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At least 991 records · Page 55Linked to original sources
PubMed1975

Inhibition of implantation in the golden hamster by zona-precipitating antibody.

Antisera prepared against saline extracts of hamster ovary, and made specific to ovary by absorption with small intestine, precipitated the zona pellucida of provulatory hamster ova and all early embryonic stages examined, including the pronuclear, 2-, 4-, 8-, and 16-cell, morula, and blastocyst stages; this indicates that (1) the zona antigen is present during oocyte maturation and early embryonic development and (2) the antigen does not change its ability to react with zonaprecipitating antibody. Embryos in the morula and blastocyst stages, treated in vitro with zona-precipitating antibody, pre-immunization rabbit serum, or control media were transferred into synchronized pseudopregnant recipients. Precipitation of zonae by specific antibody inhibited implantation by blocking the process known as zona shedding, and thereby prevented the embryo from making contact with the uterus.

Animals↗
PubMed2001

Separation of chondroitin sulfate and hyaluronic acid fragments by centrifugal precipitation chromatography.

Centrifugal precipitation chromatography (CPC) was applied for the first time to the separation of fragments of chondroitin sulfate (ChS) and hyaluronic acid (HA). The separation was performed using a gradient elution system between ethanol and water since solubility of these biopolymers highly depends on the concentration of ethanol in aqueous solution. ChS and HA were each eluted into several peaks through a flow-through UV detector at 275 nm, despite they have almost no absorbance at this wavelength in an aqueous solution. The separation was also confirmed by redissolving the dried fraction in water and measuring the absorbance at 210 nm. These results suggest that the CPC system can detect small precipitates of these biopolymers by light scattering at 275 nm. The separated fragments of biopolymers are not easily characterized because no suitable analytical method is available for identification of these compounds. However, the overall results demonstrate that CPC may be a useful separation of biopolymers such as glycosaminoglycans which quantitatively produce precipitates in an organic solvent mixture.

Centrifugation↗
PubMed1986

Calcium oxalate precipitation in a flow system: an attempt to simulate the early stages of stone formation in the renal tubules.

This paper describes in vitro studies on the generation of supersaturation and the early stages of calcium oxalate (CaOx) precipitation using a reverse osmosis hollow-fiber membrane to simulate the precipitation processes occurring in the distal convoluted tubule and the collecting system of the kidney. The article reports on the preliminary results of using a plug-flow configuration to simulate the reabsorption of water and generation of supersaturation during the approximately three-minute biological residence time of the urine in the upper part of the urinary tract. The results suggest that microcrystallization of CaOx . 2H2O in the renal tubules may play a role in stone formation processes. A survey of the effect of various inhibitors of CaOx precipitation indicates that pyrophosphate, magnesium, glutamic acid, heparin and citric acid reduce the tendency of CaOx crystals formed to agglomerate in this system.

Calcium Oxalate↗
PubMed2003

Effects of pH and precipitation on autohydrogenotrophic denitrification using the hollow-fiber membrane-biofilm reactor.

Experiments carried out in a hollow-fiber, membrane-biofilm reactor (HFMBR) showed that the optimum pH for autotrophic denitrification was in the range 7.7-8.6, with the maximum efficiency at 8.4. Increasing the pH above 8.6 caused a significant decrease in nitrate removal rate and a dramatic increase in nitrite accumulation. The pH rose by 1.2 units when a large buffer was not added, suggesting that some field applications may require pH control. Precipitation of Ca(2+) occurred in every experiment. Precipitation was the largest sink for carbonate, and it also offset alkalinity production by denitrification. Although the alkalinity increased in most cases, systems with a high carbonate buffer and high pH accentuated precipitation, and the net change in alkalinity was negative. The long-term success of field applications of the HFMBR may depend upon the interactions among calcium concentration, total carbonate concentration, pH, and alkalinity changes.

Biofilms↗
PubMed2001

Pesticides in precipitation in the Gdańsk region (Poland).

