formation to compare artificial humic acids with soil humic acids, and to make efforts to find a good model or to prepare artificial humic acids comparable to soil humic acids under laboratory conditions. For this purpose, first of all, the author prepared artificial humic acids from glucose, hydroquinone and lignin, and their absorption spectra were determined.     

Combination reaction between humic acid and calcium ions

In the previous paper (1), liming an acid humus volcanic ash soil resulted in the formation of humic acids combined with calcium, but had no significant effect on acid brown forest soils containing humic acids of a lower degree of humification. Subsequently, the authors examined the humus composition of the soils treated with calcium acetate, and conducted some experiments on the combination reaction between humic acid and calcium ions. The results obtained are presented in this paper.     

Effect of temperature on the fragmentation of humic acids in alkaline solutions

The fragmentation of one synthetic and four soil humic acids was studied in solutions of sodium hydroxide (pH 13) at different temperature between 0 and 90°C. The dissolved parts of the initial amounts of humic acids decreased to a minimum with the increase in temperature from 0 to 10°C. The fragmentation in this region was a function of both; temperature and concentration. At 15–20°C all of the initial amounts of humic acids were dissolved. The rate of fragmentation increased rapidly between 15 and 20°C and later slowed down between 20 and 40°C. This was due to the reaggregation of the particles of the produced hymatomelanic acids into particles of similar solubilities as those of the residual nonfragmented parts of the humic acids. This reaggregation took place probably through the formation of hydrophobic bonds. The fragmentation increased at temperatures above 40°C, and reached a maximum between 50 and 70°C depending on the type of the humic acid. The decline in fragmentation at temperatures higher than those corresponding to the maxima is most probably due to chemical reactions, in which the fragmentation products especially fulvic acids recombine together at about 60°C. Importance of these results in analytical methods of extraction and characterisation of humic acids is discussed.     

Inhibition of malate dehydrogenase by humic acids

Malate dehydrogenase (from pig heart mitochondria) is markedly inhibited by a number of humic acids extracted from different types of soil or prepared synthetically. The inhibitors were found to be competitive for both substrates of the forward reaction, whereas inhibition is of the mixed type with NADH in the reverse reaction. In both directions, inhibition is strictly dependent on the number of phenolic hydroxyl groups on the humic acids. The affinity of the inhibitors for the enzyme is increased in such a way that it is readily reversible in the forward reaction but becomes more irreversible in the opposite direction.Studies on complex formation between humic acids and NAD⁺ led to the conclusion that different effects on both reactions are due to the formation of such a complex. Enzyme activity could be recovered in the presence of calcium ions. This is assumed to be due to changes in the electron structure of the humic acid particles.     

紫色水稻土胡敏酸的形成——稻草腐解试验

土壤腐植酸类物质的形成是土壤固碳的重要过程,但对腐植酸类物质形成过程的了解仍不甚清楚,为了丰富土壤腐植酸类物质形成理论,采用富立叶变换红外光谱和固态交叉极化-魔角旋转^13C-核磁共振光谱技术分析了紫色水稻土稻草腐解过程中胡敏酸的波谱学特征。结果表明,稻草腐解的前期,胡敏酸的红外光谱所有吸收峰（3364、2933、1653、1599、1508、1461、1421、1331、1225、1126、1033cm^-1）强度皆有明显减弱,核磁共振光谱的烷基、多羟基和芳基的共振峰明显减弱且甲氧基的共振峰显著增强,即表明提取的胡敏酸为类胡敏酸的木质素;随着腐解的进行,胡敏酸的红外光谱的吸收峰强度皆显著增强,核磁共振光谱的烷基、芳基和羰基的共振峰增强,即表明此时的胡敏酸已是以木质素残体为核心并结合烷基、酰胺以及糖类物质反应形成的高分子聚合体;稻草腐解的后期,胡敏酸的红外光谱的2933cm^-1处的吸收峰强度减弱,1651、1599、1508、1461、1422和1224cm^-1处的吸收峰小幅增强,核磁共振光谱的烷基共振峰减弱,甲氧基共振峰增强,表明此时的胡敏酸发生脱烷基（主要是甲基）过程。因此,红外光谱吸收峰强度与核磁共振光谱共振峰强度的规律性变化反映了稻草腐解过程紫色水稻土胡敏酸的形成过程具有阶段性,紫色水稻±胡敏酸的形成过程符合木质素学说。     

