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1.
《Applied Geochemistry》2003,18(10):1573-1582
The effects of the ionic strength (maintained by LiCl, NaCl or KCl) and Ca2+ and Mg2+ concentration on the coagulation of purified humic acids (HA) was studied. Solutions of known ionic strengths, pcH, Ca2+ and Mg2+ concentrations were prepared with HA and filtered to obtain the fraction with a size smaller than 100 kD. After a 50 day storage, samples of these solutions were filtered again (100 kD) and the total organic C (TOC) of the filtered solutions measured. The HA coagulation increased with salt concentration, with the cationic charge, and for cations of the same charge, with the cationic charge density. The coagulation decreased for pcH values of 4 to 7–8 in the absence of and presence of Mg2+ and Ca2+. In the absence of the divalent cations, the coagulation has a constant value for pcH>8, but, in the presence of Mg2+ and Ca2+, increases at pcH values greater than 9. The coagulation of humic materials occurs whether the samples are exposed to light or kept in the dark, although the coagulation kinetics are slower for the samples kept in the dark. The size distribution of size-fractionated humic solutions changes over time to a size distribution similar to that of the original humic solution before it was size-fractionated. The results are explained by the DLVO theory.  相似文献   

2.
Framboidal pyrite has been prepared by precipitation of oxyhydroxides of iron, peptized by humic acids using a solution of Na-sulphate or hydrogen sulphide, spherical grains of elemental sulphur being present. By peptization of iron oxyhydroxides using humic acids, a stable negatively charged colloidal system arises. At room temperature and a pressure of 1 atm., and at pH widely ranging between 6.5–7.5, sulphidation of this colloidal system gives rise to a monodispersive sulphidic sol whose stability depends on the concentration of iron in the solution, the amount of humic acids and the presence of electrolytes. In the presence of spherical grains of sulphur, arising by rapid oxidation (acidification) of Na2S solution or a saturated solution of hydrogen sulphide, particles of the sulphidic sol precipitate on their surface and the grains become gradually replaced by sulphides of iron. At the same time, framboids of an average diameter of 14 μm are generated.  相似文献   

3.
Soil interstitial waters in the Green Lakes Valley, Front Range, Colorado were studied to evaluate the capacity of the soil system to buffer acid deposition. In order to determine the contribution of humic substances to the buffering capacity of a given soil, dissolved organic carbon (DOC) and pH of the soil solutions were measured. The concentration of the organic anion, Ai−, derived from DOC at sample pH and the concentration of organic anion, Ax− at the equivalence point were calculated using car☐yl contents from isolated and purified humic material from soil solutions. Subtracting Ax− from Ai− yields the contribution of humic substances to the buffering capacity (Aequiv.−). Using this method, one can evaluate the relative contribution of inorganic and organic constituents to the acid neutralizing capacity (ANC) of the soil solutions. The relative contribution of organic acids to the overall ANC was found to be extremely important in the alpine wetland (52%) and the forest-tundra ecotone (40%), and somewhat less important in the alpine tundra sites (20%). A failure to recognize the importance of organic acids in soil solutions to the ANC will result in erroneous estimates of the buffering capacity in the alpine environment of the Front Range, Colorado.  相似文献   

4.
利用三维荧光激发.发射光谱(3DEEMs)及荧光偏振法研究了3例腐殖酸和1例湖泊溶解有机物(DOM)在不同腐殖酸浓度、离子强度和pH条件下的荧光光谱特性.实验结果表明,随着浓度增大,各腐殖酸样的荧光强度增大,其中垃圾渗滤液腐殖酸和Pahokee泥炭腐殖酸的荧光峰出现红移.随着浓度进一步增大,腐殖酸的荧光偏振值增大,由此推断在此浓度范围内腐殖酸由于分子间的排斥作用使其构型出现伸展.离子强度增大导致腐殖酸及阿哈湖DOM的荧光强度降低.随着氯化钾(KCI)浓度增大,Fluka腐殖酸的荧光峰A蓝移,荧光峰B的荧光偏振值出现减小,推测是由于静电中和作用使其荧光基团发生卷曲造成的.离子强度对其余腐殖酸样和阿哈湖DOM的其他荧光特性没有明显的影响.总的来说,pH值的变化对腐殖酸和湖泊DOM的荧光特征的影响是很明显的.随着pH值增大,腐殖酸和湖泊DOM的荧光强度增强.而pH值减小时,Fluka腐殖酸和Pahokee泥炭腐殖酸的荧光峰(A峰)蓝移,当pH值降到5时,Fhka腐殖酸的荧光峰突然红移到最大,随后又继续蓝移;垃圾渗滤液腐殖酸和阿哈湖DOM的荧光峰位无明显的漂移.所有样品的荧光偏振值都减小(但阿哈湖DOM的A峰变化不大),但在pHi≤5时又增大,这种现象表明随着pH值降低,腐殖酸和湖泊DOM中有机大分子发生卷曲,但在pH≤5时由于羧基的质子化又以平面伸展构型出现在溶液中.  相似文献   