Selected organonitrogen, organophosphorus and organochlorine pesticides have been determined in precipitation samples collected at 10 sites in the Gdańsk region (northern Poland) over a period of one year (1998). Compounds which were detected most often included simazine (0.11-5.80 ng/l), fenitrothion (0.1-2.10 ng/l), chlorfenvinfos (0.1-1.30 ng/l), gamma-HCH (0.012-5.06 ng/l), heptachlor epoxide (0.05-3.28 ng/l) and aldrin (0.02-3.28 ng/l). The pesticide concentrations in precipitation samples revealed seasonal fluctuations, with higher concentrations observed during the application periods (June and July). The concentrations observed were also affected by the inflow of polluted air masses from the southwest. The total pesticide concentration in the precipitation samples was strongly related to the abundance of green areas in the vicinity of the sampling sites. A weak correlation was also found between the total concentration of organonitrogen and organophosphorus pesticides, and the total concentration of organochlorine pesticides in the samples collected.

Air Pollutants↗
PubMed2002

Long-term assessment of the wet precipitation chemistry in Austria (1984-1999).

The aim of the present study was to determine the long-time trends in concentrations and depositions of major ions in wet precipitation samples collected at 11 sampling sites from the Austrian precipitation chemistry network in the period 1984-1999. The analytical results were treated by the use of least square linear regression method. It is shown that a serious decrease of sulfate (between 30% and 60% for the period) and hydrogen ion (between 60% and 102% for the period) concentrations and depositions is achieved at almost all sampling sites and in most of these cases the linear trend proves to be statistically significant. Nitrogen containing ions and base cations do not reveal a distinct trend of changing and in the majority of the sites the linear models are not adequate. In principle, an overall slight concentration and deposition decrease for these major ions is observed (up to 30% for the period of observation) but some substantial exceptions are also found (site Haunsberg or site Lobau). The changes in chloride concentration and deposition, too, do not indicate significant linear trend and, in general, are decreasing for the period of monitoring. In order to give some explanation of the exceptional behaviour of some of the major ions in several sites, an additional comparison with Austrian emission data (sulfur dioxide, nitrogen oxides, ammonium) and with data from five EMEP sites from neighbouring countries is performed. A significant West-East trend of acidity increase is found as well as a good correlation with the emission trends. Therefore, both transboundary and specific local factors could be substantial factors in the wet precipitation chemistry in the region.

Austria↗
PubMed2002

Effects of solution conditions on the precipitation of phosphate for recovery. A thermodynamic evaluation.

To understand the effects of solution conditions on the precipitation of calcium phosphates from wastewater for recovery, a computer programme PHREEQC was employed to calculate the speciation and saturation-index (SI) with respect to hydroxyapatite of a chemically defined precipitation system, which contains phosphate of 1-200 mg P/l, with Ca/P molar ratios of one to 10 times of the stoichiometric calcium to phosphorus molar ratio of hydroxyapatite, at a pH range of 7.0-11.0. The results show that the SI is respectively the logarithmic function of the phosphate concentration and the calcium concentration, increasing with the increase of either of them; the SI is a polynomial function of the solution pH value and increases with its increase, and the effect of solution pH value is due to its influence on base uptake of the precipitation reaction and the speciation of phosphate and calcium ions; the SI is also a logarithmic function of the solution ionic strength but decreases with its increase; at the temperature range of 5-30 degrees C the SI increases linearly with solution temperature and the effect of temperature is also due to its influence on the speciation of phosphate and calcium ions.

Calcium↗
PubMed2003

TEM study of calcium phosphate precipitation on HA/TCP ceramics.

This study focuses on phase identification of precipitation on bioactive calcium phosphate (BCP) surfaces in vitro and in vivo. The BCP used in this study consisted of 70 wt% hydroxyapatite (HA) and 30 wt% beta-tricalcium phosphate. Single crystalline precipitates of calcium phosphates on porous BCP bioceramics obtained after immersion in dynamic simulated body fluid (SBF) and after implantation in pig muscle were examined using electron diffraction in transmission electron microscope. The crystals formed in vitro in dynamic SBF were identified as octacalcium phosphate (OCP), instead of apatite. Most of the precipitated crystals in vivo samples had an HA structure; while OCP and dicalcium phosphate dihydrate were also identified. The evidence from single diffraction patterns indicates that apatite formation on bioactive ceramics is a complicated process, particularly in physiological environments where formation might include a transient stage of intermediate phases.

Adsorption↗
PubMed2004

Precipitation casting of polycaprolactone for applications in tissue engineering and drug delivery.

