Pyrolysis-GC-FTIR for structural elucidation of aquatic humic substances

Substructure components of various aquatic humic substances were investigated by a coupled pyrolysis — gas chromatography — Fourier-transform infrared spectroscopy (Py-GC-FTIR) procedure. The humic substances studied gave similar pyrolysis products, but in varying proportions. Many of the pyrolysis products (e.g. methanol, acetone, alkylbenzenes, cyclopentane, aliphatic and aromatic organic acids, acetamide, pyrrole and phenols) could be identified by their FTIR spectra using a digital library for automatic comparison. Some of the compounds are related to lignin fragments which form a large part of the humic substances investigated. Other products give hints to the involvement of tetrapyrroles, fatty acids, furanoses and amino compounds in the structure of humic macromolecules.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Quantitative comparison of the nitrogen-containing pyrolysis products and amino acid composition of soil humic acids

Pyrrole and acetonitrile, major pyrolysis products of soil humic substances, vary characteristically in abundance with the degree of humification of the organic matter in the soil. Their origin, however, is uncertain because of the large amount of unidentifiable soil nitrogen. A quantitative relationship between amino acid composition and pyrrole and acetonitrile abundances has been established by Curie-point pyrolysis-gas chromatography of a group of test proteins, using polystyrene as an internal standard. The pyrolysis yields of these products from three humic acids extracted from the surface horizons of Scottish brown forest soils (Cambisols or Ochrepts) were entirely accounted for by the known hydrolysable amino acid content and composition, and the products were related to individual amino acids. The peptide amino acid was also found to be the overall source of the aromatic pyrolysis products toluene, phenol and p-cresol.     

Sorption of benzene derivatives onto insolubilized humic acids

New environmental friendly sorption materials were synthesized and studied to remove organic contaminants in wastewater purification. Humic acids extracted from green-waste compost (HA_comp) and from leonardite (HA_leo) were chemically characterized by infrared spectroscopy, carbon nitrogen and hydrogen analysis, ash content, hydrophobicity tests, and molecular weight distribution. Humic acids were thermally immobilized at 330 °C for 1.5 h and their sorbent properties towards of some benzene derivatives (toluene, o-xylene, phenol, and benzyl alcohol) with the batch equilibrium method were studied. HA_comp was found to be less rich in aromatic rings and more hydrophobic than HA_leo. The maximum amount of sorbate bound at the equilibrium was consistently higher for the immobilized HA from compost than from leonardite and increased with the n-octanol/water partition coefficient of the adsorbate. The data point to hydrophobic interactions as the main force involved in the sorption of the compounds tested. The results showed that these materials can have potential applications in wastewater purification.     

Zur Charakterisierung von Boden-Huminstoffen

Summary Humic acids prepared from four horizons of a Podzol in the Segeberger Forest as well as different fractions of humic substances (fulvi acid, humic acid, and humin) of the Ahe horizon were characterized by a combination of analytical methods. As basis served the data from elemental analyses, UV/VIS-, FTIR-, and ¹³C-NMR spectroscopy, gel permeation chromatography using Fractogel TSK, and vapor pressure osmometry. Utilizing pyrolysis in direct coupling with field ionization mass spectrometry, more detailed information about structural features of the humic substances in soils could be obtained. In this manner, the different importance of carbohydrates, aromatic, and lipidic components in the various fractions is observed. The characteristic temperature dependence of the averaged molecular weights of the pyrolyzates indicates a basic structural skeleton, which is quite similar for the humic acids isolated from the different horizons. By degradation of the carbohydrates and increasing incorporation of lipidic components an enhanced biotransformation takes place with increasing depth of the soil profile.

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Gewidmet Herrn Professor Dr. W. Fresenius zum 75. Geburtstag     

The nature of lignin from steam explosion/enzymatic hydrolysis of softwood

Effective utilization of the lignin by-product is a prerequisite to the commercial viability of ethanol production from softwood wastes using a steam explosion (SE)/enzymatic hydrolysis (EH)/fermentation process. Changes in the chemical composition of Douglas fir wood on SO₂-catalyzed SE followed by EH were assessed using conventional analytical methods and new halogen-probetechniques. A significant solubilization of hemicelluloses was observed in the SE stage, the severity of which affected subsequent fermentation of cellulose and sorption of enzymes. SE of softwood resulted in dramatic changes in the chemical structure of lignin in the residual material involving chemical reactions via the benzyl cation. This leads to a more condensed lignin with partly blocked α-reaction centres. Possible uses for this lignin are discussed.     

