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PubMed2002

Warm balanced salt solution for clearing tear film precipitation during cataract surgery.

Adequate anterior segment visualization during cataract surgery can be hindered when excessive tear film secretions precipitate on the corneal surface before the initial corneal incision is made. In most cases, room-temperature balanced salt solution applied to the corneal surface clears the debris. However, in cases in which tear film precipitates persist after the use of room-temperature balanced salt solution, the application of warm balanced salt solution can provide rapid and sustained dispersion of the precipitates. We present our experience using this technique.

Adult↗

PubMed2003

Confirmation of ofloxacin precipitation in corneal deposits by microbore liquid chromatography-quadrupole time-of-flight tandem mass spectrometry.

We investigated the corneal precipitate of a 6-year-old boy with vernal keratoconjunctivitis (VKC), treated with topical ofloxacin 0.3% eyedrops. Because of the extremely small sample amount (corneal scraping), a very sensitive and specific method was needed with the possibility of an unambiguous identification of ofloxacin, supposed to be present in the precipitate. In this respect, tandem Q-TOF mass spectrometry combined with micro LC (1 mm I.D.) was chosen. Confirmation of the presence of ofloxacin in the deposit was obtained by means of the characteristic product ion spectrum produced by CID. This clearly indicated that the precipitate, removed by corneal scraping from the 6-year-old boy with VKC, contained ofloxacin.

Anti-Infective Agents↗

PubMed2001

Effect of beta-lactoglobulin and precipitation of calcium phosphate on the thermal coagulation of milk.

The effect of beta-lactoglobulin and heat-induced precipitation of calcium phosphate on the pH dependence and mechanism of thermal coagulation of milk throughout the pH range 6.3-7.3 was studied using serum protein-free milk and sodium caseinate as models for micellar and non-micellar milk protein systems respectively. It appears that the specific effect of beta-lactoglobulin at the pH of maximum stability may be related to its ability to chelate calcium. The effect of beta-lactoglobulin at the pH of minimum stability does not appear to be directly related to heat-induced dissociation of K-casein or micellar integrity but may be due to its ability to sensitize casein micelles to heat-induced precipitation of calcium phosphate, by increasing micellar hydrophobicity. The extent of heat-induced precipitation of calcium phosphate, as a function of pH, is an inverse reflection of the pH dependence of heat stability. Micellar integrity appears to play a critical role in the heat stability of milk but for reasons not previously appreciated.

Animals↗

PubMed2004

The precession technique in electron diffraction and its application to structure determination of nano-size precipitates in alloys.

Crystal structure of nano-scale precipitates in age-hardening aluminum alloys is a challenge to crystallography. The utility of selected area electron diffraction intensities from embedded precipitates is limited by double scattering via matrix reflections. This effect can be signally reduced by the precession technique, which we have used to collect extensive intensity data from the semicoherent, metastable eta-precipitate in the Al-Zn-Mg alloy system. A structure model in the space group P-62c is proposed from high-resolution microscopy and electron diffraction intensities. The advantages of using the precession technique for quantitative electron diffraction is discussed.

Alloys↗

PubMed2002

Method for the fractionation of dextran by centrifugal precipitation chromatography.

Recent advances in biotechnology and biochemistry have been facilitated by efficient separation methods for biopolymers, such as proteins and nucleic acids. On the other hand, research on polysaccharides is hindered by problems in their fractionation. For many decades, polysaccharides have been fractionated by stepwise ethanol precipitation, and even at the present time, almost all of their purification protocols include at least one such step, although it is tedious and inefficient. This paper describes a novel approach for chromatographic fractionation of polysaccharides by ethanol gradient precipitation using an open column under a centrifugal force field. Using a unique column design, chromatographic separation of polymers is achieved by subjecting the sample to a repetitive process of precipitation and dissolution along a long, spiral channel. In this article, we fully describe the principle, design of the prototype, and basic studies on various parameters for optimization of chromatographic conditions, using dextran as an example.

Chromatography↗

PubMed1999

Precipitation of an insoluble product on enzyme monolayer electrodes for biosensor applications: characterization by Faradaic impedance spectroscopy, cyclic voltammetry, and microgravimetric quartz crystal microbalance analyses.

