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1.
《Cryptogamie Algologie ☆》2001,22(1):109-126
Tychoplanktonic and epilithic diatom samples were taken monthly during one year at 18 sites in small lowland rivers in the northern central region of Portugal. Canonical correspondence analysis was used to explore the relationships between measured environmental variables and patterns in the diatom assemblages. Conductivity, HCO3−, and chemical oxygen demand (COD) were the most significant environmental variables influencing the structure of the tychoplankton and of the epilithon. Other less important variables, such as K+, Fe, N(NO3−), and Na+ also explained significant (P < 0.05) amounts of variance. The ordination diagrams showed very similar distribution of the tychoplanktonic and epilithic diatom samples. At sites with similar geomorphology as in this study, it is possible to use only one of these samples for water quality evaluation. The optima and tolerances of some diatom taxa were calculated for the most influential variables. Although the diatoms showed high tolerances to some environmental parameters, it was possible to establish groups of taxa with defined and distinctive ecological preferences. Two species groups stood out depending on the alkalinity and mineralization of the water. With a moderate conductivity (> 600 μS·cm−1), alkaline pH, HCO3− concentrations equal or higher than 150 mg·l−1, the first group includes Achnanthes hungarica Grunow, Amphora pediculus (Kützing) Grunow, Bacillaria paxillifera (O. F. Müller) Hendey, Cymatopleura solea (Brébisson) W. Smith, Navicula accomoda Hustedt, Navicula lanceolata (Agardh) Ehrenberg, Navicula trivialis Lange-Bertalot, Nitzschia hungarica Grunow. In waters of lower conductivity (varying between 72 and 262 μS·cm−1) slightly acid pH (6 to 6.5) and HCO3−1 lower than 46 mg·l−1 the following species were common: Achnanthes oblongella Östrup, Achnanthes subatomoides (Hustedt) Lange-Bertalot, et Archibald, Cymbella gracilis (Ehrenberg) Kützing, Cymbella naviculiformis Auerswald, Diatoma mesodon (Ehrenberg) Kützing, and Eunotia exigua (Brébisson) Rabenhorst. Considering COD, two further groups were distinguished. At high values (> 40 mg·l−1) the following taxa were observed: Achnanthes delicatula (Kützing) Grunow, Navicula capitata Ehrenberg var. hungarica (Grunow) Ross, Nitzschia nana Grunow, Pinnularia interrupta W. Smith, Thalassiosira pseudonana Hasle & Heimdal, Thalassiosira weisflogii (Grunow) Fryxell et Hasle. For lower values than 19 mg·l−1, we found Cymbella naviculiformis Auerswald, Diatoma mesodon (Ehrenberg) Kützing, Eunotia exigua (Brébisson) Rabenhorst, Fragilaria arcus (Ehrenberg) Cleve, and Nitzschia epithemioides Grumow var. disputata (Carter) Lange-Bertalot. 相似文献
2.
BackgroundThe impact of chemical elements on the biosphere is a function of their concentration and chemical form. Elucidation and prognosing of the latters in water basins and soil extracts is of particular significance for the assessment of their bioaccumulation in plants and animals.ObjectivesTrace metals dynamics in the system water – soil–plant–wild rats – Hymenolepis diminuta in two agro-industrial zones (East and West) around Maglizh city, Bulgaria were investigated through experimental studies and thermodynamic modelling of the chemical species.MethodsSamples from surface waters of rivers, their nearby uncultivated soils, meadow uncultivated vegetation (Ranunculus acris and Gramineae) and field rats were collected. In situ measurements and laboratory analyses were performed for the determination of the physico-chemical characteristics and total concentrations of Al, Fe, Mn, Ni, Cu, Zn and Pb. The distribution of their dissolved chemical species in water samples and in the aqueous soil extracts was calculated using a thermodynamic approach. The relationship chemical species - bioaccumulation was discussed.ResultsWaters and soils in the East zone of Maglizh area were found to be more polluted compared to those in the West one, regarding Ni, Mn, Zn, Pb and Cu, while Mn and Cu displayed the highest mobility in West zone soils. Trace metals contents in Ranunculus acris exceed that in Gramineae, since the highest accumulation factors were calculated for Cu and Zn. The highest accumulation in rats was found for Zn followed by Cu, being higher in the West zone. Thermodynamic modelling shows that Mn2+ free ions are dominant in both waters and aqueous soil extracts. Ni2+ and Zn2+ ions followed by metal-organic complexes are dominant in waters of East zone while metal-organic complexes followed by free ions are dominant in waters of West zone and both soil extracts. Metal-organic complexes are dominant for Fe, Cu and Pb in all samples studied, while mainly hydroxy forms (Al(OH)4−) followed by metal-organic complexes are typically for Al depending on pH.ConclusionsExperimentally established bioaccumulation of trace metals in the studied vegetation and rats is a consequence of the total concentration of trace metals in waters and soils, their mobility and chemical species. The dominance of organic complexes of trace metals is a prerequisite for their bioaccumulation in plants. Rats are in direct contact with the soil solution and therefore, of importance is the content of free ions of Mn2+, Ni2+, Zn2+, which are easily absorbed through the skin. The host-helminth system wild rat/H. diminuta could be used as a bioindicator for trace metals pollution. 相似文献
3.
