Interaction of atrazine with Laurentian fulvic acid: binding and hydrolysis

Ultrafiltration fractionation and liquid chromatography (LC) have been applied to the study of the binding and hydrolysis of the polar herbicide atrazine on a stoichiometrically well characterized fulvic acid. Binding requires extensive carboxylate site protonation but the binding sites represent a very small fraction of total carboxylate. The data show that binding of atrazine is not competitive with binding of the hydrolytic product hydroxyatrazine. However, smaller molecular weight fractions of the fulvic acid mixture compete with atrazine for sites on the larger molecular weight fraction. Binding equilibrium is not rapid. A model of binding involving hydrogen bonding and/or charge-transfer complexing to specific sites created dynamically by the conformational equilibria of the higher molecular weight polymeric fulvic acid fractions is proposed as the best accommodation of the variety of observed facts.     

Fluorescence quenching of three molecular weight fractions of a soil fulvic acid by UO(2)(II)

A soil fulvic acid isolated from a Korean forest was divided into three different molecular weight fractions (F1: less than 220 Da; F2: 220-1000 Da; and F3: 1000-4000 Da) by gel filtration chromatography and the fractions were studied by synchronous fluorescence (SyF) spectroscopy. Analysis of the SyF spectra for the fulvic acid fractions showed that the fractions with molecules of larger sizes have a higher content of condensed aromatic compounds. The information about their interaction with UO(2)(II) ions in an aqueous solution (100 mg l(-1) of fulvic acid, in 0.1 M NaClO(4) at pH 3.5) was obtained from the measurement of SyF spectra at increasing concentrations of metal ions. Self-modeling mixture analysis of the quenching spectra gives two distinct peak components having a maximum peak position of 386 (type I) and 498 nm (type II) for all the size-fractionated fulvic acids. From the analysis of the quenching profiles of the peaks, using a non-linear method, the concentration of binding sites (C(L)), and the corresponding stability constants (logK) were calculated. The stability constants of the UO(2)(II)-fulvate complexes ranged from 4.10 to 5.33, and increased with higher molecular weight fractions, which indicates a stronger affinity for UO(2)(II) in the fraction with molecules of larger size.     

Molecular and quantitative aspects of the chemistry of fulvic acid and its interactions with metal ions and organic chemicals : Part II. The fluorescence spectroscopy approach

Information in the literature on the use of fluorescence spectroscopy for the study of the chemistry of fulvic acid and its interactions with metal ions and organic chemicals is discussed. Basic principles, instrumentation, procedures, methodology and limitations of the fluorescence technique and the fluorescence polarization method are briefly summarized. This is followed by an extended discussion on the direct information that fluorescence spectra can furnish on the properties and nature of fluorescing structures in fulvic acids. The effects of molecular parameters and environmental factors (molecular weight, concentration, pH, ionic strength, temperature and redox potential) on the fluorescence behaviour of fulvic acids are discussed. Particular attention is devoted to the indirect information that fluorescence quenching and fluorescence polarization studies provide on molecular and quantitative aspects of the chemistry of fulvic acid in solution, especially in relation to molecular conformation and binding with metal ions and organic chemicals. The potential advantage of this non-separative, non-destructive technique for the study of environmental samples such as fulvic acids is emphasized.     

Characterization of humic and fulvic acids from Gorleben groundwater

Summary The humic material extracted from one of the Gorleben groundwaters is separated into humic and fulvic acids, and characterized, together with a commercial humic acid from Aldrich Co., for their chemical composition, size distribution, proton exchange capacity and spectroscopic characteristics. The results are compared with one another and with the literature data of other humic acids. The humic acid is fractionated by gel permeation chromatography into different size groups and the fractions are subjected to IR and ¹H-NMR spectroscopy. The high molecular weight fractions (>70000 Dalton) are poor in carboxylic groups, whereas the major fractions (approx. 10000 Dalton) contain organic acids of large molecular entities.     

Fluorescence polarization studies of the conformation of soil fulvic acid

The conformation of soil fulvic acid was studied by fluorescence polarization as a function of pH, concentration, and ionic strength. Rotational relaxation times were measured from the slopes of plots of polarization vs. the ratio of temperature to viscosity. The rotational relaxation time did not change over the pH range 5–8 or over the concentration range 3.3 X 10^-5–3.3 × 10^-4 M fulvic acid. This suggests that fulvic acid does not aggregate or change conformation. Changes in ionic strength also do not cause a measurable change in rotational relaxation time. A net rotational relaxation of 2.0 ns was calculated for fulvic acid. This value is based on a fluorescence lifetime of 2.1 ns which is the best single exponential fit to the observed fluorescence decay. A molecular weight of 2400 was calculated for fulvic acid assuming that fulvic acid is spherical. The discrepancy between this value and the true number-average molecular weight of 990 suggests that fulvic acid exists in a flat extended conformation.     

