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1.
To obtain information on the contribution of aromatic fragments to the chemical structure of humic substances, we carried out a study on the [1H]NMR and [13C]NMR spectra of humic and fulvic acids and their oxidative degradation products extracted from an Andosol soil.[1H]NMR spectra of all organic fractions present considerable adsorption between 7.4 and 8.8 ppm, due to the presence of aromatic protons.The percentages of aromatic protons in respect to the total amount of protons are as follows: FA 20%, HA 19%, degraded FA < 12%, degraded HA 14%. The values indicate that the contribution of aromatic structures to the humic substances is significant, also considering that they are highly substituted.The degraded fractions contain smaller amounts of aromatic protons, because degradation causes the opening of the aromatic rings. Thus results obtained from the degradation do not seem to be reliable for defining the importance of aromatic structures in humic substances.Also the [13C]NMR spectra show signals in the aromatic region which derive from unsubstituted carbon atoms, while signals originating from tertiary carbon atoms merge with the noise. We believe that, at present, [1H]NMR spectroscopy is more suited for studying the role played by aromatic compounds in organic soil fractions.  相似文献   

2.
Carboxyl groups are abundant in natural organic molecules (NOM) and play a major role in their reactivity. The structural environments of carboxyl groups in IHSS soil and river humic samples were investigated using 2D NMR (heteronuclear and homonuclear correlation) spectroscopy. Based on the 1H-13C heteronuclear multiple-bond correlation (HMBC) spectroscopy results, the carboxyl environments in NOM were categorized as Type I (unsubstituted and alkyl-substituted aliphatic/alicyclic), Type II (functionalized carbon substituted), Type IIIa, b (heteroatom and olefin substituted), and Type IVa, b (5-membered heterocyclic aromatic and 6-membered aromatic). The most intense signal in the HMBC spectra comes from the Type I carboxyl groups, including the 2JCH and 3JCH couplings of unsubstituted aliphatic and alicyclic acids, though this spectral region also includes the 3JCH couplings of Type II and III structures. Type II and III carboxyls have small but detectable 2JCH correlations in all NOM samples except for the Suwannee River humic acid. Signals from carboxyls bonded to 5-membered aromatic heterocyclic fragments (Type IVa) are observed in the soil HA and Suwannee River FA, while correlations to 6-membered aromatics (Type IVb) are only observed in Suwannee River HA. In general, aromatic carboxylic acids may be present at concentrations lower than previously imagined in these samples. Vibrational spectroscopy results for these NOM samples, described in an accompanying paper [Hay M. B. and Myneni S. C. B. (2007) Structural environments of carboxyl groups in natural organic molecules from terrestrial systems. Part 1: Infrared spectroscopy. Geochim. Cosmochim. Acta (in press)], suggest that Type II and Type III carboxylic acids with α substituents (e.g., -OH, -OR, or -CO2H) constitute the majority of carboxyl structures in all humic substances examined. Furoic and salicylic acid structures (Type IV) are also feasible fragments, albeit as minor constituents. The vibrational spectroscopy results also suggest that much of the “Type I” signal observed in the HMBC spectrum is due to carboxylic acid esters and possibly α-substituted alicyclic acids.  相似文献   

3.
The composition of humic acids (HAs) isolated from an agricultural soil and a lignite deposit was examined via H2O2 and RuO4 oxidation. The oxidation digests were separated into lipophilic and hydrophilic components. Information with regard to the source, degree of humification and preservation of easily degradable constituents of the HAs was obtained and results were compared with those obtained earlier for base hydrolysates of solvent-extracted fractions.H2O2 oxidation of both HAs afforded lipophilic fractions containing high molecular weight compounds. The composition of the base hydrolysates of the lipophilic fractions strongly differed with the origin of the HA. The lipophilic components of the soil HA derived mainly from the higher plant polyesters cutin and suberin. The lipophilic components of the lignite HA predominantly comprised long chain alkanoic acids and alkanols. The patterns for the hydrophilic components released upon H2O2 oxidation were found to be identical irrespective of the origin of the HA. The hydrophilic fractions comprised aliphatic (poly)carboxylic acids related to carbohydrate moieties and benzene polycarboxylic acids. The relative abundance of benzene polycarboxylic acids increased with the degree of humification.For both HAs, RuO4 oxidation resulted in a lipophilic fraction containing low molecular weight products identical to those found in the base hydrolysate of the lipophilic fraction released upon H2O2 oxidation. The hydrophilic components released upon RuO4 oxidation were independent of the HA origin and consisted mainly of monosaccharides and disubstituted aromatic compounds. In agreement with the greater aromaticity of lignite HA, the aromatic compound/carbohydrate ratio was higher for lignite HA than soil HA. The results show that the fused aromatic structures had a small size and that carbohydrates could escape degradation during the humification process.  相似文献   