Bacterial bioluminescence was applied to detection of general toxicity (MIT test) and genotoxicity (SOS-lux test) of some chemicals, seawater, and fresh water. The SOS-induced luminescence of E. coli WP2s (cda::luxCDABE) cells was higher than in E. coli C 600 (cda::luxCDABE) at 37°C and pH 6.5. The mutagenic effect of N-methyl-N′-nitro-N-nitrosoguanidine (MNNG), mitomycin C, and hydrogen peroxide determined from the induction of E. coli WP2s cell luminescence was detected at lower concentrations than in the assessment of reversion frequencies. General toxicity was demonstrated by using luminescence inhibition for hydrogen peroxide, Zn2+, and Cd2+ at low concentrations. Regions of the Krasnodar Krai where sea and fresh waters exerted toxic action on luminescence were determined by the microbioluminescent method. 相似文献
4.
Effect of salts on luminescence of natural and recombinant luminescent bacterial biosensors 总被引:1,自引:0,他引:1
Effect of cations K+, Na+, Mg2+, and Ca2+ and anions Cl?, SO 4 2? , HCO 3 ? , and CO 3 2? on the luminescence intensity of the marine luminescent bacterium Photobacterium phorphoreum (Microbiosensor B-17 677f) and the recombinant strain Escherichia coli with cloned lux operon of P. leiognathi (Ecolum-9). It is found that small concentrations of chlorides and sulfates of the cations studied had a concentration-dependent stimulatory effect on bacterial bioluminescence; as the concentration of agents increased, activation was succeeded by quenching. The strength of the inhibitory effect, which is characterized by EC50, decreased in the series Ca2+ > Na+ > Mg2+ > K+. Carbonates and hydrocarbonates had a pronounced inhibitory effect on the bioluminescence intensity, determined by an increase in pH. We showed that some types of highly mineralized water with a high hydrocarbonate content have a marked inhibitory effect on the luminescence intensity of microbial luminescent biosensors, mimicking the effect of chemical pollutants. 相似文献
5.
《Journal of Fermentation and Bioengineering》1993,75(4):304-308
Propionate and NH4+ were accumulated in the effluent during anaerobic treatment of five-fold diluted distillery wastewater from shochu making. Propionate could be removed efficiently during biological denitrification by the addition of NO3− (4.2 g/l) to the anaerobically treated wastewater. At a hydraulic retention time of more than 2 h, a TOC removal efficiency of 90% could be achieved. The wastewater was then treated aerobically by biological nitrification. With a hydraulic retention time of more than 14 h the efficiency of reduction of NH4+ could be maintained above 97%. In order to reduce the amount of NO3− addition necessary for the removal of propionate, simultaneous removal of propionate and NH4+ was studied by recirculating the effluent from a nitrification process to a denitrification process using denitrification and nitrification reactors connected in series. At a recirculation ratio of 2, the amount of NO3− that had to be added was reduced to 0.3 g/l of anaerobically treated wastewater, which corresponds to 6.9% of the theoretical value. Under the same conditions except for the addition of NO3− at 1.0 g/l, TOC and BOD in the effluent from the nitrification were 23 and 5 mg/l respectively, which are sufficiently low to allow discharge into river water. Moreover, the NO3− concentration in the effluent decreased with increases in the recirculation ratio. 相似文献
6.
