Metal distribution and binding in balneological peats and their aqueous extracts

Binding of metals in typical bath peat samples ("Grosses Gifhomer Moor", Sassenburg/North Germany) and their aqueous extracts was characterized by means of a multi-method approach. For that purpose a sequential extraction procedure based on peat-filled chromatography columns was developed. Water-soluble metal and DOM (dissolved organic matter) fractions were subdivided by use of a stepwise increased pH gradient (pH 3.8-5), finally by the chelator EDTA and 0.1 mol L(-1) hydrochloric acid. Metal fractions very strongly bound to peat were assessed by an aqua regia extraction. Metal determinations required were performed by atomic spectrometry methods (AAS, ICP-OES, and TXRF). The metal and DOM concentrations in the peat extracts varied significantly, depending on the natural variety of the peat matter under study (e.g., Al: 25-674, Cd: 0.05-0.2, Cu: 5-15.4, Fe: 77-1785, Mn: 21-505, Ni: 2-33, Pb: < 1, Zn: 9-715 (microg L(-1)); Na: 8-45, K: 1.3-14.9, Ca: 2-51, Mg: 1.1-7.9 (mg L(-1)); 26-73 mg L(-1) DOC). An increase of the pH increased the DOC (dissolved organic carbon) of the peat extracts, but hardly the concentration of heavy metals. The latter could only be re-mobilized by EDTA and dilute hydrochloric acid. Additional investigations of the peat extracts using tangential-flow ultrafiltration revealed that the heavy metals extracted at pH < 4 were predominantly dissociated. At higher pH (pH > 4.5) they were preferentially bound to macromolecular DOM. Moreover, using multistage ultrafiltration the size distribution of the DOM and their metal species was assessed.     

Assessment of total arsenic and arsenic species stability in alga samples and their aqueous extracts

In order to achieve reliable information on speciation analysis, it is necessary to assess previously the species stability in the sample to analyse. Furthermore, in those cases where the sample treatment for species extraction is time-consuming, an assessment of the species integrity in the extracts is of paramount importance. Thus, the present paper reports total arsenic and arsenic species stability in alga samples (Sargassum fulvellum and Hizikia fusiformis), as well as in their aqueous extracts, which were stored in amber glass and polystyrene containers at different temperatures. Total arsenic determination was carried out by inductively coupled plasma atomic emission spectroscopy (ICP-AES), after sample acid digestion in a microwave oven, while arsenic speciation was conducted by anion exchange high performance liquid chromatography on-line coupled to ICP-AES, with and without sample introduction by hydride generation (HPLC-ICP-AES and HPLC-HG-ICP-AES), after aqueous microwave-assisted extraction. The results obtained for solid alga samples showed that total arsenic (for Hijiki alga) and arsenic species present (As(V) for Hijiki and NIES No. 9 Sargasso) are stable for at least 12 months when samples are stored in polystyrene containers at +20 degrees C. On the other hand, a different behaviour was observed in the stability of total arsenic and As(V) species in aqueous extracts for both samples, being the best storage conditions for Sargasso extracts a temperature of -18 degrees C and polystyrene containers, under which they are stable for at least 15 days, while Hijiki extracts must be stored in polystyrene containers at +4 degrees C in order to ensure the stability for 10 days.     

Radiation-chemical reduction of CO2+ ions in aqueous solution. Metal sols and their properties

The radiation-chemical reduction of Co²⁺ ions in an aqueous solution of Co(ClO₄)₂ containing sodium formate was studied. Stable metal sols containing spherical particles with a diameter of 2–4 nm are formed under γ-irradiation in the presence of polyacrylate as the stabilizing additive. An aqueous solution of colloidal cobalt has an optical absorption that increrases smoothly in the UV region without a maximum to 200 nm (ɛ₂₀₀=1.3·10⁴ mol^-1 L cm^-1). It is established that the radiation-chemical reduction of the Co²⁺ ions occursvia an autocatalytic mechanism. The metal sols catalyze the reduction of the Co²⁺ ions by Co₂ ⁻ radical ions formed under irradiation. The properties of the sols were studied, and it is shown that they are readily oxidized by hydrogen peroxide and other oxidants. The mechanism of chemical reactions involving the sols is discussed. Tranalated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1959–1964, October, 1998.     