Microporous materials have been produced by gradual precipitation from solutions of poly(epsilon-caprolactone) (PCL) in acetone induced by solvent extraction across a semi-permeable PCL membrane which is formed in situ at the polymer solution/non-solvent interface. Microparticulates of hydroxyapatite and inulin polysaccharide, respectively, were incorporated in precipitation cast PCL matrices to illustrate potential applications in hard tissue repair and macromolecular drug release. Microporous PCL and HA filled PCL materials were found to provide a favourable surface for attachment and growth of primary human osteoblasts in cell culture. The in vitro degradation characteristics of microporous PCL and inulin/PCL materials in PBS at 37 degrees C were monitored over 45 months. Microporous PCL demonstrated zero weight loss, minor changes in molecular weight characteristics and a fairly constant indentation resistance of around 1 MN/m2. Inulin-loaded PCL materials exhibited a total weight loss of approximately 17% after 12 months in PBS. The indentation resistance decreased by 50% from an initial value of 28 MN/m2 in the first 2 months and then remained stable. Precipitation cast materials based on PCL are expected to be useful for formulating long-term, controlled release devices for bioactive molecules such as growth factors and hormones and extended-residence supports for cell growth and tissue development.

Bone Substitutes↗
PubMed1997

Fast precipitation of calcium phosphate layers on titanium induced by simple chemical treatments.

A simple two-step chemical treatment, i.e. etching with HCl and H2SO4 followed by immersion in boiling dilute NaOH solution, has been developed by our group to prepare bioactive microporous titanium surfaces allowing fast deposition of a calcium phosphate layer (CPL) from an in vitro supersaturated calcification solution (SCS). In this work, a precalcification (Pre-Ca) procedure was applied by soaking the two-step treated titanium in Na2HPO4 and then saturated Ca(OH)2 solution before immersion in SCS to accelerate further the CPL precipitation. The treated titanium surfaces with Pre-Ca were characterized after 1, 2, 4, 8 and 16 h of immersion in SCS by means of scanning electron microscopy together with energy dispersive X-ray analysis, X-ray diffraction and infrared absorption analysis. It was observed that the CPL precipitation rate with Pre-Ca averaged 1 microm h-1, twice as fast as without Pre-Ca. No precipitation was observed on untreated titanium with Pre-Ca up to day 14 of immersion in the SCS.

Calcium Hydroxide↗
PubMed2001

Rapid non-equilibrium aluminium-ligand interactions: studies on the precipitation of aluminium by laser light scattering, ultrafiltration and centrifugation.

The study aimed to develop simple assays to study aluminium-ligand interactions in natural/biological systems where equilibrium is rarely reached and thus where the initial seconds or hours of interactions are important. The immediate and non-equilibrium precipitation of aluminium hydroxide, in aqueous solution at neutral pH, was therefore studied by laser light scattering (diffraction), ultrafiltration and centrifugation. The interaction of weak ligands, present in the gastrointestinal lumen, on the precipitation of aluminium hydroxide was also investigated. The initial kinetics and particle sizes of precipitated aluminium hydroxide were sensitive to a number of external factors, including the presence of weak ligand (bicarbonate), sheer force (stirring), electrolyte concentration and initial (i.e. added) aluminium concentration. However, after a few seconds (no weak ligand), or several hundred seconds (with weak ligand), the subsequent observed changes to the solid phase were of small magnitude and occurred slowly. Thus, a 25-min window, within 5 and 30 min of pH adjustment, can be used to study the interactions of aluminium-ligand. This may approximate better to most natural systems where unperturbed aluminium-ligand equilibrium must rarely exist.

Aluminum↗
PubMed2004

DNAPL remediation with in situ chemical oxidation using potassium permanganate. II. Increasing removal efficiency by dissolving Mn oxide precipitates.

In situ chemical oxidation (ISCO) schemes using MnO4- have been effective in destroying chlorinated organic solvents dissolved in ground water. Laboratory experiments and field pilot tests reveal that the precipitation of Mn oxide, one of the reaction products, causes a reduction of permeability, which can lead to flow bypassing and inefficiency of the scheme. Without a solution to this problem of plugging, it is difficult to remove DNAPL from the subsurface completely. In a companion paper, we showed with batch experiments that Mn oxide can be dissolved rapidly with certain organic acids. This study utilizes 2-D flow-tank experiments to examine the possibility of nearly complete DNAPL removal by ISCO with MnO4-, when organic acids are used to remove Mn oxide. The experiments were conducted in a small 2-D glass flow tank containing a lenticular silica-sand medium. Blue-dyed trichloroethylene (TCE) provided residual, the perched and pooled DNAPL. KMnO4 at 200 mg/l was flushed through the DNAPL horizontally. Once plugging reduced permeability and prevented further delivery of the oxidant, citric or oxalic acids were pumped into the flow tank to dissolve the Mn oxide precipitates. Organic ligands removed the Mn oxide precipitates relatively quickly, and permitted another cycle of MnO4- flooding. Cycles of MnO4-/acid flooding continued until all of the visible DNAPL was removed. The experiments were monitored with chemical analysis and visualization. A mass-balance calculation indicated that by the end of the experiments, all the DNAPL was removed. The results show also how heterogeneity adds complexity to initial redistribution of DNAPL, and to the efficiency of the chemical flooding.