4.
The structural characteristics of humic acids (HAs) from two different depths of a sedimentary sequence representing the last 13 kyr in the valley of Guadiana river estuary (SW Portugal/Spain border) have been approached using a combination of spectroscopic techniques, wet chemical degradation methods (sequential oxidation with sodium persulfate followed by KMnO4, and oxidation with RuO4) and analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) in the presence and absence of tetramethylammonium hydroxyde (TMAH). The aim was to obtain complementary information on the sources and alteration of the organic matter (OM) provided by a previous study on the vertical distribution of terrestrial and phytoplankton biogeochemical markers in the sequence. Both the FT-IR (Fourier transformed infrared) and 13C NMR (nuclear magnetic resonance) spectra showed a close similarity with the structural characteristics of the HA samples. NMR signals in the alkyl region (0–45 ppm) as well as FT-IR band patterns typical for methoxyl-substituted aromatic rings pointed to the presence of an important aliphatic domain, as well as to lignin-derived compounds. This finding was confirmed using analytical pyrolysis. In addition, the main TMAH thermochemolysis products were typical lignin-derived methoxyphenols with both guaicyl and syringyl nuclei. The detection of methoxyphenol units with three to six carbon atom (C3–C6) side chains suggests that lignin and possibly suberin were only partially degraded. Compounds arising from proteins and polysaccharides were also detected, although in lesser and varying amount. The major products from persulfate oxidation were series of n-alkanes (C16–C33 with clear odd/even predominance) and n-fatty acids, both saturated (C10–C26 with strong even/odd predominance) and unsaturated, which may arise from the above aliphatic biomacromolecules. The major products from permanganate oxidation of the persulfate residue were α,ω-diacids (C6–C11) originating from oxidation of the ether bonds linking the building blocks constituting the core of the HA structure. Aromatic compounds (phenols, methoxy-dimethoxybenzene carboxylic acid and benzene di-, tri-, tetra- and pentacarboxylic acids), most probably derived from the aromatic backbone of the HAs, that may also include lignin moieties as well as other polyphenols (flavonoids and tannins) were also detected. The RuO4 oxidation also released series of n-alkanes (C16–C33), linear saturated fatty acids (C10–C28) and α,ω-diacids (C7–C25), as well as traces of benzene polycarboxylic acids. Regarding the usefulness of the various techniques used, they provide complementary information. Indeed, spectroscopic techniques and analytical pyrolysis provide information on the backbone of the HAs, and on their origin, whereas the oxidative degradations provide different information on the structural features of the HA, particularly the nature of the linking between the building blocks. In general, the data support the idea that the HAs still contain information about the signature of aliphatic and aromatic biomacromolecules contributing to the OM deposited. The presence of lignin-derived residues suggests a large input from terrestrial carbon throughout the core.  相似文献   

5.
A sequential fractionation procedure employing a series of selected mild organic solvents of different polarity has been applied for the isolation of chemically different organic fractions from a brown coal humic acid. Elemental composition, molecular weight distribution, i.r. and electron spin resonance analysis were carried out on the isolated humic fractions. They were characterized by: (a) a low polydispersity, (b) a decreasing aliphatic and increasing aromatic character along the series, (c) very different molecular weight which significantly correlated with E4/E6 ratios (particle aggregation and molecular association) and free radical concentrations (chemical and biochemical activity). Significant correlations were found between physico-chemical parameters of the isolated humic fractions, i.e. Mn, Mw, E4/E6 ratios, spins/g contents and the dielectric constants of the solvents used. This suggested the efficiency of the applied procedure in isolating chemically different organic fractions from the bulk, original humic acid.  相似文献   

