Ultrafiltration and determination of Zn- and Cu-humic substances complexes stability constants

This study exhibits that size fractionation of humic substances (HS) and their metal complexes by ultrafiltration is an efficient procedure for simultaneous determination of stability constants. Using sequential-stage ultrafiltration and a radiotracer technique the HS–Cu and HS–Zn complexes studied can gently be size-fractionated and their free metal fractions simply be discriminated. The conditional stability constants Ki obtained for size fractions of these HS metal complexes exhibit a clear molecular size dependence. Accordingly, the highest Ki values (6.6 for Zn and 6.4 for Cu) are found in the HS fractions of >105 kDa. Moreover, the overall stability constants K found for Cu (log K=5.5) and Zn complexes (log K=4.5) of the aquatic HS complexes studied are quite comparable to those reported in the literature.     

Fluorescence sensing of Cu and Hg by a dipyrene ligand involving an excimer-switch off mechanism

A novel dipyrene ligand 1 has been designed which shows intramolecular excimer formation in solution. Its specific interaction with Cu²⁺ or Hg²⁺ leads to the disruption of the excimer and results in a fluorescence-mediated sensing of these ions in a mixed organic-aqueous solution. Apart from steady-state studies, time-resolved fluorescence measurements also reveal that excimer-switch off caused by metal ion coordination leads to the selective detection of these ions.     

A study of complexation thermodynamic of humic acid with cadmium (II) and zinc (II) by Schubert's ion-exchange method

The complexation of humic acid from Azraq Oasis with two heavy metal ions Cd(II) and Zn(II) was investigated at pH 4 and 5 under constant ionic strength of 0.1 and at different temperatures (25, 35, 45, 55 and 65 °C). This investigation was done by using Schubert's ion-exchange equilibrium method, and its modified version.The derived conditional stability constants (log β_n) for these two metal-humate complexes were determined; they formed 1:1 and 1:2 complexes. It was found that the conditional stability constants (log β_n) increased by increasing pH and temperatures for all metal-humate complexes. It was found that the conditional stability constant log β₁ for Cd-humate is bigger than Zn-humate at all the desired temperatures and at pH 4 and 5.The derived constants and their temperature dependences have been used to calculate the corresponding thermodynamic parameters ΔG, ΔH, and ΔS, the results indicate that the stability of these complexes derives from very favorable entropy.     

Capillary electrophoretic separation of humic substances using hydroxyethyl cellulose as a buffer additive and its application to characterization of humic substances in a river water sample

We have developed a concise tool for the investigation of the transition of humic substances in environmental water. The separation of water-soluble humic substances was achieved rapidly and effectively by capillary electrophoresis using a polyacrylamide-coated capillary and a phosphate electrophoretic buffer solution (pH 7.0) containing hydroxyethyl cellulose. The separation mechanism was assessed using the ultrafiltration technique. The effect of the complexation of humic substances with metal ions was studied by using the proposed method. When Fe(III) ions or EDTA was added to the sample solution of fulvic acid, a distinct change in the electropherogram pattern based on the conformational change of fulvic acid was observed. The successful application of the proposed method to the characterization of humic substances in a river water sample was also demonstrated. Figure Addition of Fe(III) ions or EDTA to a solution containing fulvic acid (FA) results in a distinct change in the electropherogram pattern, which reflects the conformational change of FA: this forms the basis for the characterization of humic substances in river water samples     

Novel calix[4]arene-thiacrown ether for selective and efficient extraction of Ba(II), Pb(II), and Hg(II)

A di-ionizable p-tert-butylcalix[4]arene-1,3-thiacrown-5 ether extractant was synthesized. Its cone conformation and polyether ring attachment regioselectivity were verified by NMR spectroscopy. The metal ion-complexing properties of this ligand were evaluated by solvent extractions of metal cations from aqueous solutions into chloroform. The ligand was found to be an efficient extractant with Ba²⁺ selectivity in competitive solvent extraction of alkaline earth metal cations. It also exhibits high extraction ability for Pb²⁺ and for Hg²⁺ in single species solvent extractions.     

