Reduced heterogeneity of a lignite humic acid by preparative HPSEC following interaction with an organic acid. Characterization of size-separates by Pyr-GC-MS and 1H-NMR spectroscopy

Molecular Weight Distribution of Humic Acids Isolated from Calcic Cryosol in Central Yakutia, Russia

The transition of soils into fallow state has a significant impact on the accumulation and transformation of soil organic matter (SOM). However, the issue of SOM transformation as a result of soil transition to fallow state in cryolithozone conditions is insufficiently studied. The aim of this study is to investigate the molecular weight (MW) distribution of humic acids (HAs) isolated from soils of central Yakutia. Native, fallow and agricultural soils in the vicinity of Yakutsk city were studied. MW distributions of HA preparations were obtained on an AKTAbasic 10 UPS chromatographic system (Amersam Biosciences, Uppsala, Sweden) using a SuperdexTM 200 10/300 GL column (with cross-linked dextran gel, fractionation range for globular proteins 10-600 kDa). The data on the molecular-mass distribution of HAs of fallow and agricultural soils of Central Yakutia were obtained for the first time. According to the obtained data, it was found that the highest carbon content in the structure of HAs was observed in agricultural soils (52.56%), and is associated with soil cultivation and fertilizer application. Among the HAs of fallow soils, we note that those soils that are in the process of self-vegetation have a relatively high carbon content in the HAs (45.84%), but the highest content was observed in fallow soils used as hayfields (49.98%), indicating that the reinvolvement of agriculture in fallow soils leads to an increase in the carbon content of HAs. According to the data of the MW distribution of HAs, it was found that the highest content of a high MW fraction of HAs was recorded in native soil (18.8%); this is due to the early stages of humification and the low maturity of organic matter. The highest content of a low MW fraction of HAs was recorded in agricultural soil (73.3%); this is due to the formation of molecular complexes of a "secondary" nature, which are more stable in the environment than the primary transformation products of humification precursors. The molecular composition of the HAs of fallow soils in the process of self-overgrowing is characterized by values closer to the HAs of native soils, which indicates their transformation towards HAs of native soils. The obtained results indicate that the reinvolvement of fallow soils leads to the transformation of the molecular composition of HAs towards HAs of agricultural soils, and to an increase in the resistance of SOM to biodegradation.

Influence of Manure as a Complex Mixture on Soil Sorption of Pharmaceuticals-Studies with Selected Chemical Components of Manure

Pharmaceutically active compounds (PhACs) enter soil with organic waste materials such as manure. Such complex substrates differently affect PhACs' soil sorption. For the first time, batch experiments were conducted using five selected chemicals as model constituents to elucidate the effects. Urea, phosphate (KH₂PO₄), acetic acid, phenol and nonadecanoic acid (C:19) altered the sorption strength and/or nonlinearity of sulfadiazine, caffeine, and atenolol in an arable Cambisol topsoil. The nonlinear Freundlich model best described sorption. Overall, the PhACs' Freundlich coefficients (sorption strength) increased in the sequence urea < phosphate < phenol < C:19 < acetic acid, while the Freundlich exponents largely decreased, indicating increasing sorption specificity. The effects on sulfadiazine and caffeine were rather similar, but in many cases different from atenolol. Phosphate mobilized sulfadiazine and caffeine and urea mobilized sulfadiazine, which was explained by sorption competition resulting from specific preference of similar sorption sites. Soil sorbed phenol strongly increased the sorption of all three PhACs; phenolic functional groups are preferred sorption sites of PhACs in soil. The large increase in sorption of all PhACs by acetic acid was attributed to a loosening of the soil organic matter and thus the creation of additional sorption sites. The effect of C:19 fatty acid, however, was inconsistent. These results help to better understand the sorption of PhACs in soil-manure mixtures.

Humic substances from composted fennel residues control the inflammation induced by Helicobacter pylori infection in AGS cells

Helicobacter pylori (H. pylori) is a common human pathogen causing inflammation. Recent studies have suggested a sophisticated interplay between mitochondria, innate immunity and inflammatory response, thus proposing mitochondrial disfunction as the hallmark of severe inflammatory disorders. In this study, humic substances isolated from composted fennel residues (HS-FEN) were tested as potential therapeutical strategy to restore the mitochondrial physiology and control the inflammation associated with H. pylori infection. The molecular features of HS-FEN were characterized by infrared spectrometry, thermochemolysis-GC/MS, NMR spectroscopy, and high-performance size-exclusion chromatography (HPSEC), which revealed the presence of aromatic polyphenolic components arranged in a rather stable conformation. In vitro results showed antioxidant and anti-inflammatory properties of HS-FEN, that was found to increase the expression level of OPA-1 and SOD-2 genes and in AGS cells stimulated with H. pylori culture filtrate (Hpcf) and concomitantly decrease the expression level of Drp-1 gene and IL-12, IL-17 and G-CSF proteins. The hydrophobic features of HS, their conformational arrangement and large content of bioactive molecules may explain the beneficial effects of HS-FEN, that may potentially become an interesting source of anti-inflammatory agents capable to counteract or prevent the H. pylori-related inflammatory disorders.

Antiflammatory activity and potential dermatological applications of characterized humic acids from a lignite and a green compost

Long-term exposure to air pollution has been associated with the development of some inflammatory processes related to skin. The goal of modern medicine is the development of new products with antiflammatory action deriving from natural sources to improve environmental and economic sustainability. In this study, two different humic acids (HA) were isolated from from lignite (HA-LIG) and composted artichoke wastes (HA-CYN) and characterized by infrared spectrometry, NMR spectroscopy, thermochemolysis-GC/MS, and high-performance size-exclusion chromatography (HPSEC), while their antiflammatory activity was evaluated on HaCaT cells. Spectroscopic results showing the predominance of apolar aliphatic and aromatic components in HA-LIG, whereas HA-CYN revealed a presence of polysaccharides and polyphenolic lignin residues. The HA application on human keratinocyte pre-treated with Urban Dust revealed a general increase of viability suggesting a protective effect of humic matter due to the content of aromatic, phenolic and lignin components. Conversely, the gene expression of IL-6 and IL-1β cytokines indicated a significant decrease after application of HA-LIG, thus exhibiting a greater antiflammatory power than HA-CYN. The specific combination of HA protective hydrophobic components, viable conformational arrangements, and content of bioactive molecules, suggests an innovative applicability of humic matter in dermatology as skin protectors from environmental irritants and as antiflammatory agents.