Fractionation analysis of trace metals in humic substances of soils irrigated with wastewater in Central Mexico by particle induced X-ray emission

The Mezquital Valley in Central Mexico has received wastewater from Mexico City for nearly 100 years. Wastewater brings in organic matter and nutrients but also trace metals. Humic substances, the main components of organic soil matter, are responsible for retaining and regulating the mobility of trace metals in soils. In this study, humic substances were extracted from the soil and separated into distinct fractions (humic acids, fulvic acids and humins). The particle induced X-ray emission (PIXE) technique was applied to determine the metal content in bulk soil as well as in humic acids and fulvic acids not soluble in H₃PO₄. In order to assess whether the long-term input of organic matter and metals modifies the metal association with these humic substances, parcels irrigated for three time periods (5, 47 and 89 years) were selected for this study. It was observed that metals such as Zn and Cu are mainly associated with the humic acids. Fulvic acids retain mainly Cr while Pb is distributed among humic and fulvic acids. It was also observed that in general, metal retention by humic substances increases with irrigation time. Depth also affects metal association with the humic substances.     

The uniqueness of humic substances in each of soil,stream and marine environments

Definitive compositional differences are shown to exist for both fulvic acids and humic acids from soil, stream and marine environments by five different methods (¹H and ¹³C NMR spectroscopy, ¹⁴C age and δ¹³C isotopic analyses, amino acid analyses and pyrolysis-mass spectrometry). Definitive differences are also found between fulvic acids and humic acids within each environment. These differences among humic substances from various sources are more readily discerned because the method employed for the isolation of humic substances from all environments excludes most of the non-humic components and results in more purified humic isolates from water and soils. The major compositional aspects of fulvic acids and humic acids which determine the observed characteristic differences in each environment are the amounts and composition of saccharide, phenolic, methoxyl, aromatic, hydrocarbon, amino acids and nitrogen moieties.     

Modeling sorption of soil organic matter on mineral surfaces: wood-derived polymers on mica

Molecular mechanics and molecular dynamics calculations were carried out on model organo–mineral composites typical of both paper products and soil. Sorption energy of neutral model linear chains of lignin, carbohydrate, and humic substances on muscovite mica depends on the mutual orientation of organic and mineral components, spatial organization and functionality of the organic chain, and the presence of metal cations. Carbohydrates are characterized by their higher affinity towards the mineral surface than the more flexible helical aromatic polymers. In the model calculations, sorption energies are twice as high. Oxidation of lignin into respective humic acids does not lead to better sorption. Unlike metal cations, water molecules interlacing between organic and mineral surfaces do not act as bridges and sharply decrease sorption energy. Flexible linear polymers may undergo drastic conformational changes when approaching the mineral surface, to ensure a gain in the interaction energy that more than compensates a loss in the conformational energy proper.     

A fluorescence method for studies of spent sulfite liquor and humic substances in sea water.

A fluorimetric method is described for the determination of lignin sulfonates and humic substances simultaneously in sea water. To express the concentrations in absolute values, dissolved humic substances were isolated from river water and used as a standard along with a lignin sulfonate standard. In the two-component system, measurements at two wavelengths were used to determine the concentrations or lignin sulfonates and humic substances in mixtures, since their fluorescence intensities were found to be additive. The method can be used to detect lignin sulfonates in sea water at concentration levels down to 0.01 p.p.m. when the content or humic substance is 3 p.p.m.     

GC-MS analysis of metabolites from soxhlet extraction,ultrasound-assisted extraction and supercritical fluid extraction of Salacca zalacca flesh and its alpha-glucosidase inhibitory activity

Abstract

Different extraction processes were employed to extract bioactive metabolites from Salacca zalacca flesh by a range of aqueous and organic solvents. The highest extraction yield was obtained by 50% ethanol extract of SE (73.18?±?4.35%), whereas SFE_1 showed the lowest yield (0.42?±?0.08%). All extracts were evaluated for in vitro α-glucosidase inhibitory activity, measured by their IC₅₀ values in comparison to that of quercetin, the positive control (IC₅₀ = 2.7?±?0.7?μg/mL). The lowest α-glucosidase inhibitory activity was indicated by water extract of SE (IC₅₀ = 724.3?±?42.9?μg/mL) and the highest activity was demonstrated by 60% ethanol extract by UAE (IC₅₀ = 16.2?±?2.4?μg/mL). All extracts were analysed by GC-MS and identified metabolites like carbohydrates, fatty acids, organic acids, phenolic acids, sterols and alkane-based compounds etcetera that may possess the potential as α-glucosidase inhibitor and may attribute to the α-glucosidase inhibitory activity.     