Adsorption of humic substances by macro weakly basic ion-exchange resin and their effects on removal of Cu2+ and Pb2+

<正>Adsorption ofhumic,tannic and gallic acids by a macro weakly basic ion-exchange resin JN-01 was studied.The adsorption capacity of this resin for gallic and tannic acids is much higher than that for humie acid,which can be explained on the basis of both their molecular size and ionization degree.Furthermore,humic acid is separated into different components with molecular weight in the range from 2000 Da to 100000 Da by ultra-filter,and their adsorption isotherms on resin JN-01 indicate that humic acid's molecular weight is an important factor which makes significant influence on adsorption.Finally,changes in the amount of Cu~(2+) and Pb~(2+) adsorbed on resin JN-01 as a function of the concentration of each of these three acids were studied.A large increase in the heavy metal ions uptake is observed in the presence of humic substance,such advantages are due to the interactions between the heavy metal ions and the unbound functional groups of the adsorbed organic acids.     

Synthesis,characterization and fluorescence spectra of mononuclear Zn(II), Cd(II) and Hg(II) complexes with 1,10-phenanthroline-5,6-dione ligand

The mononuclear complexes of Zn(II), Cd(II) and Hg(II), [Zn(phen-dione)Cl₂], [Cd(phen-dione)Cl₂] and [Hg(phen-dione)Cl₂], where phen-dione?=?1,10-phenanthroline-5,6-dione, have been synthesized and characterized by elemental analysis and IR, ¹H?NMR and electronic absorption spectroscopies. The ν(C=O) of coordinated phen-dione ligands in these complexes shows that the phen-dione is not coordinated to metal ion from its C=O sites. Electronic spectra of the complexes show two absorption bands for intraligand transitions. These absorption bands show dependence on the dielectric constant of solvents. These complexes exhibit an intense fluorescence band around 545?nm in DMSO when the excitation wavelengths are 200?nm at room temperature.     

Enhancing the microdialysis recovery for sampling of Cu and Ni by incorporating humic acid in the perfusion liquid

A strategy to enhance the microdialysis relative recovery for sampling of Cu and Ni ions is presented. Enhanced recovery was achieved by incorporating humic acid, a binding agent, in the microdialysis perfusion liquid during sampling from a Cu and Ni standard solution mixture. All microdialysis sampling experiments were carried out at room temperature under quiescent conditions using a concentric type of microdialysis probe with an adjustable effective dialysis length. For all metal determinations electrothermal atomic absorption spectrometry was employed. Metal recoveries were shown to be dependent on the membrane molecular weight cut-off, perfusion rate, sample solution pH, perfusion liquid composition as well as perfusion liquid pH. Complete recoveries (100%) of Cu and Ni were obtained by microdialysis sampling using a 10 kDa molecular weight cut-off polysulfone membrane at a flow-rate of 2 μl/min employing a 0.05% (w/v) optimal composition of humic acid incorporated in the perfusion liquid. The optimal sampling pH of humic acid was determined to be 6 where most oxygen containing functional groups are dissociated and available for metal binding. These data have important ramifications for sampling and determination of metal ions in small sample solutions (∼10 ml) at very low concentrations in the ppb range.     

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

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

Ratiometric fluorescence chemodosimeter for mercuric ions through the Hg(II)-mediated propargyl amide to oxazole transformation

A coumarin-based alkyne was developed as a fluorescent chemodosimeter for the selective detection of mercuric ion. The probe showed a highly selective and ratiometric response toward Hg(II) ion over other metal ions with a micromolar level of limit of detection.     

Synthesis,spectral characterization and biological activity of benzofuran Schiff bases with Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) complexes

New Schiff bases have been synthesized from benzofuran-2-carbohydrazide and benzaldehyde, [BPMC] or 3,4-dimethoxybenzaldehyde, [BDMeOPMC]; complexes of the type MLX₂, where M = Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II), L = BPMC or BDMeOPMC and X = Cl, have been prepared. Structures have been elucidated on the basis of elemental analysis, conductance measurements, magnetic properties, spectral studies i.e., ¹H NMR, electronic, ESR and IR studies show that the Schiff bases are bidentate through the azomethine nitrogen and oxygen of the carbonyl. We propose tentative structures for all of these complexes. The antifungal and antibacterial activities of the ligands and their metal complexes have been screened against fungi Aspergillus niger and Aspergillus fumigatus and against bacteria Escherichia coli and S. aurious.     

Spectrophotometric determination of stability constants of Ni(II) and Cu(II) complexes with N-substituted hydrazinedithiocarboxylic acids

The stability constants of Ni(II) complexes with 2-methylhydrazinedithio-carboxylic and 3,3-dimethylhydrazinedithiocarboxylic acids and Ni(II) and Cu(II) complexes with 3-methyl-3-phenylhydrazinedithiocarboxylic acid have been determined in aqueous solution at 25°C and I = 0.01 M. The Bjerrum method of corresponding solutions has been applied, revealing the simultaneous presence of 1:1 and 1:2 complexes in solution.     

