Mechanochemical modification of peat humic acids

It was demonstrated that the mechanochemical modification of humic acids in the presence of iron oxyhydroxides facilitated the occurrence of solid-phase reactions due to an increase in the concentrations of phenol, carboxyl, and methoxy groups and quinoid fragments. The modified humic acids possessed an increased catalytic activity caused by the presence of quinoid fragments, phenol hydroxyls, and the humic complexes of transition metals.     

Valency changes of metal ions in the interaction with humic acids

On the basis of the interaction of humic acids with metallic ions, taking into account literature references and the author's experimental results, humic acids have been placed within the range of reversible redox systems. The reversible redox-system character of humic acids is illustrated and discussed in both laboratory and natural circumstances.     

Variation of the metal complexing ability of humic acids with coal rank

The variation of the metal complexing ability of humic acids with the rank of the parent coal was investigated by determining the conditional stability constants of complexes formed between cupric ions and humic acids from several coals. Humic acids were extracted from four Spanish coals varying in rank from peat to subbituminous coal. The stability constants were determined at pH 5.0 and μ = 0.1 by a modified version of Schubert's ion exchange method. The stability of the metal-humic acid bonds decreases with the rank of parent coal. The stoichiometry of the complexes tends to 1:1 with increasing coalification of humic acids. The influence of oxidative conditions of extraction on the conditional stability constants of complexes was also examined and it was found that they do not affect significantly the elemental composition or the metal complexing ability of regenerated humic acids.     

含金属离子赖氨酸水溶液的萃取分离

采用二(2-乙基己基)磷酸(P204)作萃取剂,航空煤油作稀释剂,对含有钙、镁、钠、钾等金属离子的赖氨酸水溶液进行萃取,以蒸馏水作为反萃取剂对有机相进行反萃取分离实验.结果表明,原料液初始pH值在4～5、P204与煤油体积比为3:2、有机相与水相比为2:1、反应萃取时间大于30min、搅拌转速约200rpm时,能够取得较好的萃取效果.以初始pH值≥3.5的蒸馏水为反萃取剂,蒸馏水与有机相体积比4:1,在150rpm的转速下搅拌20min能够较为完全地分离出赖氨酸,然后在其它条件相同的情况下,用初始pH＜1的蒸馏水对有机相再次反萃取可分离出金属离子,从而实现萃取剂的重复利用.     

Formation and reactions of cluster ions from aromatic carboxylic acids together with amino acids

The cluster formation of several aromatic carboxylic acids, ferulic acid, vanillic acid, sinapinic acid, and 3,4-dihydroxybenzoic acid was investigated by means of laser desorption into a supersonic beam followed by multiphoton ionization-time-of-flight mass spectrometry. The formation of not only homogeneous clusters, but also of heterogeneous clusters with some small amino acids was studied. The different neutral clusters formed in the supersonic expansion were ionized by a multiphoton process employing either nano- or femtosecond laser pulses. Strong differences in the detection of cluster ions due to the laser pulse length employed for multiphoton ionization were observed. Only femtosecond activation led to mass spectra with intense signals of the cluster ions. In addition, in the case of femtosecond ionization, protonated amino acids were detected in the mass spectra. As direct ionization of the free amino acids is not possible under the chosen ionization conditions because they lack an adequate chromophore, these protonated amino acids are assumed to be formed via an intracluster proton transfer in the heterogeneous dimer and subsequent decay of the ionized cluster (dissociative proton transfer). Such well-known processes for heterogeneous clusters consisting of a substituted aromatic molecule and small polar solvent molecules may be involved in the matrixassisted laser desorption ionization (MALDI) process.     

含氟取代基的不对称变色酸双偶氮试剂与金属离子显色反应性能的研究

系统研究了４种（膦类、胂类、羧类、羟类）共１１个含氟取代基的不对称变色酸双偶氮类试剂与３６个金属离子显色反应的性能。考察了反应酸度、配合物的最大吸收峰的位置和反应灵敏度等。探讨了金属离子的种类、性质及试剂分子结构与显色反应性能之间的关系。     

Behaviour in solution of humic acids from lignite in the presence of calcium ions

Humic acids (HA) extracted from Spanish lignite, were studied to discover their Ca-complexing capacity and their coagulation threshold. It was found that the concentration of Ca^{+ +} ions necessary for the complete flocculation increased with the increase of pH and ionic strength (μ) and it was linearly dependent on the concentration of HA. The calcium-complexing capacity of HA increased with the increase of pH and registered lower values as μ was increased. The i.r. spectra of the Ca-humic acid complexes show that the metal is complexed mainly by carboxylic groups from the HA.     

