Gel-Forming Properties of Pectins from Callus Culture of Lemna minor

Chemistry of Natural Compounds - A pectin fraction (LMC-I) with the best gel-forming properties as compared to LMC was obtained from Lemna minor L. callus culture and characterized by separation of...     

Enzyme-catalysed nitrate reduction-themes and variations as revealed by protein film voltammetry

Protein film voltammetry has been used to define the catalytic performance of two nitrate reductases: the respiratory nitrate reductase, NarGH, from Paracoccus pantotrophus and the assimilatory nitrate reductase, NarB, from Synechococcus sp. PCC 7942. NarGH and NarB present distinct "fingerprints" of catalytic activity when viewed in this way. Potentials that provide insufficient driving force for significant rates of nitrate reduction by NarB result in appreciable rates of nitrate reduction by NarGH. However, both enzymes display complex modulations in their rate of substrate reduction when viewed across the electrochemical potential domain.     

Multiple DNA binding modes of a metallointercalator revealed by DNA film voltammetry

Binding and the redox reaction of the metallointercalator Ru(bpy)2(dppz)2+ (bpy = 2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine) with DNA was investigated by DNA film voltammetry. Calf-thymus DNA (CT-DNA) was assembled on a tin-doped indium oxide electrode by layer-by-layer electrostatic adsorption. Voltammetry of Ru(bpy)2(dppz)2+ (Ru-dppz) bound to the DNA film was measured in a redox-free electrolyte and showed strong dependence on the concentration of the metallointercalator. At low Ru-dppz concentrations, a single oxidation peak was observed, the potential of which shifted from 1.25 to 1.1 V with increasing Ru-dppz concentration (peak 1). At high metal chelate concentrations, an additional oxidation peak emerged with a potential of 1.25 V which was unaffected by the Ru-dppz concentration (peak 2). Three experiments were performed to investigate the mechanism and structural basis of the multiple peaks. First, voltammetry of Os(bpy)2(dppz)2+ bound to the CT-DNA film displayed only one peak at its oxidation potential of about 0.75 V. Second, the concentration dependence of Ru-dppz bound to a poly-(AU) film (which does not contain any guanine bases) exhibited only one oxidation peak at about 1.22 V that was independent of the Ru-dppz concentration. Third, when the guanine concentration in a mixed film of CT-DNA and poly-(AU) was changed and the bound Ru-dppz was kept constant, a pre-peak emerged and shifted to 1.1 V with increasing guanines. Based on these results, the appearance of two peaks in the voltammetric measurements of CT-DNA was rationalized by invoking two different DNA binding modes for the Ru-dppz complex: intercalation and electrostatic association. Peak 2 arises from slow oxidation of guanines catalyzed by Ru-dppz electrostatically associated with the DNA film, since the addition of Mg2+ decreases the magnitude of peak 2. Peak 1 was not affected by Mg2+ ions, leading us to conclude that it is due to intercalated Ru-dppz. The intercalation positions the metal complex in close contact with the guanines inside DNA resulting in fast electrocatalytic reaction, giving rise to a catalytic pre-peak.     

Determination of cobalt in plant digests by adsorption stripping voltammetry

The procedure involves adsorption of cobalt onto a static mercury drop as its dimethylgloximate complex (pH 9.3, adsorption potential ?0.70 V, adsorption time 2 min), followed by a d.c. cathodic scan, effecting reduction at ?1.15 V (SCE). Of the dominant electroactive trace elements in plants (Mn, Fe, Zn), only zinc interfered; it was masked by nitrolotriacetic acid (2 × 10^?4 M). The detection limit is 0.01 μg l^?1 cobalt in the digest; the relative standard deviation is 2.5% at 0.75 μg l^?1. Calibration is linear in the range 0–6.0 μg l^?1 cobalt. Results obtained by the voltammetric method, by electrothermal atomic absorption spectrometry and neutron activation analysis are compared for seven pasture samples containing 0.1–0.2 mg kg ^?1 cobalt. The activation method provides validation for the same preparation and voltammetric results.     

