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Metal Hydroxides (metal + hydroxide)
Selected AbstractsInfrared Spectroscopic Observation of the Group 13 Metal Hydroxides, M(OH)1,2,3 (M: Al, Ga, In, and Tl) and HAl(OH2)CHEMINFORM, Issue 22 2007Xuefeng Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Effect of alkali metal hydroxides on the enantioseparation of amines using di- O -isopropylidene-keto- L -gulonic acid as the selector in NACEELECTROPHORESIS, Issue 22 2006Ylva Hedeland Dr. Abstract The present work demonstrates the importance of the ionic composition in the BGE for enantioseparation. (,)-2,3:4,6-di- O -Isopropylidene-2-keto- L -gulonic acid ((,)-DIKGA) has been used as the chiral selector in methanolic and ethanolic BGEs. The influence of added alkali metal hydroxides on the EOF and the chiral separation of amines (atenolol, isoprenaline, pindolol and propranolol) have been studied. The ion-pair formation constants in ethanol were determined by precision conductometry for the enantiomers of pindolol with (,)-DIKGA, for Li+, Na+ and Cs+ with (,)-DIKGA, and also for the corresponding alkali metal hydroxides. The effective mobilities and the enantiomeric mobility differences were affected by the type of alkali metal hydroxide (LiOH, NaOH, KOH, RbOH or CsOH) added to the BGE. The effective mobility and mobility difference were increased with decrease in solvated radius of the alkali metal cation. These differences could partly be correlated to the ion-pair formation constants of the alkali metal cations with the chiral selector, affecting the equilibrium concentration of the free selector. The electroosmosis was also affected by the alkali metal hydroxide added to the BGE. The cathodic electroosmosis decreased with decreasing solvated radius of the alkali metal cation added to the BGE. Interestingly, the cathodic EOF was even reversed, i.e. became anodic in the ethanolic BGEs containing KOH, RbOH or CsOH and the methanolic ones with RbOH and CsOH. [source] Acute toxicity of heavy metals to acetate-utilizing mixed cultures of sulfate-reducing bacteria: EC100 and EC50ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2001Vivek P. Utgikar Abstract Acid mine drainage from abandoned mines and acid mine pit lakes is an important environmental concern and usually contains appreciable concentrations of heavy metals. Because sulfate-reducing bacteria (SRB) are involved in the treatment of acid mine drainage, knowledge of acute metal toxicity levels for SRB is essential for the proper functioning of the treatment system for acid mine drainage. Quantification of heavy metal toxicity to mixed cultures of SRB is complicated by the confounding effects of metal hydroxide and sulfide precipitation, biosorption, and complexation with the constituents of the reaction matrix. The objective of this paper was to demonstrate that measurements of dissolved metal concentrations could be used to determine the toxicity parameters for mixed cultures of sulfate-reducing bacteria. The effective concentration, 100% (EC100), the lowest initial dissolved metal concentrations at which no sulfate reduction is observed, and the effective concentration, 50% (EC50), the initial dissolved metal concentrations resulting in a 50% decrease in sulfate reduction, for copper and zinc were determined in the present study by means of nondestructive, rapid physical and chemical analytical techniques. The reaction medium used in the experiments was designed specifically (in terms of pH and chemical composition) to provide the nutrients necessary for the sulfidogenic activity of the SRB and to preclude chemical precipitation of the metals under investigation. The toxicity-mitigating effects of biosorption of dissolved metals were also quantified. Anaerobic Hungate tubes were set up (at least in triplicate) and monitored for sulfate-reduction activity. The onset of SRB activity was detected by the blackening of the reaction mixture because of formation of insoluble ferrous sulfide. The EC100 values were found to be 12 mg/L for copper and 20 mg/L for zinc. The dissolved metal concentration measurements were effective as the indicators of the effect of the heavy metals at concentrations below EC100. The 7-d EC50 values obtained from the difference between the dissolved metal concentrations for the control tubes (tubes not containing copper or zinc) and tubes containing metals were found to be 10.5 mg/L for copper and 16.5 mg/L for zinc. Measurements of the turbidity and pH, bacterial population estimations by means of a most-probable number technique, and metal recovery in the sulfide precipitate were found to have only a limited applicability in these determinations. [source] The RNA-Cleaving Bipartite DNAzyme Is a Distinctive MetalloenzymeCHEMBIOCHEM, Issue 1 2006Anat R. Feldman Dr. Abstract Much interest has focused on the mechanisms of the five naturally occurring self-cleaving ribozymes, which, in spite