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At least 433 records · Page 24Linked to original sources

PubMed1994

Probing the conformation of protein (bFGF) precipitates by fluorescence spectroscopy.

Aggregation and precipitation are major events in the handling and aging of most protein pharmaceuticals. We demonstrate the utility of fluorescence spectroscopy in determining protein conformation in precipitates using basic fibroblast growth factor (bFGF) as an example. Conversion of the native to the soluble denatured from by chaotropes was accompanied by an increase in tryptophan emission. The emission spectra of resuspended precipitates were as reproducible as the spectra of the soluble form. The sum of emission spectra of native soluble bFGF and denatured precipitated bFGF was superimposable on the spectrum of the unfractionated suspension, suggesting that quantitative analysis of denatured aggregates in turbid protein formulations is possible. The ratio of tryptophan to tyrosine emissions increased with increasing extent of denaturation both in solution and in suspension. For example, salting out by ammonium sulphate increased the fluorescence index (indicative of denaturation) which was reversible upon dissolution. In addition, aging (35 degrees C) of bFGF in the presence of sulphated ligands produced precipitates with native-like fluorescence index, in contrast to denatured precipitates formed without ligands.

Chromatography, High Pressure Liquid↗

PubMed2005

Climate change and changes in global precipitation patterns: what do we know?

The objective of this paper is to synthesize the large literature recording changing patterns of precipitation in the observed data, thus indicating that climate change is already a reality. Such a synthesis is required not only for environmental researchers but also for policy makers. The key question is the broad picture at major regional and continental levels. Some interesting conclusions for this survey are emerging. For example, the review shows increased variance of precipitation everywhere. Consistent with this finding, we observe that wet areas become wetter, and dry and arid areas become more so. In addition, the following general changing pattern is emerging: (a) increased precipitation in high latitudes (Northern Hemisphere); (b) reductions in precipitation in China, Australia and the Small Island States in the Pacific; and (c) increased variance in equatorial regions. The changes in the major ocean currents also appear to be affecting precipitation patterns. For example, increased intensity and frequency of El Niño and ENSO seem associated with evidence of an observed "dipole" pattern affecting Africa and Asia, although this time series is too short so far. But the changing pattern calls for renewed efforts at adaptation to climate change, as the changing precipitation pattern will also affect the regional availability of food supply.

Data Collection↗

PubMed2004

Study on the precipitation reaction between baicalin and berberine by HPLC.

The solubility product equilibrium constant for the precipitation between baicalin and berberine was investigated because of the current interest in decocting process of complex prescription of Chinese herbal medicine. HPLC was used for determining two compounds' equilibrium concentrations at different precipitate conditions to calculate thermodynamic constants and study kinetic process. The analysis was performed on a Kromasil C(18) column with TEA-adjusted 0.02 mol/L H(3)PO(4) (pH 4.82)-acetonitrile (75:25) as mobile phase at a flow-rate of 1.0 ml/min, with detection at 254 nm. According to the experiment result, the molar ratio of baicalin and berberine in precipitate is about 1:1. The experimental K(sp) values are (1.01 +/- 0.12) x 10(-9)mol(2)/L(2) at 20 degrees C in 0.02 mol/L NaH(2)PO(4)-Na(2)HPO(4) (pH 4.82), and (3.20 +/- 0.46) x 10(-9)mol(2)/L(2) at 40 degrees C in the same buffer. The precipitate reaction is an exothermic process and occurs immediately, even though the precipitate cannot be observed in time because the precipitate is light, yellow, flocculous and suspending in the yellow solution.

Anti-Asthmatic Agents↗

PubMed2005

EELS study of niobium carbo-nitride nano-precipitates in ferrite.