Characterizing dissolved organic matter in aquatic environments by size exclusion chromatography coupled with multiple detectors

Size exclusion chromatography (SEC) is one of the most commonly used techniques to detect the molecular weight (MW) of dissolved organic matter (DOM) in aquatic environments. The significant improvement and focus of this method have been the application of multiple detectors, which contribute to providing fundamental physicochemical properties of various MW fractions. This study has coupled SEC with multiple detectors to simultaneously detect ultraviolet absorbance, fluorescence, dissolved organic carbon, and dissolved organic nitrogen of different MW fractions. The detection limits for the organic carbon and nitrogen detectors were 0.20 μg C L^-1 and 0.14 μg N L^-1, respectively. Furthermore, we gave an interpretation of the nature and evolution of DOM in surface water based on the comparison and analyses of the combined chromatogram obtained from multiple detectors. Fractions assigned as hydrophobic humic-like substances, hydrophilic humic-like substances, low-MW microbial extracellular metabolites and low-MW hydrophobic protein-like substances were first established in this study and attributed to the presence of a fluorescence detector. We believe that the developed method provides in-depth knowledge of the structure and composition of DOM and could be used as a potential analytical tool in environmental organic chemistry, humus chemistry and supramolecular chemistry.

Stoichiometry between Humate Unit Molecules and Metal Ions in Supramolecular Assembly Induced by Cu2+ and Tb3+ Measured by Gel Electrophoresis Techniques

Humic acid (HA), a fraction of humic substances, can strongly complex with metal ions to form a supramolecular assembly via coordination binding and other intermolecular forces. However, determining the supramolecular size distribution and stoichiometry between small HA unit molecules constituting HA supramolecules and metal ions has proven to be challenging. Here, we investigated the changes in the size distributions of HAs induced by Cu²⁺ and Tb³⁺ ions using unique PAGE for the separation and quantification of HA complexes and metal ions bound, followed by UV-vis spectroscopy and excitation-emission matrix-parallel factor analysis. By determining the concentrations of HA and metal ions, it was possible to estimate the stoichiometry of the HA unit molecule to metal ions in supramolecular complexes. It was found that the supramolecular behaviors of Cu²⁺ and Tb³⁺ complexes with HA collected from peat (PAHA) and deep groundwater (HHA) differed. For example, two HHA unit molecules form a supramolecule via cross-linking by a Cu²⁺ ion in the case of Cu²⁺-HHA. Our results suggest that this supramolecular stoichiometry is related to the abundance of sulfur atoms in the elemental composition of HHA. Our experimental results and analysis provide new insights into HA supramolecules formed via metal complexation.

Supramolecular aggregation of colloidal natural organic matter masks priority pollutants released in water from peat soil

Natural organic matter (NOM) from Sphagnum peat soil is extracted in water and subjected to several investigations to obtain structural and conformational information. Data show that the extracted NOM is self-organized in colloidal aggregates of variable sizes (from nano to micro scales, depending on the solvent composition, i.e., ultrapure water, solutions with denaturing agents, acetone, ethanol). Aggregates are formed by highly heterogeneous classes of organic compounds. According to the results of nuclear magnetic resonance and fluorescence measurements, the three-dimensional structure of aggregates, revealed by scanning electron microscope imaging, is supposed to be stabilized by the exposition of polar functional groups to the solvent, with consequent formation of hydrogen bonds, dipole-interactions and cation bridging. In contrast, the inner part of the aggregates displays hydrophobic features and is hypothesized to be further reinforced by the establishment of π-stacking interactions. The structure is assumed to be a supramolecular aggregation of small-medium oligomeric fragments (Max 750 Da) in which priority pollutants are entrapped by dispersive forces. The structures are shown to be nanosized spheroidal particles further aggregated to form higher dimension supra-structures. Carbohydrates play primary role, stabilizing the structure and giving marked hydrophilic properties to the aggregates.

Activation of Humic Acid in Lignite Using Molybdate-Phosphorus Hierarchical Hollow Nanosphere Catalyst Oxidation: Molecular Characterization and Rice Seed Germination-Promoting Performances

Although solid-phase activation of lignite using a nanocatalyst has great potential in producing low-cost and sustainable humic acid, the large-scale application of this technology still faces challenges because of the high price and toxicity of the nanocatalyst. Additionally, the specific molecular components of humic acid in activated lignite remain unknown. In this work, a multifunctional molybdate-phosphorus hierarchical hollow nanosphere (Mo-P-HH) catalyst was successfully manufactured by a simple way followed by phosphorization. In comparison with a commercial Pd/C catalyst, the multifunctional Mo-P-HH catalyst was more effective in producing water-soluble humic acid with small molecular functional groups from lignite via solid-phase activation. Moreover, Fourier transform ion cyclotron resonance mass spectrometry revealed the molecular compositions of humic acid in activated lignite. Compared with that from raw lignite, the humic acid after Mo-P-HH activation had less aromatic structure but higher content of lipids, proteins, amino sugar, and carbohydrates. In addition, the activated humic acid simulated seed germination and seedling growth. Therefore, this study provided a high-performance hierarchical hollow nanocatalyst for activation of humic acid and also offered the theoretical basis for the application of humic acid in agriculture.

Reciprocal interference of clay minerals and nanoparticulate zero-valent iron on their interfacial interaction with dissolved organic matter

With increasing environmental application of nanoparticulate zero-valent iron (nZVI), it is essential to explore the interaction of nZVI with dissolved organic matter (DOM) and clay mineral particles (CMPs) and its potential effect on the formation of DOM-mineral complex that may impact the carbon sequestration. The aggregation and adsorption behaviors of nZVIs (two bare nZVIs of different sizes and one carboxymethyl cellulose coated nZVI (CMC-nZVI)) and CMPs (kaolinite and montmorillonite) coexisting in DOM (humic acid and fulvic acid) solutions were systematically investigated. The bare nZVIs more easily formed heteroaggregates with montmorillonite than kaolinite in DOM solutions, while the CMC-nZVI tended to attach on kaolinite surface. The heteroaggregation and competition between nZVIs and CMPs could change their interfacial interaction with DOM and the ultimate immobilization of DOM was determined by the formed nZVI-CMP complexes, irrelevant to the addition sequence of nZVIs and CMPs. Compared with the individual CMPs alone, the formed bare-nZVIs-CMP heteroaggregates promoted the sequestration of DOM especially its aromatic carbon fractions, while the CMC-nZVI had no such effect. These findings will be helpful for the understanding of nZVI interaction with DOM and CMPs and the effect on the immobilization of organic carbon in the environment.