6.
The IR and 1H-NMR spectra of fulvic acids (FA) are discussed. The FA, extracted by traditional methods, were fractionated on the basis of molecular weight (m.w.). Three fractions were obtained labelled FA I (m.w. > ～ 2000), FA II (m.w. > ～ 12000) and FA III (～2000 < m.w. < ～ 12000). Fraction FA II was methylated with CH3I-Ag2O. The 1H-NMR spectra of unmethylated FA fractions show some signals common to all three fractions and some differences in the 3–5 ppm range due to the resonances of OCH3 and O-CH2 groups. The proton spectrum of the methylated fraction shows absorption areas for OCH3 groups of phenols and carboxyls. The results confirm that NMR spectroscopy is a convenient technique which can contribute to defining the chemical structure of humic substances.  相似文献   

7.
In situ biotransformation of oil to methane was investigated in a reservoir in Dagang, China using chemical fingerprinting, isotopic analyzes and molecular and biological methods. The reservoir is highly methanogenic despite chemical indications of advanced oil degradation, such as depletion of n-alkanes, alkylbenzenes and light polycyclic aromatic hydrocarbon (PAH) fractions or changes in the distribution of several alkylated polycyclic aromatic hydrocarbons. The degree of degradation strongly varied between different parts of the reservoir, ranging from severely degraded to nearly undegraded oil compositions. Geochemical data from oil, water and gas samples taken from the reservoir are consistent with in situ biogenic methane production linked to aliphatic and aromatic hydrocarbon degradation. Microcosms were inoculated with production and injection waters in order to characterize these processes in vitro. Subsequent degradation experiments revealed that autochthonous microbiota are capable of producing methane from 13C labelled n-hexadecane or 2-methylnaphthalene and suggest that further methanogenesis may occur from the aromatic and polyaromatic fractions of Dagang reservoir fluids. The microbial communities from produced oil–water samples were composed of high numbers of microorganisms (on the order to 107), including methane producing Archaea within the same order of magnitude. In summary, the investigated sections of the Dagang reservoir may have significant potential for testing the viability of in situ conversion of oil to methane as an enhanced recovery method and biodegradation of the aromatic fractions of the oil may be an important methane source.  相似文献   

8.
The role of organic matter (OM) concentration, structure and composition and how these relate to mineral protection is important for the understanding of long term soil OM dynamics. Various OM–clay complexes were constructed by sequential sorption of lignin and dodecanoic acid to montmorillonite. Humic acid–montmorillonite complexes were prepared at pH 4 and 7 to vary OM conformation prior to sorption. Results obtained with constructed OM–clay complexes were tested with isolated mineral fractions from two soils. Oxidation with an acidic NaClO2 solution was used to chemically oxidize lignin in the OM–clay complexes, sand-, silt- and clay-size soil fractions to test whether or not it can be protected from chemical attack. Gas chromatography–mass spectrometry was used to analyze lignin-derived phenols, cutin OH–acid (after CuO oxidation), fatty acid and n-alkanol concentrations and composition. We found that carbon content was not solely responsible for lignin stability against chemical oxidation. Lignin was protected from chemical oxidation through coating with dodecanoic acid and sorption of humic acid to clay minerals in a stretched conformation at pH 7. Therefore, interactions between OM constituents as well as OM conformation are important factors that protect lignin from chemical oxidation. Lignin-derived phenol dimers in the Grassland-Forest Transition soil fractions were protected from chemical oxidation to a greater extent compared to those in Grassland soil fractions. Therefore, although lignin was protected from degradation through mineral association, the extent of this protection was also related to OM content and the specific stability of lignin components.  相似文献   

9.
Although direct microbial reduction of Cr(VI) and U(VI) is known, few studies have examined the kinetics and the underlying mechanisms of the reduction of these contaminants by different natural organic matter (NOM) fractions in the presence or absence of microorganisms. In this study, NOM was found to chemically reduce Cr(VI) at pH 3, but the reduction rates were negligible at pH ∼7. The abiotic reduction of U(VI) by NOM was not observed, possibly because of the presence of small amounts of nitrate in the reactant solution. However, all NOM fractions, particularly the soil humic acid (HA), enhanced the bioreduction of Cr(VI) or U(VI) in the presence of Shewanella putrefaciens CN32. The reduction rates varied greatly among NOM fractions with different chemical and structural properties: the polyphenolic-rich NOM-PP fraction appeared to be the most reactive in abiotically reducing Cr(VI) at a low pH, but soil HA was more effective in mediating the microbial reduction of Cr(VI) and U(VI) under anaerobic, circumneutral pH conditions. These observations are attributed to an increased solubility and conformational changes of the soil HA with pH and, more importantly, its relatively high contents of polycondensed and conjugated aromatic organic moieties. An important implication of this study is that, depending on chemical and structural properties, different NOM components may play different roles in enhancing the bioreduction of Cr(VI) and U(VI) by microorganisms. Polycondensed aromatic humic materials may be particularly useful in mediating the bioreduction and rapid immobilization of these contaminant metals in soil.  相似文献   

