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PubMed2004

Formation of metal-arsenate precipitates at the goethite-water interface.

Little information is available concerning cosorbing oxyanion and metal contaminants in the environment, yet in most metal-contaminated areas, cocontamination by arsenate [AsO4, As(V)] is common. This study investigated the cosorption of As(V) and Zn on goethite at pH 4 and 7 as a function of final solution concentration. Complimentary extended X-ray absorption fine structure (EXAFS) spectroscopic data were collected at the As and Zn K-edges in order to glean information about the coordination environment of As and Zn at the goethite-water interface. Macroscopic sorption studies revealed that As(V) and Zn sorption on goethite increased in cosorption experiments beyond that suggested by single sorption isotherms. At pH 4 and 7, As(V) surface saturation was 3.2 and 2.2 micromol m(-2), respectively, and Zn surface saturation was absent at pH 4 and approximately 1.0 micromol m(-2) at pH 7. Arsenate sorption on goethite increased in the presence of Zn by 29% and by more than 500% at pH 4 and 7, respectively. In the presence of As(V), Zn sorption on goethite increased by 800 and 1300% at pH 4 and 7, respectively. More As(V) than Zn sorbed on goethite below surface saturation at pH 7. Above surface saturation, the Zn:As surface density ratio (SDR) remained constant at 0.91 +/- 0.03. At pH 4, the Zn:As SDR was less than 1 throughout the concentration range. Below As(V) surface saturation on goethite, As(V) formed bidentate binuclear bridging complexes on Fe and/or Zn octahedra, while Zn mainly formed edge-sharing complexes with Fe at the goethite surface. Above surface saturation, Zn was increasingly complexed by AsO4, gradually forming an adamite-like [Zn2(AsO4)OH] surface precipitate on goethite. Precipitated contaminants are more stable due to the limited dissolution kinetics of their solid phase. This study may therefore prove useful in remediation strategies of sites knowingly contaminated with oxyanions and metals.

Adsorption↗
PubMed2005

Simultaneous application of dissolution/precipitation and surface complexation/surface precipitation modeling to contaminant leaching.

This paper discusses the modeling of anion and cation leaching from complex matrixes such as weathered steel slag. The novelty of the method is its simultaneous application of the theoretical models for solubility, competitive sorption, and surface precipitation phenomena to a complex system. Selective chemical extractions, pH dependent leaching experiments, and geochemical modeling were used to investigate the thermodynamic equilibrium of 12 ions (As, Ca, Cr, Ba, SO4, Mg, Cd, Cu, Mo, Pb, V, and Zn) with aqueous complexes, soluble solids, and sorptive surfaces in the presence of 12 background analytes (Al, Cl, Co, Fe, K, Mn, Na, Ni, Hg, NO3, CO3, and Ba). Modeling results show that surface complexation and surface precipitation reactions limit the aqueous concentrations of Cd, Zn, and Pb in an environment where Ca, Mg, Si, and CO3 dissolve from soluble solids and compete for sorption sites. The leaching of SO4, Cr, As, Si, Ca, and Mg appears to be controlled by corresponding soluble solids.

Adsorption↗
PubMed2004

Annual variations of pesticide concentrations in Great Lakes precipitation.

Twenty pesticides and related analytes were measured in 28-day integrated precipitation samples from five U.S. sites in the Integrated Atmospheric Deposition Network (IADN) between 1997 and 2002. Consistent, significant decreases in concentration as a function of time were observed only for p,p'-DDE and p,p'-DDD, while increases in beta-HCH were observed at all sites. Significant annual variations were observed for most analytes at each site with higher concentrations in the summer for current-use pesticides (endosulfan and gamma-HCH) and peaks in the winter for most others. The increased concentrations in the winter are likely the result of the increased scavenging efficiency of snow compared to rain and, for some analytes, higher concentrations in the particulate phase during winter. These seasonal differences appear to account for a large portion of the observed variability in pesticide concentrations in precipitation samples.