Micro-alloying steels allow higher strength to be achieved, with lower carbon contents, without a loss in toughness, weldability or formability through the generation of a fine ferrite grain size with additional strengthening being provided by the fine scale precipitation of complex carbo-nitride particles. Niobium is reported to be the most efficient micro-alloying element to achieve refinement of the final grain structure. A detailed microscopic investigation is one of the keys for understanding the first stages of the precipitation sequence, thus transmission electron microscopy (TEM) is required. Model Fe-(Nb,C) and Fe-(Nb,C,N) ferritic alloys have been studied after annealing under isothermal conditions. However the nanometre scale dimensions of the particles makes their detection, structural and chemical characterization delicate. Various imaging techniques have then been employed. Conventional TEM (CTEM) and high resolution TEM (HRTEM) were used to characterise the morphology, nature and repartition of precipitates. Volume fractions and a statistical approach to particle size distributions of precipitates have been investigated by energy filtered TEM (EFTEM) and high angle annular dark field (HAADF) imaging. Great attention was paid to the chemical analysis of precipitates; their composition has been quantified by electron energy loss spectroscopy (EELS), on the basis of calibrated 'jump-ratios' of C-K and N-K edges over the Nb-M edge, using standards of well-defined compositions. It is shown that a significant addition of nitrogen in the alloy leads to a complex precipitation sequence, with the co-existence of two populations of particles: pure nitrides and homogeneous carbo-nitrides respectively.

Journal Article↗

PubMed2005

Long-term trend of chemical constituents in precipitation in Tokyo metropolitan area, Japan, from 1990 to 2002.

In order to understand the actual status and mechanism of acid rain, it is important to know the pH of precipitation and its chemical constituents on a continuous and regular basis over a wide area. This study examines acid rain over a wide area using an observational network in the Tokyo metropolitan area of Japan, and analyzes the major chemical constituents of every precipitation sample. Precipitation was collected continuously for a period of 12 years from June 1990 to May 2002 at several sampling sites in the Tokyo metropolitan area, and its pH and chemical constituent concentrations were measured. The average pH ranged from 4.23 to 4.62, clearly indicating acidification of precipitation over the entire Tokyo metropolitan area. A time-trend model was applied to describe temporal variations of chemical constituent concentrations, including annual change rate, seasonal variation, and precipitation effects. Seasonal and annual trends for the past 12 years were examined with the model, using the least squares method. Nonsea salt (nss)-Ca2+ shows a maximum value in early spring, a seasonality probably caused by calcium-rich particles in airborne yellow dust from Asia. Slightly decreasing annual trends of nss-SO4(2-) may correspond to the recent decreasing trend of atmospheric SO2 gas concentrations in the Tokyo metropolitan area. The annual trends of NO3-, NH4+, and nss-Ca2+ show a large site-to-site difference. The increasing NO3-, NH4+, and nss-Ca2+ concentrations at inland suburban sites may be caused by increases in their local sources such as vehicle traffic and municipal waste incineration. The annual change rate of H+ is slightly negative or almost zero at every site, so the acidification of precipitation has not become worse since 1990 over the Tokyo metropolitan area.

Journal Article↗

PubMed2002

An immuno-precipitation assay for determining specific interactions between antibodies and phage selected from random peptide expression libraries.

Libraries of random peptides displayed by bacteriophage can be screened to select phage expressing peptides that specifically bind antibodies, so that the peptide sequence motifs expressed by the phage can help to define the epitopes of the antibodies. It is often desirable to screen antibody-selected phage for binding of the selecting antibody in an immunoassay in order to verify the specificity of the interaction. Enzyme-linked immunosorbent assays (ELISAs) are commonly used for this purpose. However, for many antibodies, the best techniques for measuring specific, high affinity interactions are immuno-precipitation assays. Immuno-precipitation was therefore investigated as a means of measuring interactions between antibodies and phage clones selected from random peptide display libraries. Three mouse monoclonal antibodies specific for glutamic acid decarboxylase were used to select peptides as 9-mers on T7 phage, linear 12-mers on pIII of M13 phage, or constrained 15-mers on pVIII of M13 phage. Following the cloning and sequencing of selected phage, mixtures of antibody and phage were incubated in solution and the immune complexes were precipitated with Protein G bound to Sepharose beads. In order to detect and quantitate the phage that had formed immune complexes and been precipitated, advantage was taken of the biological properties of the phage by inducing infection of Escherichia coli by the precipitated phage. The aim was to quantitate the phage precipitated by determining the number of plaques produced, which would therefore be proportional to the degree of interaction between the phage and the antibody in solution. The results presented here indicate that this method of measuring monoclonal antibody interactions with phage selected for expression of peptides recognised by the monoclonal antibody is highly specific and sensitive.