Percent respiration was measured in over 1,100 arctic and subarctic marine water and sediment samples using14C-labeled glucose and glutamate. These measurements were made at different times of the year in 4 regions. Percent respiration values were typically lower in regions where the waters of large rivers mixed with seawater. They were also lower in sediments and in waters collected near the bottom than in surface waters. They were higher in winter arctic waters than water samples collected in the summer; however, a similar seasonal trend was not observed in subarctic waters. There were a number of studies in which there were significant positive rank correlations between percent respiration and salinity and between percent respiration and temperature. From what is known about the range of temperature and salinity encountered in samples collected during these studies and the results of temperature and salinity effects experiments, it was concluded that changes in these 2 variables did not explain the variation observed in percent respiration. Correlations between percent respiration and the inorganic nutrients PO4
–3, NH4
+ and NO3
– showed that of the 3 variables, only NO3
– showed relatively high correlations with all the same sign. From this it was concluded that there may be situations in which NO3
– levels may influence percent respiration in nearshore marine waters. It is also likely that qualitative characteristics of the available organic nutrients may also influence percent respiration levels. Although no organic nutrient data is available for statistical analysis, the patterns of percent respiration near river plumes and the relatively strong negative correlation often observed between uptake rates (heterotrophic activity) and percent respiration suggests that organic nutrients may be a factor in controlling percent respiration. It is suggested that there are situations in which percent respiration measurements may be used to document stress in natural microbial populations due to nutrient deficiencies. 相似文献
7.
《Cytokine》2016
BackgroundSystemic reactions are related to the pathogenesis of Aspirin Exacerbated Respiratory Disease (AERD). With this work we wanted to study the changes in the systemic levels of inflammatory mediators in both baseline and after oral aspirin challenge in patients with and without AERD.MethodsPatients with nasal polyposis and asthma with AERD (n = 20) and without (n = 18) were orally challenged with aspirin in a single-blind placebo controlled study. Serum samples and urine were collected before and 6 h after placebo and aspirin oral challenges. Serum levels of inflammatory mediators were assayed by using the Luminex technology and ELISA. The concentrations of 9-alpha, 11-beta prostaglandin F2, and leukotriene E4 (uLTE4) were measured in urine samples by ELISA. The expression of T-cell surface markers was analyzed in peripheral blood mononuclear cells isolated before and after the challenges.ResultsAERD patients showed significantly higher baseline levels of s-IL-5R-alpha, uLTE4 and percentage of CD4+CD25+CD127pos and CD4+CD45RA−CD45RO+ but decreased levels of TGF-β1 and number of CD4+CD25+CD127neg cells. Aspirin challenge induced the release of uLTE4, IL-6 and increased the number of CD4+CD45RA−CD45RO+ memory T-cells only in AERD patients but failed to reduce the levels of sCD40L as observed in non-AERD subjects. Further, IL-8 and sIL-5R-alpha levels directly correlated with the PD20ASA and the effects of aspirin on IL-6 and number of memory T-cells was more pronounced in subjects showing more strong reaction (bronchial and nasal).ConclusionsAERD patients have a differential baseline inflammatory pattern that supports the role inflammation as underlying mechanism of the disease. Systemic response to oral aspirin challenge was related to an increase in serum IL-6 and the number of circulating memory T-cells in AERD patients. 相似文献
8.
Functional indicators are being increasingly used to assess waterway health but their responses to pressure in non-wadeable rivers have not been widely documented or applied in modern survey designs that provide unbiased estimates of extent. This study tests the response of river metabolism and loss in cotton strip tensile strength across a land use pressure gradient in non-wadeable rivers of northern New Zealand, and reports extent estimates for river metabolism and decomposition rates. Following adjustment for probability of selection, ecosystem respiration (ER) and gross primary production (GPP) for the target population of order 5–7 non-wadeable rivers averaged −7.3 and 4.8 g O2 m−2 d−1, respectively, with average P/R < 1 indicating dominance by heterotrophic processes. Ecosystem respiration was <−3.3 g O2 m−2 d−1 for 75% of non-wadeable river length with around 20% of length between −10 and −20 g O2 m−2 d−1. Cumulative distribution functions of cotton strength loss estimates indicated a more-or-less linear relationship with river km reflecting an even spread of decay rates (range in k 0.0007–0.2875 d−1) across non-wadeable rivers regionally. A non-linear relationship with land cover was detected for GPP which was typically <5 g O2 m−2 d−1 where natural vegetation cover was below 20% and greater than 80% of upstream catchment area. For cotton strength loss, the relationship with land cover was wedge-shaped such that sites with >60% natural cover had low decay rates (<0.02 d−1) with variability below this increasing as natural cover declined. Using published criteria for assessing waterway health based on ER and GPP, 232–298 km (20–29%) of non-wadeable river length was considered to have severely impaired ecosystem functioning, and 436–530 km (42–50%) had no evidence of impact on river metabolism. 相似文献
9.