10.
Sorption of Ni2+ on Na-rectorite as a function of contact time, temperature, pH and fulvic acid (FA)/humic acid (HA) was studied under ambient conditions. A pseudo-second-order rate equation was used to simulate the kinetic sorption. The removal of Ni2+ increased with increasing pH. The presence of FA/HA enhanced the sorption of Ni2+ at low pH values, whereas no drastic effect of FA/HA on Ni2+ uptake to rectorite was found at high pH values. The diffuse layer model (DLM) fitted the experimental data of Ni2+ sorption in the absence and presence of FA/HA very well with the aid of FITEQL 3.2. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms of Ni2+ at different temperatures. The thermodynamic data (ΔH0, ΔS0, ΔG0) were calculated from the temperature dependent sorption isotherms and the results suggested that the sorption process of Ni2+ on rectorite was spontaneous and endothermic. The sorption and species of Ni2+ on rectorite in the presence and absence of FA/HA was also investigated and characterized by XPS. The spectroscopic analysis indicated no drastic structural changes of Na-rectorite and the sorption of Ni2+ mainly occurred on the surface and at the edge position of Na-rectorite.  相似文献   

11.
The phosphorus content of marine humic acids (HA) is in the range of 0.1–0.2%. The C/P ratios of the HA are 300 to 400. Marine fulvic acids (FA) contain 0.4–0.8% P and have C/P ratios of 80 to 100. High molecular weight organic matter dissolved in pore waters (DOM) contains 0.5% P and has C/P of 90. The data suggest that during the formation sequence: Plankton → DOM → FA → HA → Kerogen, phosphorus is lost, mainly in the FA → HA (and possibly also in the HA → Kerogen) step. Diagenesis of sedimentary humic acids is accompanied by loss of phosphorus (as well as of nitrogen) to form HA with C/P ratios of 1000.Soil humic substances resemble marine humates in P content (0.3%) and soil FA's are about three to fivefold enriched in P relative to HA. C/P ratios are lower in soil HA (ca. 200) as compared with marine HA. Humic acids from diagenetic products such as peat and lignite are highly depleted in P. Rough calculations indicate that humate bound P may account for 20–50% of the organic phosphorus reservoir in sediments. The chemical speciation of this P is unknown, but lack of correlation with ash, Fe, Ca or Al content (in marine humates, at least) indicates that it is organically bound.  相似文献   

12.
Fluorescence and absorption spectra of sedimentary humic acid (HA) and fulvic acid (FA), with molecular weights ranging from < 10,000 to >300,000, were measured at 20°C and pH 8. The maximum excitation and emission wavelengths of HA were longer than those of FA, being independent of molecular weight. The excitation and emission maxima can be utilized to differentiate between sedimentary HA and FA. It is suggested that the fluorophors in HA are of a higher molecular weight aromatic groups than those in FA.Smaller molecules were found to have a greater fluorescence than larger ones for sedimentary humic substances and this phenomenon is similar to those obtained for humic substances of terrestrial origin. The absorption coefficient (1/g/cm) of HA decreased, while that of FA increased with the increase in molecular weight. It was shown that fluorescence intensity per weight concentration unit of HA increases and that of FA decreases with increasing absorption coefficient.  相似文献   

13.
Surface tension of sedimentary fulvic acid (FA) and humic acid (HA) with molecular weight from < 10,000 to > 300,000 was measured at 5°C and 25°C, over a wide range of concentrations (0.114-107.4 g/l) at pH 8. HA was in the form of sodium humate. Surface tension decreases with an increase in HA and FA concentration and both HA and FA were found to be surface active materials with FA exhibiting the lowest surface tension (31 dynes/cm).Plots of surface tension vs. log concentration gave two straight lines with a break at a certain concentration similar to surfactants. From the concentration at the break point, aggregation concentration (AGC) was determined. For HA with molecular weight above 10,000, the AGC decreased with an increase in molecular weight. The more hydrophobic the HA, the greater was the tendency to form aggregates. Surface excess (surface concentration) was determined (2.3 × 10?10?5.5 × 10?10mol/cn2) from the slope of the plot of surface tension vs. log concentration for concentrations lower than the AGC. Adsorption of HA into the surface layer increased with increasing molecular weight of HA.  相似文献   