Chemical Precipitation↗
PubMed2001

Successful vaccination against Leishmania donovani infection in Indian langur using alum-precipitated autoclaved Leishmania major with BCG.

Autoclaved Leishmania major (ALM) along with BCG, presently undergoing phase II clinical trial by WHO for its vaccine potential against cutaneous leishmaniasis, has been successfully evaluated in single and triple dose schedules against L. donovani in Indian langurs (Presbytis entellus). Encouraged with the results, another formulation alum-precipitated ALM (provided by WHO) along with BCG has been evaluated in this system. Eight monkeys were vaccinated with alum-precipitated ALM + BCG (1 mg of each per animal) while four were kept as unvaccinated controls. All were challenged with 100 x 10(6) amastigotes i.v. on day 60 post vaccination. Parasitic assessment in splenic tissue was performed on day 45, 90 and 180 p.c. Initially, seven of the eight vaccinated monkeys developed infection (two to six amastigotes per 1000 cell nuclei), which resolved by day 180 p.c., while the eighth monkey had a parasite burden of 14 amastigotes per 1000 cell nuclei on day 45 p.c. and died on day 130 p.c. On the other hand, there was progressive infection in unvaccinated control animals and three out of four died between days 110 and 120 p.c., and one monkey, which had low parasite burden, died on day 178 p.c. Prior to challenge, there was an initial rise in antileishmanaial antibodies in the vaccinated group compared to the unvaccinated control group, which later came down to normal level, while it remained higher in the unvaccinated control group. An increasing pattern of antigen-specific proliferative responses and interferon-gamma level to the two antigens--autoclaved L. donovani (ALD) and ALM--was observed in vaccinated monkeys throughout the experiment. There was a good correlation between parasite burden and IFN-gamma level on days 90 and 180 p.c., indicating IFN-gamma response as a sensitive parameter of immune status. The findings suggest alum-precipitated ALM+BCG as a potential vaccine against visceral leishmaniasis and warrants clinical trials.

Alum Compounds↗
PubMed1998

Bilirubin as an anti precipitant against copper mediated denaturation of bovine serum albumin: formation of copper-bilirubin complex.

BR forms a beautiful 1:1 greenish complex with Cu2+, having a characteristic absorption maximum at 343 nm. To our knowledge, this is the first metal complex of bilirubin in aqueous solution so far to be reported. It has also been shown that bilirubin (BR) at a concentration more than protein binding capacity has a definite role as an anti precipitant of bovine serum albumin by excess copper. At a concentration of 1 x 10(-3) moll-1 of the Cu-BR complex, the colour becomes greenish black. The rate of formation of this Cu-BR complex when BR extracts copper from copper-albumin complex as obtained in our experiment is 34.981 mol-1 s-1. The Cu-BR complex is stable at a pH ranging from 3.5 to 13.2, and also can scavenge radicals like CCl3OO., eaq- and OH.. Addition of excess copper sulfate to the solution of this complex causes a greenish black precipitate which can be re dissolved in HCl but insoluble in 99% ethanol. The complex does not give positive test in Gmelin reaction for bile pigments. The fluorescence spectrum of the complex in solution exhibits a peak at 450 nm when excited at 343 nm. The precipitated complex is insoluble in a number of solvents like ether, xylene, benzene, acetone, chloroform-methanol mixture and DMSO. These results show that BR may protect mammals from copper poisoning.

Animals↗
PubMed1992

Increased efficiency of gene transfection in primary cultures of adult rat hepatocytes stimulated to proliferate: a comparative study using the lipofection and the calcium phosphate precipitate methods.