Einfluß der Konzentration der Huminsäuren auf ihre Fragmentierung in Alkalilösungen

The influence of concentration of humic acids on their fragmentation in alkaline solutions The fragmentation of synthetic and other four natural humic acids with accending concentrations in sodium hydroxide solutions would be examined. It was found that the fragmentation decreases with increase of concentration of the humic acids. A critical concentration at 0,2% is needed for the begin of retard reactions and the micell formation. The fragmentation of humic acids with high fragmentation rate will be less influenced by change of the concentration than those whose fragmentation rate are low.     

Characterization of fungal melanins and soil humic acids by chemical analysis and infrared spectroscopy

Summary Humic acids from two Brazilian topsoils under savanna grassland and five soil fungal melanins were characterized by elemental, functional group and infrared analysis. C, N, total acidity, COOH, and phenolic OH contents were within the ranges reported for several other fungal melanins and soil humic acids. Compared with the soil humic acids, the infrared spectra of the fungal melanins showed greater detail, indicative of higher aliphaticity. They were similar to the type III infrared spectra of humic acids, which are characteristically high in proteinaceous material and polysaccharides. The infrared spectra of the humic acids from the two Brazilian soils studied were classified as type I, which includes most soil humic acids. Notwithstanding the greater detail, in some areas the fungal melanin spectra were similar to those reported for other fungal melanins and humic acids of different origins. The probable contribution of the melanic fungi to the formation of soil humic polymers is discussed.     

Elemental,functional group and infrared spectroscopic analysis of actinomycete melanins from brazilian soils

Eleven actinomycete melanins were characterized by elemental and functional group and infrared analysis. A soil humic acid from a Brazilian topsoil, a darkred latosol under savanna grassland, analysed previously, was used for comparative purposes. C, N, total acidity, COOH, and phenolic OH contents were within the ranges reported for soil humic acids and fungal melanins. Compared to the soil humic acid, the actinomycete melanins showed greater detail, indicative of higher aliphaticity. Most of these were, in varying degrees, similar to the type III IR spectra of humic acids, which are characteristically high in proteinaceous material, and with variable amounts of polysaccharides. The exceptions were two melanin spectra that showed more resemblance to the humic acid from the dark-red latosol, which belongs to the type I spectra of soil humic acids, a category that includes most soil humic acids. The probable participation of melanic actinomycetes in the formation of humic polymers in discussed.     

Free-radical condensation as a natural mechanism of the formation of humic acids

Recently suggested structural models of humic acids (Schulten, Schnitzer, etc.) do not agree with the existing notions on the biochemical origin of some fragmentary groups composing a significant part of the molecules of humic acids. It is hypothesized that free-radical reactions of the polycondensation of low-molecular organic compounds derived directly from soil biota, from primary products of its posthumous decomposition, and from fulvic acids represent an obligatory stage of natural humus formation. Calculations demonstrate that different natural sources of free hydroxyl radicals (forming in the troposphere and deposited with atmospheric precipitation, produced by soil prokaryotes, etc.) ensure the possibility of free-radical condensation of organic substances and the formation of humic acids in the pedosphere of the Earth; moreover, the actual supply of free hydroxyl radicals exceeds the necessary amount by several orders of magnitude. The development of this concept allows us to assume the existence of a general evolutionary scheme of transformation of organic residues of biological origin on the Earth with the formation of stable products (humic substances, peat, and coal).     