《Harmful algae》2014
The West Florida Shelf (WFS) encompasses a range of environments from inshore estuarine to offshore oligotrophic waters, which are frequently the site of large and persistent blooms of the toxic dinoflagellate, Karenia brevis. The goals of this study were to characterize the nitrogen (N) nutrition of plankton across the range of environmental conditions on the WFS, to quantify the percentage of the plankton N demand met through in situ N regeneration, and to determine whether planktonic N nutrition changes when high concentrations of Karenia are present. In the fall of 2007, 2008, and 2009 we measured ambient nutrient concentrations and used stable isotope techniques to measure rates of primary production and uptake rates of inorganic N (ammonium, NH4+, and nitrate, NO3−), and organic N and carbon (C; urea and amino acids, AA) in estuarine, coastal, and offshore waters, as well as coastal sites with Karenia blooms present. In parallel, we also measured rates of in situ N regeneration – NH4+ regeneration, nitrification, and photoproduction of NH4+, nitrite and AA. Based on microscope observations, ancillary measurements, and previous monitoring history, Karenia blooms sampled represented three bloom stages – initiation in 2008, maintenance in 2007, and late maintenance/stationary phase in 2009. Nutrient concentrations were highest at estuarine sampling sites and lowest at offshore sites. Uptake of NH4+ and NO3− provided the largest contribution to N nutrition at all sites. At the non-Karenia sites, in situ rates of NH4+ regeneration and nitrification were generally sufficient to supply these substrates equal to the rates at which they were taken up. At Karenia sites, NO3− was the most important N substrate during the initiation phase, while NH4+ was the most important N form used during bloom maintenance and stationary phases. Rates of NH4+ regeneration were high but insufficient (85 ± 36% of uptake) to support the measured NH4+ uptake at all the Karenia sites although nitrification rates far exceeded uptake rates of NO3−. Taken together our results support the “no smoking gun” nutrient hypothesis that there is no single nutrient source or strategy that can explain Karenia's frequent dominance in the waters where it occurs. Consistent with other papers in this volume, our results indicate that Karenia can utilize an array of inorganic and organic N forms from a number of N sources. 相似文献
10.
《FEBS letters》1997,400(2-3):191-195
The different murine D2-type dopamine receptors (D2L, D2S, D3L, D3S, and D4) were expressed in Xenopus laevis oocytes. The D2-type receptors were all similarly and efficiently expressed in Xenopus oocytes and were shown to bind the D2 antagonist [125I]sulpride. They were all shown to activate Cl− influx upon agonist stimulation. Using the diagnostic inhibitor bumetanide, we were able to separate the Na+/K+/2Cl− cotransporter component of the Cl− influx from the total unidirectional Cl− influx. The D3L subtype was found to operate exclusively through the bumetanide-insensitive Cl− influx whereas the other D2-type receptors acted on the Na+/K+/2Cl− cotransporter as well. The pertussis toxin sensitivity of the receptor-activated chloride influx via the Na+/K+/2Cl− cotransporter varied between the various D2-type receptors showing that they may couple to different G proteins, and activate different second messenger systems. 相似文献
11.