14.
Average proton binding constants (KH,i) for structure models of humic (HA) and fulvic (FA) acids were estimated semi-empirically by breaking down the macromolecules into reactive structural units (RSUs), and calculating KH,i values of the RSUs using linear free energy relationships (LFER) of Hammett. Predicted log KH,COOH and log KH,Ph-OH are 3.73 ± 0.13 and 9.83 ± 0.23 for HA, and 3.80 ± 0.20 and 9.87 ± 0.31 for FA. The predicted constants for phenolic-type sites (Ph-OH) are generally higher than those derived from potentiometric titrations, but the difference may not be significant in view of the considerable uncertainty of the acidity constants determined from acid-base measurements at high pH. The predicted constants for carboxylic-type sites agree well with titration data analyzed with Model VI (4.10 ± 0.16 for HA, 3.20 ± 0.13 for FA; Tipping, 1998), the Impermeable Sphere model (3.50-4.50 for HA; Avena et al., 1999), and the Stockholm Humic Model (4.10 ± 0.20 for HA, 3.50 ± 0.40 for FA; Gustafsson, 2001), but differ by about one log unit from those obtained by Milne et al. (2001) with the NICA-Donnan model (3.09 ± 0.51 for HA, 2.65 ± 0.43 for FA), and used to derive recommended generic values. To clarify this ambiguity, 10 high-quality titration data from Milne et al. (2001) were re-analyzed with the new predicted equilibrium constants. The data are described equally well with the previous and new sets of values (R2 ? 0.98), not necessarily because the NICA-Donnan model is overparametrized, but because titration lacks the sensitivity needed to quantify the full binding properties of humic substances. Correlations between NICA-Donnan parameters are discussed, but general progress is impeded by the unknown number of independent parameters that can be varied during regression of a model fit to titration data. The high consistency between predicted and experimental KH,COOH values, excluding those of Milne et al. (2001), gives faith in the proposed semi-empirical structural approach, and its usefulness to assess the plausibility of proton stability constants derived from simulations of titration data.  相似文献   

15.
《Applied Geochemistry》2006,21(7):1226-1239
Natural organic matter (NOM) from the Han River, Korea was fractionated into humic and non-humic fractions by absorbing onto XAD-7HP, and these fractions were analyzed using UV-absorption, and for dissolved organic C (DOC). The humic fraction (i.e. humic substances; HS) was extracted and its characteristics were compared to commercial humic materials using various spectroscopic methods such as Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (1H-NMR) and fluorescence spectroscopy. The humic fraction as organic C was 47.0% on the average, however, a rainfall event brought a higher humic fraction into Han River water. The molar ratios of H/C and O/C in the HS from Han River water (HRHS) were 1.40 and 0.76, respectively, and the ratio of aliphatic to aromatic protons in the HS (PAl/PAr ratio) was 5.8. Aromaticity and humification degree (i.e., degree of condensation) of HRHS were relatively lower than those from other humic materials, while the portion of oxygenated functional groups was relatively higher. FT-IR, 1H-NMR and fluorescence spectroscopy showed distinct differences between HRHS and the commercial humic materials. Commercial humic materials are not representative of HS extracted from Han River water. The fluorescence spectra, relatively simple measurements, were found to be most useful as fingerprints for humic materials from particular sources.  相似文献   

16.
Algal humic-like substances were oxidized with KMnO4. The oxidation products were analyzed by GC-MS. Normal and branched fatty acids, dicarboxylic and benzene carboxylic acids were identified. Aliphatic acids were by far the most prominent compounds. Similarities between humic and fulvic acids of both Fucus and Laminaria algae were apparent. Fucus humic acids, however, showed a more aromatic structure than their Laminaria counterpart. The contribution of algae to marine sedimentary humus is discussed.  相似文献   