of catalyzing the same reaction, adopt divergent strategies. These ribozymes, with the exception of the recently described glmS ribozyme, do not absolutely require divalent metal ions for their catalytic chemistries in vitro. A mechanistic investigation of an in vitro-selected, RNA-cleaving DNA enzyme, the bipartite, which catalyzes the same chemistry as the five natural self-cleaving ribozymes, found a mechanism of significant complexity. The DNAzyme showed a bell-shaped pH profile. A dissection of metal usage indicated the involvement of two catalytically relevant magnesium ions for optimal activity. The DNAzyme was able to utilize manganese(II) as well as magnesium; however, with manganese it appeared to function complexed to either one or two of those cations. Titration with hexaamminecobalt(III) chloride inhibited the activity of the bipartite; this suggests that it is a metalloenzyme that utilizes metal hydroxide as a general base for activation of its nucleophile. Overall, the bipartite DNAzyme appeared to be kinetically distinct not only from the self-cleaving ribozymes but also from other in vitro-selected, RNA-cleaving deoxyribozymes, such as the 8,17, 10,23, and 614. [source] Effect of alkali metal hydroxides on the enantioseparation of amines using di- O -isopropylidene-keto- L -gulonic acid as the selector in NACE (vol. 27, issue 22, pp.ELECTROPHORESIS, Issue 24 20064469-4479) No abstract is available for this article. [source] Effect of alkali metal hydroxides on the enantioseparation of amines using di- O -isopropylidene-keto- L -gulonic acid as the selector in NACEELECTROPHORESIS, Issue 22 2006Ylva Hedeland Dr. Abstract The present work demonstrates the importance of the ionic composition in the BGE for enantioseparation. (,)-2,3:4,6-di- O -Isopropylidene-2-keto- L -gulonic acid ((,)-DIKGA) has been used as the chiral selector in methanolic and ethanolic BGEs. The influence of added alkali metal hydroxides on the EOF and the chiral separation of amines (atenolol, isoprenaline, pindolol and propranolol) have been studied. The ion-pair formation constants in ethanol were determined by precision conductometry for the enantiomers of pindolol with (,)-DIKGA, for Li+, Na+ and Cs+ with (,)-DIKGA, and also for the corresponding alkali metal hydroxides. The effective mobilities and the enantiomeric mobility differences were affected by the type of alkali metal hydroxide (LiOH, NaOH, KOH, RbOH or CsOH) added to the BGE. The effective mobility and mobility difference were increased with decrease in solvated radius of the alkali metal cation. These differences could partly be correlated to the ion-pair formation constants of the alkali metal cations with the chiral selector, affecting the equilibrium concentration of the free selector. The electroosmosis was also affected by the alkali metal hydroxide added to the BGE. The cathodic electroosmosis decreased with decreasing solvated radius of the alkali metal cation added to the BGE. Interestingly, the cathodic EOF was even reversed, i.e. became anodic in the ethanolic BGEs containing KOH, RbOH or CsOH and the methanolic ones with RbOH and CsOH. [source] Zinc hydroxystannate-coated metal hydroxides as flame retardant and smoke suppression for flexible poly vinyl chlorideFIRE AND MATERIALS, Issue 4 2009Hongqiang Qu Abstract Zinc hydroxystannate (ZHS)-coated metal hydroxides were prepared. The effects of ZHS-coated metal hydroxides on flame retardancy and smoke suppression of flexible poly vinyl chloride were studied by means of the limiting oxygen index, smoke density rating and the char yield test. The mechanism was investigated by thermogravimerty (TG), differential thermal analysis, and differential TG analysis and scanning electron microscopy. The results showed that ZHS-coated metal hydroxides are more effective flame retardant and smoke suppressant than metal hydroxides, and it appears that tin compound may exert its action in both the condensed and vapor phases, but mainly in condensed phases as a Lewis acid. Copyright © 2009 John Wiley & Sons, Ltd. [source] Flame retardant properties of EVA-nanocomposites and improvements by combination of nanofillers with aluminium trihydrateFIRE AND MATERIALS, Issue 5 2001Günter Beyer Flame retardant nanocomposites are synthesized by melt-blending ethylene,vinyl acetate copolymers (EVA) with modified layered silicates (montmorillonites). Thermogravimetric analysis performed under different atmospheres (nitrogen and air) demonstrated a clear increase in the thermal stability of the layered silicate-based nanocomposites. The use of the cone calorimeter to investigate the fire properties of the materials indicated that the nanocomposites caused a large decrease in heat release. The char-formation is the main factor important for improvement and its function is outlined. Further improvements of the flame retardancy by combinations of nanofillers and traditional FR-additives on the basis