5.
Physiological responses and metal accumulation in Vallisneria spiralis L. exposed to copper and cadmium contaminated sediment were examined at different metal concentrations and the influence of humic acids on copper and cadmium accumulation was also studied. The plants of V. spiralis accumulated high amount of copper and cadmium. The maximum accumulation of 396 and 114 mg kg−1 DW copper were found in the roots and shoots, respectively, at 614 mg kg−1 DW after 21 days’ copper exposure; they were 63.8 and 48.0 mg kg−1 DW for cadmium at 88.69 mg kg−1 DW. The plants showed decrease in chlorophyll content with the increasing concentration of copper/cadmium in sediment. With addition of humic acids from 3.09 to 7.89 g kg−1 DW, both copper and cadmium accumulation in V. spiralis were significantly inhibited (p < 0.01). The cadmium concentrations of roots and shoots of plant decreased 26.4–50.3 and 14.3–33.0% under cadmium treatments, respectively; copper accumulation decreased much more with 44.0–77.0 and 35.0–62.7%, respectively. It was concluded that V. spiralis appeared to be an ideal candidate for the phytoremediation of copper and cadmium polluted sediments, and humic acids had an important role in regulating copper and cadmium bioavailability and toxicity in sediments.  相似文献   

6.
A dialysis procedure was used to assess the distribution coefficients of ∼50 major and trace elements (TEs) between colloidal (1 kDa–0.22 μm) and truly dissolved (<1 kDa) phases in Fe- and organic-rich boreal surface waters. These measurements allowed quantification of both TE partitioning coefficients and the proportion of colloidal forms as a function of solution pH (from 3 to 8). Two groups of elements can be distinguished according to their behaviour during dialysis: (i) elements which are strongly associated with colloids and exhibit significant increases of relative proportion of colloidal forms with pH increase (Al, Ba, Cd, Co, Cr, Cu, Fe, Ga, Hf, Mn, Ni, Pb, rare earth elements (REEs), Sr, Th, U, Y, Zn, Zr and dissolved organic C) and (ii) elements that are weakly associated with colloids and whose distribution coefficients between colloidal and truly dissolved phases are not significantly affected by solution pH (As, B, Ca, Cs, Ge, K, Li, Mg, Mo, Na, Nb, Rb, Sb, Si, Sn, Ti, V). Element speciation was assessed using the Visual MINTEQ computer code with an implemented NICA-Donnan humic ion binding model and database. The model reproduces quantitatively the pH-dependence of colloidal form proportion for alkaline-earth (Ba, Ca, Mg, Sr) and most divalent metals (Co, Cd, Mn, Ni, Pb, Zn) implying that the complexation of these metals with low molecular weight organic matter (<1 kDa fraction) is negligible. In contrast, model prediction of colloidal proportion (fraction of 1 kDa–0.22 μm) of Cu2+ and all trivalent and tetravalent metals is much higher than that measured in the experiment. This difference may be explained by (i) the presence of strong metal-binding organic ligands in the <1 kDa fraction whose stability constants are several orders of magnitude higher than those of colloidal humic and fulvic acids and/or (ii) coprecipitation of TE with Fe(Al) oxy(hydr)oxides in the colloidal fraction, whose dissolution and aggregation controls the pH-dependent pattern of TE partitioning. Quantitative modeling of metal – organic ligand complexation and empirical distribution coefficients corroborate the existence of two colloidal pools, formerly reported in boreal surface waters: “classic” fulvic or humic acids binding divalent transition metals and alkaline-earth elements and large-size organo-ferric colloids transporting insoluble trivalent and tetravalent elements.  相似文献   