17.
《Applied Geochemistry》2005,20(3):537-544
Thermal analyses (TG–DTA), elemental composition and isotope analyses (13C and 15N) were performed on humic acids (HA) from peats, leonardites and lignites, in order to investigate their structure and the changes taking place during the humification process. Thermal analyses showed structural differences between HA samples in relation to their coalification rank. In particular the lignite HA were characterized by a more stable chemical composition at high temperatures.The δ13C and δ15N values can provide information on the biogeochemical processes involved in HA formation. In particular, peat HA were linked to anoxic environments that enable plant residues to persist in their structure. In contrast, leonardite and lignite HA formation seems to be governed by different biogeochemical processes from those responsible for peat diagenesis. However, the isotopic analyses did not provide any distinction between leonardite and lignite HA. On the basis of the data presented in this study, it may be concluded that TG–DTA and isotope ratio measurements are powerful tools for investigating the formation pathway of humic substances from coals.  相似文献   

18.
The degradation and preservation affecting the biomarker record of ancient metazoa are not fully understood. We report on a five month experiment on the fate of fatty acids (FAs) during the degradation of recent whale vertebrae (Phocoena phocoena). Whale bones were analysed for extractable FAs and macromolecularly bound n-acyl compounds. Fresh bone showed extractable FAs dominated by 16:1ω7c, 16:0, 18:1ω9c and 18:0. Calculated degradation rate constant (k) values showed a rapid decrease in FA concentration, with k values higher for unsaturated than for saturated compounds (0.08/day for 18:1ω9c, 0.05/day for 16:0). The appearance or increased abundance of distinctive methyl branched (e.g. i/ai-15:0 and -17:0, 10Me-16:0) and hydroxy FAs (e.g. 10OH-16:0 and 10OH-18:0) were observed, providing clear evidence for the microbial degradation of bone organic matter and an input of lipids from specialised bacteria. Catalytic hydropyrolysis (HyPy) of demineralised extraction residues released up to 0.13% of the total n-C16 and n-C18 moieties in the degraded bones. This revealed that only a small, yet sizeable, portion of bone-derived fatty acyl units was sequestered into (proto)kerogen during the earliest stages of degradation.  相似文献   

19.
Structural studies of a sulphur-rich kerogen and macromolecular oil fractions from the Monterey Formation were performed by selective sequential chemical degradation. The method provides low-molecular weight compounds as former building blocks of the network which allow detailed analyses on a molecular level. The degradation sequence is based on three subsequently performed reactions—a selective cleavage of sulphur bonds in the first step carried out with Ni(0)cene/LiAlD4, an ether and ester bond cleavage (BCl3), and an oxidation of aromatic entities by ruthenium tetroxide as a final step. Each step of this sequence afforded a considerable amount of low-molecular weight material which was separated chromatographically and studied by GC and GC/MS, while the high-molecular weight or insoluble fractions were subjected to the next reaction step.The chemical degradation products—hydrocarbons and carboxylic acids—are discussed in terms of incorporation into the macromolecular structure, distribution of heteroatomic bridges and the genetic relationships between the different macromolecular crude oil fractions and kerogen.Labelling experiments with deuterium provided evidence for a simultaneous linkage by oxygen and sulphur functionalities or by aromatic units and sulphur bonds of cross-linking macromolecular network constituents.The determination of sulphur positions in the macromolecule suggests early diagenetic sulphur incorporation into the biological precursor compounds and subsequent formation of a cross-linked network.  相似文献   

20.
Two fractions of soil fulvic acid (FA) were separated by gel filtration chromatography. An observed increase in volume of the heavier fraction (FA I) with increasing pH was attributed to aggregation, intramolecular negative charge repulsions and the rupture of hydrogen bonds, which control molecular conformation. Optical absorption properties and elemental analyses of both fractions were determined. The stability constants and stoichiometries of FA complexes with vanadyl, VO2+, at pH 5.0 and ionic strength of 0.04 M were measured by electron paramagnetic resonance (EPR) spectroscopy. EPR spectra of model VO2+ complexes with phthalic and salicylic acids, which are the probable functional groups present in FA, are identical to those of the VO2+-FA complexes. Aggregation of FA I occurs in the presence of VO2+ to form a complex that can be approximated as ‘(VO)2(FA I)6’. The average site distance between vanadyl ions in this complex is shown to be greater than 1.2 nm. EPR parameters for FA I suggest binding by carboxylate groups. These parameters are compared with those of other vanadyl complexes with fulvic and humic acids reported by others. Reduction of VO3? to VO2+ by these materials is discussed.  相似文献   

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