Molecular dynamics simulation of the interaction of water and humic acid in the adsorption of polycyclic aromatic hydrocarbons

Humic acid (HA) and water play an important role in polycyclic aromatic hydrocarbons (PAHs) adsorption and biodegradation in soil. In this work, molecular dynamics (MD) and electrostatic potential surfaces (EPSs) simulations are conducted to research the contribution of quartz surface, leonardite humic acid (LHA), and water to PAH adsorption. The adsorption energies between PAHs and LHA are much higher than that between PAHs and quartz. Simulation shows that the hydroxyl and carboxyl groups' attraction by LHA is the main adsorption force between PAHs and LHA. The π-π interaction between PAHs and LHA also contributes to the adsorption process. In addition, the mobility of water on quartz surface is much higher than that of LHA. Water should be regarded as an adsorbate in the system as well as PAHs. However, the presence of water has a remarkable negative effect on the adsorption of PAHs on LHA and quartz. The bridging effect of water could only enhance the stability of the aggregation system. The adsorption contribution of quartz and LHA to PAHs in the soil model tends to 0 if the water layer reaches 2.0 nm. Graphical abstract.

Redox reactions between chromium(VI) and hydroquinone: Alternative pathways for polymerization of organic molecules

Chromium (VI) reduction by organic compounds is one of the major pathways to alleviate the toxicity and mobility of Cr(VI) in the environment. However, oxidative products of organic molecules receive less scientific concerns. In this study, hydroquinone (H₂Q) was used as a representative organic compound to determine the redox reactions with Cr(VI) and the concomitant oxidative products. Spectroscopic analyses showed that Cr(III) hydroxides dominated the precipitates produced during redox reactions of Cr(VI) and H₂Q. For the separated filtrates, the acidification induced the oxidative polymerization of organic molecules, accompanied with the complexation with Cr(III). The aromatic domains dominated the chemical structures of the black and fluffy organic polymers, which was different to the natural humic acids due to the shortage of aliphatic chains. Results of linear combination fitting (LCF) for Cr K-edge X-ray absorption near edge structure (XANES) spectra demonstrated that up to 90.4% of Cr inventory in precipitates derived after the acidification of filtrates was Cr(III) complexed with humic-like polymers, suggesting that Cr(III) possibly acted as a linkage among organic molecules during the polymerization processes of H₂Q. This study demonstrated that Cr(VI) may lead to the polymerization of organic molecules in an acidic solution, and thus, it could raise scientific awareness that the oxidative decomposition of organic molecules may not be the only pathway while interacting with the strong oxidant of Cr(VI).

Relation between changes in organic matter structure of poultry litter and heavy metals solubility during composting

Poultry litter (PL) is widely used as fertilizer because of its rich N, P and Ca content. When PL is applied to previously untreated soil, it is a potential contaminant. Composting is an alternative for stabilizing organic and mineral components. This study aimed to elucidate the structural changes and its influence on the solubility of heavy metals in poultry litter during the first 30 d of composting, which is the period when the most intense transformations occur. For this analysis, the transformation dynamics of the organic structures and the availability of mineral elements were studied via spectroscopic characterization, total heavy metal content determination and chemical fractionation at three composting times (0, 15, and 30 d). During composting, the material's aromaticity increased, while its aliphaticity decreased, and the hydrophobicity index increased as the polarity decreased. These results indicate that during the first 30 d, PL composting occurs via transformation of the most labile structures (carbohydrate, peptide and fatty acid fragments), thereby preserving the most stable and least functionalized structures. Composting increased the concentrations of Cu, Cr, Pb and Zn and the transformation of C_Alk-O and C_Alk-di-O associated with peptides and carbohydrates and favored solubilizing and leaching a water-soluble fraction rich in these compounds. The labile fractions of Fe and the humified organic matter fractions of Cu, Fe, Mn, Zn, and Al increased. The structural changes reduced heavy metal solubility, thus indicating that after 30 d of composting, the heavy metal contamination risk is low.

An overview of the uses of high performance size exclusion chromatography (HPSEC) in the characterization of natural organic matter (NOM) in potable water, and ion-exchange applications

Natural organic matter (NOM) constitutes the terrestrial and aquatic sources of organic plant like material found in water bodies. As of recently, an ever-increasing amount of effort is being put towards developing better ways of unraveling the heterogeneous nature of NOM. This is important as NOM is responsible for a wide variety of both direct and indirect effects: ranging from aesthetic concerns related to taste and odor, to issues related to disinfection by-product formation and metal mobility. A better understanding of NOM can also provide a better appreciation for treatment design; lending a further understanding of potable water treatment impacts on specific fractions and constituents of NOM. The use of high performance size-exclusion chromatography has shown a growing promise in its various applications for NOM characterization, through the ability to partition ultraviolet absorbing moieties into ill-defined groups of humic acids, hydrolysates of humics, and low molecular weight acids. HPSEC also has the ability of simultaneously measuring absorbance in the UV-visible range (200-350 nm); further providing a spectroscopic fingerprint that is simply unavailable using surrogate measurements of NOM, such as total organic carbon (TOC), ultraviolet absorbance at 254 nm (UV₂₅₄), excitation-emission matrices (EEM), and specific ultraviolet absorbance at 254 nm (SUVA₂₅₄). This review mainly focuses on the use of HPSEC in the characterization of NOM in a potable water setting, with an additional focus on strong-base ion-exchangers specifically targeted for NOM constituents.

Molecular Size Distribution of Fluorophores in Aquatic Natural Organic Matter: Application of HPSEC with Multi-Wavelength Absorption and Fluorescence Detection Following LPSEC-PAGE Fractionation

Analytical high performance size exclusion liquid chromatography (HPSEC) with multiwavelength absorbance and fluorescence detections was used for the analysis of molecular size distribution and optical properties of dissolved natural organic matter. Experiments were conducted on Suwannee River organic matter (SRNOM) and its fractions A, B, C+D preliminary obtained by combination of preparative low pressure size exclusion chromatography and polyacrylamide gel electrophoresis (LPSEC-PAGE) and purified by dialysis on membrane with nominal cutoff 10 kDa, the fractions molecular size varied in order A > B > C + D > 10 kDa. The multistep fractionation of SRNOM enabled the size-separation of at least five types of humic-like fluorophores within NOM showing emission maxima at 465, 450, 435, 420, and 405 nm. The decrease of the humic-like emission maxima paralleled the decrease of the nominal molecular size of fluorescent SRNOM. The protein-like fluorescence was split into tyrosine-like and tryptophan-like fluorophores and only detected in fractions A and B. This work provides new data on the optical properties of size-fractionated NOM, which consistent with the formation of supramolecular NOM assemblies, likely controlled by association of low-molecular size components. It is clearly observed for the high molecular size fraction A, containing free amino acids or short peptides. The combination of several different fractionation procedures is very useful for obtaining less complex NOM compounds and understanding the NOM function in the environment.