7.
Due to the widespread contamination of groundwater resources with arsenic (As), controls on As mobility have to be identified. In this study we focused on the distribution of As in the dissolved, colloidal and particulate size fraction of experimental solutions rich in ferric iron, dissolved organic matter (DOM) and As(V). Size fractions between <5 kDa and >0.2 μm were separated by filtration and their elemental composition was analyzed. A steady-state particle size distribution with stable element concentration in the different size classes was attained within 24 h. The presence of DOM partly inhibited the formation of large Fe-(oxy)hydroxide aggregates, thus stabilized Fe in complexed and colloidal form, when initially adjusted molar Fe/C ratios in solution were <0.1. Dissolved As concentrations and the quantity of As bound to colloids (<0.2 μm) increased in the presence of DOM as well. At intermediate Fe/C ratios of 0.02-0.1, a strong correlation between As and Fe concentration occurred in all size fractions (R2 = 0.989). At Fe/C ratios <0.02, As was mainly present in the dissolved size fraction. These observations indicate that As mobility increased in the presence of DOM due to (I) competition between As and organic molecules for sorption sites on Fe particles; and (II) due to a higher amount of As bound to more abundant Fe colloids or complexes <0.2 μm in size. The amount of As contained in the colloidal size fractions also depended strongly on the initial size of the humic substance, which was larger for purified humic acids than for natural river or soil porewater samples. Arsenic in the particle size fraction >0.2 μm additionally decreased in the order of pH 4 ? 6 > 8. The presence of DOM likely increases the mobility of As in iron rich waters undergoing oxidation, a finding that has to be considered in the investigation of organic-rich terrestrial and aquatic environments.  相似文献   

8.
Aqueous solutions of increasing pH (7.0, 10.6 and 12.6) were used to extract exhaustively the organic matter (OM) from a pelo-stagnogley (heavy clay) soil in long term cultivation. OM yield was 1.7 times greater when the extracts were processed using an XAD-8 and XAD-4 resin-in-tandem procedure than that from the procedure of the International Humic Substances Society (IHSS). The substantial difference can be attributed to the amount retained by the XAD-4 resin, which is lost in the IHSS process. Elemental, δ13C, δ15N, cation exchange capacity, neutral sugars, amino acids and solid state CPMAS 13C NMR analyses indicated significant, but rational similarities and differences between the various fractions isolated. There was strong NMR evidence for material derived from lignin in all the humic and fulvic acid isolates. The signals were attenuated in the more transformed/oxidized fractions isolated at lower pH. Novel humic acid fractions enriched in carbohydrate/peptide functionalities were isolated from the more hydrophobic extracts at pH 10.6 and 12.6. Isolates from XAD-4, of microbial origin, were enriched in neutral sugars but not in amino acids, and had minimal aromaticity. Components isolated from the cultivated soil were broadly similar to those from a comparable soil in long term grassland. The compositions of fractions isolated from the drainage water were similar to those extracted from the soil but had higher carboxyl content. The amount and composition of the various organic fractions in grassland and the continuously cropped soil are discussed in terms of their potential to contribute to carbon sequestration by soil under similar management regimes.  相似文献   

9.
Colloids act as vectors for pollutants in groundwater, thereby creating a series of environmental problems. While managed aquifer recharge plays an important role in protecting groundwater resources and controlling land subsidence, it has a significant effect on the transport of colloids. In this study, particle size and zeta potential of colloidal humic acid (HA) have been measured to determine the effects of different hydrochemistry conditions. Column experiments were conducted to examine the effects on the transport of colloidal HA under varying conditions of pH (5, 7, 9), ionic strength (<0.0005, 0.02, 0.05 M), cation valence (Na+, Ca2+) and flow rate (0.1, 0.2, 0.4 ml/min) through collectors (glass beads) to model the properties and quality of artificial recharge water and changes in the hydrodynamic field. Breakthrough curves showed that the behavior of colloidal HA being transported varied depending on the conditions. Colloid transport was strongly influenced by hydrochemical and hydrodynamic conditions. With decreasing pH or increasing ionic strength, a decrease in the peak effluent concentration of colloidal HA and increase in deposition could be clearly seen. Comparison of different cation valence tests indicated that changes in transport and deposition were more pronounced with divalent Ca2+ than with monovalent Na+. Changes in hydrodynamic field (flow rate) also had an impact on transportation of colloidal HA. The results of this study highlight the need for further research in this area.  相似文献   