Characterization of humic substances: Implications for trihalomethane formation

Humic substances are precursors of carcinogenic trihalomethanes (THMs) formed during disinfection by chlorination in water treatment processes. In an effort to understand the relationship between trihalomethane formation potential (THMFP) and physicochemical properties of humic substances, UV-visible absorbance, fluorescence in emission and synchronous scan modes, and NMR spectra were measured for several aquatic fulvic and humic acids. For comparison, a soil fulvic acid was also examined using these methods. The feasibility of the gradient modified spin-echo (GOSE) NMR experiment to selectively measure singlet resonances arising from isolated protons was examined. In addition, diffusion coefficients were measured for DMSO solutions of the fulvic acids using BPPLED and GOSE-edited pulse sequences. Although none of the methods tested produced results that correlated with THMFP, the GOSE intensities determined for different regions of the NMR spectra did reflect the relative abundance of different types of functional groups produced by lignin oxidation. In addition, the GOSE-edited diffusion results suggest that the isolated protons, those most reactive to chlorination, are more likely contained in the larger molecular weight fractions of fulvic acids.     

Investigation of the elemental composition and chemical association of several elements in fulvic acids dietary supplements by size-exclusion chromatography UV inductively coupled plasma mass spectrometric

Four fulvic acid dietary supplement samples were obtained for this study with the intention of investigating the elemental composition and association of fulvic acids found in fulvic acid supplements. This was achieved by coupling size-exclusion chromatography (SEC) sequentially with UV-vis and inductively coupled plasma mass spectrometric (ICP-MS) detectors. The combination of UV and ICP-MS offered highly sensitive and selective detection. This technique was used in the present study to initially investigate the chemical association of several different elements including, Cr, Co, Ca, Fe, I, Mg, Zn, Se, Cu, Mn, Mo, As, Hg, Pb, and Ag, by observing the elution profile of the fulvic acids obtained with UV detection and matching their retention times with the peaks measured with ICP-MS. The results found based on this type of analysis suggest that there was some association of the elements to the fulvic acids. It was also of interest to observe the stability of these complexes upon human digestion; therefore a gastric digestion was mimicked. In the fulvic acid dietary supplement samples studied, fulvic acids were present in the samples and there was elemental association based on the retention time overlap in the UV as well as the ICP-MS. The fulvic complexes found in the samples were of a low molecular weight As a result of the digestion the SEC-ICP-MS chromatographic profile in some of the samples changed, which may infer that the elemental association had changed.     

Vapor-pressure osmometric study of the molecular weight and aggregation tendency of a reference-soil fulvic acid

The molecular weight and aggregation tendency of a reference-soil fulvic acid in Armadale horizon Bh were determined by vapor-pressure osmometry using tetrahydrofuran and water as solvents. With tetrahydrofuran, number-average molecular weight values of 767 ± 34 and 699 ± 8 daltons were obtained from two separate sets of measurements. Two sets of measurements with water also yielded values within this range (754 ± 70 daltons) provided that the fulvic acid concentration in water did not exceed 7 mg ml^?1; at higher concentrations (9.1–13.7 mg ml^?1) a number-average molecular weight of 956 ± 25 daltons was resolved, providing evidence of molecular aggregation. Extension of these studies to 80% neutralized fulvic acid showed that a sizeable fraction of the sodium counter ion is not osmotically active.     

Preparation and characterization of humic and fulvic acid working standards—practical experience

Two fractions of both fulvic acids (FA) and humic acid (HA) were prepared by fractionation method of Pierce and Felbeck⁵ involving acid hydrolysis of soil rests. This step increases recovery of both FA and HA considerably what suggest us need for slight modification of IHSS method in some cases. The weight loss, change in organic carbon content and visible spectra are figures of merit discussed. After detailed characterization these humic substances (HS) will serve as the working standards for study of interactions between organomercurials and organic part of soil.     