A rapid method for the detection of humic acid based on the poly(thymine)-templated copper nanoparticles

A label-free fluorescent method for sensitive detection of humic acid based on poly(thymine)-templated copper nanoparticles is reported.     

Combining electrophoresis with detection under ultraviolet light and multiple ultrafiltration for isolation of humic fluorescence fractions

Polyacrylamide gel electrophoresis of chernozem soil humic acids (HAs) followed by observation under UV (312 nm) excitation light reveals new low molecular weight (MW) fluorescent fractions. Ultrafiltration of HAs sample in 7 M urea on a membrane of low nominal MW retention (NMWR, 5 kDa) was repetitively used for separation of fluorescent and non-fluorescent species. Thirty ultrafiltrates and the final retentate R were obtained. Fluorescence maxima of separate ultrafiltrates were different and non-monotonously changed in the range of 475–505 nm. Fluorescence maxima of less than 490 nm were detected only in the four first utrafiltrates. For further physical–chemical analyses all utrafiltrates were combined into a fraction called UF < 5 (NMW < 5 kDa). Retentate R demonstrated very weak fluorescence under 270 nm excitation, while fluorescence intensity of UF < 5 was about six times higher than of the bulk HAs. Fraction UF < 5 was further ultrafiltrated on membranes of MNWR 3 kDa and 1 kDa, yielding three subfractions UF3-5, UF1-3 and UF < 1 with NMW 3–5 kDa, 1–3 kDa and <1 kDa, respectively. The validation of the UF procedure was performed by size exclusion chromatography on Sephadex G-25 column. The fluorescence maxima were found to be at 505, 488 and 465 nm for UF3-5, UF1-3 and UF < 1, respectively, with increasing of fluorescence intensity from UF3-5 to UF1-3 to UF < 1 fraction. EPR analysis showed that the amount of free radicals was the largest in retentate R and drastically decreased in fluorescent ultrafiltrates. The results demonstrate that more than one fluorophore is present in chernozem soil HAs complex.     

Cu(II)-Cu(Hg)体系在蔗糖水溶液中的电化学行为

糖及其聚合物有着重要的生理功能,研究它们的热力学性质具有重要的意义[1 5]。本文考察Cu(II)在蔗糖水溶液中的电化学行为,获得了一些重要信息。1　实验部分使用试剂均为分析纯。蔗糖(北京化学试剂总厂)在343K时真空干燥6h。LiClO4(上海化学试剂总厂)在403K时减压干燥后保存在干燥器中。硝酸铜(北京化学试剂总厂)。所用溶液均采用重量法用二次蒸馏水配制。配好的溶液测定前用通过焦性没食子酸溶液的氮气来除氧。测定温度为298±1K。极谱和伏安测定在微机电化学分析系统(LK98A型)上进行,该机由天津市兰力科化学电子高技术有限公司制…     

Potentiometric studies on the complexation of copper(II) by phenolic acids as discrete ligand models of humic substances

Studies on the complexation of copper(II) by phenolic acids, as ligand models of humic substances were done by potentiometry. The acids under study were: 3,4-dihydroxyhydrocinnamic acid or hydrocaffeic acid (1), 3,4-dihydroxyphenylacetic acid (2) and 3,4-dihydroxybenzoic acid or protocatechuic acid (3). Acidity constants of the ligands and the formation constants of metal-ligand complexes were evaluated by computer programs. The carboxylic group of the phenolic acids has different pK_a1 values, being the dissociation constants intrinsically related with the distance between the function and the aromatic nucleus. The results obtained allow concluding that acidity constants of the catechol moiety of the compounds are similar with pK_a2 and pK_a3 values between 9.47-9.41 and 11.55-11.70. The complexation properties of the three ligands towards copper(II) ion are quite similar, being the species found not different either in nature or stability. Although the model ligands have some structural differences no significant differences were found in their complexation properties towards copper(II). So, it can be postulated that complexation process is intrinsically related with the presence of a catechol group.     

The influence of the cyclopeptide sequence on its coordination abilities towards Cu(II)

The binding abilities of three novel cyclohexapeptides with three histidyl residues are presented. The analysis of the potentiometric and spectroscopic results, together with the theoretical calculations, allow the characterization of the coordination abilities of c(GlyHisArgHisHisGly), c(GlyHisArgHisGlyHis), c(GlyHisArgGlyHisHis) towards copper(II) ions and the impact of the peptide sequence on the efficiency in Cu(II) binding, and the type of formed complexes is also presented.     