Effect of organic amendment on amount and chemical characteristics of humic acids in upland field soils

To assess the effect of continuous organic material (OM) application on soil humic acids, the amount and chemical characteristics of humic acids in various types of soils (n = 10) were compared between plots treated with farmyard manure (FYM) or rice straw compost (RSC) plus chemical fertilizer (CF) and plots treated with CF alone. The degree of humification (degree of darkening), molecular size distribution and ¹³C cross polarization/magic angle spinning nuclear magnetic resonance spectra of humic acids from CF‐treated soils showed wide variation among the soils. Humic acid content was generally larger in OM + CF soils than in corresponding CF soils, and the stable C isotopic ratio suggested partial replacement of indigenous humic acids with OM‐derived ones even where no apparent increase in humic acid content was observed. The rate of OM application and the indigenous humic acid content were related positively and negatively, respectively, to the apparent accumulation rate of humic acids among soils. The degree of humification of humic acids was generally smaller in OM + CF soils than in CF soils. Humic acids extracted from FYM and RSC exhibited chemical characteristics typical of humic acids having a smaller degree of humification, which suggested the contribution of OM‐derived humic acids to the differences between OM + CF and CF soil humic acids, such as larger average molecular sizes and smaller and larger proportions of aromatic C and O‐alkyl C, respectively, relative to total C in the OM + CF soil humic acids. Little change was observed in the chemical characteristics of humic acids when the degree of humification of indigenous humic acids was small. The effect of OM application on the chemical characteristics of humic acids was most conspicuous in soils containing humic acids having an intermediate degree of humification, possibly resulting from the combination of accelerated degradation of indigenous humic acids and the accumulation of OM‐derived humic acids.     

Effects of some dicarboxylic acids on the association of dissolved humic substances

Changes in molecular size distributions of four different humic materials were evaluated through high performance size-exclusion chromatography (HPSEC), before and after treating humic solutions with naturally occurring dicarboxylic (oxalic, malonic, succinic and glutaric) acids. Chromatograms of dissolved humic substances showed a decrease in peak absorbance as well as an increase in peak elution volume when the solution pH was lowered from 7 to 3.5 by addition of dicarboxylic acids before HPSEC analysis. The resulting reduction in molecular size is explained by the disruption of unstable humic superstructures into smaller-sized associations stabilized by the formation of strong intra- and inter-molecular hydrogen bonds among humic molecules. The extent of humic size variation was in the order: oxalic相似文献   

Effects of mineral and monocarboxylic acids on the molecular association of dissolved humic substances

The conformational structure of dissolved humic substances is an important property that controls the reactivity of humus in the soil solution. High performance size-exclusion chromatography was used here to study the changes in molecular size of different humic substances brought about by addition of mineral (HCl) and monocarboxylic (formic, acetic, propionic, and butyric) acids. The CPMAS-NMR spectra showed that humic substances had varying chemical composition and that the ratio of hydrophilic to hydrophobic carbon (HI/HB) was greater for a humic acid from soil than for ones from oxidized coal and lignite. All humic substances showed a decrease in UV absorbance of chromatographic peaks when treated with either HCl or monocarboxylic acids. This was due to the hypochromic effect by which the absorptivity of associated molecules is decreased when they are separated. We attributed the molecular separation upon acid treatment to the formation of intermolecular hydrogen bonding that alters the original conformation stabilized mainly by weaker hydrophobic interactions. Addition of organic acids not only further decreased peak absorbances of humic acids but also caused their shift to larger elution volumes, indicating a larger conformational disruption than with HCl. The extent of the molecular size changes showed a relation to the number of carbons of monocarboxylic acids and to the HI/HB ratios of humic materials. The larger the carbon content of organic acids and the smaller the HI/HB ratio of humic materials, the larger was the decrease of the average molecular size of humic acids. These results suggest that dissolved humic substances associate predominantly by hydrophobic forces and that the apolar components of humic substances largely control their aggregation and reactivity in the environment.     