Rodlike micelles of dimethyloleylamine oxide in aqueous NaCl solutions,and their flexibility and size distribution

Angular dependence of light scattering from aqueous NaCl solutions of dimethyloleylamine oxide has been measured in the presence of NaCl from 5×10^–4 M to 10^–1 M at 25 °C. The molecular weight and radius of gyration of micelles increase with increasing micelle concentration and reach constant values, suggesting occurrence of the sphere-rod equilibrium dependent on the micelle concentration. With increasing NaCl concentration, rodlike micelles are larger in molecular weight and become longer. The micelles formed at NaCl concentrations higher than 10^–3 M are nearly monodisperse when the micelle concentration is high.Rodlike micelles of dimethyloleylamine oxide in 10^–2 M and 5 × 10^–2 M NaCl solutions have molecular weights of 4,760,000 and 6,900,000, respectively, and behave as semi-flexible or wormlike chains. In 5×10^–2 M NaCl they have a contour length of 5750 Å and a persistence length of 1760 Å. These micelle parameters correspond to the end-to-end distance of 3780 Å and the number of Kuhn's statistical segments of 1.64. The large aggregation number of the rodlike micelles is induced by the strong cohesion of long hydrocarbon chains in solution, and their flexibility is caused by the hydration of amine oxide groups.     

Antioxidant activity of organic and aqueous leaf extracts of Cassia occidentalis L. in relation to their phenolic content

In this study, the antioxidant potency of sequential organic and aqueous leaf extracts of Cassia occidentalis was investigated, employing various established in vitro systems such as nitric oxide scavenging (NOS) activity, β-carotene-linoleic acid model system, hydroxyl radical scavenging (HRS) activity, reducing power, metal chelating activity (MCA) and superoxide radical scavenging (SRS) activity. The aqueous extract of the leaves of C. occidentalis was found to be most effective against free radicals, followed by the methanolic, chloroform, petroleum ether and benzene extracts, respectively. A preliminary study of qualitative and quantitative estimations of phenolics was performed, and the results were correlated with different antioxidant tests. A positive and significant (p?相似文献   

CZE for the speciation of arsenic in aqueous soil extracts

We developed two separation methods using CZE with UV detection for the determination of the most common inorganic and methylated arsenic species and some phenylarsenic compounds. Based on the separation method for anions using hydrodynamic sample injection the detection limits were 0.52, 0.25, 0.27, 0.12, 0.37, 0.6, 0.6, 1.2 and 1.0 mg As/L for phenylarsine oxide (PAO), p-aminophenylarsonic acid (p-APAA), o-aminophenylarsonic (o-APAA), phenylarsonic acid (PAA), 4-hydroxy-3-nitrobenzenearsonic acid (roxarsone), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenite or arsenious acid (As(III)) and arsenate (As(V)), respectively. These detection limits were improved by large-volume sample stacking with polarity switching to 32, 28, 14, 42, 22, 27, 26 and 27 microg As/L for p-APAA, o-APAA, PAA, roxarsone, MMA, DMA, As(III) and As(V), respectively. We have applied both methods to the analysis of the arsenic species distribution in aqueous soil extracts. The identification of the arsenic species was validated by means of both standard addition and comparison with standard UV spectra. The comparison of the arsenic species concentrations in the extracts determined by CZE with the total arsenic concentrations measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) indicated that CZE is suited for the speciation of arsenic in environmental samples with a high arsenic content. The extraction yield of phenylarsenic compounds from soil was derived from the arsenic concentrations of the aqueous soil extracts and the total arsenic content of the soil determined by ICP-AES after microwave digestion. We found that 6-32% of the total amount of arsenic in the soil was extractable by a one-step extraction with water in dependence on the type of arsenic species.     