Amino Acid Sequence↗

PubMed2002

Spatial and temporal variation of polychlorinated biphenyl (PCB) in precipitation in southern Sweden.

Spatial and temporal variations in polychlorinated biphenyl (PCB) concentrations were studied in precipitation at 11 sampling-sites over a period of 1 year and compared with PCB concentrations in the air. The study was carried out in a region of southern Sweden approximately 11 000 km2 in area. The PCB concentration in precipitation ranged between 1.18 and 81.4 ng l(-1). Two of the sampling sites showed concentrations that were approximately 30 times higher than at the rest of the sites. The variation in concentration between sites may be explained by location as well as by differences in weather conditions and particle content in the air. Wind direction played an important role for PCB concentration in precipitation in coastal areas, while at the inland sites this variable seemed to have a minor influence. We found no seasonal trends in PCB concentration in precipitation or any dependence on air temperature. To examine the intensity of precipitation scavenging, the total washout ratios (Wt) were calculated. There was a large variation in Wt over time, and the highest ratios were observed at the two sites where PCB concentration in the air was high. Furthermore, high concentrations of PCB in precipitation correlated with a high-chlorinated pattern, as shown by principal component analysis. For most of the sites there was a significantly negative relationship between PCB concentration and rain volume.

Air Pollutants↗

PubMedDate not supplied

Precipitated cannabinoid withdrawal is reversed by Delta(9)-tetrahydrocannabinol or clonidine.

The availability of the cannabinoid antagonist, SR 141716A, to precipitate withdrawal following repeated cannabinoid administration provides a model to investigate the mechanisms underlying cannabinoid dependence as well as potential treatments to alleviate withdrawal symptoms. The goal of the present study was to determine whether SR 141716A-precipitated withdrawal symptoms in Delta(9)-tetrahydrocannabinol (Delta(9)-THC)-tolerant mice could be alleviated by either readministration of Delta(9)-THC or clonidine, an alpha(2)-receptor agonist. SR 141716A elicited paw tremors in Delta(9)-THC-tolerant mice, but produced a significant increase in head shakes independently of repeated Delta(9)-THC treatment. Readministration of Delta(9)-THC, following SR 141716A-precipitated withdrawal, reversed paw tremors (ED(50)=9.9 mg/kg), but failed to reduce head shaking behavior. Clonidine reversed SR 141716A-precipitated paw tremors (ED(50)=0.18 mg/kg) and blocked head shakes at all doses tested. The reversal effects did not appear to be the result of motor impairment because neither decreases in spontaneous locomotor activity nor motor incoordination, as assessed in the inverted screen test, could account for the effects. These findings suggest that SR 141716A precipitates paw tremors in mice by competing with Delta(9)-THC at the CB(1) receptor, though it also produced head shaking in nondependent animals. Finally, the observation that clonidine alleviated SR 141716A-precipitated paw tremors suggests its potential as a treatment for cannabinoid dependence.

Adrenergic alpha-Agonists↗

PubMedDate not supplied

Selective precipitation of DNA by spermine during the chemical extraction of insoluble cytoplasmic protein.

The direct chemical extraction of recombinant L1 protein (the major capsid protein of human papillomavirus type 16) from the cytoplasm of E. coli HMS174(DE3) has recently been demonstrated at high cell density (to OD(600) = 160) without the use of reducing agent (1). Coextraction of DNA at high concentration prevents direct coupling to postextraction recovery operations including expanded bed adsorption. In this study, spermine is used to selectively precipitate DNA during chemical extraction. Highly efficient and selective DNA precipitation was achieved. An approximate 10-fold increase in the specific spermine concentration (mg of spermine/mg of DNA) was required to precipitate DNA when 8 M urea was added to the extraction buffer. EDTA (3 mM), required for effective chemical extraction, does not significantly inhibit DNA precipitation. Precipitation selectivity was demonstrated in a bovine serum albumin spiking test, with almost complete recovery of the spiked protein. During studies on the direct extraction of L1 protein from cells at OD(600) = 80, high DNA removal efficiency (>85%) and negligible L1 protein coprecipitation were achieved. This selective precipitation technique simply requires the addition of spermine to the chemical extraction buffer and therefore does not increase technique complexity. This modification enhances the method's general applicability and enables direct coupling to downstream recovery units following chemical extraction at high cell and product concentrations.