Hydrophilic PVA-co-PE nanofiber membrane functionalized with iminodiacetic acid by solid-phase synthesis for heavy metal ions removal

A novel hydrophilic poly(vinyl alcohol-co-ethylene) (PVA-co-PE) nanofiber membrane for heavy metal ions removal was fabricated by the solid phase synthesis of iminodiacetic acid (IDA) on nanofiber membrane surfaces. The hydrophilic PVA-co-PE nanofiber membranes were activated with cyanuric chloride. The IDA was then covalently linked to the activated PVA-co-PE nanofiber membranes. The chemical structures of activated and functionalized PVA-co-PE nanofiber membranes were confirmed with FTIR–ATR. The morphology of PVA-co-PE nanofiber membranes were characterized with SEM. The increase in the amount of IDA on functionalized PVA-co-PE nanofiber membranes significantly improved the adsorption amount of Cu²⁺. The IDA functionalized PVA-co-PE nanofiber membranes demonstrated excellent adsorption capability of Cu²⁺, Co²⁺, Zn²⁺ and Ni²⁺. The adsorption of above heavy metal ions could be repeatedly regenerated by desorbing the ions adsorbed on nanofiber membranes. The novel IDA functionalized PVA-co-PE nanofiber membranes have great potential in the application of industry and drinking water treatment.     

Mechanochemical solid-phase reaction between polyvinylidene fluoride and sodium hydroxide

Grinding a mixture of polyvinylidene fluoride (PVDF) and NaOH was conducted by a planetary ball mill at atmospheric condition to investigate mechanochemical reaction between the two substances. The grinding stimulates the reaction to form NaF and organic composites. Yield of fluorine converted from PVDF to NaF increases with an increase in grinding time and reaches 90% at 60 min or more. As for the organic phase, oxygen-bearing compounds are formed due to substitution of fluorine by OH base. The organic compounds are classified into water-soluble and insoluble ones, depending on their structures. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2249–2252, 2001     

Removal of metal ions from electrochemical decontamination solution using organic acids

Applicability of the organic acids and cyclodextrin (CD) for the removal of Fe, Co and Ni from the spent electro-decontamination solution was investigated. Oxalic acid showed the highest removal efficiency: 90% for 0.89 M Fe and 95% for 0.0089 M Co and Ni, respectively. The metal–oxalate precipitates were characterized by differential scanning calorimetry/thermogravimetry analysis (DSC/TGA), Fourier transform infrared (FTIR) and X-ray fluorescence (XRF). After thermal decomposition at >300°C, the metal–oxalate precipitates were transformed into metal oxides (Fe₂O₃, FeO, CoO and NiO) and pure metals (Co and Ni). The results imply that organic acids have a high potential for the removal of heavy metals from electro-decontamination solutions.     

Potentiometric titration of humic acids

The acid-base properties of humic acids from the brown coal of the Aleksandriiskoe deposit (Ukraine) were investigated. The possibility of determining COOH and OH groups in humic acid macromolecules by different experimental methods was analyzed. It was found that the results of potentiometric titration depend on the method of titration (homogeneous or heterogeneous), the concentration of humic substances in the system, and the time taken to establish an equilibrium value of pH in the titrate. It was shown that the amount of accessible functional groups (COOH and OH) in humic acid macromolecules, which can be determined by a potentiometric method, is greater in homogeneous titration and at low concentrations of humic substances in solution. It was established that the total amount of acid groups determined by a barium method is higher than that measured with the use of potentiometric titration. The concentration of carboxyl groups determined by an acetate method is much lower than the results of potentiometric titration and the barium method. It was shown that the potentiometric titration of homogeneous systems (sodium humate + HCl) is preferable in the analysis of the acid-base properties of humic acids.     

Comparison of five humic acids

The ultimate analyses, u.v-visible absorption spectra, fluorescence spectra and i.r. spectra of five humic acids have been studied. One was obtained commercially from peat, two from organic-rich soils, one from an estuary and one from a marine sediment. The u.v. spectra were used to compare average molecular weights which varied from 800 to 7000 and increased with the atomic $\text{H}\text{C}$ ratio. Fluorescence appeared to be due to poly-nuclear aromatic structures. All the humic acids showed maximum excitation at 360 nm and developed maximum emission in the range 430–455 nm but the humic acids from sediments showed an additional emission maximum at ~410 nm. Fluorescence from the peat humic acid was broad and secondary emission was observed with a maximum at 520 nm which was attributed to the formation of excimers. Fluorescence has been used to monitor the interaction of cations with humic acids in solutions of different ionic strengths which shows promise for distinguishing between metat—humate complex formation and the coagulation of a colloid. The structures of the humic acids are discussed in terms of the structures possessed by lignites.     