High-performance liquid chromatographic fractionation and characterization of fulvic acid

High-performance immobilized metal ion affinity chromatography (HP-IMAC) was used to fractionate humic substances (HS) based on their affinity for the immobilized copper(II) ion using acidic and glycine eluents. The work was carried out with two naturally occurring aqueous fulvic acids and commercially available Suwannee River fulvic acid. The IMAC-fractionated HS were then characterized by reversed-phase high-performance liquid chromatography (RP-HPLC) and size exclusion chromatography. The results showed that the affinity HS fraction eluted first using an acidic pH=2 eluent exhibited a relatively high hydrophilic character, whereas the fraction eluted later using a glycine eluent exhibited both a higher hydrophobic character and larger molecular size. On the other hand, the HS fraction with no affinity for the immobilized copper had low molecular size. The affinity of the HS fraction for copper(II) increased with increasing molecular weight. Based on the composite results of three different HS, it is evident that strong relationships exist between affinity, molecular weight, and hydrophilic/hydrophobic properties during the HP-IMAC fractionation. The results presented here have significance for understanding the nature of chemical interactions at the molecular level between dissolved organic matter and trace metals. IMAC, coupled with other liquid chromatographic strategies, is a promising tool for chemical fractionation and characterization of HS.     

Copper speciation in aqueous solutions of fulvic acid and related molecular weight distributions

Potentiometric and fluorescence measurements of aqueous solutions of fulvic acid containing Cu(NO₃)₂ or Cu(ClO₄)₂, respectively, were carried out at 25?°C and pH 5.5 to determine naturally occurring Cu species. The fulvic acid used was isolated by XAD-8 from filtrated (0.3 μm) water of a peat bog in the Dachauer Moos near Munich. From the results an operational molecular weight of fulvic acid of about 750 g/ mol was estimated, which was confirmed by molecular weight distributions determined by high-performance size-exclusion chromatography (HPSEC), gel permeation chromatography (GPC) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Using this molecular weight and assuming that mainly 1:1 Cu-fulvic acid complexes are formed, a conditional stability constant of the Cu-fulvic acid complex of 10^5.9 could be calculated. These data are essential for the assessment of organic carrier-mediated migration of Cu as well as of the toxicological risk potential of Cu in aqueous environment and can be used as input parameters for geochemical modeling of the Cu species distribution in aqueous solutions.     

土壤腐殖质各组分红外光谱研究

土壤腐殖质是土壤中所特有的一类特殊的高分子化合物,具有重要的肥力和环境调节功能。其中胡敏素的提取和纯化很困难,从而限制了对其性质和结构的研究。为揭示胡敏素的结构性质,本研究按Pallo分组,将胡敏酸(HA)分为焦磷酸钠提取的胡敏酸(HAP)、氢氧化钠提取的胡敏酸(HAS);富里酸(FA)分为焦磷酸钠提取的富里酸(FAP)和氢氧化钠提取的富里酸(FAS);胡敏素(HM)分为铁结合胡敏素(HMi)、粘粒结合胡敏素(HMc)和不溶性胡敏素(HMr)三个组分,采用红外光谱法对黑土、草甸土以及黑土底土加入大量玉米秸秆培养后腐殖质各组分的结构特征进行研究。腐殖质各组分按Pallo法分组。结果表明:铁结合胡敏素(HMi)、粘粒结合胡敏素(HMc)与胡敏酸(HA)、富里酸(FA)具有相似的光谱特征,但存在明显差异。黑土、草甸土中HMi和HMc的脂族性强于HA和FA;HMi与HMc相比,HMi具有较高的脂族性。黑土中氢氧化钠提取的胡敏酸(HAS)的脂族性强于焦磷酸钠提取的胡敏酸(HAP);NaOH提取的富里酸(FAS)的脂族性强于Na4P2O7提取的富里酸(FAP)。草甸土中HAP的脂族结构较多,而HAS脂族结构相对较少。在培养土中,新形成的FA脂族性强于HA、HMi和HMc组分。新形成的HMc脂族性强于HMi和HMc的脂族性强于HAP,而弱于HAS。     

Probing the molecular weight distributions of non-boiling petroleum fractions by Ag+ electrospray ionization mass spectrometry