Air Pollutants↗
PubMed2006

Effect of strontium contaminants upon the size and solubility of calcite crystals precipitated by the bacterial hydrolysis of urea.

The nucleation and growth of calcite precipitates induced by the bacterial hydrolysis of urea (ureolysis) from a Sr-contaminant inclusive, and a Sr-free artificial groundwater (AGW) mimicking the composition of the 90Sr contaminated Snake River Plain aquifer were investigated. Sr-free experiments exhibited a gradual increase in mean calcite crystal diameter (<1000 nm) from day (D) 1 to 6, while in the Sr-inclusive experiments, daily diameters were approximately constant from D1 to D6, and crystals were smaller (mean <840 nm). These data demonstrate a steady state had been attained early in the Sr-inclusive experiments from growth inhibition by Sr. Modeling of the crystal growth mechanisms on the USGS GALOPER software suggested crystal size distributions in the Sr-inclusive and Sr-free experiments were generated in the nucleation stage by a decreasing nucleation rate with surface-controlled growth, followed by supply-controlled and random growth. This occurred despite the availability of Ca2+ and HCO3-, implying crystal growth is limited bythe rate of solute advection to the crystal surface. Calculation of the solubility constant (In KsO(A)) demonstrates smaller crystals are more soluble, reflecting a higher molar surface area. The coprecipitation of Sr therefore generates smaller and thus more soluble crystals. However, this is unlikely to dramatically reduce the long-term effectiveness of Sr immobilization because when crystal growth had ceased in the Sr-inclusive AGW, > 99% of calcite precipitated and Sr coprecipitated occurred in large crystals with a low solubility.

Bacteria↗
PubMed2006

Observation of surface precipitation of arsenate on ferrihydrite.

X-ray diffraction and Raman spectroscopy were used in this study to characterize arsenate phases in the arsenate-ferrihydrite sorption system. Evidence has been obtained for surface precipitation of ferric arsenate on synthetic ferrihydrite at acidic pH (3-5) underthe following experimental conditions: sorption density of As/Fe approximately 0.125-0.49 and arsenic equilibrium concentration of <0.02-440 mg/L. Surface precipitation occurred under apparently undersaturated (in the bulk solution phase) conditions, and probably involved initial uptake of arsenate by surface complexation followed by transition to ferric arsenate formation on the surface as indicated by XRD analysis. At basic pH (i.e., pH 8), however, no ferric arsenate was observed in arsenate-ferrihydrite samples at a sorption density of As/Fe approximately 0.125-0.30 and an arsenic equilibrium concentration of 2.0-1100 mg/ L. At pH 8, arsenate is sorbed on ferrihydrite predominantly via surface adsorption, and the XRD patterns resemble basically that of ferrihydrite.

Adsorption↗
PubMed2006

Effects of carbonate precipitates on long-term performance of granular iron for reductive dechlorination of TCE.

Long-term column experiments were conducted to evaluate the effects of secondary carbonate minerals on permeability and reactivity of commercial granular iron treating trichloroethene (TCE). The results showed that carbonate precipitates caused a decrease in reactivity of the iron, and spatially and temporally varying reactivity loss resulted in migration of mineral precipitation fronts, as well as profiles of TCE, pH, alkalinity, calcium, and dissolved iron. In the columns receiving solutions of dissolved calcium carbonate, porosity gradually decreased in proportion to the source concentrations, as carbonate minerals accumulated. However, the rate of porosity loss slowed over time because of the declining reactivity of the iron. Thus, secondary minerals are not likely to accumulate to the extent that there is a substantial reduction in hydraulic conductivity. The reactivity of the iron was found to decrease as an exponential function of the carbonate mineral volume fraction. This changing reactivity of iron should be incorporated into predictive models for improved designs of iron permeable reactive barriers (PRBs).

Calcium Carbonate↗
PubMed2005

Reversible precipitation of casein micelles with a cationic hydroxyethylcellulose.