Water-Soluble Lignins from Different Bioenergy Crops Stimulate the Early Development of Maize (Zea mays, L.)

The molecular composition of water-soluble lignins isolated from four non-food bioenergy crops (cardoon CAR, eucalyptus EUC, and two black poplars RIP and LIM) was characterized in detail, and their potential bioactivity towards maize germination and early growth evaluated. Lignins were found to not affect seed germination rates, but stimulated the maize seedling development, though to a different extent. RIP promoted root elongation, while CAR only stimulated the length of lateral seminal roots and coleoptile, and LIM improved only the coleoptile development. The most significant bioactivity of CAR was related to its large content of aliphatic OH groups, C-O carbons and lowest hydrophobicity, as assessed by ³¹P-NMR and ¹³C-CPMAS-NMR spectroscopies. Less bioactive RIP and LIM lignins were similar in composition, but their stimulation of maize seedling was different. This was accounted to their diverse content of aliphatic OH groups and S- and G-type molecules. The poorest bioactivity of the EUC lignin was attributed to its smallest content of aliphatic OH groups and largest hydrophobicity. Both these features may be conducive of a EUC conformational structure tight enough to prevent its alteration by organic acids exuded from vegetal tissues. Conversely the more labile conformational arrangements of the other more hydrophilic lignin extracts promoted their bioactivity by releasing biologically active molecules upon the action of exuded organic acids. Our findings indicate that water-soluble lignins from non-food crops may be effectively used as plant biostimulants, thus contributing to increase the economic and ecological liability of bio-based industries.

Interactions between natural organic matter and organic pollutants as revealed by NMR spectroscopy

Natural organic matter (NOM) plays a critical role in regulating the transport and the fate of organic contaminants in the environment. NMR spectroscopy is a powerful technique for the investigation of the sorption and binding mechanisms between NOM and pollutants, as well as their mutual chemical transformations. Despite NMR relatively low sensibility but due to its wide versatility to investigating samples in the liquid, gel, and solid phases, NMR application to environmental NOM-pollutants relations enables the achievement of specific and complementary molecular information. This report is a brief outline of the potentialities of the different NMR techniques and pulse sequences to elucidate the interactions between NOM and organic pollutants, with and without their labeling with nuclei that enhance NMR sensitivity.

Off-line TMAH-GC/MS and NMR characterization of humic substances extracted from river sediments of northwestern São Paulo under different soil uses

Humic substances (HS) vary according to the physical and chemical factors present in the environment. Thus, the characterization of HS is very important because it improves the understanding of the groups that comprise the chemical structure. Sediment HS were extracted from four locations representative of sugar cane cultivation, pasture, urban area and the impoundment of the Água Vermelha Hydroelectric Power Plant. Characterization using nuclear magnetic resonance (NMR) allowed us to infer that the HS from an area predominantly characterized by sugar cane cultivation (41.9%) and a typical rural area (35.0%) showed the highest aromaticity percentage. Using the off-line TMAH-thermochemolysis-GC-MS, we inferred that the HS of a typical rural area had a structure rich in plant waxes, plant biopolyester and a large amount of fatty acid methyl ester, which are related to the large amount of humic acid in the structure. The HS samples from the sugar cane cultivation area and the impoundment receiving all of the pollution load from the Turvo/Grande Hydrographic Basin (Bacia Hidrográfica do Turvo/Grande-BHTG) contained contributions from compounds rich in lipids and fatty acid methyl esters, highlighting the presence of the breakdown of petroleum-derived hydrocarbons in the area receiving the entire pollution load. We conclude that the HS extracted from the sediments of the Preto, Turvo and Grande rivers showed well-defined characteristics that varied depending on soil use and occupation, especially the HS extracted from sediments sampled in areas typically planted with sugar cane and rural areas, whose structures contained more aromatic groups.

H-binding of size- and polarity-fractionated soil and lignite humic acids after removal of metal and ash components

A fractionation technique, combining dialysis removal of metal and ash components with hydrofluoric acid and pH 10 citrate buffer followed by chromatography of dialysis permeate on XAD-8 resin at decreasing pH values, has been applied to lignite humic acid (lignite-HA) and soil humic acid (soil-HA). H-binding data and non ideal competitive adsorption-Donnan model parameters were obtained for the HA fractions by theoretical analysis of H-binding data which reveal a significant increase of the carboxyl and the phenolic charge for the lignite-HA fractions vs. the parental lignite humic acid (LParentalHA). The fractionated lignite-HA material consisted mainly of permeate fractions, some of which were fulvic acid-like. The fractionated soil-HA material consisted mainly of large macromolecular structures that did not permeate the dialysis membrane during deashing. Chargeable groups had comparable concentrations in soil-HA fractions and parental soil humic acid (SParentalHA), indicating minimal interference of ash components with carboxyl and phenolic (and/or enolic) groups. Fractionation of HA, combined with theoretical analysis of H-binding, can distinguish the supramolecular vs. macromolecular nature of fractions within the same parental HA.

Molecular characterization of an end-residue of humeomics applied to a soil humic acid

Humeomics encompasses step-wise chemical fractionation and instrumental determination to fully characterize the heterogeneous molecular composition of natural organic matter.

Fractionation and characterization of humic acids from organic amended rice paddy soils

Humic acids (HAs), mixture of several complex-structured aromatic and aliphatic compounds, are ubiquitous in the terrestrial environment. In this study, HAs were fractionated on the basis of their polarity (degree of humification). The fractions namely 200P, 300P and 400P were comparatively more humified than fractions like 800P and 800S. The application of organic amendments significantly increased concentrations of HA fractions especially the more humified fractions in rice paddy soils. Among the different fractions, 300P fraction was the most abundant in rice paddy soils and its concentration was significantly increased due to compost application. The compounds like methyl ketone and 3-phenylprop-2-enal contributed almost 90% of 300P fraction.

Co-polymerization of penta-halogenated phenols in humic substances by catalytic oxidation using biomimetic catalysis

INTRODUCTION

A synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of iron(III) chloride, Fe-(TDCPPS)Cl, was employed to catalyze the oxidative co-polymerization of penta-halogenated phenols in two humic materials of different origin.

MATERIALS AND METHODS

Co-polymerization of pentachlorophenol (PCP) was followed by high-performance size-exclusion chromatography (HPSEC), the unbound PCP recovered from reacting humic solutions was evaluated by gas-chromatography/electron capture detector, and the oxidative catalyzed coupling of pentafluorophenol (PFP) into humic matter was assessed by liquid-state (19)F-NMR spectroscopy. HPSEC showed that the catalyzed oxidative coupling between PCP and humic molecules increased the apparent weight-average molecular weight (M(w)) values in both humic substances.