Applications of polarography and voltammetry to marine and aquatic chemistry

Summary Toxic metals in sea and inland waters have become a significant research topic in the chemistry of the marine and inland aquatic environment. Advanced polarographic and voltammetric methods offer an expectional efficient and versatile approach to the determination, speciation and physicochemical characterization of those metals. These potentialities are reflected by a reliable method based on differential pulse anodic stripping at an in situ mercury film coated rotatable glassy carbon electrode for the simultaneous determination of ultra-trace levels of Cd, Pb and Cu dissolved in sea water and inland waters and accumulated in marine organisms.In speciation studies at trace levels differential pulse polarographic measurements revealed the influences of sea water components on the chelation of Cd with NTA and by the application of an advanced version of linear sweep anodic stripping voltammetry kind and stability of Pb-carbonato complexes existing in sea water could be elucidated.

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Anwendungen der Polarographie und Voltammetrie in der Chemie des Meeres und der BinnengewässerII. Die polarographische Bestimmung und Speziation toxischer Spurenmetalle in der marinen Umwelt

Zusammenfassung Toxische Metalle im Meer und in Binnengewässern sind eine wichtige Forschungsaufgabe in der Chemie dieser Umweltkompartimente. Fortgeschrittene polarographische und voltammetrische Methoden bieten außergew öhnlich effiziente und vielseitige Möglichkeiten zur Bestimmung, Speziation und physikochemischen Charakterisierung der vorliegenden Metalle. Diese Möglichkeiten werden einmal demonstriert durch eine neue zuverlässige Simultanbestimmung der in Meerwasser und Binnengewässern gelöst vorliegenden Spurengehalte von Cd, Pb und Cu mit inversvoltammetrischer differentieller Pulse-Polarographie an einer in situ mit einem dünnen Quecksilberfilm bedeckten rotierbaren Glaskohleelektrode sowie durch Ermittlung der in marinen Organismen angereicherten Spurenmetallgehalte. In Untersuchungen zur Speziation im Ultraspurenbereich wurden unter Einsatz der differentiellen PulsePolarographie die Einflüsse der Makrokomponenten des Meerwassers auf die Chelierung von Cd mit NTA aufgeklärt und mit Hilfe einer fortgeschrittenen Version der Inversvoltammetrie mit linear sweep die Art und Stabilität der im Meerwasser existierenden Pb-Carbonatokomplexe ermittelt.

Dedicated to Dr. G. C. Barker on his 60th birthday.     

Assessment of the Effects of Chitosan,Chitooligosaccharides and Their Derivatives on Lemna minor

Chitosan, chitooligosaccharides and their derivatives’ production and use in many fields may result in their release to the environment, possibly affecting aquatic organisms. Both an experimental and a computational approach were considered for evaluating the effects of these compounds on Lemna minor. Based on the determined EC₅₀ values against L. minor, only D-glucosamine hydrochloride (EC₅₀ = 11.55 mg/L) was considered as “slightly toxic” for aquatic environments, while all the other investigated compounds, having EC₅₀ > 100 mg/L, were considered as “practically non-toxic”. The results obtained in the experimental approach were in good agreement with the predictions obtained using the admetSAR2.0 computational tool, revealing that the investigated compounds were not considered toxic for crustacean, fish and Tetrahymena pyriformis aquatic microorganisms. The ADMETLab2.0 computational tool predicted the values of IGC₅₀ for Tetrahymena pyriformis and the LC₅₀ for fathead minnow and Daphnia magna, with the lowest values of these parameters being revealed by totally acetylated chitooligosaccharides in correlation with their lowest solubility. The effects of the chitooligosaccharides and chitosan on L. minor decreased with increased molecular weight, increased with the degree of deacetylation and were reliant on acetylation patterns. Furthermore, the solubility mainly influenced the effects on the aqueous environment, with a higher solubility conducted to lower toxicity.     