Capsid Proteins↗

PubMedDate not supplied

Precipitation at equivalence and equilibrium: a method for the determination of equilibrium constants of reaction between multideterminant antigen and specific polyclonal antibodies.

A theoretical approach for the determination of the equilibrium constant, Ka, of the reaction between a multideterminant antigen (Ag) and specific polyclonal antibodies (Ab) forming the insoluble Ab/Ag immune complex, is derived. The constant can be expressed as a function of the two accessible experimental parameters, the precipitating concentration of the antigen and the Ab/Ag molar ratio. For this purpose Ab/Ag immune complex must be prepared at equivalence, and equilibrium between precipitated and soluble species must be reached. The proposed method is experimentally tested on the system human serum albumin (HSA) and polyclonal rabbit antibodies. The Ab/Ag precipitates are prepared by the direct mixing of biological fluids in which immunoreacting components naturally occur. Previous separation, purification, or labeling of immunoreacting components are not required. The conditions for the precipitation of Ab/Ag complexes at equivalence, the stoichiometric composition or the average number of Ab molecules bound to one Ag molecule, and the solubility of the immunoprecipitating components are determined by a rectangular two-dimensional double immunodiffusion. Since the solubility determined under the conditions of a double immunodiffusion is a result of the interaction of the global diffusion of the precipitating components and particle growth kinetics, it mostly refers to the dynamic conditions. To find the solubility under equilibrium conditions, it is sufficient to determine the minimal factor by which the solutions of both immunoprecipitating components should be diluted so that no precipitate is formed upon their mixing at equivalence. The dilution factor is determined by a measurement of the laser light scattering of the immunoprecipitating systems prepared with serially diluted Ag and Ab solutions.

Animals↗

PubMed2003

Environmental, mineralogical, and genetic characterization of ochreous and white precipitates from acid mine drainages in Taebaeg, Korea.

X-ray diffraction, energy-dispersive X-ray fluorescence, thermal analysis, scanning electron microscopy, inductively coupled plasma emission spectroscopy, and ion chromatography were used for the environmental, mineralogical, and genetic characterization of brownish yellow, reddish brown, and white precipitates from acid mine drainage in Taebaeg, Korea. Ferrihydrite+goethite, schwertmannite, and Al-sulfate were precipitated under different chemical environments on the stream bottom of acid mine drainages. The brownish yellow precipitates (Munsell color 9.5YR hues) consist mainly of schwertmannite with traces of quartz, illite, pyrophyllite, goethite, lepidocrocite, and gypsum. The reddish brown precipitates (Munsell color 3.5YR hues) consist mainly of ferrihydrite with small amount of goethite. The white precipitates consist mainly of poorly crystalline Al-sulfate with small amounts of quartz, gypsum, and calcite. Thermal decomposition due to dehydration of ferrihydrite and schwertmannite takes place at approximately 120 degrees C and 140 degrees C, respectively. Al-sulfate converts to gamma-alumina at 850 degrees C. SEM study shows that the spheroid and rod-shaped precipitates characteristic of Gallionella consist of iron hydroxide with varying chemical compositions.

Acids↗

PubMed2004

Effect of storage on the isotopic composition of nitrate in bulk precipitation.

Stable isotopic analysis of atmospheric nitrate is increasingly employed to study nitrate sources and transformations in forested catchments. Large volumes have typically been required for delta18O and delta15N analysis of nitrate in precipitation due to relatively low nitrate concentrations. Having bulk collectors accumulate precipitation over an extended time period allows for collection of the required volume as well as reducing the total number of analyses needed to determine the isotopic composition of mean annual nitrate deposition. However, unfiltered precipitation left in collectors might be subject to microbial reactions that can alter the isotopic signature of nitrate in the sample. Precipitation obtained from the Turkey Lakes Watershed was incubated under conditions designed to mimic unfiltered storage in bulk precipitation collectors and monitored for changes in nitrate concentration, delta15N, and delta18O. Results of this experiment indicated that no detectable nitrate production or assimilation occurred in the samples during a two-week incubation period and that atmospheric nitrate isotopic ratios were preserved. The ability to collect unfiltered precipitation samples for an extended duration without alteration of nitrate isotope ratios is particularly useful at remote study sites where daily retrieval of samples may not be feasible.