RESULTS AND DISCUSSION

HPSEC further indicated that the co-polymerization reaction turned the loosely bound humic supramolecular structures into more stable conformations, which could no longer be disrupted by the disaggregating effect of acetic acid. The occurrence of covalent linkages established between PCP and humic molecules was also suggested by the very little amount of PCP found free in solution after the catalyzed co-polymerization. (19)F-NMR spectroscopy suggested that also PFP could be oxidatively coupled to humic materials. PFP-humic co-polymerization reaction produced (19)F-spectra with many more (19)F signals and wider chemical shifts spread than for PFP alone or PFP subjected to catalyzed coupling without humic matter.

CONCLUSIONS

These findings show that biomimetic iron-porphyrin is an efficient catalyst for the covalent binding of polyhalogenated phenols to humic molecules, thereby suggesting that the co-polymerization reaction may become a useful technology to remediate soils and waters contaminated by polyhalogenated phenols and their analogues.

Adsorption of humic acid onto carbonaceous surfaces: atomic force microscopy study

The adsorption of humic acid (HA) onto highly ordered pyrolytic graphite (HOPG) surfaces at different concentrations has been studied by atomic force microscopy. When HA concentration was increased from 10 to 1,000 mg/L, HA can sequentially form spherical particles, layered structures, and connected blocks on HOPG surfaces. The findings of the layer structures and small amount of fine chains have been verified and discussed. When HA was acidified by addition of acetic acid, it changed into small rigid particles. These results indicated that HA can be considered as supramolecular associations of self-assembling heterogeneous and relatively small molecules, and a small amount of polymers. The present results are important for understanding HA molecular structures and their adsorption characteristic on carbonaceous surfaces.

Mobile aliphatic domains in humic substances and their impact on contaminant mobility within the matrix

Using a novel NMR option, magic angle spinning pulsed field gradient (MAS PFG) NMR, the mobility of aliphatic domains in humic substances in the presence of toluene (about 4.5 wt. %) has been monitored. Results show a strong correlation between the diffusivities of the mobile aliphatic chains and those of the adsorbed toluene molecules in the matrix as a function of temperature. Particularly, a strong influence of structural relaxation of the humic matrix on the diffusivity of toluene is observed. Our findings confirm that the aliphatic domains in humic substances play an important role in the mobility of sorbed contaminants within this matrix. These findings further confirm the potential of MAS PFG NMR method in monitoring diffusion processes in particulate humic substances.

Europium(III) complexed by HPSEC size-fractions of a vertisol humic acid: small differences evidenced by time-resolved luminescence spectroscopy

The size fractionation of a humic acid (HA) by high performance size exclusion chromatography (HPSEC) was used as a proxy for the filtration effect during HA transport through a porous medium with minimum specific chemical interactions. The modification of the Eu(III)-HA complexes' formation with the different size-fractions, as compared to the bulk HA, was studied in time-resolved luminescence spectroscopy (TRLS). Clear modifications in Eu(III)-HA complexes' structures were shown and related to the molecular characteristics of the separated size-fractions. The properties of most of size-fractions did not induce a major alteration of the affinity towards Eu(III). Only the most hydrophilic fractions eluted in the tail of the chromatographic peak, representing about 11% of total fractions-weight, gave some significantly different parameters. Using a simplistic complexation model, it was found that the available complexation sites decreased with the size reduction of humic fractions.

Basis of a humeomics science: chemical fractionation and molecular characterization of humic biosuprastructures

We propose a mild stepwise fractionation of molecular components of a humic acid (HA) suprastructure and their structural identification by advanced analytical methods. This procedure may be the basis of a "Humeomics" approach to characterize natural humic molecules and clarify their relations with ecosystems functions. Sequential fractionation included: (1) organic solvent extraction, (2) transesterification with boron trifluoride in methanol (BF(3)-CH(3)OH), (3) methanolic alkaline hydrolysis (KOH-CH(3)OH), and (4) cleavage of ether and glycosidic bonds with HI. Structural identification of initial and final material, separated organo-soluble and hydrosoluble fractions, and subfractions was conducted by GC-MS, HPSEC-ESI-MS (high-resolution, Orbitrap), and solid- and liquid-state NMR. GC-MS revealed in organosoluble unbound fractions the presence of both saturated and unsaturated, linear and branched, alkanoic, hydroxyalkanoic and alkandioic acids, n-alkanes, and n-alkanols. These components decreased progressively in fractions obtained after weak and strong ester cleavage. Unsubstituted alkanoic acids with variable chain length were ubiquitously detected in all fractions, thereby suggesting their fundamental function in the architecture of humic suprastructures. An important role in differentiating supramolecular associations should also be attributed to substituted alkanoic acids that were detected in variable amounts in different fractions. The content of aromatic acids and steroids was only noticed in the latter fractions. HPSEC-ESI-MS of initial and final solid fractions showed similar compounds, as indicated by GC-MS, whereas the hydrosoluble fraction after transesterification revealed fewer of these compounds but noticeable nitrogen-containing acids. A large amount of "cyclic" acids were identified by MS empirical formula in initial HA, and, to a lesser extent, in the final fractionation residue as well as in the hydrosoluble fraction. The predominant alkyl NMR signals in organosoluble extracts and those of CH-N, CH-O, and O-CH-O groups in hydrosoluble fraction confirmed mass spectrometry results. Homo- and heterocorrelated liquid-state NMR spectra indicated spin systems interactions varying with separated fractions. Solid-state and dipolar-dephasing NMR spectra of final residue showed predominance of sp(2) carbons, 66% of which were quaternary carbons, and a significant increase in conformational rigidity with respect to initial HA. Separated fractions accounted for 60% of initial HA weight, and losses were attributed to hydration water, liberated volatile compounds, and decarboxylation. Quantization of analytes showed that the sum of compound classes in separated fractions was greater than that for the initial HA, thereby showing that stepwise fractionation increased significantly the analytical identification of humic molecules. Our results suggest this "Humeomics" approach as a valid path for mapping humic molecular composition and assess humus origin and formation.