Separation and preconcentration of chromium species by selective absorption on Lemna minor and determination by slurry atomisation electrothermal atomic absorption spectrometry

A novel method for the separation and preconcentration of Cr(III)/Cr(VI) with Lemna minor and determination by slurry atomization electrothermal atomic absorption spectrometry (ETAAS) was developed. A sample solution was added to a polyethylene beaker containing 10 mg of 160 mesh pre-treated Lemna minor, adjusted to pH 1.0, stirred for 8 min for selective absorption of Cr(III) and then centrifuged. The upper layer of solution was transferred into another polyethylene beaker containing 10 mg of 160 mesh pre-treated Lemna minor, adjusted to pH 5.0, stirred for 12 min for adsorption of the residual Cr(VI) and centrifuged. The two residues in two centrifuge tubes were washed twice with water, 2 ml of agar solution added, stirred for 2 min, then two slurries were prepared and used for the determination of Cr(III) and Cr(VI) by ETAAS. Detection limits (3sigma) of 0.01 microg L(-1) for Cr(III) and 0.03 microg L(-1) for Cr(VI) were obtained. The relative standard deviation was 2.8% for Cr(III) and 3.3% for Cr(VI) at the 1 microg L(-1) level. The method was applied to the determination of Cr(III)/Cr(VI) in water samples. The analytical recoveries of Cr(III) and Cr(VI) added to samples were 97-102 and 96-103%, respectively.     

Overview of Allelopathic Potential of Lemna minor L. Obtained from a Shallow Eutrophic Lake

Allelopathy is an interaction that releases allelochemicals (chemicals that act allelopathically) from plants into the environment that can limit or stimulate the development, reproduction, and survival of target organisms and alter the environment. Lemna minor L. contains chemicals that are allelopathic, such as phenolic acids. Chemical compounds contained in L. minor may have a significant impact on the development and the rate of multiplication and lead to stronger competition, which may enhance the allelopathic potential. Allelopathic potential may exist between L. minor and C. glomerata (L) Kütz. because they occupy a similar space in the aquatic ecosystem, have a similar preference for the amount of light, and compete for similar habitat resources. L. minor and C. glomerata can form dense populations on the water surface. Allelopathy can be seen as a wish to dominate one of the plants in the aquatic ecosystem. By creating a place for the development of extensive mats, an interspecific interaction is created and one of the species achieves competitive success. It is most effective as a result of the release of chemicals by macrophytes into the aquatic environment. Therefore, allelopathy plays a significant role in the formation, stabilization, and dynamics of the structure of plant communities.     

Two minor phytoecdysteroids of the plant Silene viridiflora

Chemical investigations of Silene viridiflora (L.) yielded a new ecdysteroid, 20-hydroxyecdysone 20,22-monoacetonide-25-acetate (1), and a known ecdysteroid, 2-deoxypolypodine B-3-beta-D-glucoside (2). The elucidation of the chemical structures was established by 1D and 2D NMR experiments.     

The application of multielemental analysis in the elaboration of technology of mineral feed additives based on Lemna minor biomass

Supplementation of microelements (Mn, Zn, Cu, Cr) to livestock diet is of particular concern. There are various mineral feed additives available on the market. The most frequently used are inorganic feed additives, characterized with low bioavailability and high toxicity. Also, organic feed additives are used, including amino acids chelates, in which bioavailability was greatly improved and toxicity reduced. The problem is high price of these products. Therefore, there is the need to search for new biological mineral feed additives with designed composition, that would be characterized with high bioavailability, low toxicity, low cost and that would also possess a nutritional value. Such a possibility offers biological materials. It was found that biomaterials have metal-binding capabilities. Metal ions may be bound to biomass via either biosorption or bioaccumulation process.

When elaborating technology of the production of feed additives, containing simultaneously various elements, it is necessary to use the tool of multielemental analysis in order to simultaneously analyze the content of Mn, Zn, Cu, Cr. In the present work, ICP-OES multielemental analysis was used to investigate the process of production of mineral feed additives based on the biomass of aquatic plant Lemna minor. The effectiveness of the processes of biosorption and bioaccumulation of microelements by an aquatic plant L. minor was studied. The mechanism of the process as well as equilibrium was investigated with the use of multielemental analysis by ICP-OES Vista-MPX instrument from Varian (Australia).     