Hydrophilic interaction liquid chromatography method for measuring the composition of aquatic humic substances

A hydrophilic interaction liquid chromatography (HILIC) method was developed to measure the composition of humic substances from river, reservoir, and treated wastewater based on their physicochemical properties. The current method fractionates the humic substances into four well-defined groups based on parallel analyses with a neutral and a cationic HILIC column, using mobile phases of varied compositions and pH. The results indicate that: (i) the proportion of carboxylic acids in the humic substances from terrestrial origins is less than half of that from treated wastewater (Jeddah, KSA), (ii) a higher content of basic compounds was observed in the humic substances from treated wastewater and Ribou Reservoir (Cholet, France) than in the sample from Loire River (France), (iii) a higher percentage of hydrophobic macromolecules were found in the humic substances from Loire River than in the other samples, and (iv) humic substances of treated wastewater contained less ionic neutral compounds (i.e., pK_a 5–9) than the waters from terrestrial origins. The physicochemical property disparity amongst the compounds in each humic substances sample was also evaluated. The humic substances from the lightly humic Loire river displayed the highest disparity, whereas the highly humic Suwannee river (Georgia, USA) showed the most homogeneous humic substances.     

Humic substances in surface waters of the Ukraine

The results of studies of humic substances in water bodies of different types (lakes, rivers, and reservoirs) are given. It is shown that concentration of these natural organic compounds varies in a wide range of values (from 1.2 to 126.5 mg L^?1) due to different sources of their formation. The highest concentrations of humic substances are characteristic for rivers of the Pripyat’ River basin flowing through the wetland. As we move from the north to the south, the content of humic substances is reduced. So, in the Kakhovka Reservoir, closing the Dnieper cascade of reservoirs, the concentration of humic substances is almost thrice as low as in the Kiev Reservoir, which is at the head of the cascade. Seasonal changes of humic substances concentration and the reasons for these changes are discussed. The prevailing fraction in the composition of humic substances is represented by fulvic acids, the content of which reaches 80.8–94.8% of the total. The results of studies of the molecular weight distribution of humic substances and the reasons for changes in the ratio of their individual fractions, depending on the detection method (spectrophotometric and fluorescence methods), are considered. The values of the number average (M _n) and weight average (M _w) molecular weight of humic substances and the degree of polydispersity are calculated. It is shown that M _w varies seasonally. In spring and summer it is lower, but significantly increased in autumn. The reason for this phenomenon is degradation of high-molecular fractions of humic substances under the influence of UV light of solar radiation and increased microbiological activity during the summer season. As a result of these processes high-molecular fractions of humic substances are transformed into fractions with lower molecular weight, which become predominant.     

Stabilized Silver Nanoparticles and Nanoclusters Ag<Subscript>n</Subscript> in Humic-Based Bioactive Nanocomposites

Silver-containing nanocomposites synthesized from the compounds of a humic series have been studied using modern physical–chemical methods (EPR, TEM, IR and XRD, etc.). It is shown that the humic substances with different functional groups and isolated from different sources have also different ability of stabilizing the silver nanoparticles. Long-term stable nanoparticles and silver clusters have been found. A multiplet, observed in the EPR spectra of silver-containing nanocomposites, which are obtained from humic substances isolated from therapeutic muds and shales, is assigned to the formed Ag_n nanoclusters. Formation of the silver molecular clusters depends on the kind of humic substances and depth of their decomposition.     

Polarographic investigation of the tautomeric transformations of β-formylacrylic acid and of the hydrolysis of its ethyl pseudoester. I

A polarographic method was used to study the cis (HA_c), trans (HA_t), and lactol (L) forms of formylacrylic acid (FAA) and its ethyl pseudoester (E) and their interconversions. It is shown that the slow step in the process E?L?HA_c?A_c ^? is hydrolysis of E. The pH of the solution has a substantial effect on the state of the equilibrium in all of the steps because of the shift in the equilibrium HA_c?A_c ^?. The equilibrium constants of all of the steps and the rate constant of the hydrolysis of E as a function of the pH of the solution were found. The most stable of the three forms of FAA is HA_t. The cis form exists only in solutions. The polarographic reduction of HA_c and HA_t at the ethylene bond proceeds at more positive potentials than the reduction of maleic and fumaric acids. In contrast to HA_c, HA_t does not form a polarographic dissociation curve; this is explained by the closeness of the potentials for the reduction of HA_t and A_t ^?.     