10.
The ultrafiltration of solutions of well characterized samples of fulvic and humic acids or their salts, using two different techniques, show that these materials are retained by commercial ultrafiltration membranes with molecular weight cut-off values far higher than the reported molecular weights of fulvic or humic acid. The lower molecular weight fulvic acid or its Na+ -salt is retained even better than the higher molecular weight Na+-salt of humic acid. Both stirred cell and hollow fiber techniques can be employed to concentrate or desalt solutions of these humic materials, with relatively small solute losses. Very high simple electrolyte backgrounds (above 1 M) lower the performance of a given membrane considerably, moderate concentrations of simple electrolyte do not influence the ultrafiltration efficiency.  相似文献   

11.
Humic substances (HS) were isolated from Penwhirn Reservoir (PR) and Esthwaite Water (EW) and their removal from solution by centrifugation was studied as a function of pH, humic concentration and molecular weight, and CaCl2 concentration. Large amounts (up to 50%) of PR HS could be removed but only small amounts (? 3%) of EW HS. At pH ? 5 removal of PR HS by Ca2+ can be explained satisfactorily in terms of decreases in humic solubilities induced by complexation with the cation. However, removal induced by protonation of the PR HS is unusual in that it decreases with increasing humic concentration.The results suggest that PR HS comprise a range of molecules differing in solubility, with the high-molecular-weight (40,000) components being the least soluble. The EW HS consist of molecules of weight-average molecular weight 5000 and resemble similarly sized PR HS in that they remain unaggregated in solution even when highly complexed with Ca2+.  相似文献   

12.
The influence of humic acids (HA) on the retention of Th(IV) onto the surface of Fe oxides has been investigated. Thorium (IV) is here considered as an analogue of tetravalent radionuclides (Zr, Hf, U, Np, Pu). Hematite (α–Fe2O3) and gœthite (α–FeOOH) have been chosen as model phases because of their widespread presence in the earth's crust. Retention experiments were performed by batch procedure at constant ionic strength and varying pH in the range 2–10; the HA concentration varied in the range 1–100 mg l−1. Compared with the former data obtained on the retention of Th(IV) with the same hematite sample free of HA, the study of a ternary system (i.e. hematite–HA–Th), clearly shows the influence of HA on the retention mechanisms of Th(IV) even in neutral to slightly alkaline medium. In particular, it is illustrated that the retention of Th(IV) onto Fe oxides closely depends upon the ratio between humic and surface (Fe oxide) sites. This ratio has to be greater than a critical value in order to impede the sorption of Th(IV).  相似文献   

13.
《Applied Geochemistry》2000,15(2):133-139
The sorption of Yb3+, UO2+2, Zn2+, I− and SeO2−3 onto Al2O3, Fe2O3 and SiO2 were determined by a batch technique in the presence and absence of fulvic acids. The effects of fulvic acid on sorption were compared. The existing general consensus, that humic substances tend to enhance metal cation sorption at low pH, reduce metal cation sorption at high pH and reduce inorganic anion sorption between pH values 3 to 10, was generally shown to be true. However, in this work many exceptions to the general consensus were found. The study indicated that the effect of humic substances on sorption of inorganic cations or anions depends not only on pH, but also on the nature of the oxide, the nature of humic substance, fractionation of the humic substance by sorption, the relative strength of complexes of both soluble and sorbed humic substances, the extent of surface coverage by humic substance, the initial concentration of humic substance and the inorganic electrolyte composition.  相似文献   

14.
Analogue models often require that materials with specific physical properties be engineered to satisfy scaling conditions. To achieve this goal we investigate the rheology of aqueous solutions of Natrosol 250 HH, a rheology modifier employed in various industries to thicken viscous solutions. We report the rheological properties as functions of the concentration and temperature and discuss the advantages and limitations of these materials in view of their use in analogue modelling experiments. The solutions are linear visco-elastic for low stresses (or strain-rates), becoming shear-thinning for larger stresses. For the typically slow analogue experiments of tectonics, the solutions can be considered linear visco-elastic with a Maxwell relaxation time much smaller than the characteristic observation time. This simplification is even more appropriate when the solutions are employed at temperatures higher than 20 °C, since the solutions then display a behaviour that is more viscous, less elastic at the same shear-rate, while the Newtonian viscosity reduces and the shear-rate limit between Newtonian and shear-thinning behaviours increases. The Newtonian viscosity is shown to increase non-linearly with concentration and decrease non-linearly with temperature. With concentrations between 0 and 3% and temperature between 20 and 40 °C, the viscosity varied between 10−1 and 4000 Pa s, while the density remained close to the density of water. Natrosol 250 HH thus offers the possibility to control the viscosity of a solution without significantly affecting the density, thereby facilitating the design and setup of analogue experiments.  相似文献   