The cationic hydroxyethylcellulose Polyquaternium 10 (PQ10) was found to produce a dose-dependent destabilization of casein micelles from whole or skim milk without affecting the stability of most of the whey proteins. The anionic phosphate residues on caseins were not determinant in the observed interaction since the destabilization was also observed with dephosphorylated caseins to the same extent. However, the precipitation process was completely inhibited by rising NaCl concentration, indicating an important role of electrostatic interactions. Furthermore, the addition of 150 mM NaCl solubilized preformed PQ10-casein complexes, rendering a stable casein suspension without a disruption of the internal micellar structure as determined by dynamic light scattering. This casein preparation was found to contain most of the Ca2+ and only 10% of the lactose originally present in milk and remained as a stable suspension for at least 4 months at 4 degrees C. The final concentration of PQ10 determined both the size of the casein-polymer aggregates and the amount of milkfat that coprecipitates. The presence of PQ10 in the aggregates did not inhibit the activity of rennet or gastrointestinal proteases and lipases, nor did it affect the growth of several fermentative bacteria. The cationic cellulose PQ10 may cause a reversible electrostatic precipitation of casein micelles without disrupting their internal structure. The reversibility of the interaction described opens the possibility of using this cationic polysaccharide to concentrate and resuspend casein micelles from whole or skim milk in the production of new fiber-enriched lactose-reduced calcium-caseinate dairy products.

Animals↗
PubMed2004

Phospholipase D-mediated aggregation, fusion, and precipitation of phospholipid vesicles.

Large unilamellar vesicles with a diameter of 100 nm were prepared from the zwitterionic phospholipid POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) at pH 8.0. After addition to these vesicles of the enzyme phospholipase D (PLD) from Streptomyces sp. AA586 at 40 degrees C, the terminal phosphate ester bond of POPC was hydrolyzed, yielding the negatively charged POPA (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidic acid) and the positively charged choline. While the reaction yield in the presence of 1 mM Ca2+ reached 100%, the yield was only approximately 68% in the absence of Ca2+. Furthermore, in the absence of Ca2+, the size of the vesicles did not change significantly with time upon PLD addition, as judged from turbidity, dynamic light scattering, and electron microscopy measurements. In the presence of 1 mM Ca2+, however, PLD addition resulted in vesicle aggregation, fusion, and precipitation, originating from the interaction of Ca2+ ions with the negatively charged phospholipids formed in the membranes. Vesicle fusion was monitored by using a novel fusion assay system involving vesicles containing entrapped trypsin and vesicles containing entrapped chymotrypsinogen A. After vesicle fusion, chymotrypsinogen A transformed into a-chymotrypsin, catalyzed by trypsin inside the fused vesicles. The alpha-chymotrypsin formed could be detected with benzoyl-L-Tyr-p-nitroanilide as a membrane permeable chymotrypsin substrate. The observed vesicle precipitation occurring after vesicle fusion in the presence of 1 mM Ca2+ was correlated with an increase of the main phase transition temperature, Tm, of POPA to values above 40 degrees C.

Calcium↗
PubMed2004

Nucleation and growth rates of poly(L-lactic acid) microparticles during precipitation with a compressed-fluid antisolvent.

We measured nucleation and growth rates of poly(L-lactic acid) (PLLA) microparticles produced during precipitation with a compressed-fluid antisolvent (PCA). The injector/precipitator used in this study satisfied the constraints and assumptions incorporated in the development of the mixed-suspension, mixed-product-removal population balance theory. A semicontinuous operation mode with batch product filtering was developed, and results from product particle size distributions allowed nucleation and growth rates to be determined through the use of population balances. Kinetic data, obtained by operating the precipitator under various degrees of supersaturation and suspension density, were used to generate a nucleation rate model for PLLA. Model results indicate a relative kinetic order of 1 and a linear dependence of the nucleation rate on the suspension density. First-order dependence of the nucleation rate on suspension density suggests secondary nucleation mechanism(s) are operative within this PCA flow system and may explain the relative insensitivity of particle size distributions to changes in PCA operating conditions.