Characterization and grouping of aquatic fulvic acids isolated from clear-water rivers and lakes in Japan

Characteristics of aquatic fulvic acids (FAs) from 10 clear waters in Japan (around the temperate zone) were revealed by several analytical techniques-high performance size exclusion chromatography (HPSEC), elemental analysis, liquid-state (13)C NMR spectroscopy, isotopic analyses (delta(13)C and delta(15)N), and compared with those of International Humic Substances Society (IHSS) standard samples including FAs from brown waters (Suwannee, Pony, and Nordic FAs). Generally clear-water FAs were different from brown-water FAs in chemical properties. Weight-average molecular weights (Mw) of the clear-water FAs were similar to each other, whereas their elemental compositions and carbon species distribution were different. The clear-water FAs all exhibited a high proportion of alkyl carbons, which may be attributed to microbial activity. delta(13)C and delta(15)N values of the FAs indicated that there would be a huge gap between origin and chemical structure of clear-water FA. Results of the chemical structural analyses described above were not always linked to those of the isotopic analyses (delta(13)C and delta(15)N). Multivariate statistical analysis, i.e. cluster and principal component analysis was applied to reveal differences or similarities in a more objective manner. The FAs were always classified into two clear-water groups and one brown-water group. Aryl-C and O-Alkyl-C contents were important for the grouping. We speculate that the grouping might depend on the differences of aquatic microbial activity caused by the differences of residence time of water.

Bioactivity of chemically transformed humic matter from vermicompost on plant root growth

Chemical reactions (hydrolysis, oxidation, reduction, methylation, alkyl compounds detachment) were applied to modify the structure of humic substances (HS) isolated from vermicompost. Structural and conformational changes of these humic derivatives were assessed by elemental analyses, size exclusion chromatography (HPSEC), solid-state nuclear magnetic resonance ((13)C CPMAS-NMR), and diffusion ordered spectroscopy (DOSY-NMR), whereas their bioactivity was evaluated by changes in root architecture and proton pump activation of tomato and maize. All humic derivatives exhibited a large bioactivity compared to original HS, both KMnO(4)-oxidized and methylated materials being the most effective. Whereas no general relationship was found between bioactivity and humic molecular sizes, the hydrophobicity index was significantly related with proton pump stimulation. It is suggested that the hydrophobic domain can preserve bioactive molecules such as auxins in the humic matter. In contact with root-exuded organic acids the hydrophobic weak forces could be disrupted, releasing bioactive compounds from humic aggregates. These findings were further supported by the fact that HS and all derivatives used in this study activated the auxin synthetic reporter DR5::GUS.

Nonlinear binding of phenanthrene to the extracted fulvic acid fraction in soil in comparison with other organic matter fractions and to the whole soil sample

Fractions of soil organic matter in a natural soil were extracted and sorption (or binding) characteristics of phenanthrene on each fraction and to the whole sample were investigated. The organic carbon normalized single point sorption (or binding) coefficient followed lipid > humin (HM) > humic acid (HA) > fulvic acid (FA) > whole soil sample, while the nonlinear exponent exhibited lipid > FA > HA > whole soil sample > HM. FA showed nonlinear binding of phenanthrene as it often does with other fractions. HM and HA contributed the majority of organic carbon in the soil. The calculated sorption coefficients of the whole soil were about two times greater than the measured values at different equilibrium phenanthrene concentrations. As for phenanthrene, the sorption capacity and nonlinearity of the physically mixed HA-HM mixtures were stronger as compared to the chemically reconstituted HA-HM composite. This was attributed to (besides the conditioning effect of the organic solvents) interactions between HA and HM and acid-base additions during fractionation.

Chemical composition and bioactivity properties of size-fractions separated from a vermicompost humic acid

Preparative high performance size-exclusion chromatography (HPSEC) was applied to humic acids (HA) extracted from vermicompost in order to separate humic matter of different molecular dimension and evaluate the relationship between chemical properties of size-fractions (SF) and their effects on plant root growth. Molecular dimensions of components in humic SF was further achieved by diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY-NMR) based on diffusion coefficients (D), while carbon distribution was evaluated by solid state (CP/MAS) (13)C NMR. Seedlings of maize and Arabidopsis were treated with different concentrations of SF to evaluate root growth. Six different SF were obtained and their carbohydrate-like content and alkyl chain length decreased with decreasing molecular size. Progressive reduction of aromatic carbon was also observed with decreasing molecular size of separated fractions. Diffusion-ordered spectroscopy (DOSY) spectra showed that SF were composed of complex mixtures of aliphatic, aromatic and carbohydrates constituents that could be separated on the basis of their diffusion. All SF promoted root growth in Arabidopsis and maize seedlings but the effects differed according to molecular size and plant species. In Arabidopsis seedlings, the bulk HA and its SF revealed a classical large auxin-like exogenous response, i.e.: shortened the principal root axis and induced lateral roots, while the effects in maize corresponded to low auxin-like levels, as suggested by enhanced principal axis length and induction of lateral roots. The reduction of humic heterogeneity obtained in HPSEC separated size-fractions suggested that their physiological influence on root growth and architecture was less an effect of their size than their content of specific bioactive molecules. However, these molecules may be dynamically released from humic superstructures and exert their bioactivity when weaker is the humic conformational stability as that obtained in the separated size-fractions.

Effects of a humic acid and its size-fractions on the bacterial community of soil rhizosphere under maize (Zea mays L.)

The effects of a humic acid (HA) and its size-fractions on plants carbon deposition and the structure of microbial communities in the rhizosphere soil of maize (Zea mays L.) plants were studied. Experiments were conducted in rhizobox systems that separate an upper soil-plant compartment from a lower compartment, where roots are excluded from the rhizosphere soil by a nylon membrane. The upper rhizobox compartment received the humic additions, whereas, after roots development, the rhizosphere soil in the lower compartment was sampled and sliced into thin layers. The lux-marked biosensor Pseudomonas fluorescens 10586 pUCD607 biosensor showed a significant increase in the deposition of bioavailable sources of carbon in the rhizosphere of soils when treated with bulk HA, but no response was found for treatments with the separated size-fractions. PCR-DGGE molecular fingerprintings revealed that the structure of rhizosphere microbial communities was changed by all humic treatments and that the smaller and more bioavailable size-fractions were more easily degraded by microbial activity than the bulk HA. On the other hand, highly hydrophobic and strongly associated humic molecules in the bulk HA required additional plant rhizodeposition before their bio-transformation could occur. This work highlights the importance of applying advanced biological and biotechnological methods to notice changes occurring in plant rhizodeposition and rhizosphere microbial activity. Moreover, it suggests correlations between the molecular properties of humic matter and their effects on microbial communities in the rhizosphere as mediated by root exudation.