Precipitation of an insoluble, insulating product on monolayer-functionalized electrodes enables the development of new electrochemical biosensors. Faradaic impedance spectroscopy and cyclic voltammetry are used to probe the electron-transfer resistance at the conductive support upon the accumulation of the insoluble product on the electrode surface. Similarly, microgravimetric quartz crystal microbalance, QCM, analyses were used to assay the formation of the precipitate on the electrode. A horseradish peroxidase, HRP, monolayer electrode is used to analyze H2O2 via the biocatalyzed oxidation of 4-chloro-1-naphthol (1) and the precipitation of the insoluble product (2). A bienzyme-layered electrode consisting of HRP and glucose oxidase, GOx, is used to sense glucose. Biocatalyzed oxidation of glucose by O2, in the presence of GOx, yields H2O2, and the generated hydrogen peroxide effects the formation of the insoluble product (2) in the presence of HRP. The insoluble product accumulated on the electrode, and the extent of the resulting electron-transfer resistance, correlated with the amounts of H2O2 or glucose, and appropriate calibration curves are extracted.

Biosensing Techniques↗

PubMed1997

Multiple interactions between polyphenols and a salivary proline-rich protein repeat result in complexation and precipitation.

Polyphenols (tannins) in the diet not only precipitate oral proteins, producing an astringent sensation, but also interact with dietary proteins and digestive enzymes in the gut, resulting in a variety of antinutritive and toxic effects. Salivary proline-rich proteins (PRPs), which are secreted into the oral cavity, form complexes with and precipitate dietary polyphenols, and thus, they constitute the primary mammalian defense directed against ingested tannins. In order to characterize the interaction, NMR studies were performed which involved titrating a series of polyphenols into a synthetic 19-residue PRP fragment. The results show that the predominant mode of association is a hydrophobic stacking of the polyphenol ring against the pro-S face of proline and that the first proline residue of a Pro-Pro sequence is a particularly favored binding site. Measurement of dissociation constants indicates that the larger and more complex polyphenols interact more strongly with the PRP fragment; the order of binding affinity was determined as procyanidin dimer B-2 > pentagalloylglucose > trigalloylglucose >> proanthocyanidin monomer (-)-epicatechin approximately propyl gallate. Smaller polyphenols can bind with one phenolic ring stacked against each proline residue, whereas larger polyphenols occupy two or three consecutive prolines. The more complex polyphenols interact with the PRP fragment in a multidentate fashion; moreover, they self-associate or stack when bound. Thus, a model is proposed in which multiple polyphenol/polyphenol and polyphenol/PRP interactions act cooperatively to achieve precipitation.

Amino Acid Sequence↗

PubMedDate not supplied

Carbon dioxide induced soybean protein precipitation: protein fractionation, particle aggregation, and continuous operation.

A novel protein fractionation technique using a volatile electrolyte has been developed. Carbon dioxide was used to isoelectrically precipitate 80% and 95% pure glycinin and beta-conglycinin fractions from soybean isolate. The protein fractions precipitated as primary particles 0.2-0.3 microm in diameter, which under optimum conditions may be recovered as aggregates up to 500 microm in diameter. The dependency of protein fractionation efficiency on aggregate settling rates has been demonstrated. The isoelectric points of the two main soybean fractions, glycinin and beta-conglycinin, were calculated to be pH 5.2 and 4.95, respectively. Solution pH was accurately controlled by pressure in the isoelectric pH range of the different soybean protein fractions, and a pH "overshoot" was eliminated. Volatile electrolyte technology was also applied to a continuous process in order to eliminate the particle recovery concerns associated with batch precipitation and to demonstrate the potential for scale-up. Glycinin was effectively recovered on-line (94% glycinin recovery) with a purity approaching that of the batch process (95%).

Biotechnology↗

PubMedDate not supplied

Precipitation of lysozyme nanoparticles from dimethyl sulfoxide using carbon dioxide as antisolvent.

The protein lysozyme has been precipitated as amorphous nanoparticles from a DMSO solution using dense carbon dioxide as antisolvent, by applying the so-called gas antisolvent recrystallization technique in a 400-mL precipitator. The objective is to investigate the possibility of tuning the particle properties by changing the key process parameters, namely, antisolvent addition rate, initial solute concentration, and temperature. It is shown that none of these operating parameters has a major effect on the average particle size or the particle size distribution. The former is mostly between 200 and 300 nm and exhibits no evident trend. The latter is always unimodal and rather narrow and exhibits increasing agglomeration at higher temperature and initial solute concentration. Up to 75% of the protein activity measured in the starting crystalline material is retained by the precipitated amorphous nanoparticles. The present experimental results compare well with data about the same system obtained in a different experimental setup, which were previously reported in the literature, thus pointing at the reproducibility and robustness of GAS antisolvent recrystallization. Moreover, these are consistent with the theoretical understanding of gas antisolvent recrystallization as achieved by using a recently developed model of the process.