Die Veränderung von Huminsäuren in alkalischer Lösung

The change of humic acids in alkaline solution Five natural humic acids were fragmented under the conditions of the conventional method of extraction of humic substances with sodium hydroxide. Fulvic acid, hymatomelanic acid and a water soluble fraction (at pH 2) could be isolated as fragmentation products. The three fractions were formed directly after the treatment with sodium hydroxide, their quantities depend on the concentration and time of treatment with sodium hydroxide and from the function of the system. The deviating, differentiating and reproducing formation of fragments is explained by partial reversible reactions. Therefore fulvic acid and hymatomelanic acid must be regarded as artefacts. existing during the procedure of isolation of humic substances at high pH-values. Therefore the conventional isolation of humic substances from soils should always be accompanied by experiments, which inform about the arteficial production of ‘fulvic acids’ and ‘hymatomelanic acids’ during the procedure of isolation.     

The effect of humic acids on the availability of phosphorus fertilizers in alkaline soils

Abstract. The effect of humic acids on transformation of phosphorus fertilizer was studied in an alkaline soil. Soil P was fractionated following 4 and 15 days incubation after humic acids were applied with phosphorus fertilizer to the soil. The availability of phosphate in the soil and total phosphorus in plants were determined at earing stage and at maturity in a pot experiment, and wheat yield was examined in a field trial. Addition of humic acids to soil with P fertilizer significantly increased the amount of water soluble phosphate, strongly retarded the formation of occluded phosphate and increased P uptake and yield by 25%.     

Fe2+与胡敏酸的络合特征及其抗氧化性和生物有效性研究

在研究不同来源胡敏酸性质的基础上,研究了Fe2+与胡敏酸的络合特征以及络合态Fe2+的抗氧化性和生物有效性。结果表明,来源于土的胡敏酸属于A型,而来源于腐解秸秆、粪肥的胡敏酸属于RP型。A型胡敏酸与Fe2+络合能力大于RP型。HA-Fe2+络合物的络合稳定常数越大,络合物中Fe2+抗氧化性越强,玉米叶片中全铁含量也越高,但存在活性铁含量和全铁含量不一致现象。     

Effects of HCl–HF purification treatment on chemical composition and structure of humic acids

Sample preparation for the study of humic acids involves a purification treatment to remove both mineral and organic components extracted along with the humic substances. The effects of HCl–HF purification on the chemical composition and structure of humic acids were studied in samples from eight different composts. Only small increases in the concentrations of C, N and H and a decrease in O were found in purified humic acids when compared with the unpurified materials, no more than 10% of average concentration. Total and phenolic acidity increased in the purified materials, whereas carboxylic and carbonyl acidity showed no statistically significant differences as a result of the purification. Gel permeation chromatography showed that only minor changes occurred in molecular size distribution of the humic acids, and the infrared spectra showed no appreciable differences between the purified humic acids and the untreated materials. We conclude that the HCl–HF treatment successfully reduced the ash contents of the humic acids without modifying their chemical composition and structure significantly.     

Natural Remediation of Surface Water Systems Contaminated with Nuclear Waste via Humic Substances in South Ural

Radiological waste disposal and accidents from radionuclide production over several decades have resulted in widespread radioactive contamination of surface water systems in South Ural. Natural attenuation of radioactive contamination of freshwater can be considered as an alternative to manage radioactive materials released into the environment. A management alternative takes advantage of natural remediation processes, especially the binding of radionuclides and their compounds to water body solids via humic substances. The formation of radionuclide complexes with humic acids removes and converts radionuclides to a less hazardous form and is followed by a decrease in radionuclide bioavailability to freshwater biota, especially fish and benthos. Here, we present an investigation and quantification of natural remediation of highly contaminated surface water systems located in South Ural via humic substances. Based on a large set of experimental data, we state that in the surface water systems, humic acids promote the immobilization of radionuclides and thus decrease their bioavailability for fish in the investigated water bodies. We examine the influence of humic substance on the chemical and biological interactions between radionuclides and the environment that has experienced increasing interest concerning the remedial uses of humic materials.