Carbon Dioxide↗
PubMed2006

Apparent solubility of hydroxyapatite in aqueous medium and its influence on the morphology of nanocrystallites with precipitation temperature.

Two differing wet-chemical synthesis routes, Ca(OH)2 + H3PO4 and CaCl2 + Na3PO4/NaOH, were used to prepare hydroxyapatite (HA) at various temperatures ranging from 30 to 95 degrees C. The electrical conductivity of the solution was measured at regular intervals of time during H3PO4 and Na3PO4 addition to the suspension/solution containing Ca2+ ions. The rate of change of conductivity is used to note the end point of the reaction. X-ray diffraction of the dried, precipitated particles revealed HA as the predominant phase, and the FTIR spectroscopy studies indicated the presence of CO3(2-) groups which substituted PO4(3-) groups in the HA lattice (B-type). FESEM observations revealed that the aspect ratio of the particles decreased with increasing precipitation reaction temperature in one system [Ca(OH)2 + H3PO4] and in the other system it increased with increasing temperature. The changes in the morphology with temperature were analyzed through conductivity measurements and the thermochemical properties of the reaction systems. Conductivity measurements showed that the concentration of dissolved ions at the end point of the reaction between Ca(OH)2 and H3PO4 increased, indicating an increased apparent solubility of HA with increasing temperature, whereas the end-point conductivity did not increase noticeably in the other reaction system.

Chemical Precipitation↗
PubMedDate not supplied

One-pot glyco-affinity precipitation purification for enhanced proteomics: the flexible alignment of solution-phase capture/release and solid-phase separation.

A one-pot affinity precipitation purification of carbohydrate-binding protein was demonstrated by designing thermally responsive glyco-polypeptide polymers, which were synthesized by selective coupling of pendant carbohydrate groups to a recombinant elastin-like triblock protein copolymer (ELP). The thermally driven inverse transition temperature of the ELP-based triblock polymer is maintained upon incorporation of carbohydrate ligands, which was confirmed by differential scanning calorimetry and (1)H NMR spectroscopy experiments. As a test system, lactose derivatized ELP was used to selectively purify a galactose-specific binding lectin through simple temperature-triggered precipitation in a high level of efficiency. Potential opportunities might be provided for enhanced proteomic, cell isolation as well as pathogen detection applications.

Amino Acid Sequence↗
PubMed1997

Selective precipitation separation and inductively coupled plasma mass spectrometric determination of trace metal impurities in high purity silver.

A simple and rapid method for the determination of some trace element impurities in high purity silver, combining the isolation of analytes from the silver matrix with selective precipitation followed by ICP-MS determination was developed. On the basis of an extreme difference in the solubilities of the chlorides of silver and the other accompanying trace elements, silver can be separated completely through the addition of hydrochloric acid. The sample of silver was at first dissolved in 7 M nitric acid followed by addition of hydrochloric acid to remove the silver matrix by formation of a silver chloride precipitate, while leaving the trace element impurities in the solution, which was subsequently analysed by ICP-MS. Eleven elements (Al, Au, Cd, Co, Cu, Fe, Mg, Mn, Ni, Pb and Sn) were determined with good accuracy and precision. The limits of detection (based on the 3 sigma criterion) of these elements were 10(-1)-10(-3) ng g-1. The proposed method was successfully applied to the determination of metal impurities in high-purity silver samples (EM9465 and EM 9343) and validated by the analysis of NIST SRM 8171 (Fine Silver FS 14).

Chemical Precipitation↗
PubMed2005

Regular Liesegang patterns and precipitation waves in an open system.