15.
The naturally abundant nitrogen in soil and aquatic NOM samples from the International Humic Substances Society has been characterized by solid state CP/MAS 15N NMR. Soil samples include humic and fulvic acids from the Elliot soil, Minnesota Waskish peat and Florida Pahokee peat, as well as the Summit Hill soil humic acid and the Leonardite humic acid. Aquatic samples include Suwannee River humic, fulvic and reverse osmosis isolates, Nordic humic and fulvic acids and Pony Lake fulvic acid. Additionally, Nordic and Suwannee River XAD-4 acids and Suwannee River hydrophobic neutral fractions were analyzed. Similar to literature reports, amide/aminoquinone nitrogens comprised the major peaks in the solid state spectra of the soil humic and fulvic acids, along with heterocyclic and amino sugar/terminal amino acid nitrogens. Spectra of aquatic samples, including the XAD-4 acids, contain resolved heterocyclic nitrogen peaks in addition to the amide nitrogens. The spectrum of the nitrogen enriched, microbially derived Pony Lake, Antarctica fulvic acid, appeared to contain resonances in the region of pyrazine, imine and/or pyridine nitrogens, which have not been observed previously in soil or aquatic humic substances by 15N NMR. Liquid state 15N NMR experiments were also recorded on the Elliot soil humic acid and Pony Lake fulvic acid, both to examine the feasibility of the techniques, and to determine whether improvements in resolution over the solid state could be realized. For both samples, polarization transfer (DEPT) and indirect detection (1H–15N gHSQC) spectra revealed greater resolution among nitrogens directly bonded to protons. The amide/aminoquinone nitrogens could also be observed by direct detection experiments.  相似文献   

16.
The present work investigated the adsorption and mobility (desorption) of Sb(V) on kaolinite using batch experiments. The adsorption of Sb(V) on kaolinite was studied as a function of contact time, pH, ionic strength, humic acid (HA), initial Sb(V) concentration and temperature. Kinetic studies suggest that the equilibrium is achieved within 24 h. The adsorption of Sb(V) was strongly affected by changes in I at low ionic strength and unaffected at high ionic strength. The adsorption is weakly dependent on the presence of humic acid, but is strongly dependent on pH. Within the range tested, the optimal pH for Sb(V) adsorption is 3.6, and close to 75% removal can be achieved. Desorption is dependent on the original suspension pH. The addition sequence of Sb(V)/HA do not influence the adsorption of Sb(V) on kaolinite. The adsorption data fit both the Freundlich and Langmuir isotherm. The thermodynamic parameters (ΔH 0, ΔS 0 and ΔG 0) were calculated from the temperature dependence, and the results suggest the endothermic and spontaneous nature of the process.  相似文献   

17.
The role of aluminum and silica in the formation of colloids during granodiorite weathering was studied on the basis of long-term experiments in batch reactors. Rock samples were dissolved in un-buffered solutions of initial pH 3.2, 5.4, and 9.9 at ambient conditions for 500 days. During weathering, extremely high supersaturation with respect to various secondary solids was attained in the solutions. Consequently, new solids, part of which was conserved in solutions as colloids, condensed. The mean concentrations of colloidal Si reached values of 70, 50, and 48 mol 1–1 in the alkaline, neutral, and acid solutions, respectively. The mean concentrations of colloidal Al, reached values of 34, 22, and 12 mol 1–1 in the alkaline, neutral, and acid solutions, respectively. The concentration of colloids gradually decreased after 200-400 days of experiment. This phenomenon was interpreted as being due to the competition between homogeneous nucleation and crystal growth. At the initial stages of the experiments, the colloidal species (predominantly colloidal Al) comprised a large proportion of the total amounts of aqueous species. Their share, however, decreased with time. The molar Al/Si-ratios of colloids were as high as 2–2.5 at the early stages of the experiment. After 250–300 days of experiments, on the other hand, these ratios decreased to values of about 0.5 in both the neutral and alkaline solutions and to a value of 0.15 in the acid solution. The evolution of colloids was consistent with the evolution of secondary solids in the sequence Al-hydroxides – clay minerals (illite, chlorite), in both the neutral and alkaline solutions. In acid solutions, the evolution of Al/Si-colloids was influenced by the presence of sulfate ion and Al-sulfate precipitation. Besides Al and Si, other elements, in particular Ca or Mg as a major component and Na, K, P, S, and Cl as minor components, readily participated in the formation of colloids.  相似文献   