《Harmful algae》2015
The nitrogen (N) uptake kinetic parameters for Microcystis field assemblages collected from the San Francisco Bay Delta (Delta) in 2012 and non-toxic and toxic laboratory culture strains of M. aeruginosa were assessed. The 15N tracer technique was used to investigate uptake of ammonium (NH4+), nitrate (NO3−), urea and glutamic acid over short-term incubations (0.5–1 h), and to study inhibition of NO3−, NH4+ and urea uptake by NH4+, NO3− and NH4+, respectively. This study demonstrates that Delta Microcystis can utilize different forms of inorganic and organic N, with the greatest capacity for NH4+ uptake and the least for glutamic acid uptake, although N uptake did not always follow the classic Michaelis–Menten hyperbolic relationship at substrate concentrations up to 67 μmol N L−1. Current ambient N concentrations in the Delta may be at sub-saturating levels for N uptake, indicating that if N loading (especially NH4+) were to increase, Delta Microcystis assemblages have the potential for increased N uptake rates. Delta Microcystis had the highest specific affinity, α, for NH4+ and the lowest for NO3−. In culture, N uptake by non-toxic and toxic M. aeruginosa strains was much higher than from the field, but followed similar N utilization trends to those in the field. Neither strain showed severe inhibition of NO3− uptake by NH4+ or inhibition of NH4+ uptake on NO3−, but both strains showed some inhibition of urea uptake by NH4+. 相似文献
12.
Masashi Tazawa 《Journal of plant research》1975,88(3):219-229
The cell sap of the internode ofNitella flexilis was replaced with the isotonic artificial pond water of high Ca2+-concentration (0.1 mM KCl, 0.1 mM NaCl, 10 mM CaCl2 and 275 mM mannitol) and changes in osmotic value and concentrations of K+, Na+ and Cl− of the cells were followed. When the operated cells were incubated in the artificial pond water containing 0.1 mM each of KCl, NaCl, CaCl2, they survived for only a short period of time (<10 hr). The cells did not absorb ions from the artificial pond water and showed a conspicuous decrease in the rate of cytoplasmic streaming. In such cell the concentration of K+ in the protoplasm decreased significantly. In order to reverse normal concentration gradients of K+ and Na+ across the protoplasmic layer, the cells of low vacuolar ionic concentrations were incubated in the artificial cell sap (90 mM KCl, 40 mM NaCl, 15 mM CaCl2, 10 mM MgCl2). It was found that the cells rapidly absorbed much K+, Na+ and Cl− and survived for a longer period (1–2 days). During this period the rate of cytoplasmic streaming was nearly normal. Furthermore, the cell lost much mannitol, indicating an enormous increase in permeability to it. Since both absorption of ions and leakage of mannitol at 1 C occurred at nearly the same rates as at 22 C, the processes are assumed to be passive. 相似文献
13.
《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1996,113(2):149-155
This review will focus on cases where it might be possible that the toxicity of the heavy metal mercury results from an interaction with osmoregulatory mechanisms. It is shown that mercury-induced impairment of osmoregulatory capability in the sense of severe modifications of the blood osmotic concentration is more pronounced in brachyuran decapod species adapted to dilute waters. The rationale for considering these effects is based on a comparison between mercury effects on three species of decapod crustaceans exhibiting various degrees of osmoregulation capability: the strong regulator crab Eriocheir sinensis, the weak regulator Carcinus maenas, both of them being euryhaline, and the stenohaline osmoconformer Cancer pagurus. It is established that a synergistic effect exists between salinity and HgCl2 toxicity in euryhaline species which are hyperregulators in dilute media, that is, E. sinensis and C. maenas only. Depth study of E. sinensis as a model demonstrates that Na+ and Cl− permeabilities of the gill epithelium is affected by mercury, as well as the Na+ and Cl− active transport processes located at the same level. Evidences are brought showing that mercury drastically disturbs the Na+/K+ pump and the Cl− channels located in the serosal baso-lateral membranes of the posterior gills. 相似文献
14.