Clay-Catalyzed Ozonation of Organic Pollutants in Water and Toxicity on Lemna minor: Effects of Molecular Structure and Interactions

The use of clays as adsorbents and catalysts in the ozonation of organic pollutants (Atrazine, bis-Phenol A, Diazinon, and Diclofenac sodium) allowed simulating their natural oxidative degradation in clay soils and to evaluate the ecotoxicity of mixtures partially oxidized on the species Lemna minor, a biodiversity representative of plants in the aquatic environment. Kinetic data showed that the adsorption of organic pollutants on clay particles obeys the pseudo-second-order model, while the adsorption isotherms satisfactorily fit the Langmuir model. Adsorption reduces the dispersion of the organic pollutant in the environment and prolongs its persistence and its natural degradation probability. Measurements of the Zeta potential and particle size as a function of pH demonstrate that the catalytic activity of clay depends on its cation, its silica/alumina ratio, and therefore on its permanent and temporary ion exchange capacities. These factors seem to govern its delamination and dispersion in aqueous media, its hydrophilic-hydrophobic character, and its porosity. Tests conducted on Lemna minor in contact with ozonation mixtures revealed that the toxicity could be due to pH decrease and to the toxicity of the intermediates yielded. Ecotoxicity would depend on the structure of the organic molecules, the chemical composition of the clay surface and ozonation time, which determines the oxidation progress. These results are of great importance for further research because they allow concluding that the negative impact of the persistence of an organic molecule in clay-containing media depends on the type and composition of the very clay mineral.     

高效液相色谱法测定顺铂注射液中顺铂的含量

顺铂含量的测定方法有灼烧重量法[1]、高效液相色谱法[2,3]、络合滴定法[4]。顺铂注射液作为新剂型,其主含量顺铂的分析方法一直为省级标准,采用SnCl2显色法[5],该法所测值是二价铂化合物的总含量,对顺铂无选择性。文献上也有采用高效液相色谱法[6]的报道,但该法存在着:1.杂质峰与主峰分离度不够(Rs<1.5);2.方法重现性较差;3.对柱效要求高的缺点,其主要原因是所选色谱系统不理想。为此,本研究以高效液相色谱法测定顺铂注射液中顺铂的含量,取得了满意的结果。1　实验部分1.1　仪器和试剂SHIMADZULC 10A系统,双LC 10AD高压泵,DGU…     

Characterization of low-molecular-weight metal species in plant extracts by using HPLC with pulsed amperometric detection and cyclic voltammetry

An analytical separation scheme is presented for the isolation of low-molecular-weight metal species (< 10 kDa) in plants. After ultrafiltration of the aqueous plant extracts isotachophoresis or gel chromatography is used for pre-separation and HPLC at a cyclodextrin-phase for further separation of metal containing fractions. Trace metals are detected off-line by using either adsorptive stripping voltammetry for platinum or AAS for zinc and magnesium. It is shown that platinum and zinc detection closely correlate with pulsed amperometric detection (PAD), while magnesium behaves differently. PAD is carried out after post-column addition of sodium hydroxide, thus enabling a sensitive and selective detection of carbohydrates. It is demonstrated that cyclic voltammetry is a useful tool for further characterization of the PAD-detectable metal species. By comparison of the cyclic voltammograms of carbohydrate standards, including carbohydrate-metal species, with the respective voltammograms obtained from HPLC fractions, carbohydrate species isolated from the samples can be considered as being either partly oxidized sugars (sugar alcohols or sugar acids) or glycosidically bound sugars.     

Characterization of low-molecular-weight metal species in plant extracts by using HPLC with pulsed amperometric detection and cyclic voltammetry

An analytical separation scheme is presented for the isolation of low-molecular-weight metal species (< 10 kDa) in plants. After ultrafiltration of the aqueous plant extracts isotachophoresis or gel chromatography is used for pre-separation and HPLC at a cyclodextrin-phase for further separation of metal containing fractions. Trace metals are detected off-line by using either adsorptive stripping voltammetry for platinum or AAS for zinc and magnesium. It is shown that platinum and zinc detection closely correlate with pulsed amperometric detection (PAD), while magnesium behaves differently. PAD is carried out after post-column addition of sodium hydroxide, thus enabling a sensitive and selective detection of carbohydrates. It is demonstrated that cyclic voltammetry is a useful tool for further characterization of the PAD-detectable metal species. By comparison of the cyclic voltammograms of carbohydrate standards, including carbohydrate-metal species, with the respective voltammograms obtained from HPLC fractions, carbohydrate species isolated from the samples can be considered as being either partly oxidized sugars (sugar alcohols or sugar acids) or glycosidically bound sugars. Received: 26 January 1998 / Revised: 19 June 1998 / Accepted: 24 June 1998     