Liquid-vapor distribution of amines and acid ionization constants of their ammonium salts in aqueous systems at high temperature

Ammonia and volatile organic amines are used to treat the water in steam generating systems to afford protection of the steam- and feedwater circuits from corrosion by acidic condensate. The base strength and the volatility of the reagent used are two important parameters that have bearing on its ability to inhibit corrosion; they determine the pH of the solution produced from condensing steam. The distribution of thirteen amines between water and steam in the temperature range 150 to 325°C was studied. The amines were chosen on the basis of their known room-temperature base strength. The acid ionization constant of the ammonium salts of seven of these amines was determined by conductivity measurement in the temperature range 25 to 275°C. Amines with high room-temperature base strength and distribution coefficient in the optimum range were chosen for the high-temperature base strength determination. The results of these studies were used to estimate the effectiveness of these amines in raising the pH of the condensate from steam containing carbon dioxide and acetic acid, to provide the basis for further studies on the corrosion inhibition properties of the amines.     

Metal oxide solubility behavior in high temperature aqueous solutions

The solubility behavior of metal oxides in sub- and super-critical aqueous solutions is quantified using thermodynamic concepts. Three physicochemical phenomena are discussed: (1) metal oxide solid phase stability; (2) metal oxide dissolution reaction equilibria; and (3) metal ion hydroxocomplex formation. Thermochemical properties of metal oxides/ions representative of the most common constituents of construction metal alloys, i.e., elements having atomic numbers between 22 (Ti) and 30 (Zn), are summarized on the basis of metal oxide solubility studies conducted at General Electric and elsewhere.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991.     

Chelerythrine chloride binding of guanosine in aqueous solution

In this work, the interaction between chelerythrine (CHE) and guanosine is studied using UV-vis and fluorescence measurements at various temperatures. The UV-vis spectra show that the increasing guanosine concentrations result in the decreasing absorption intensity and red shift of CHE E absorption band (267 nm). The fluorescence spectra are fitted to linear analysis, yielding a binding constant of 1.04×104 L/mol at 298.15 K of CHE with guanosine. Besides, with △rHΘm =-8.26 kJ/mol, △rGmΘ = -22.90 kJ/mol,and △rSmΘ = 49.38 J/(mol K) the interaction should be entropy-driven and exterothermic.     

Selective binding behaviors of p-sulfonatocalixarenes in aqueous solution

The complex structures, binding abilities, molecular selectivities, and thermodynamic origin of p-sulfonatocalixarenes upon complexation with kinds of guests are outlined in this review article, including inorganic cations, organic ammonium cations, pyridiniums and viologens, neutral organic molecules, dye molecules, and others. Calorimetric and spectroscopic investigations afford the complex stability constants, thermodynamic parameters and binding manners of the inclusion complexation of p-sulfonatocalixarenes with guest molecules. The π-stacking, hydrophobic and charge interactions are the main driving-forces during the course of the host–guest inclusion complexation. The molecular binding abilities and selectivities are influenced by not only the frameworks of calixarene cavities, structures of guest molecules, and their binding manners but also the conditions of solutions (mainly pH), which are discussed from the correlation between the structural features and molecular-recognition abilities. Moreover, the further applications and potentials of p-sulfonatocalixarenes are briefly described.     

Selective binding of L-glutamate derivative in aqueous solvents

A chiral bisguanidinium macrocycle binds N-Boc-L-glutamate in a 1 : 1 stoichiometry with significant selectivity in competitive solvent (DMSO-H(2)O).     

Hydroxide-ion binding to nonionic interfaces in aqueous solution

The mechanism of hydroxide ion binding to nonionic surfaces is explored by variation of the properties of the water-aggregate interface and by variation of the type of the aggregate.     

Counterion binding to cationic polyelectrolytes in aqueous solution

The mean ion activity coefficient, (γ_±)_px/(γ_±)_salt for different high-linear charge density cationic polyelectrolyte fluoride, bromide, chloride and nitrate has been determined. The order found is: F^? > CI^? ≧ Br^? > NO. The results obtained with added nitrate were compared with those predicted by Iwasa, Guéron, and Weisbuch and Manning's models. The latter presents the best agreement for polyion chloride and bromide. It was possible to establish the most probable microconfiguration for the polyions studied here. Manning's theory gives a moderate agreement for polyion fluoride values compatible with a lower charge density than for polyelectrolyte chloride and bromide.     