This work explores the possibility of Ag+ electrospray ionization mass spectrometry (ESI-MS) to determine the molecular weight distributions of non-boiling petroleum fractions. Information about the molecular weight distributions is needed for fundamental studies on the nature of heavy crude oils and bitumens and for the development of novel recovery and processing methods. The method does not depend on thermal processes for the introduction of the fractions into the gas phase of the mass spectrometer, which is a considerable advantage over most other ionization methods. The Ag+ electrospray mass spectra of the fractions analyzed by using a toluene/methanol/cyclohexane (60:28:12%) solvent system display bimodal distributions in the ranges m/z approximately 300 to approximately 3000 and m/z 3000 to approximately 20,000. The abundances of the high molecular weight peak distributions can be reduced by in-source collisional activation experiments. Comparisons with the results obtained for model heteroatom-containing compounds (molecular weight < 600 Da) and high molecular weight polystyrene standards (up to one million Da) indicate that the majority of the structures in the saturate, naphthenoaromatic and polar aromatic fractions, and a significant portion of the asphaltenes, are small molecules. However, a considerable portion of the asphaltenes and some portion of the other fractions contain high molecular weight structures bound by covalent or strong non-covalent bonds. The results obtained by the Ag+ ESI method in this study for the saturate, aromatic, and polar fractions in a bitumen are in qualitative agreement with published molecular weight average results obtained for Cold Lake bitumen fractions analyzed by conventional gel permeation chromatography and field desorption mass spectrometry. Further work is needed to study the nature of the bonds and the interactions of the molecules in the asphaltene fractions by Ag+ ESI-MS.     

Isolation and seasonal effects on characteristics of fulvic acid isolated from an Australian floodplain river and billabong

Fulvic acids from an Australian floodplain river and billabong were isolated using DEAE and DAX-8 resins, and characterised with the use of size exclusion chromatography and solid-state CP-MAS (13)C NMR spectroscopy. Differences between the two resin isolates were evident. Fulvic acids isolated using DEAE-cellulose had higher apparent M(n) and M(w) values, while the DAX-8 resin showed a slight preference for aliphatic components. Fulvic acids from the river and billabong had the same functional groups present, however, the river fulvic acids had higher apparent M(n) (number average molecular weight) and M(w) values (weight average molecular weight), and were more polydisperse than the billabong fulvic acid. There were no significant changes in the characteristics of the fulvic acid isolated from the river at four sampling times: summer, autumn, winter and spring. In contrast, fulvic acids isolated from a billabong displayed seasonal variation in molecular weights. This work emphasizes the importance in ecological studies of isolation procedure for the operationally defined fulvic acids.     

Factors that affect molecular weight distribution of Suwannee river fulvic acid as determined by electrospray ionization/mass spectrometry

Effects of methylation, molar response, multiple charging, solvents, and positive and negative ionization on molecular weight distributions of aquatic fulvic acid were investigated by electrospray ionization/mass spectrometry. After preliminary analysis by positive and negative modes, samples and mixtures of standards were derivatized by methylation to minimize ionization sites and reanalyzed.Positive ionization was less effective and produced more complex spectra than negative ionization. Ionization in methanol/water produced greater response than in acetonitrile/water. Molar response varied widely for the selected free acid standards when analyzed individually and in a mixture, but after methylation this range decreased. After methylation, the number average molecular weight of the Suwannee River fulvic acid remained the same while the weight average molecular weight decreased. These differences are probably indicative of disaggregation of large aggregated ions during methylation. Since the weight average molecular weight decreased, it is likely that aggregate formation in the fulvic acid was present prior to derivatization, rather than multiple charging in the mass spectra.     

Influence of humic substances on sorption and methylation processes of inorganic- and organo-tin species

The influence of humic substances on sorption and methylation processes for inorganic- and organotin species is presented. Four sediment samples from different locations of the Rivers Elbe, Mulde and Spittelwasser, Germany, with different organotin and humic contents were selected to extract the humic and fulvic acids. The various fractions—the original sediment, the humic acid, the fulvic acid and the residual sediment—were analysed for their organotin content. The individual buyltin species show quite different distribution patterns. Monobutyltin is found mostly associated with humic acids. Dibutyltin shows a nonunique behaviour. At low total organotin content, dibutyltin is found bonded to humic and fulvic acids, whereas at high organotin content dibutyltin is distributed more with the residual sediment. Most of the tributyltin remains in the sediment unextracted; only small quantities of it are in the fulvic acid fraction. Tetrabutyltin is only in the humic acid fraction when it binds to humic matter; it mostly remains in the sediment. General observations indicate that ionic butyltin species bind to fulvic acids whereas the non-polar tetrabutyltin is not found in the fulvic acid fractions in any of the samples. The appearance of monomethyl- and dimethyl-tin species in the humic and fulvic acid fractions after the alkaline extraction was surprising. There is a correlation between the humic content of the sample and the formation of methyltin species. Evidence is provided by experiments that humic substances act as methylation agents.     