of metal hydroxides were also studied. Copyright © 2002 John Wiley & Sons, Ltd. [source] On the nature of Ti(IV)-pillared layered metal hydroxides prepared from green, water-soluble Ti-peroxideAICHE JOURNAL, Issue 5 2010Jing He Abstract Ti-peroxide pillared layered double hydroxides (LDHs) have been prepared for the first time using water-soluble Ti-peroxide as an intercalating precursor. It is novel and alluring that the whole preparation procedure does not involve any usage of organic or chlorine-containing hazards. Intercalated into the LDH interlayer region, Ti-peroxide is prevented partially from condensation in the solvent evaporation. The interlayer TiO2 unit exists in triangular (,2) structure with C2, symmetry in most cases, giving an interlayer gallery of 0.50,0.60 nm. But in the case of pH 4.0, monodentate (,1) structure is also observed, giving an interlayer gallery of 0.70 nm. All the Ti-peroxide pillared LDHs prepared in this work show catalytic activity in the selective oxidation of thioether. The Ti-peroxide introduced into the interlayer regions of Mg/Al LDH with a particle size of around 50,120 nm exhibits better recyclability than Ti-peroxide gel, either in bulk or adsorbed on the exterior surface of LDH particles. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Sources and bioavailability of phosphorus fractions in freshwaters: a British perspectiveBIOLOGICAL REVIEWS, Issue 1 2001C. S. REYNOLDS ABSTRACT This paper seeks a perspective on the forms of phosphorus which promote aquatic eutrophication, with the particular quest of establishing their sources. A short background traces the development of understanding of nutrient enrichment and the suppositions about the relative contributions of agriculture, sewage and detergent residues. Most aquatic systems, and their primary producers, are naturally deficient in biologically-available phosphorus. Aquatic plants have evolved very efficient phosphorus uptake mechanisms. The biomass responses to an increase in the supply of phosphorus are stoichiometrically predictable. The most bioavailable forms of phosphorus are in solution, as orthophosphate ions, or are readily soluble or elutable from loose combinations. Ready bioavailability coincides well with what is measurable as molybdate-reactive (MRP) or soluble-reactive phosphorus (SRP). Most other forms, including phosphates of the alkaline earth metals, aluminium and iron are scarcely available at all. Orthophosphate ions sorbed to metal oxides and hydroxides are normally not biologically available either, except through weak dissociation (,desorption'). The production of alkaline phosphatase provides organisms with an additional mechanism for accelerating the sequestration of phosphate from organic compounds. Bioavailable phosphate is liberated when redox- or alkali-sensitive metal hydroxides dissolve but these processes are minor contributors to the biological responses to nutrient enrichment. Most of the familiar eutrophication is attributable to the widespread application of secondary sewage treatment methods to the wastes emanating from a burgeoning and increasingly urbanised human population. The use of polyphosphate-based detergents, now in decline, has contributed to the problem. In aquatic systems, the additional phosphorus raises the biological supportive capacity, sometimes to the capacity of the next limiting factor (carbon, light, hydraulic retention or of another nutrient). At high orthophosphate loadings, the straight stoichiometric yield relationship between biomass yield and phosphorus availability is lost. Movements of phosphorus and its recycling within aquatic systems do not prevent the slow gravitation of phosphorus to the bottom substrata. The phosphorus retentivity of sediments depends upon their chemical composition. While oxide-hydroxide binding capacity in the surface sediments persists, they act as a sink for phosphorus and a control on further cycling. Iron-rich and clay-rich sediments perform best in these conditions; calcareous sediments least so. Eutrophication may lead to the exhaustion of sediment P-binding capacity. Non-sorbed phosphate is readily recyclable if primary producers have access to it. Recycling is most rapid in shallow waters (where sediment disturbance, by flow, by wind action and through bioturbation, is frequent) and least in deep ventilated sediments. The contributions of phosphorus from catchments are assessed. The slow rate of weathering of (mostly apatitic) minerals, the role of chemical binding in soils and the incorporation and retentivity by forested terrestrial ecosystems each contribute to the minimisation of phosphorus leakage to drainage waters. Palaeolimnological and experimental evidence confirms that clearance of land and ploughing its surface weakens the phosphorus retentivity of catchments. The phosphorus transferred from arable land to drainage remains dominated by sorbed fractions which are