Synthesis,thermal, rheological characteristics,and enzymatic degradation of aliphatic polyesters with lignin‐based aromatic pendant groups

This research aims to produce lignin‐based biodegradable polyesters with improved thermal quality. A series of aliphatic polyesters with lignin‐based aromatic side groups were synthesized by conventional melt‐polycondensation. Decent molecular weight (21–64 kg mol^?1) was achieved for the polymerizations. The molecular structures and thermal and mechanical properties of the obtained polyesters were characterized. As a result, the obtained polyesters are all amorphous, and their glass‐transition temperature (T_g) depends on the size of the pendant aromatic group (31–51 °C). Furthermore, according to the TGA results, the thermal decomposition temperatures of the polyesters are all above 390 °C, which make them superior compared with commercial biodegradable polyesters like polylactic acid or polyhydroxyalkanoates. Finally, rheological characteristics and enzymatic degradation of the obtained polyesters were also measured. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2314–2323     

Hydrophobic organic micropollutants in samples of coastal waters: efficiencies of solid-phase extraction in the presence of humic substances

Solid-phase extraction (SPE) has been used to enrich organic micropollutants (hydrophobic chlorinated and polycyclic aromatic hydrocarbons, CHC and PAH) from coastal water samples and to systematically study the influence of humic substances (HS) on SPE. A reversed phase (RP) system with high flow rates (rapid chromatography, RC) was used to show the basic adsorption principles and interaction processes which influence the enrichment of organic compounds. A model humic substance was found to hinder the enrichment of individual hydrophobic micropollutants (MP), depending on their octanol-water distribution coefficient P _OW. This effect was found to be lower with natural humic substances. For longer contact time between water sample and adsorption material, the pollutant/humic substance bonding proved to be reversible.     

Comparative characteristic studies on soil and commercial humic acids

Summary Two commercial and eight soil humic acids were characterized to evaluate the use of commercial humic materials in soil and environmental studies. Significant differences between commercial and soil humic acids were observed in ash content, major and micro-element constituents, E₄/E₆ ratio, total acidity and ¹³C-NMR spectroscopy; but data from stability constant and IR-spectroscopy were almost identical. The commercial materials appeared to be significantly less aromatic and more aliphatic in nature as compared with representative soil humic acids. The above discrepancies were interpreted as indicating an origin of the respective commercial product other than soil. The two commercial humic acids investigated may not originate from the same source material as evidenced by clear-cut differences in the intensity of the ¹³C-NMR spectra in almost all chemical shift regions. Due to the observed structural, compositional and characteristic dissimilarities, both between soil and commercial humic acids and between different commercial ones, the commercial humic products are not recommended to be used as analogues of real soil humic acids in soil and environmental studies.     

Synthesis and characterization of poly benzoylpropionamides

Linear polyamides having viscosities in the range of 0.12–0.41 dl/g have been prepared from bisbenzoyl propionic acids and aromatic diamines by low temperature solution polycondensation in 80–85% yield. Their solubility characteristics were studied in various solvents e.g. DMF, DMAC, HMPT, H₂SO₄. These polyamides are amorphous in nature; their densities range from 1.2 to 1.8 g/cm³. Their thermal properties were examined by TGA and DTA. The two stage decomposition phenomenon observed in TGA is in agreement with the DTA results. The integral procedural decomposition temperatures were calculated and found to exceed 250 in almost all cases.     

A solid-phase extraction procedure for the clean-up of thiram from aqueous solutions containing high concentrations of humic substances

A simple solid-phase extraction (SPE) procedure with an octadecyl bonded phase silica (C₁₈) was developed for clean-up of the fungicide thiram from aqueous solutions containing high concentrations of humic substances, for future studies of thiram adsorption onto solid humic substances or soils. Suspensions of humic acids and soil, in aqueous 0.01 M CaCl₂ solution, were prepared and used as samples. These extracts were spiked with thiram and immediately applied to a C₁₈-SPE cartridge. Thiram was eluted with chloroform and its concentration measured by spectrophotometry at 283 nm. Non-spiked aqueous extracts (blanks) and a control sample of thiram in 0.01 M CaCl₂ aqueous solution were also prepared and submitted to the same SPE procedure. The results show that humic substances are extensively retained by the C₁₈ cartridge but are not eluted with CHCl₃. Recoveries of 100-104% were obtained for thiram in the presence of humic substances. The SPE procedure described in this work is an efficient clean-up step to remove the interference of humic substances absorbance and to be coupled to any spectrophotometric or HPLC-UV method, usually used for thiram analysis in food extracts.     

Tefluthrin Sorption to Mineral Particles: Role of Particle Organic Coatings

Abstract

The sorption of tefluthrin was studied on “pure” clay minerals and those that had been coated with aquatic humic substances over a mass percent carbon range of 0.02 to 2.15. Tefluthrin sorption onto humic-coated minerals was significantly greater than on to the clean minerals and increased with increasing quantities of sorbed humic substances. Humic acid, the most aromatic coating, was the strongest sorbent, followed by fulvic acid, hydrophilic macromolecular acid and natural coatings on estuarine suspended particles. This shows the significant impact of humic coatings on the sorptive capacity of mineral particles. The sorption was linear, also consistent with the operation of a partition process. The partition coefficient normalised to organic carbon (K_oc) after deduction of the contribution from the clean mineral, ranged from 120000 to 770000 and was highest for the most aromatic humic acid fraction.