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PubMed1999

Alcohol Rinsing and Crystallization Behavior of Precipitated Titanium Oxide.

In our present study, the effects of alcohol washing on the crystallization behavior of precipitated titanium oxide were investigated using Fourier-transformed infrared spectroscopy (FT-IR), thermogravimetry, differential scanning calorimetry, X-ray powder diffraction, and Raman spectroscopy. Alcohol rinsing of the precipitated titania powder having an amorphous hydrated form retarded its crystallization to the anatase phase. The crystallization temperature for 390 degrees C of nonrinsed (water-washed only) powder was increased to 467 degrees C with the alcohol rinse. The retardation was attributed to the formation of oxo-alkoxides on the particle surfaces. FT-IR analysis demonstrated that the alcohol-rinsed powder had a dehydration rate much lower than that of the nonrinsed powder as temperatures were increased. Therefore, it was suggested that the presence of oxo-alkoxides in the alcohol-rinsed powder decreased the dehydration rate, which, in turn, retarded crystallization to the anatase structure. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Magnetite Nanoparticles Prepared by Precipitation from Partially Reduced Ferric Chloride Aqueous Solutions.

Spherical magnetite particles with mean diameter of about 10 nm or less were prepared by means of a reduction-precipitation method with ferric chloride as starting material, which was partially reduced to ferrous salts by Na2SO3 before alkalinizing with ammonia. It was found that the nature of the product depends strongly on the initial ratio R0 = [Fe3+]0/[SO2-3]0. The most appropriate ratio was 3 as proved by X-ray diffraction analysis on the samples although the initial concentration of ferric chloride can be different. Particle diameter increased from ca. 3 to ca. 11 nm with an increase of the concentration of aqueous ferric chloride from 0.075 to 0.45 mol dm-3. The advantage of this method lies in the formation of a red intermediate during the reduction process, which enables us to prevent the reoxidation of the ferrous ions by adding precipitation agents at the end of the reduction reaction without the protection of nitrogen or argon. Copyright 1999 Academic Press.

Journal Article↗
PubMed2000

Precipitation of Zinc Sulfide Particles from Homogeneous Solutions.

Zinc sulfide particles were homogeneously precipitated by thermal decomposition of thioacetamide in acidic aqueous solutions in a one-step process. The influence of the operating conditions (initial concentration of zinc ion and TAA) on the nucleation time and number concentration of the generated particles was investigated. The experimental results show that the model of homogeneous nucleation previously developed and successfully tested for silver particle generation by a chemical reduction method can also be applied to the formation of zinc sulfide particles by homogeneous precipitation. Furthermore, in the particle formation method in which the nucleation time t* can be measured, the particle number concentration n* can be predicted by the simple relation n*=1/(4pir*Dt*) (r* is the critical nucleus radius, and D the monomer diffusion coefficient). Thus the particle number concentration can be easily predicted even if the rate expression and the critical supersaturation concentration are unknown. Copyright 2000 Academic Press.

Journal Article↗
PubMed1999

Preparation of Uniform Needle-Like Aragonite Particles by Homogeneous Precipitation.

Uniform needle-like aragonite particles were obtained by aging solutions of calcium salts in the presence of urea at 90 degrees C. The effects of various experimental conditions, such as the concentration of reactants, temperature, aging time, agitation, mixing procedure, and the addition of divalent cations, surfactants, and polymers, on the precipitation of aragonite were investigated. It was found that the formation of different polymorphs of calcium carbonate was affected mostly by agitation and concentration of reactants, as well as by the mixing procedure. Thus, under otherwise the same experimental conditions, needles of aragonite were formed without stirring or at low-power ultrasound; rhombohedral calcite appeared when aging experiments were carried out under the influence of magnetic stirring, while irregular particles of mixed vaterite and calcite crystal structure were generated at higher CaCl(2) concentrations. Mixing the preheated reactant solutions resulted in unique "flower-type" vaterite particles. Finally, the presence of sulfonate or sulfate ions promoted precipitation of vaterite and calcite. Copyright 1999 Academic Press.

Journal Article↗
PubMed2000

Anatase-Rutile Transition of Precipitated Titanium Oxide with Alcohol Rinsing.

The effect of alcohol washing on the anatase-rutile transition of precipitated titanium oxide was investigated using X-ray powder diffraction, Fourier-transform IR spectroscopy, and thermogravimetry. Alcohol (butanol) rinsing accelerated the anatase-rutile transition of precipitated titanium oxide powder so that the onset temperature of transition decreased drastically from 800 degrees C for water-washed powder to 550 degrees C for alcohol-rinsed powder. Alternation of transition kinetics and mechanisms by rinsing media could be confirmed from the analysis of temperature and time dependence of rutile content. The attributability of the chemical state of anatase after crystallization, which contained H(2)O, OH, and organic residues, to the change of transition kinetics with alcohol rinsing will be discussed. Two mechanisms, the effect of residual organics and/or H(2)O(OH), could be suggested on the basis of analysis of the difference between chemical states of water-washed anatase and alcohol-rinsed powder. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Formation of Layered Single- and Double-Metal Hydroxide Precipitates at the Mineral/Water Interface: A Multiple-Scattering XAFS Analysis.