scarcely bioavailable. Some forms of intensive market gardening or concentrated stock rearing may mobilise phosphates to drainage but it is deduced that drainage from agricultural land is not commonly a major source of readily bioavailable phosphorus in water. Careful budgeting of the phosphates in run-off from over-fertilised soils may nevertheless show that a proportionately small loss of bioavailable phosphorus can still be highly significant in promoting aquatic plant production. The bioavailable-phosphorus (BAP) load achieving the OECD threshold of lake eutrophy (35 mg P m,3) is calculated to be equivalent to a terrestrial loss rate of approximately 17.5 kg BAP km,2 year,1), or only 1,2% of a typical fertiliser application. The output is shown to be comparable with the P yield from secondary treatment of the sewage produced by a resident population of 30,44 persons km,2. With tertiary treatment, the equivalence is with approximately 200 persons km,2. [source] Precipitation and recovery of metal sulfides from metal containing acidic wastewater in a sulfidogenic down-flow fluidized bed reactorBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2009Marisol Gallegos-Garcia Abstract This study reports the feasibility of recovering metal precipitates from a synthetic acidic wastewater containing ethanol, Fe, Zn, and Cd at an organic loading rate of 2.5 g COD/L-day and a COD to sulfate ratio of 0.8 in a sulfate reducing down-flow fluidized bed reactor. The metals were added at increasing loading rates: Fe from 104 to 320 mg/L-day, Zn from 20 to 220 mg/L-day, and Cd from 5 to 20 mg/L-day. The maximum COD and sulfate removals attained were 54% and 41%, respectively. The biofilm reactor was operated at pH as low as 5.0 with stable performance, and no adverse effect over COD consumption or sulfide production was observed. The metals precipitation efficiencies obtained for Fe, Zn, and Cd exceeded 99.7%, 99.3%, and 99.4%, respectively. The total recovered precipitate was estimated to be 90% of the theoretical mass expected as metal sulfides. The precipitate was mainly recovered from the bottom of the reactor and the equalizer. The analysis of the precipitates showed the presence of pyrite (FeS2), sphalerite (ZnS) and greenockite (CdS); no metal hydroxides or carbonates in crystalline phases were identified. This study is the first in reporting the feasibility to recover metal sulfides separated from the biomass in a sulfate reducing process in one stage. Biotechnol. Bioeng. 2009;102: 91,99. © 2008 Wiley Periodicals, Inc. [source] Cobalt Coordination and Clustering in ,-Co(OH)2 Revealed by Synchrotron X-ray Total ScatteringCHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2010James Abstract Structures of layered metal hydroxides are not well described by traditional crystallography. Total scattering from a synthesis-controlled subset of these materials, as described here, reveals that different cobalt coordination polyhedra cluster within each layer on short length scales, offering new insights and approaches for understanding the properties of these and related layered materials. Structures related to that of brucite [Mg(OH)2] are ubiquitous in the mineral world and offer a variety of useful functions ranging from catalysis and ion-exchange to sequestration and energy transduction, including applications in batteries. However, it has been difficult to resolve the atomic structure of these layered compounds because interlayer disorder disrupts the long-range periodicity necessary for diffraction-based structure determination. For this reason, traditional unit-cell-based descriptions have remained inaccurate. Here we apply, for the first time to such layered hydroxides, synchrotron X-ray total scattering methods,analyzing both the Bragg and diffuse components,to resolve the intralayer structure of three different ,-cobalt hydroxides, revealing the nature and distribution of metal site coordination. The different compounds with incorporated chloride ions have been prepared with kinetic control of hydrolysis to yield different ratios of octahedrally and tetrahedrally coordinated cobalt ions within the layers, as confirmed by total scattering. Real-space analyses indicate local clustering of polyhedra within the layers, manifested in the weighted average of different ordered phases with fixed fractions of tetrahedrally coordinated cobalt sites. These results, hidden from an averaged unit-cell description, reveal new structural characteristics that are essential to understanding the origin of fundamental material properties such as color, anion exchange capacity, and magnetic behavior. Our results also provide further insights into the detailed mechanisms of aqueous hydrolysis chemistry of hydrated metal salts. We emphasize the power of the methods used here for establishing structure,property correlations in functional materials with related layered structures. [source] | |||||||||||||