Molecular rigidity and diffusivity of Al3+ and Ca2+ humates as revealed by NMR spectroscopy

NMR techniques were applied to follow changes in molecular rigidity and diffusion of complexes formed between a humic acid (HA) and either aluminum or calcium ions, added in amounts ranging from 0.05% to 1% of HA carboxylic acidity. Spin-lattice relaxation time in the rotating frame (T1rho,(H)) and diffusion coefficients (D) of humic-metal complexes were obtained from 13C cross-polarization magic angle spinning (CP-MAS), and 1H-diffusion order spectroscopy (DOSY) spectra, respectively. Molecular rigidity of humic complexes increased significantly with metal addition throughout the full carbon spectral region, being more pronounced for triple-charged Al than for double-charged Ca. However, T1rho(H) values of spectral intervals suggested that molecular rigidity increase was generally in the following order: aliphatic C > aromatic/double bonds C > carboxyl C. Concomitantly, DOSY spectra showed that addition of both Al and Ca decreased substantially the diffusivity of humic alkyl components and increased that of aromatic and hydroxyalkyl components, thereby indicating that complexation induced a molecular-size increase in the former and a decrease in the latter. These results suggest that saturated and unsaturated long-chain alkanoic acids in HA were preferentially involved in metal complexation with Al and Ca, with consequentincrease of conformational rigidity and molecular size of humic hydrophobic domains. Conversely, more hydrophilic or mobile humic components appeared relatively less affected by the molecular and intermolecular rearrangements induced in HA by complexation with metals. Such NMR approach appears thus liable to evaluate the response to metal complexation of specific chemical entities present in the bulk HA and provides a further insight in the molecular architecture of humic-metal complexes.

Molecular size distribution of compost-derived humates as a function of concentration and different counterions

Conformational changes in the structures of humic acids (HA) extracted from compost with varying degrees of maturity were monitored by high performance size exclusion chromatography (HPSEC). The molecular size distribution of HA was compared in solutions containing sodium or ammonium counterions at pH 7 and pH 4.5. These findings indicate that the humates' molecular size depended not only on the nature of the counterions but also on their concentration in the solution. The physicochemical nature of sodium counterions determined smaller molecular sizes than those of the more hydrated ammonium counterions, at low concentrations of humates. Conversely, at higher humate concentrations, the more compact conformation of sodium humates produced larger molecular sizes than those of ammonium humates due to the aggregation of more hydrophobic surfaces in the sodium humates. Composting led to the degradation of labile microbial components with accumulation of hydrophobic constituents. This caused self-association of hydrophobic compounds into humic superstructures of larger molecular size over composting time. At lower pH, changes in conformational stability by the addition of acetic acid to humate solutions were explained by the supramolecular model of humified organic matter.

Reduced toxicity of olive mill waste waters by oxidative coupling with biomimetic catalysis

Large quantities of environmentally toxic olive mill waste waters (OMWW) result from olive oil production worldwide. A synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of iron(III) chloride (FePha) was used as biomimetic catalystto oxidatively couple toxic phenols in OMWW fractions obtained by micro-, ultra-, and nanofiltration, and reverse osmosis. The occurrence of oxidative coupling in different OMWW size-fractions was assessed by high performance size exclusion chromatography (HPSEC), before and after conformational disruption with acetic acid, and measurements of proton spin-lattice relaxation time in the rotating frame (T1(rho)H) through 13C-CPMAS-NMR spectroscopy. The concurrent reduction in toxicity of OMWW size-fractions brought about by the FePha treatment was monitored by an algal bioassay. HPSEC chromatograms of OMWW samples subjected to catalyzed coupling showed apparent weight-average molecular weight (Mwa) values varying from 18 to 185% larger than for control. Moreover, when such FePha-treated fractions were added to acetic acid prior to HPSEC, the Mwa values still ranged from 14 to 162% larger than for control fractions similarly treated with acetic acid. This evidence of polymerization among toxic phenols was confirmed by T1(rho)(H) values which were significantly enhanced by the FePha treatment, thereby indicating an increased conformational rigidity of OMWW materials. These molecular changes were reflected in a significantly reduced toxicity exerted on microalgae by the OMWW size-fractions subjected to catalyzed oxidative couplings. Our results suggest that OMWW can be effectively treated with a biomimetic catalyst to induce oxidative phenol polymerization and reduce their toxicity before amendments to soils or other disposal means.

Optimization of conditions for high-performance size-exclusion chromatography of different soil humic acids

A method of high-performance size-exclusion chromatography (HPSEC) for a wide variety of soil humic acids (HAs) was developed. Two types of soil HAs (Cambisol and Andosol HAs), which have substantially different chemical properties, showed different effects of salt and organic solvent concentrations in the eluent on chromatograms. A Shodex OHpak SB-805 HQ column with 10 mM sodium phosphate buffer (pH 7.0) containing 25% of acetonitrile (v/v) was found to be applicable for different HAs, and showed high reproducibility and recovery (87.0 - 94.5%). The Cambisol HA was fractionated into five fractions using an ultrafiltration with different molecular-weight cut-offs. The order of the molecular weights of the five fractions calculated from the HPSEC analysis corresponded to that defined by ultrafiltration. This supported the reliability of the method.

Biobased surfactant-like molecules from organic wastes: the effect of waste composition and composting process on surfactant properties and on the ability to solubilize Tetrachloroethene (PCE)

In this work, four surfactant-like humic acids (HAs) obtained from garden lignocellulose wastes and kitchen food wastes mixed with garden-lignocellulose wastes, both before and after composting, were tested for surfactant properties and the ability to solubilize tetrachloroethene (PCE). The waste-derived HAs showed good surfactant properties, lowering the water surface tension from 74 mN m(-1) to 45.4 +/- 4.4 mN m(-1), with a critical micelle concentration (CMC) of 1.54 +/- 1.68 g L(-1), which is lower than many synthetic ionic surfactants. CMC was affected by both waste origin and composting processes. The addition of food waste and composting reduced CMC by adding alkyl-C (measured by CP MAS 13C NMR) and N- and S-HA contents (amide molecules), so that a multistep regression was found [CMC = 24.6 - 0.189 alkyl C - 2.64 (N + S); R2 = 0.77, P < 0.10, n = 6]. The four HAs solubilized PCE at the rate of 0.18-0.47 g PCE/g aqueous biosurfactant. These results were much higher than those reported in the literature for a commercial HA (0.026 g/g), but they were in line with those measured in this work for nonionic surfactants such as Tween-80 (0.69 g/g) and Triton X-100 (1.08 g/g).