Transfection of the beta-galactosidase gene in quiescent cultures of adult rat hepatocytes with the calcium phosphate precipitate or the lipofection methods gave a higher level of beta-galactosidase gene expression with the lipofection than with the calcium phosphate precipitate method, but the transfection efficiency was weak in both cases. Transfection of hepatocytes stimulated to proliferate before transfection either in vivo by partial hepatectomy or in vitro by epidermal growth factor was more efficient than transfection of quiescent hepatocytes, and the lipofection method gave better results than the calcium phosphate precipitate method.

Animals↗
PubMed2001

Practice of solid-phase extraction and protein precipitation in the 96-well format combined with high-performance liquid chromatography-ultraviolet detection for the analysis of drugs in plasma and brain.

C18 Empore 96-well extraction disc plates have been employed for the analysis of three drugs with different polarities in plasma in conjunction with HPLC-UV, rufinamide, ICL670 and an anticonvulsant agent (AA1) in an early stage of development. With the most polar compound (AA1), ion-pair extraction at pH 12 was applied. The method developed for the assay of AA1 in plasma was applied to its determination in brain using an Oasis HLB plate following homogenisation in a pH 7.4 buffer and protein precipitation with NaOH-ZnSO4, thereby saving time for method development. Protein precipitation in the 96-well format with filtration of the precipitate was applied to the determination of ICL670, a highly protein-bound compound (>99.5%), with a good recovery (78%). Reversed-phase chromatography was applied using a short 5 cm column packed with 3 microm particles for the determination of ICL670 and AA1 and two parallel columns (15 cm long) for the determination of rufinamide. The methods were used routinely, one plate per analysis day being processed, resulting in increase in sample throughput and saving in solvents.

Animals↗
PubMed2002

Factors affecting incorporation of drug into solid solution with HPMCP during solvent change co-precipitation.

Drug-hydroxypropyl methylcellulose phthalate (HPMCP) mixtures were completely dissolved in acetone, and the resulting solution was added drop-wise into HCl(aq). Resulting co-precipitates were filtered, and then dried under vacuum at 45 degrees C, -800 mbar for 24 h. Modulated differential scanning calorimetry, thermogravimetric analysis, X-ray powder diffraction and HPLC were used to detect and quantify different phases present in co-precipitates. A 1/8 factorial study followed by a circumscribed central composite (CCC) study of significant factors, were used to detect and quantify respectively, the effects that processing factors had on the percentage of drug present in co-precipitates which was incorporated into solid solution (the response). Robustness of the model obtained from the CCC study was tested. Statistically significant factors were found to be the percentage of drug added into solvent, stirrer speed, and antisolvent pH. The statistically significant mathematical model obtained from the CCC study predicted that the dominant factor influencing the response is the percentage of drug added into solvent. The effect of stirrer speed on the response includes a local maximum at stirrer speed approximately 700 rpm. Both stirrer speed and antisolvent pH showed interactions with the percentage of drug added into solvent. The model obtained from this study indicated the possibility of two opposing phenomena influencing the response: crystallization inhibition by HPMCP, and solvent-antisolvent plasticization. Testing of this model using eight experimentally determined points showed reasonable robustness, with six out of eight points lying inside 95% prediction intervals.

Acetone↗
PubMed2003

A semi-automated 96-well protein precipitation method for the determination of montelukast in human plasma using high performance liquid chromatography/fluorescence detection.

A simple, semi-automated, protein precipitation assay for the determination of montelukast (SINGULAIR, MK-0476) in human plasma has been developed. Montelukast is a potent and selective antagonist of the cysteinyl leukotriene receptor used for the treatment of asthma. A Packard MultiPROBE II EX is used to transfer 300 microl of plasma from sample, standard, and QC sample tubes to a microtiter plate (96-well). After addition of the internal standard by a repeating pipettor, a Tomtec QUADRA 96 adds 400 microl of acetonitrile to all plasma sample wells, simultaneously, in the microtiter plate. The Tomtec is also used to transfer the acetonitrile supernatant from the plasma protein precipitation step, batchwise, to another microtiter plate for analysis by HPLC with fluorescence detection. This assay has been validated and implemented for a clinical study of over 1300 plasma samples and is comparable to manual assays in the LLOQ (lower limit of quantitation, 3 ng/ml) and in stability. This is the first semi-automated protein precipitation assay published for the analysis of montelukast in human plasma and it results in significant time savings over the manual methods, both in sample preparation and in HPLC run time.

Acetates↗