We investigate the regular and moving Liesegang pattern formation phenomena in an open system. First, simulations have been performed at fixed coupling between the reactive medium and the reservoir, later this control parameter was varied during the simulations resulting in various phenomena. We predicted and monitored for the first time various--dynamically changing--precipitation structures and a spatial hysteresis phenomenon, which is beyond the scope of the Turing instability. The dynamics of the reaction is well detectable using specific quantities: the total amount of precipitate and its center of gravity.

Chemical Phenomena↗
PubMed1969

The precipitation of toroidal collagen fibrils.

The morphology of aggregates of calf-skin tropocollagen, precipitated by continuous injection into neutral phosphate buffers at 35 degrees , has been studied by electron microscopy. Although most of the collagen is precipitated as normal native fibrils, a small proportion forms closed toroidal structures having the usual native band-interband pattern. Theoretical considerations, based on elastic energies in a general microfibril model, predict that the toroids should have a simple super-helical structure, and this is not inconsistent with the observations. From the theoretical energies it was possible to estimate a crude lower limit of 3kcal./mole for the free energy of association of the tropocollagen macromolecules.

Animals↗
PubMed1975

The use of ammonium acetate in the precipitation of ribonucleic acid.

Ammonium acetate (0.24M) in combination with cold 66% (v/v) ethanol quantitatively precipitated RNA from very dilute solutions (greater than or equal to mug/ml) after centrifugation for 2.5 X 10(6)g-min. There was also less co-precipitation of detergents with ammonium acetate than NaCl.

Animals↗
PubMed2001

Zinc salts precipitate unconjugated bilirubin in vitro and inhibit enterohepatic cycling of bilirubin in hamsters.

BACKGROUND: We have evidence for enterohepatic cycling of bilirubin experimentally and in vivo in humans. This study was designed to investigate whether Zn salts might inhibit such cycling of bilirubin. MATERIALS AND METHODS: Micellar bile salt solutions with unconjugated bilirubin were prepared, appropriate concentrations of Zn salts were added, and unconjugated bilirubin precipitation was measured. Hamsters and Wistar rats were fed a chow diet or a chow diet enriched with 1% ZnSO4, and bilirubin secretion rates were monitored. RESULTS: Unconjugated bilirubin was precipitated maximally (90%) after a 10-min incubation with 5 mM Zn salts in the pH range of 6.8-9.0. In control hamsters, total bilirubin secretion rates into bile were 36.0 +/- 2.8 nmol h(-1) 100g(-1) body weight, whereas they were 25.0 +/- 3.3 nmol h-1 100(-1) g in the ZnSO4 group (P < 0.05). CONCLUSIONS: Zn salts that flocculate at physiological pH adsorb unconjugated bilirubin almost completely from unsaturated micellar BS solutions. In addition, Zn salts administered orally suppress biliary bilirubin secretion rates in hamsters. These findings suggest that the administration of Zn salts may inhibit the enterohepatic cycling of unconjugated bilirubin in humans who are predisposed to pigment gallstone formation due to diet, disease or drugs.

Animals↗
PubMedDate not supplied

The use of pluronic polyols in the precipitation of plasma proteins and its application in the preparation of plasma derivatives.

Pluronic F-38 was used a precipitant of plasma proteins under varying conditions of pH and polymer concentration. Results indicated that marked differences in the solubility of the plasma proteins in F-38 solutions can be appled to the separation of plasma components. The feasibility of the industrial application of this fractionation method was tested in several experiments. Conditions were established for the preparation of albumin, human plasma protein fraction (HPPF), and immune serum globulin (ISG) with similar yield and purity as those prepared by the Cohn methods. Current procedures for the preparation of antihemophilic A (Facor VIII) concentrate and prothrombin complex (Factors II, VII, IX, and X) were adapted to the F-38 process by removal of the clotting factors from the starting plasma prior to polymer precipitation. In addition, a plasma protein solution free of lipoproteins, isoagglutinins, and clotting factors was developed which has proven useful as a perfusion medium in organ preservation.

Blood Preservation↗