Physiological and Biochemical Parameters of Common Duckweed Lemna minor after the Exposure to Tetracycline and the Recovery from This Stress

In this study, the ability of Lemna minor L. to recover to normal growth, after being degraded in a tetracycline-containing medium, was extensively investigated. The plants were exposed to tetracycline (TC) at concentrations of 1, 2.5, and 10 mM. Subsequently, their physiological status was analysed against the following criteria: rate of plant growth; free radical accumulation; antioxidant enzyme activity; chlorophyll content; HSP70 protein content; cell membrane permeability, and mitochondrial activity. The study showed that duckweed can considerably recover from the damage caused by antibiotics, within a week of cessation of stress. Of the plant properties analysed, mitochondrial activity was the most sensitive to antibiotic-induced disturbances. After transferring the plants to a tetracycline-free medium, all plant parameters improved significantly, except for the mitochondrial activity in the plants grown on the medium containing the highest dose of tetracycline. In the plants treated with this antibiotic at the concentration of 10 mM, the proportion of dead mitochondria increased and was as high as 93% after one week from the beginning of the recovery phase, even after the transfer to the tetracycline-free medium.     

Determination by MS-MS of 1,1-dichlorodimethyl sulfone from pulp mill bleach plant effluents in aquatic organisms

Gas chromatography (GC) with electron capture detection (ECD), GC combined with mass spectrometry (MS), GC with multi-stage mass spectometry (MS-MS), and direct inlet MS-MS have been used to determine 1,1-dichlorodimethyl sulfone (DDS) in aquatic organisms in the receiving waters outside a pulp mill bleach plant. Both GC-MS-MC and direct inlet MS-MS of tissue extracts of fish and mussel appear to be sensitive, selective, and rapid analytical techniques for the determination of DDS.     

Determination of promethazine by anodic differential-pulse voltammetry

A differential-pulse voltammetric method is described for the determination of promethazine hydrochloride. The method is based on the anodic oxidation of promethazine on a glassy carbon electrode at + 0.64 V vs. SCE in Prideaux buffer of pH 2.3. The reversibility of the oxidation was tested by cyclic voltammetry; the electrode process is quasi-reversible. From the results of microcoulometric experiments and a study of acid—base equilibria, a mechanism for the electrochemical oxidation is presented. The method is applied to determine promethazine hydrochloride in pharmaceutical formulations. Calibrations are linear over the 0.1–1 and 1–5 mg/50 cm³ ranges.     

Determination of palladium by adsorptive stripping voltammetry

 Adsorptive accumulation of the Pd(II) complex with dimethylglyoxime was evaluated for stripping voltammetry with respect to different parameters. The sensitivity of the method and the linearity between the peak current and the concentration of Pd(II) depends on the ionic strength, the electrode area, the preconcentration time, the transport rate to the electrode, and the potential scan rate. The most appropriate medium was 0.1 mol/L acetate buffer between pH 3.5 and 4. Using 2 min of preconcentration at a 2.6 mm² electrode and the differential pulse mode, a detection limit of 0.05 μg/L Pd was achieved for liquid samples and 50 ng/g for solid samples. Different aqueous and solid samples were analysed and the recovery from biological and inorganic materials investigated. Received: 29 February 1996/Revised: 29 July 1996/Accepted: 1 August 1996     

Determination of azinphos-methyl by adsorptive stripping voltammetry

A very sensitive electrochemical stripping procedure for azinphos-methyl (Guthion) is reported. Accumulation is achieved by adsorption of the compound on a hanging mercury drop electrode. The adsorptive stripping response was evaluated with respect to accumulation time and potential, concentration dependence, electrolyte and other variables. The determination limit is 0.2 ng ml^?1 after 300 s accumulation and 0.4 ng ml^?1 after 180 s accumulation. The procedure was applied to spiked river water.