Developing a genetically encoded green fluorescent protein mutant for sensitive light-up fluorescent sensing and cellular imaging of Hg(II)

Hg(II) is well-known for quenching fluorescence in a distance dependent manner. Nevertheless, when we exposed the fluorophore of a green fluorescent protein (GFP) toward Hg(II), through H148C mutation, the GFP fluorescence could be “lighted up” by Hg(II) down to sub-nM level. The detection linear range is 0.5–3.0 nM for protein solutions at 8.0 nM. The GFPH148C protein displayed a promising selectivity toward Hg(II) and also the cellular imaging capacity. Spectra measurements suggested that the ground-state redistribution of protein contributed to the fluorescence enhancement, which was found not limited to Hg(II), and thus presented an opening for building a pool of GFP-based chemosensors toward other heavy metal ions.     

Posidonomia shales (FRG) and their relation to humic substances

Summary We have used capillary gas chromatography/mass spectrometry to characterize extracts of Posidonomia shales and of fossil wood (gagat) found in these shales. Samples were obtained from Dotternhausen oil shale formation (FRG) belonging to LIAS-epsilon (Toarcien). Identified components are n-alkanes (C₇ to C₂₇), isoprenoid hydrocarbons (like pristane and phytane) and cycloalkanes with 6 to 9 carbon atoms. Aromatic hydrocarbons were also found in the low boiling fraction of extracts of fossil wood. To obtain more detailed information about genesis and maturity of the Dotternhausen sediments we also applied Cross Polarisation Magic Angle Spin-¹³C-Nuclear Magnetic Resonance (CP/MAS-¹³C-NMR) spectroscopy. We compared the solid state spectra of fossil wood out of Posidonomia shales with the solid state¹³C-NMR-spectra of humic substances of different age and different origin. We found that the solid state spectra of humic substances of increasing age and the solid state spectra of fossil wood show striking similarity. The results are discussed with respect to the maturity of the Dotternhausen sediments and the genesis of fossil fuels where humic substances may act as intermediates. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Spectral and temporal luminescent properties of Eu(III) in humic substance solutions from different origins

Although a high heterogeneity of composition is awaited for humic substances, their complexation properties do not seem to greatly depend on their origins. The information on the difference in the structure of these complexes is scarce. To participate in the filling of this lack, a study of the spectral and temporal evolution of the Eu(III) luminescence implied in humic substance (HS) complexes is presented. Seven different extracts, namely Suwannee River fulvic acid (SRFA) and humic acid (SRHA), and Leonardite HA (LHA) from the International Humic Substances Society (USA), humic acid from Gorleben (GohyHA), and from the Kleiner Kranichsee bog (KFA, KHA) from Germany, and purified commercial Aldrich HA (PAHA), were made to contact with Eu(III). Eu(III)-HS time-resolved luminescence properties were compared with aqueous Eu³⁺ at pH 5. Using an excitation wavelength of 394 nm, the typical bi-exponential luminescence decay for Eu(III)-HS complexes is common to all the samples. The components τ₁ and τ₂ are in the same order of magnitude for all the samples, i.e., 40 ≤ τ₁ (μs) ≤ 60, and 145 ≤ τ₂ (μs) ≤ 190, but significantly different. It is shown that different spectra are obtained from the different groups of samples. Terrestrial extract on the one hand, i.e. LHA/GohyHA, plus PAHA, and purely aquatic extracts on the other hand, i.e., SRFA/SRHA/KFA/KHA, induce inner coherent luminescent properties of Eu(III) within each group. The ⁵D₀ → ⁷F₂ transition exhibits the most striking differences. A slight blue shift is observed compared to aqueous Eu³⁺ (λ_max = 615.4 nm), and the humic samples share almost the same λ_max ≈ 614.5 nm. The main differences between the samples reside in a shoulder around λ ≈ 612.5 nm, modelled by a mixed Gaussian–Lorentzian band around λ ≈ 612 nm. SRFA shows the most intense shoulder with an intensity ratio of I_612.5/I_614.7 = 1.1, KFA/KHA/SRHA share almost the same ratio I_612.5/I_614.7 = 1.2–1.3, whilst the LHA/GohyHA/PAHA group has a I_612.5/I_614.5 = 1.5–1.6. This shows that for the two groups of complexes, despite comparable complexing properties, slightly different symmetries are awaited.