18.
Distribution of colloidal trace metals in the San Francisco Bay estuary   总被引：11，自引：0，他引：11  
The size distribution of trace metals (Al, Ag, Cd, Cu, Fe, Mn, Ni, Sr, and Zn) was examined in surface waters of the San Francisco Bay estuary. Water samples were collected in January 1994 across the whole salinity gradient and fractionated into total dissolved (<0.2 μm colloidal (10 KDa–0.2 μm) and < 10 kDa molecular weight phases. In the low salinity region of the estuary, concentrations of colloidal A1, Ag, and Fe accounted for ≥84% of the total dissolved fraction, and colloidal Cu and Mn accounted for 16–20% of the total. At high salinities, while colloidal Fe was still relatively high (40% of the dissolved), very little colloidal Al, Mn, and Cu (<10%) and no colloidal Ag was detectable. Colloidal Zn accounted for <3% of the total dissolved along the estuary, and colloidal Ni was only detectable (<2%) at the river endmember. All of the total dissolved Cd and Sr throughout the estuary consisted of relatively low molecular weight (<10 kDa) species. The relative affinity of metals for humic substances and their reactivity with particle surfaces appear to determine the amounts of metal associated with colloids. The mixing behavior of metals along the estuary appears to be determined by the relative contribution of the colloidal phase to the total dissolved pool. Metals with a small or undetectable colloidal fraction showed a nonconservative excess (Cd, Cu, Ni, and Mn) or conservative mixing (Sr) in the total dissolved fraction, relative to ideal dilution of river water and seawater along the estuary.

The salt-induced coagulation of colloidal A1, Fe, and Cu is indicated by their highly nonconservative removal along the salinity gradient. However, colloidal metals with low affinity for humic substances (Mn and Zn) showed conservative mixing behavior, indicating that some riverine colloids are not effectively aggregated during their transport to the sea. While colloidal metal concentrations correlated with dissolved organic carbon, they also covaried with colloidal Al, suggesting that colloids are a mixture of organic and inorganic components. Furthermore, the similarity between the colloidal metal:A1 ratios with the crustal ratios indicated that colloids could be the product of weathering processes or particle resuspension. Distribution coefficients for colloidal particles (Kc) and for large, filter-retained particles (Kd) were of the same magnitude, suggesting similar binding strength for the two types of particles. Also, the dependence of the distribution coefficients on the amount of suspended particulate matter (the so-called particle concentration effect) was still evident for the colloids-corrected distribution coefficient (Kp+c) and for metals (e.g., Ni) without affinity for colloidal particles.  相似文献   


19.
Nitrogen immobilization in soils and sediments involving the preservation of peptides is an important yet not well-understood process. Several hypotheses have been proposed for the preservation of peptides in these systems; however, to date, there is no direct molecular-level evidence for any one of several hypotheses. In this study, a synthesized peptide with 15N-labeled amino acid residues was utilized to examine the mechanism by which humic substances from a peat might chemically interact with peptides to induce preservation. Two-dimensional 15N-1H HSQC NMR experiments were performed to evaluate the bonding and nonbonding interactions between 15N-labeled peptide and an Everglades peat humic acid. The observed changes in cross peaks provide the first direct spectroscopic evidence for what we believe to be covalent binding between these substances. Noncovalent interactions between the 15N-labeled peptides and humic acid molecules are also observed in the spectra. Quinone structures in humic acids are suggested to be the important reactive groups, based on reaction of the labeled peptide with a model quinone which shows similar nitrogen-proton correlated peak patterns as is observed in the HSQC NMR spectra of humic acids reacted with the peptide. The Michael reaction with quinone structures is proposed, and this type of reaction provides a mechanism that is consistent with previous observation for the chemistry of sedimentary nitrogen species.  相似文献   

20.
13C and 1H NMR spectra were obtained for humic acids isolated from marine sediments. NMR shows great promise in identifying structural components of humic acids as some new and interesting structural features are identified. Aliphatic structures were found to constitute a much larger fraction of humic acids than previously thought, and they appeared to be highly branched. Although the aromatic content of terrestrial humic acid was found to be lower than expected, the aromaticity appears to be a specific discriminator of terrestrial/aquatic source types. A humic acid isolated from an anoxic algal sapropel was found to be composed predominantly of polyuronic acids and different than other aquatic sedimentary humic substances.  相似文献   

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