The biogeochemical cycles of nitrogen (N) and base cations (BCs), (i.e., K+, Na+, Ca2+, and Mg2+), play critical roles in plant nutrition and ecosystem function. Empirical correlations between large experimental N fertilizer additions to forest ecosystems and increased BCs loss in stream water are well demonstrated, but the mechanisms driving this coupling remain poorly understood. We hypothesized that protons generated through N transformation (PPRN)—quantified as the balance of NH4+ (H+ source) and NO3− (H+ sink) in precipitation versus the stream output will impact BCs loss in acid-sensitive ecosystems. To test this hypothesis, we monitored precipitation input and stream export of inorganic N and BCs for three years in an acid-sensitive forested watershed in a granite area of subtropical China. We found the precipitation input of inorganic N (17.71 kg N ha−1 year−1 with 54% as NH4+–N) was considerably higher than stream exported inorganic N (5.99 kg N ha−1 year−1 with 83% as NO3−–N), making the watershed a net N sink. The stream export of BCs (151, 1518, 851, and 252 mol ha−1 year−1 for K+, Na+, Ca2+, and Mg2+, respectively) was positively correlated (r = 0.80, 0.90, 0.84, and 0.84 for K+, Na+, Ca2+, and Mg2+ on a monthly scale, respectively, P < 0.001, n = 36) with PPRN (389 mol ha−1 year−1) over the three years, suggesting that PPRN drives loss of BCs in the acid-sensitive ecosystem. A global meta-analysis of 15 watershed studies from non-calcareous ecosystems further supports this hypothesis by showing a similarly strong correlation between ∑BCs output and PPRN (r = 0.89, P < 0.001, n = 15), in spite of the pronounced differences in environmental settings. Collectively, our results suggest that N transformations rather than anions (NO3− and/or SO42−) leaching specifically, are an important mediator of BCs loss in acid-senstive ecosystems. Our study provides the first definitive evidence that the chronic N deposition and subsequent transformation within the watershed drive stream export of BCs through proton production in acid-sensitive ecosystems, irrespective of their current relatively high N retention. Our findings suggest the N-transformation-based proton production can be used as an indicator of watershed outflow quality in the acid-sensitive ecosystems. 相似文献
15.
《Journal of inorganic biochemistry》1999,73(1-2):85-92
The interaction of OH− with Fe(TPP)+, Fe(TDCPP)+, Fe(TMP)+ and Fe(TFPP)+ in 1,2-dichloroethane was studied by titrating FeP solutions with aliquots of a solution of tetrabutylammonium hydroxide in acetonitrile. The number of OH− ions (n) coordinated to the FeP and the stability constants (βn) for the FeP-OH− complexes were calculated from UV-Vis absorbance data and iron spin states were determined through EPR spectroscopy. Fe(TMP)+ forms a high-spin mono-hydroxo complex, while Fe(TPP)+ and Fe(TDCPP)+ form high-spin bis-hydroxo complexes. To our knowledge, this is the first time that the formation of bis-hydroxo complexes from Fe(TPP)+ has been reported, and this was possible because the studies were carried out in basic organic media. In this same medium, FeIII-FeII reduction upon OH− addition to Fe(TFPP)+ was observed, without concomitant formation of the μ-oxo dimeric species [Fe(TFPP)]2O. 相似文献
16.
《Process Biochemistry》2014,49(12):2158-2169
To reveal the impact of ionic liquids (ILs) on the stability of proteins, a series of ILs possessing same 1-butyl-3-methylimidazolium cation [Bmim]+ with a set of Hofmeister anions such as SCN−, HSO4−, Cl−, Br−, CH3COO− and I− were used and their effects on the myoglobin (Mb) structure and stability were studied. For the sake of comparison and also to explore the extent of the stabilization behavior of ILs toward Mb stability, we have chosen a set of ionic salts (Is) of a fixed sodium cation (Na+) with the same series of anions such as SCN−, SO4−2, Cl−, Br−, CH3COO− and I−. UV–vis, fluorescence and circular dichroism (CD) spectroscopic techniques were used in order to investigate the stability behavior of Mb in ionic species (Is and ILs). The results reveal that both Is and ILs had a negative influence on the stability of Mb. Apparently, the flexibility in the native structure of Mb gradually increases with the increase in the concentration of Is and ILs at pH 7.0. Therefore, a sharp decrease in the transition temperature (Tm) of the native Mb is observed in the presence of Is and ILs. 相似文献
17.