Spectroscopic and conformational properties of size-fractions separated from a lignite humic acid

A lignite humic acid (HA) was fractionated by preparative high performance size-exclusion chromatography (HPSEC) in seven different size-fractions. The size-fractions were characterized by cross polarization (CP) magic angle spinning (MAS) (13)C NMR spectroscopy and a further analytical HPSEC elution under UV and fluorescence detection. The alkyl hydrophobic components mainly distributed in the largest molecular-size-fraction, whereas the amount of oxidized carbons increased with decreasing size of fractions. Cross polarization time (T(CH)) and proton spin-lattice relaxation time in the rotating frame (T(1rho)(H)) were measured from variable contact time (VCT) experiments. The bulk HA was characterized by the shortest T(CH) values and the longest T(1rho)(H) values which suggested, respectively, one. an aggregation of components in a large conformation that favored a fast H-C cross polarization, and, two. consequent steric hindrances that prevented fast local molecular motions and decreased proton relaxation rates. Conversely, the separated size-fractions showed longer T(CH) values and shorter T(1rho)(H) values than the bulk HA, thereby indicating that they were constituted by a larger number of mobile molecular conformations. The UV and fluorescence absorptions were both low in the large size-fractions that mainly contained alkyl carbons, whereas they increased in the olephinic- and aromatic-rich fractions with intermediate molecular-size, and decreased again in the smaller fractions which were predominantly composed by oxidized carbons. These results support the supramolecular structure of humic substances and indicate that the observed variation in conformational distribution in humic association may be used to explain environmental processes with additional precision.

Advanced TMAH and TMAAc thermochemolysis–pyrolysis techniques for molecular characterization of size-separated fractions from aquatic dissolved organic matter

The structural similarities and differences between the original DOM and the eight size fractions separated were studied in detail with the pyrolysis technique in combination with gas chromatography and mass spectrometry (Py-GC-MS) using two alkylating reagents: TMAH (tetramethylammonium hydroxide), to find both esterified and free carboxylic acids; and TMAAc (tetramethylammonium acetate), to specify only free carboxylic acids. A statistical analysis of the original multidimensional TMAH and TMAAc pyrograms disclosed that the overall structural compositions of the five most important size fractions, accounting for 84% of the original DOM, greatly resembled each other. The remaining three minor size fractions were not classified as homogeneous associations, but they also contained the same total, covalently bound and free carboxylic acid species as the other size fractions and the original DOM mixture, thus representing some kind of intermediate forms. This fundamental outcome strongly supports the opinion that the native dissolved humic-like macromolecules resemble supramolecular associations of smaller molecular size moieties with similar structural functionalities. The concentrations of free aliphatic and aromatic dicarboxylic acids in the DOM solution were so low that their effects on the potential formation of multiply charged ions in electrospray ionization-MS (ESI-MS) studies are likely insignificant.

Advanced CPMAS-13C NMR techniques for molecular characterization of size-separated fractions from a soil humic acid

A humic acid extracted from a volcanic soil was subjected to preparative high-performance size-exclusion chromatography (HPSEC) to reduce its molecular complexity and eleven different size fractions were obtained. Cross-polarization magic-angle spinning 13C NMR (CPMAS 13C NMR) analysis performed with variable contact-time (VCT) pulse sequences showed that the largest molecular-size fractions contained aromatic, alkyl, and carbohydrate-like components. The carbohydrate-like content and the alkyl chain length seemed to decrease with decreasing molecular size. Progressive reduction of aromatic carbon atoms was also observed with decreasing molecular size of the separated fractions. Mathematical treatment of the results from VCT experiments enabled cross polarization (T (CH)) and proton spin-lattice relaxation (T(1rho)(H)) times to be related to structural differences among the size fractions. The conformational distribution indicated that the eleven size fractions could be allocated to two main groups. The first group, with larger nominal molecular sizes, was characterized by molecular domains with slower local molecular motion. The second group of size fractions, with smaller nominal molecular sizes, was characterized by a larger number of molecular domains with faster local molecular motion. The T (CH) and (T(1rho)(H)) values suggested that either condensed or strongly associated aromatic systems were predominant in the size fractions with the largest apparent molecular dimensions.

Purification and characterization of novel proteinase inhibitors from dried figs

Two types of the natural organic matter P and B were isolated from dried figs by gel permeation and high-performance liquid chromatography. The characterizations of their molecular structures were also performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and infrared absorption spectrometry. As a result, these samples were revealed to inhibit the serine and cysteine proteinases chymotrypsin and papain (K(i) = 10(-)(6)-10(-)(4) M). The optimal inhibitory pH values of the P and B samples were observed to be approximately 5.5 and 5.0, respectively. The analyses of their UV-vis absorption spectra and infrared absorption spectra indicated that they would be a kind of humic substance. The mass spectrometry analyses showed that they possessed relatively small heterogeneous molecules with molecular masses around 692, 845, and 1389 Da for the P sample and around 551, 704, and 909 Da for the B sample.

NMR spectroscopy study of freshwater humic material in light of supramolecular assembly

The structural similarity-dissimilarity of several humic-type derivatives, separated from a strongly colored freshwater sample by different sorbing solid techniques, tangential-flow ultrafiltration (UF), and large-scale preparative high-performance size-exclusion chromatography (HPSEC), were in detail studied with one-dimensional liquid 1H and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, especially in light of the native humic-type dissolved organic matter (DOM-HM). The results support the applicability of functional cross-linked poly(vinylpyrrolidone) (PVP) or diethylaminoethyl-cellulose (DEAE) sorbents in concentrating representative integrated wholes of aquatic humic-type material along with a conventional nonionic XAD-8/DAX-8 (polymethyl methacrylates) technique. Apart from the fact that the acidification of the original humic water before a separation procedure seems not to be so destructive to the original structural composition of the DOM-HM as expected, the refinement of aquatic humic solutes, independent of the selected sorbing solid technique, will cause structural changes in the separated humic complexes in comparison with the situation predominating in the original starting material. Tangential-flow ultrafiltration (UF) proved an overpowering reliability to concentrate the aquatic DOM-HM. Most fundamental is the combined outcome of different HPSEC experiments and determined structural functionalities which indicate that almost all original DOM-HM solutes are aggregated mixtures consisting of structurally similar associations possessing various molecular size ranges, which can be separated from their integrated whole as nearly homogeneous and uniform species. This finding permits a reasonable starting point to go on working with more advanced multidimensional NMR techniques in resolving the uncertainty about supramolecular assembly of dissolved humic material. The tested conformity between the obtained molecular NMR descriptors and the corresponding previously collected FT-IR parameters was acceptable thus speaking for the fact that the less sensitive FT-IR spectroscopy can also provide valuable information on the structural and functional properties of heterogeneous humic-type mixtures.