Environmental Monitoring↗

PubMed2006

Effects of externally-through-internally-mixed soot inclusions within clouds and precipitation on global climate.

This paper examines the incremental global climate response of black carbon (BC), the main component of soot, due to absorption and scattering by BC inclusions within cloud and precipitation particles. Modeled soot is emitted as an externally mixed aerosol particle. It evolves to an internal mixture through condensation, hydration, dissolution, dissociation, crystallization, aqueous chemistry, coagulation, and cloud processing. Size-resolved cloud liquid and ice particles grow by condensation onto size-resolved soot and other particles. Cloud particles grow to precipitation by coagulation and the Bergeron process. Cloud and precipitation particles also undergo freezing, melting, evaporation, sublimation, and coagulation with interstitial aerosol particles. Soot, which is tracked in cloud and precipitation particles of all sizes, is removed by rainout, washout, sedimentation, and dry deposition. Two methods of treating the optics of BC in size-resolved cloud liquid, ice and graupel are compared: the core-shell approximation (CSA) and the iterative dynamic effective medium approximation (DEMA). The 10-year global near-surface incremental temperature response due to fossil fuel (ff), biofuel (bf), and biomass burning (bb) BC within clouds with the DEMA was slightly stronger than that with the CSA, but both enhancements were <+0.05 K. The ff+bf portion may be approximately 60% of the total, suggesting that BC inclusions within clouds may enhance the near-surface temperature response of ff+bf soot due to all processes (estimated as approximately 0.27 K), by <10%, strengthening the possible climate impact of BC. BC cloud absorption was also found to increase water vapor, decrease precipitation, and decrease cloud fraction. The increase in water vapor at the expense of precipitation contributed to warming in addition to that of the cloud BC absorption itself. Aerosol-hydrometeor coagulation followed by hydrometeor evaporation may have caused almost twice the BC internal mixing as aerosol-aerosol coagulation.

Journal Article↗

PubMed2003

Predicting biogeochemical calcium precipitation in landfill leachate collection systems.

Clogging of leachate collection systems within municipal solid waste landfills can result in greater potential for contaminants to breach the landfill barrier system. The primary cause of clogging is calcium carbonate (CaCO3(s)) precipitation from leachate and its accumulation within the pore space of the drainage medium. CaCO3(s) precipitation is caused by the anaerobic fermentation of volatile fatty acids (VFAs), which adds carbonate to and raises the pH of the leachate. An important relationship in modeling clogging in leachate collections systems is a yield coefficient that relates microbial fermentation of VFAs to precipitation of calcium carbonate. This paper develops a new, mechanistically based yield coefficient, called the carbonic acid yield coefficient (Y(H)), which relates the carbonic acid (H2CO3) produced from microbial fermentation of acetate, propionate, and butyrate to calcium precipitation. The empirical values of Y(H) were computed from the changes in acetate, propionate, butyrate, and calcium concentrations in leachate as it permeated through gravel-size material. The theoretical and empirical results show that the primary driver of CaCO3(s) precipitation is acetate fermentation. Additionally, other non-calcium cations (e.g., iron and magnesium) precipitated with carbonate (CO3(2-)) when present in the leachate. A common yield between total cations bound to CO3(2-) and H2CO3 produced, called the calcium carbonate yield coefficient (Yc), can reconcile the empirical yield coefficient for synthetic and actual leachates.

Algorithms↗

PubMed2000

Ammonium sulphate precipitation of recombinant adenovirus from culture medium: an easy method to increase the total virus yield.

In the majority of the methods for purifying and concentrating recombinant adenoviruses (rAds) the virus that is associated with the helper cells is harvested, while the virus that is present in the cell-culture medium is discarded. During routine propagation of adenovirus type-5 vectors at optimised conditions we noted that, on average, 47% of the total amount of virus is present in the culture medium. To recover and concentrate these rAds from the medium, we devised a method, which is based on ammonium sulphate ((NH4)2SO4) precipitation. At 40% (NH4)2SO4 saturation, 95 +/- 6% of the available virus precipitates from the medium, while the majority of the protein (85%) remains in solution. In contrast to adenovirus precipitation with polyethylene glycol, the (NH4)2SO4 precipitation technique allows collection of precipitated rAds by filtration. We demonstrate here that (NH4)2SO4 precipitation of rAds from cell-culture medium is a simple and fast technique that can be used in combination with standard virus isolation methods to increase the yields of rAds.