Animals↗

PubMed2002

Relative importance of charge neutralization and precipitation on coagulation of Kaolin with PACI: effect of sulfate ion.

The effect of the sulfate ion on coagulation with polyaluminum chloride (PACl) was investigated by using an optical monitoring technique together with the conventional jar test procedure and electrophoretic mobility (EM) measurements. The effect of the SO4(2-)/Al ratio, dosage, and pH were examined in detail. The experimental results show that sulfate has a significantly different effect on PACl coagulation as a result of preformed hydrolysis products, where charge neutralization and precipitation play different parts in the coagulation process. The increased rate of coagulation with increasing SO4(2-)/Al ratio can be partially explained by charge neutralization effects, through increased adsorption and complexation of sulfate, thus giving increased particle collision efficiency. Different PACl samples were prepared with different values of B ([OH]/[Al]). For B = 0 (i.e., AlCl3) with mainly monomers, hydroxide precipitation tends to be accelerated in the presence of sulfate, giving significant turbidity removal. The high charge neutralization ability remains for samples with B = 1.5 and 2.0, with large proportions of preformed oligomers and polymers. Sulfate promotes aggregation of hydrolyzed species for B= 2.5, causing significantly improved coagulation efficiency through an electrostatic patch effect. The results illustrate further that particle charge plays a less important role in coagulation after reaching a certain value, while precipitate formation improves coagulation significantly.

Aluminum Hydroxide↗

PubMed2002

Arsenic(III) oxidation by birnessite and precipitation of manganese(II) arsenate.

Solution chemical techniques were used to investigate the oxidation of As(III) to As(V) in 0.011 M arsenite suspension of well-crystallized hexagonal birnessite (H-birnessite, 2.7 g L(-1)) at pH 5. Products of the reaction were studied by scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), atomic force microscopy (AFM), and X-ray absorption near-edge structure spectroscopy (XANES). In the initial stage (first 74 h), chemical results have been interpreted quantitatively, and the reaction is shown to proceed in two steps as suggested by previous authors: 2>Mn(IV)O2 + H3AsO3 + H2O --> 2>Mn(III)OOH + H2AsO4- + H+ and 2>Mn(III)OOH + H3AsO3 + 3H+ --> 2Mn2+ + H2AsO4- + 2H2O. The As(III) depletion rate was lower (0.02 h(-1)) than measured in previous studies because of the high crystallinity of the H-birnessite sample used in this study. The surface reaction sites are likely located on the edges of H-birnessite layers rather than on the basal planes. The ion activity product of Mn(II) and As(V) reached after 74 h reaction time was the solubility product of a protonated manganese arsenate, having a chemical composition close to that of krautite as identified by XANES and EDS. Krautite precipitation reaction can be written as follows: Mn2+ + H2AsO4- + H2O = MnHAsO4 x H2O + H+ log Ks approximately -0.2. Equilibrium was reached after 400 h. The manganese arsenate precipitate formed long fibers that aggregated at the surface of H-birnessite. The oxidation reaction transforms a toxic species, As(III), to a less toxic aqueous species, which further precipitates with Mn2+ as a mixed As-Mn solid characterized by a low solubility product.

Arsenates↗

PubMed2003

Evidence for surface precipitation of phosphate on goethite.

Recent studies have suggested that the interaction between phosphate and goethite includes ternary adsorption/ surface precipitation as well as surface complexformation. The ternary adsorption/surface precipitation process envisioned involves the dissolution of the goethite crystal and subsequent adsorption of iron on the surface-bound phosphate. Further evidence to support the suggested process is needed. The process was investigated using two approaches. First, the sorption of iron spiked into a slurry of phosphated goethite and the effect of the iron sorption on phosphate uptake kinetics were investigated to determine whether iron would be adsorbed on the phosphated surface and whether it would enhance phosphate adsorption. Lead was also spiked into solution for comparison. Second, changes in the xi-potential of phosphated goethite were monitored with time. Adsorption of iron on the surface of phosphated goethite should increase the xi-potential of the goethite. Iron spiked into a phosphated goethite slurry was adsorbed on the solid with a concurrent adsorption of phosphate. The iron adsorption did not change the slow phosphate adsorption kinetics. Lead spiked into the solution was also sorbed but to a lesser extent than iron and with a lower apparent P:Pb mole ratio. Lead addition also changed the phosphate adsorption kinetics. With time, the xi-potential of phosphated goethite became more positive, returning almost to the potential of unphosphated goethite at low surface coverages. The slow increase in xi-potential over time indicates that long-term reactions are occurring on the goethite surface, most likely involving the dissolution of goethite to release iron and the subsequent reaction between the iron and surface-bound phosphate. These results provide strong support for the surface precipitation model, and are inconsistent with models envisioning the reaction between phosphate and the goethite surface as involving only monolayer surface complex formation.