Humic substances in surface waters of the Ukraine

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

Investigation on the binding of polycyclic aromatic hydrocarbons with soil organic matter: a theoretical approach

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants of the terrestrial environment that have been designated as Environmental Protection Agency (EPA) Priority Pollutants. In this study, molecular modeling was used to examine the physical and chemical characteristics of soil organic matter (SOM), fulvic acid (FA) and humic acid (HA), as well as their binding interactions with PAHs. The molecular structures of 18 PAHs were built by using the SYBYL 7.0 program and then fully optimized by a semiempirical (AM1) method. A molecular docking program, AutoDock 3.05, was used to calculate the binding interactions between the PAHs, and three molecular structure models including FA (Buffle's model), HA (Stevenson's model) and SOM (Schulten and Schnitzer's model). The pi-pi interactions and H-bonding interactions were found to play an important role in the intermolecular bonding of the SOM/PAHs complexes. In addition, significant correlations between two chemical properties, boiling point (bp) and octanol/water partition coefficient (Log K(ow)) and final docking energies were observed. The preliminary docking results provided knowledge of the important binding modes to FA, HA and SOM, and thereby to predict the sorption behavior of PAHs and other pollutants.     

Effect of some environmental ligands on the sorption of radionuclidesby peat humin

Summary In a previous paper we studied the interaction of the radionuclides ^110mAg, ⁶⁰Co and ⁶⁵Zn with peat humin. These nuclides are among the fission or corrosion products in nuclear reactors. The aim of this paper is to study the effect of certain ligands, which are present in the environment, such as humic acid, fulvic acid, EDTA and urea, on the sorption of these radionuclides by humin. The obtained results indicated that urea has no effect on the sorption of Co and Zn by humin, and only a little in case of Ag. However, the presence of the other ligands (humic acid, fulvic acid or EDTA) leads to different decreases in the sorption of the three nuclides by humin. The results are interpreted in the light of the complex formation between ligands and the metal cations and of the strength of binding of these cations to the humin sorbent. The release of Ag⁺in the presence of different ligands was found to follow the order: humic acid>EDTA>fulvic acid>urea. In the case of both Co²⁺and Zn²⁺, the sequence is changed to be: EDTA>humic acid>fulvic acid>urea, with a higher release in the case of Zn²⁺. The results showed that cobalt is bound more strongly to humin than silver and zinc. The sulphur content of the humic fractions plays a significant role in the competition for silver and zinc.     

Flocculation of humic substances with metal ions as followed by capillary zone electrophoresis

Humic and fulvic acids from various sources have been shown to give different electropherograms by capillary zone electrophoresis (CZE), depending on the pH of the electrolyte. This CZE work is extended here through investigations involving the titration of humic and fulvic acids with Fe(III) and Cu(II) cations. As increasing amounts of these cations were added to the humic substances (HUS), flocculation of metal-humic complexes occurred. This is believed to be caused by binding of the metal cations with negative carboxyl and phenolic sites on the HUS, resulting in a decrease of the repulsive forces that keep the HUS in a conformation more suitable for water solubility. The flocculated complexes were separated from the supernatant by centrifugation, and the supernatants were characterized as to total organic carbon (TOC) content, molecular weight (MW) using gel permeation chromatography, and average electrophoretic mobility (AEM) using CZE. The extent of flocculation correlated with both TOC and quantitative CZE measurements. The MW of the HUS remaining in solution actually decreased, presumably because of precipitation of larger molecules as they became insoluble because of reactions with the metals. Humic acids showed total precipitation of TOC with both metals at a concentration equivalent to their measured acidity. CZE demonstrated that certain fulvic acid fractions (low molecular weight phenolic acids) remained in solution even at high metal concentrations. In summary, changes in electrophoretic behavior of the soluble HUS could be related to changes in charge-to-mass ratios (charge densities) of both humic and fulvic acids with increasing metal cation concentration (neutralization). The copper treated HUS showed changes in their electrophoretic behavior even at low metal concentrations before flocculation, whereas the iron treated HUS flocculated uniformally over the range of added iron without significant changes in AEM. Thus these changes in CZE patterns illustrate different specific binding sites of the HUS for each metal.