Rheological properties of humic acids

It has been found that humic acids in aqueous solution, as previously found with their sodium salts, behave as linear polyelectrolytes. A possible explanation in terms of intermolecular associative forces is suggested.     

Catalytic ozonation of humic acids with Fe/MgO

Humic acids were degraded by ozone at room temperature in a stirred tank reactor and a fixed bed reactor with Fe/MgO catalysts. Experimental results show that the ozonation with Fe/MgO induced a significant reduction in UV absorbance of humic acids as compared to ozone alone. Fe/MgO was the most efficient catalyst to degrade humic acids in the presence of ozone. GPC (gel permeation chromatography) showed that the humic acids with high molecular weight could be severely decomposed into organic compounds with low molecular weight on the Fe/MgO catalyst, indicating that humic acids could be catalytically decomposed. The continuous reaction experiments with the palletized catalysts supported that humic acids can be removed by catalysis as well as adsorption.     

Modified humic acids from lignite

Native and modified humic acids obtained from Tisul lignite (from the Kansko-Achinsk Basin) are investigated by IR Fourier, ESR, and solid-state ¹³C NMR analysis. Treatment with hydrogen peroxide changes the functional-group composition of the humic acids and increases the sorptional capacity.     

Cooperativity on selective products in one pot reactions of 2,6-pyridinedicarboxylic acid and ethylenediamine with metal ions

Selective mixed metal complex formation in one pot reaction of 2,6-pyridinedicarboxylic acid and ethylenediamine with metal ions results from positive cooperativity.     

Shaping RNA structures with metal ions and metal ion complexes

The research in our laboratory focuses on the role of metal ions and their complexes in structure formation and folding of nucleic acids. Large catalytic RNAs, like group II introns and some riboswitches, as well as shorter RNAs and DNAs containing modified nucleotides for the assembly of nanodevices are examined. Abundant metal ions like Mg2+ or natural metabolites like coenzyme B12 are in the center of interest, but also other metal ions, complexes thereof and B12 derivatives are applied with the aim to understand the largely unknown and manifold non-covalent interactions with nucleic acids. We apply a multitude of techniques, including potentiometric pH titrations, NMR spectroscopy, X-ray crystallography, gel electrophoresis and single molecule FRET experiments. Here we briefly summarize each of our research topics emphasizing the interaction of coenzyme B12 and its derivatives with the btuB riboswitch of E. coli. This highly conserved sequence, found in the 5'-untranslated region (5'-UTR) of the btuB mRNA, is involved in the regulation of the btuB protein expression. After a summary on the historical discovery of such riboswitches and their mechanism of action, we shortly focus on our own contributions to understand the structural equilibrium, high affinity and selectivity of the interaction between this specific RNA sequence and the largest and most complex cellular metabolite, coenzyme B12.     

Bromination of humic acids of different origin

Data on the introduction of bromine atoms into the structure of humic acids isolated from the peat of Tver oblast and the brown coal of the Moscow Basin were generalized, and a comparative analysis of relevant methods was performed. It was shown that the test humic acids are similar in terms of structural parameters and demonstrate similar behaviors in the processes of bromination and hydrobromination. The dependences of the structural parameters of bromine-containing humic preparations on the mass fraction of bromine in them were obtained; correlations between the yields of humic preparations from the peat and the brown coal in the course of modifications were found; and the possible reaction paths of the bromination and hydrobromination processes were discussed. The biological activity of the bromine-containing humic preparations was tested, and its direct dependence on the mass fractions of bromine and phenolic hydroxyls in the humic preparations was found. It was shown that the modification of peat humic acids by hydrobromination is preferable for the production of biologically active humic preparations.     

Alkaline permanganate oxidation of methylated humic acids

The composition of the oxidation products from methylated humic acids of different origins was investigated by g.l.c., yielding structural information additional to that obtainable by oxidation of unprotected humic acids. The yield of methoxy aromatic acids decreased with increasing coalification of the starting materials. From the oxidation of humic acids from soil, peat and lignite, a series of methoxy benzoic acids was obtained which was similar to lignin degradation products. Slightly transformed fragments of the lignin molecule apparently took part in the formation of these humic acids.