Adsorption↗

PubMed2005

Modeling the influence of decomposing organic solids on sulfate reduction rates for iron precipitation.

The influence of decomposing organic solids on sulfate (S04(2-)) reduction rates for metals precipitation in sulfate-reducing systems, such as in bioreactors and permeable reactive barriers for treatment of acid mine drainage, is modeled. The results are evaluated by comparing the model simulations with published experimental data for two single-substrate and two multiple-substrate batch equilibrium experiments. The comparisons are based on the temporal trends in SO4(2-), ferrous iron (Fe2+), and hydrogen sulfide (H2S) concentrations, as well as on rates of sulfate reduction. The temporal behaviors of organic solid materials, dissolved organic substrates, and different bacterial populations also are simulated. The simulated results using Contois kinetics for polysaccharide decomposition, Monod kinetics for lactate-based sulfate reduction, instantaneous or kinetically controlled precipitation of ferrous iron mono-sulfide (FeS), and partial volatilization of H2S to the gas phase compare favorably with the experimental data. When Contois kinetics of polysaccharide decomposition is replaced by first-order kinetics to simulate one of the single-substrate batch experiments, a comparatively poorer approximation of the rates of sulfate reduction is obtained. The effect of sewage sludge in boosting the short-term rate of sulfate reduction in one of the multiple-substrate experiments also is approximated reasonably well. The results illustrate the importance of the type of kinetics used to describe the decomposition of organic solids on metals precipitation in sulfate-reducing systems as well as the potential application of the model as a predictive tool for assisting in the design of similar biochemical systems.

Bioreactors↗

PubMed2005

Cell-membrane damage and element leaching in transplanted Parmelia sulcata lichen related to ambient SO2, temperature, and precipitation.

Measurements were performed in lichen (Parmelia sulcata) transplants, to gain insight into the lichen vitality as possibly affected by both element deposition or lichen element content and further ambient atmospheric conditions (temperature, precipitation, SO2 levels). The electrical conductivity of rinsing solutions was used to assess cell-membrane damage in Parmelia sulcata in an experiment, which ran from August 2001 until August 2002. Element contents of the solutions and lichens were determined by inductively coupled plasma-optical emission spectrometry and by k0-instrumental neutron activation analysis, respectively. Factor analysis (MCATTFA) was used to determine grouping of elements of similar origin and/ or behavior. All in all, the data indicate that, apartfrom lichen Na and Cl levels, and for temperature and precipitation, no clear relationships with conductivity could be observed. Conductivity was mostly related to released Na, Cl, K, Mg, and Cs. On the basis of concentrations, Na, Cl, and K could be considered as largely determining the conductivity. The data suggest a different origin for K than that for Na and Cl: the latter two are most probably due to effects from sea salt sprays. Parmelia sulcata was sensitive enough to reflect appreciable ambient rises in air SO2 and resistant enough to recover afterward. MCATTFA on selected elements (K, Sc, Cu, V, As, and Sb) indicated the absence of any comparability between K and V, As and Sb, suggesting differences in origin and/or chemico-physical occurrence. Generally speaking, the present data suggest that the comparability of lichen vitality in large geographical areas may be limited and governed by the area's variability in temperature and precipitation rather than by variability in metal deposition rates. The leaching data on all elements and element groups, however, strongly suggest that wet deposition may also severely affect lichen elemental levels. This latter observation means that comparing outcomes for time or spatial series of lichen samples should be accompanied by a comparably careful monitoring of (preceding) ambient conditions.

Air Pollutants↗

PubMed2005

Inhibition of calcite precipitation by natural organic material: kinetics, mechanism, and thermodynamics.