Adenoviridae↗

PubMed1999

Precipitating factors of headache. A prospective study in a national control-matched survey in migraineurs and nonmigraineurs.

Prospective studies of precipitating factors in migraine are rare. Mig Access is a national control-matched survey conducted to evaluate the access of migraineurs to health care in France. This study allowed us to screen prospectively some precipitating factors of headache in migraineurs and in nonmigraineurs. Three hundred eighty-five migraineurs (group 1) and 313 nonmigraineurs (group 2) kept a diary for a 3-month period (a total of 35,805 day in group 1 and 29,109 days in group 2). Precipitating factors were reported for each headache period. Headache intensity was self-assessed during each headache period using a visual analog scale of 0 to 100. Headache was reported on 4274 days (12%) in group 1 and on 602 days (2%) in group 2. Headache intensity was greater in group 1 (39 +/- 20 versus 32 +/- 19, P < .05). The most frequent precipitating factors (reported at least once by more than 10% of subjects [range 18% to 80%] in both groups) were fatigue and/or sleep, stress, food and/or drinks, menstruation, heat/cold/weather, and infections in both groups. All these factors except infections were reported to cause headache more frequently in migraineurs than in nonmigraineurs. Mean intensity of headache related to fatigue and/or sleep, stress, food and/or drinks, hot/cold weather, and menstruation varied from 37 to 43 in migraineurs and from 29 to 35 in nonmigraineurs. Headache with the highest mean intensity was due to infections in the two groups (47 +/- 20 in group 1, 45 +/- 23 in group 2). Our results support that endogenous factors are the most frequent triggers of headache in migraineurs. The most frequent precipitating factors of headache appear identical in migraineurs and in nonmigraineurs. Our results suggest that similar triggers could precipitate headache of different type in these two populations.

Adult↗

PubMed2004

Precipitation of oppositely charged polyelectrolytes in salt solutions.

We study phase separation in symmetric solutions of weakly charged flexible chains of opposite sign. Precipitation is caused by effective attractions due to charge fluctuations and by short-range attractions between monomers. The contribution from charge fluctuations is computed within the random phase approximation (RPA), which takes into account the connectivity of charges in the polyions. The impenetrability of the ions is accounted for by using a modified Coulomb potential in the RPA. In good solvent conditions the precipitate monotonically swells and eventually dissolves upon addition of salt. However, near the theta-solvent condition, but still in the good solvent, the precipitate can be stable at any salt concentration. Moreover, the density of the precipitate after initial decrease can increase with addition of salt. This effect is a result of redistribution of salt between the precipitate and the supernatant, which is due to an interplay of electrostatic and hardcore interactions. For not too weakly charged polyions the precipitate properties become strongly dependent on temperature even in good solvent conditions.

Journal Article↗

PubMed2006

Identification of physical-chemical variables affecting particle size following precipitation using a supercritical fluid.

The physical-chemical processing variables affecting particle size following precipitation using the supercritical antisolvent (SAS) method were investigated by varying both the composition of the feed solvent and the structure of the solute, using a series of steroids. The key factor influencing particle size in these studies appears to be the solubility of the drug in the organic solvent/supercritical fluid mixture, where relatively high solubility causes a lower degree of supersaturation in the precipitation vessel, resulting in a relatively large particle size. Higher operating pressures result in larger particle sizes, probably through the effect of pressure on solubility. Physical properties of the carrier solvent, such as vapor pressure and dielectric constant, were not effective predictors of relative particle size of the precipitated powder, nor was solubility of the model drug in the carrier solvent. In limited studies of the physical state of the precipitated solid, higher apparent crystallinity was observed for powders with larger particle size. A precipitate of a different crystal form was observed when starting with hydrocortisone hemisuccinate monohydrate and may represent the loss of water of hydration. An amorphous solid was precipitated when starting with yttrium acetate dihydrate. Broad guidelines for effective particle size reduction using this technique are presented.

Chemical Phenomena↗