Three-dimensional distribution function theory for the prediction of protein-ligand binding sites and affinities: application to the binding of noble gases to hen egg-white lysozyme in aqueous solution

The three-dimensional distribution function theory of molecular liquids is applied to lysozyme in mixtures of water and noble gases. The results indicate that the theory has the capability of predicting the protein-ligand binding sites and affinities. First, it is shown that the theory successfully reproduces the binding sites of xenon found by X-ray crystallography. Then, the ability of the theory to predict the size selectivity of noble gases is demonstrated. The effect of water on the selectivity is clarified by a theoretical analysis. Finally, it is demonstrated that the dose-response curve, which is employed in experiments for examining the binding affinity, is realized by the theory.     

Oxygen binding of water-soluble cobalt porphyrins in aqueous solution

Water-soluble cobalt porphyrin 1Co and imidazole ligand 2 were synthesized. 1Co binds dioxygen in the presence of imidazole ligand 2 in aqueous solution. The formation of the oxygen adduct 2-1Co(O(2)) was studied using UV-vis and EPR spectroscopy. The impact of pH on the kinetic stability of the oxygen adduct was examined.     

Interaction of polyvinylpyrrolidone with methyl orange and its homologs in aqueous solution: Thermodynamics of the binding equilibria and their temperature dependences

The interaction of polyvinylpyrrolidone with methyl orange, ethyl orange, propyl orange, and butyl orange has been studied by an equilibrium dialysis method at 5, 15, 25, and 35°C. The first binding constants and the thermodynamic parameters in the course of the binding have been calculated. It was found that the free energy and the enthalpy changes are all negative and the entropy change is largely positive. The longer the alkyl chain of the dyes, the more positive is the enthalpy change (though it is always in the negative direction) and hence the larger is the entropy change. The favorable free energy of the binding of butyl orange observed for the formation of the dye–polymer complex seems to be a result of a favorable entropy change rather than any favorable enthalpy change. Temperature dependences of the thermodynamic functions were apparently observed. That is, ΔF and ΔH become larger in absolute magnitude as the temperature increases. The positive quantity of ΔS tends to decrease with increasing temperture. All these facts obtained can be interpreted satisfactorily by the hydrophobic interaction between hydrocarbon portions of the dyes and nonpolar parts of the macromolecule.     

Anion binding in aqueous media by a tetra-triazolium macrocycle

Three tetra-triazole macrocycles were synthesized in good yields by the copper(i)-catalysed cycloaddition of bis-triazole azides and bis-alkynes. One of these was alkylated to give a cyclic tetra-triazolium receptor, which complexes anions strongly in competitive DMSO-water mixtures. In 1?:?1 DMSO-water, the tetracationic receptor exhibits a preference for the larger halides, bromide and iodide, with all halides associating more strongly than the oxoanion, acetate. The sulfate dianion is complexed far more strongly than any of the monobasic anions (K(a) > 10(4) M(-1)). Quantum mechanics/molecular mechanics simulations corroborate the experimentally determined anion binding selectivity trends.     

Alcoholic Mentha extracts as inhibitors of low-carbon steel corrosion in aqueous medium

This paper presents experimental evidence of the ability of alcoholic Mentha extracts to inhibit the corrosion of low-carbon steel in aqueous acid solutions. Alcoholic extracts of Mentha spicata L., Mentha x gentilis L., Mentha crispa L., Mentha piperita L., and Mentha x piperita L. were tested. The corrosion inhibition capability of these extracts was confirmed by means of weight loss experiments, cyclic voltammetry, chronoamperometry, polarization curves, and electrochemical impedance spectroscopy.     

Single-column ion-chromatographic determination of chromium(VI) in aqueous soil and sludge extracts

Single-column ion-chromatography (SCIC) was investigated as a routine, rapid, precise and selective analytical method for the determination of chromium(VI) in aqueous extracts of soil and sewage sludge. Chromatographic parameters were optimized for determination of Cr(VI), NO(-)(3) and SO(2-)(4). A low-capacity resin-based column was used for the separation and the anions were determined by conductometric detection. p-Hydroxybenzoic acid (5mM) at pH 8.5 was used as the eluent. The limit of detection, defined as S/N = 3, was 92 mug/l. The resolution between Cr(VI) and SO(2-)(4) was 2.8, the precision ranged from 0.9% for NO(-)(3) to 2.0% for Cr(VI) with a 500-mul injection. The SCIC results for Cr(VI) agreed closely with those obtained by inductively coupled argon-plasma emission and spectrophotometry.