The inhibition of calcite precipitation by natural organic material (NOM) in solutions seeded with calcite was investigated using a pH-stat system. Experiments were carried out using three NOMs with different physical/chemical properties. For each of the materials, inhibition was found to be more effective at lower carbonate/calcium ratios and lower pH values. The reduction in the precipitation rate could be explained by a Langmuir adsorption model using a conditional equilibrium constant. By identification of the type of site on the NOM molecules that is involved in the adsorption reaction, the "conditional" equilibrium constants obtained at different solution compositions converged to a single "nonconditional" value. The thermodynamic data determined at 25 degrees C and 1 atm suggest that the interaction between NOM molecules and the calcite surface is chemisorptive in nature and that adsorption is an endothermic reaction driven by the entropy change. The greatest degree of inhibition was observed for the NOM with the highest molecular weight and aromatic carbon content. For a given type of NOM, the degree of inhibition of calcite precipitation was dictated bythe balance between the enthalpy change and the entropy change of the adsorption reaction.

Adsorption↗

PubMed2005

Effect of precipitation on low frequency electrical properties of zerovalent iron columns.

We conducted column studies to investigate the application of a noninvasive electrical method to monitor precipitation in Fe0 columns using (a) Na2SO4 (0.01 M, dissolved oxygen (DO) = 8.8 ppm), and (b) Na2CO3 (0.01 M, DO = 2.3 ppm) solutions. An increase in complex conductivity terms (maximum 40% in sulfate column and 23% in carbonate column) occurred over 25 days. Scanning electron microscopy (SEM) identified mineral surface alteration, with greater changes in the high DO sulfate column relative to the low DO carbonate column. X-ray diffractometry (XRD) identified reduced amounts of hematite/maghemite in both columns, precipitation of goethite/akaganeite in the sulfate column, and precipitation of siderite in the carbonate column. Nitrogen adsorption measurements showed increases in specific surface area of iron minerals (27.5% for sulfate column and 8.2% for carbonate column). As variations in electrolytic conductivity and porosity were minimal, electrical changes are attributed to (1) higher complex interfacial conductivity due to increased surface area and mineralogical alteration and (2) increased electronic conduction due to enhanced electron transfer across the iron-fluid interface. Our results show that electrical measurements are a proxy indicator of Fe0 surface alteration.

Chemical Precipitation↗

PubMed2002

Polyphenol/peptide binding and precipitation.

Polyphenols are largely responsible for the astringency and "mouthfeel" of tea and wine by their interactions with basic salivary proline-rich proteins. Astringency arises from precipitation of polyphenol/peptide complexes, which is an important protective mechanism in animals that consume polyphenols. This paper presents biophysical studies of the interactions between chemically defined polyphenols and peptides. It is shown that intermolecular binding is dominated by stacking of polyphenolic rings onto planar hydrophobic surfaces and is strengthened by multiple cooperative binding of polyphenolic rings. Affinities weaken at higher temperatures and are unaffected by pH between pH 3.8 and 6.0. Measurements of self-diffusion rates for peptides with increasing concentrations of polyphenol demonstrate that peptides become increasingly coated with polyphenol. When the coating is sufficiently extensive to provide cooperative polyphenol bridges, the peptide dimerizes and precipitates. Light scattering measurements and electron microscopy indicate that the insoluble particles fall into two discrete size classes of ca. 80 and 500 nm diameter. The larger particles are favored at higher temperature and pH, suggesting that the particles are in a colloidal state, with the smaller particles being stabilized by charge repulsion between particles, and that precipitation of the complexes may be a phase separation process.

Amino Acid Sequence↗

PubMed2004

Use of a byproduct of magnesium oxide production to precipitate phosphorus and nitrogen as struvite from wastewater treatment liquors.

This paper describes a series of experiments designed to recover phosphorus and nitrogen from sewage in the form of struvite (MgNH(4)PO(4).6H(2)O), a potential fertilizer. Nitrogen and phosphate were recovered from a filtrate of digested sludge dewatered at the Arroyo del Soto Waste Water Treatment Plant (WWTP) (Madrid, Spain). A byproduct of the Spanish magnesite mining and MgO production industry was used as the magnesium source. The precipitating performance of this byproduct was compared to that of conventional chemical reagents such as pure MgO. The precipitates obtained were subjected to chemical, light microscopy, and X-ray diffraction analysis. The findings indicate the precipitate recovered using this byproduct contains several minerals with a predominance of struvite. Optimal purity ( approximately 80% struvite) was achieved using the sieved <0.04 mm grain size fraction of the byproduct at doses corresponding to a molar Mg:P ratio of 1.6.

Chemical Precipitation↗