《Inorganica chimica acta》1988,144(2):275-280
The fragmentation patterns of yttrium oxide cluster species YO+, Y2O2+, Y2O3+, Y3O4+, Y4O6+, Y5O7+, Y6O8+ and Y7O10+ were investigated at collision energies 30–110 and 170 eV by fast atom bombardment tandem mass spectrometry. The collision activated dissociation (CAD) spectra obtained revealed higher thermodynamic stability for the clusters of general formula YαO(3α−1)/2+, where a is an odd number (e.g. YO+, Y3O4+, Y5O7+, Y7O10+) which are also the preferred CAD products for all oxide clusters studied. These most stable oxides are constituted by trivalent yttrium only whereas those containing formally tetravalent yttrium YaO3a/2+, (where a is even) e.g. Y2O3+ and Y4O6+, are extremely unstable. The clusters YaO(3a−2)/2+, (where a is even) containing divalent yttrium, e.g. Y2O2+ and Y6O8+, have considerable stability but their CAD products are again the thermodynamic products YaO(3a−1)/2+. Electronic structures appear to have overriding significance in determining the thermo- dynamic stabilities of the oxide cluster species. 相似文献
18.
19.
《Inorganica chimica acta》1986,115(1):101-106
Studies of mixed ligand complex formation stabilities and dissociation kinetics have been performed on lanthanide ions with macrocyclic and open- chained polyaminopolycarboxylic acids (i.e. DAPDA, DACDA, EDDA, and EDTA) and acetylacetone (acac). From UV spectroscopic evidence, it was found that Ln(DACDA)+ and Ln(EDTA)− complexes do not form mixed ligand complexes with acac under the set conditions, i.e. pH = 7.2 and complex concentration of 1 x 10−4 M. On the other hand, formation of Ln(DAPDA)(acac) and Ln(EDDA)(acac)2− complexes were readily detectable. The mixed complex forma- tion constants,β1, for the equilibrium Ln(L)+ + acac− ⇌ Ln(L)(acac), and β2, for the equilibrium Ln(L)+ + 2 acac− ⇌ Ln(L)(acac)2− were determined by potentiometric titration technique where possible. It was found that β1 values were in general greater for Ln(EDDA)+ complexes than for Ln(DAPDA)+ complexes indicating the resulting reduced charge density at the lanthanide ion of Ln(DAPDA)+ and that less space is available for the acetylacetone moiety to coordinate to the Ln(DAPDA)+ complexes due to the large size and the greater number of coordination atoms of DAPDA. The hydrolysis constants of Ln(EDDA)(H2O)n+ species were also determined and were found to be increasing with increasing atomic number of Ln. Attempts to measure the acid assisted mixed ligand complex dissociation rates by a stopped-flow spectrophotometer were not fruitful due to the much faster rates. 相似文献
20.
《Harmful algae》2019
Nodularia spumigena is a toxic cyanobacteria that blooms in the Baltic Sea every year. In the brackish water of the Baltic Sea, its toxin, nodularin, mainly affects the biota in the surface water due to the natural buoyancy of this species. However, the fate of the toxin is unknown, once the cyanobacteria bloom enters the more saline waters of the Kattegat. In order to investigate this knowledge gap, a bloom of N. spumigena was followed during its passage, carried by surface currents, from the Baltic Sea into the Kattegat area, through the Öresund strait. N. spumigena cells showed an increased cell concentration through the water column during the passage of the bloom (up to 130 103 cells ml−1), and cells (4.2 103 cells ml−1) could be found down to 20 m depth, below a pycnocline. Sedimentation trap samples from below the pycnocline (10–12 m depth) also showed an increased sedimentation of N. spumigena filaments during the passage of the bloom. The toxin nodularin was detected both in water samples (0.3–6.0 μg l−1), samples of sedimenting material (a toxin accumulation rate of 20 μg m-2 day−1), zooplankton (up to 0.1 ng ind.−1 in copepods), blue mussels (70–230 μg kg−1 DW), pelagic and benthic fish (herring (1.0–3.4 μg kg−1 DW in herring muscle or liver) and flounder (1.3-6.2 μg kg−1 DW in muscle, and 11.7-26.3 μg kg−1 DW in liver). A laboratory experiment showed that N. spumigena filaments developed a decreased buoyancy at increased salinities and that they were even sinking with a rate of up to 1,7 m day−1 at the highest salinity (32 PSU). This has implications for the fate of brackish water cyanobacterial blooms, when these reach more saline waters. It can be speculated that a significant part of the blooms content of nodularin will reach benthic organisms in this situation, compared to blooms decaying in brackish water, where most of the bloom is considered to be decomposed in the surface waters. 相似文献