Spectroscopic and microscopic studies have shown that Ni and Co sorption by clay minerals may proceed via formation of surface precipitates. Several studies employing X-ray absorption fine structure (XAFS) spectroscopy suggested the formation of turbostratic, alpha-type metal hydroxides, of layered double hydroxides (LDH) with Al-for-metal substitution, and of 1:1 or 2:1 phyllosilicates. Distinction of these phases is difficult because they have low crystallinity and/or a small mass compared to the sorbents, and because they have similar metal-metal distances in their hydroxide layers/sheets. Distinction of these phases is crucial, however, because they have substantially differing solubilities. In this paper we show that an XAFS beat pattern at about 8 Å(-1) can be used as a fingerprint to unequivocally distinguish LDH from the alpha-type hydroxides and phyllosilicates. Full multiple-scattering simulations and experimental spectra of model compounds indicate that the beat pattern is due to focused multiple scattering at Me/Al ratios between 1 and 4 (Me=Ni, Co). By applying the fingerprint method to new and to already published XAFS data on Ni and Co surface precipitates, we found that LDH preferentially forms in the presence of the Al-containing sorbents pyrophyllite, illite, kaolinite, gibbsite, and alumina above pH 7.0. However, alpha-type metal hydroxides form in the presence of the Al-free sorbents talc, silica, and rutile, and in the presence of the Al-containing clay minerals montmorillonite and vermiculite. We believe that the high permanent charge of these latter minerals prevents or retards the release of Al. When Al is available, the formation of LDH seems to be thermodynamically and/or kinetically favored over the formation of alpha-type hydroxides. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Preparation of Micrometer Size Budesonide Particles by Precipitation.

Particles of different shape, size and crystallinity of budesonide, a hydrocortisone streroid, were prepared by precipitation. The method is based on taking advantage of the different solubility of this material in certain organic solvents (ethanol, acetone) and water or alcanes. In principle, to solutions of budesonide, water was added until the solids precipitate or the same solute in mixed solvents was carefully separated by evaporation of the more volatile component at room temperature. The morphology, size, and stability of the resulting particles were sensitive to the evaporation technique, stirring, and presence of a stabilizing agent. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

H(2)O Outgassing Properties of Fumed and Precipitated Silica Particles by Temperature-Programmed Desorption.

Temperature-programmed desorption was performed at temperatures up to 850 K on as-received fumed and precipitated silica particles. Physisorbed water molecules on both types of silica had activation energies in the range of 38-61 kJ/mol. However, the activation energies of desorption for chemisorbed water varied from approximately 80 to >247 kJ/mol for fumed silica, Cab-O-Sil-M-7D, and approximately 96 to 155 kJ/mol for precipitated silica, Hi-Sil-233. Our results suggest that physisorbed water can be effectively pumped away at room temperature (or preferably at 320 K) in a matter of hours. Chemisorbed water with high activation energies of desorption (>126 kJ/mol) will not escape silica surfaces in 100 years even at 320 K, while a significant amount of the chemisorbed water with medium activation energies (80-109 kJ/mol) will leave the silica surfaces in that time span. Most of the chemisorbed water with activation energies <126 kJ/mol can be pumped away in a matter of days in a good vacuum environment at 500 K. We had previously measured about 0.1-0.4 wt% of water in silica-reinforced polysiloxane formulations containing approximately 21% Cab-O-Sil-M-7D and approximately 4% Hi-Sil-233. Comparing present results with these formulations, we conclude that the adsorbed H(2)O and the Si-OH bonds on the silica surfaces are the major contributors to water outgassing from these types of silica-filled polymers. Copyright 2000 Academic Press.

Journal Article↗
PubMed1992

Pyrophosphate synthesis from phospho(enol)pyruvate catalyzed by precipitated magnesium phosphate with "enzyme-like" activity.

The enzyme-like kinetic properties of precipitated magnesium phosphate as a catalyst for formation of pyrophosphate (PPi) from phospho(enol)pyruvate (PEP) are described. This synthesis occurs at a low temperature (37 degrees C) and represents a model that may help us understand the relevance to chemical evolution of minerals as ancient catalysts whose functions could have been taken over by contemporary enzymes. An insoluble Pi.Mg matrix was formed in a medium with 80% of the water replaced by dimethyl sulfoxide as a way of simulating conditions in a drying pond. Phospho(enol)pyruvate adsorbs onto the Pi.Mg surface according to a Langmuir isotherm, and the PEP concentration dependence of PPi formation follows a Michaelian-like function. A yield of 33% for transformation of the initially adsorbed PEP into PPi was attained after 4 days of incubation with equimolecular concentrations of Pi, MgCl2, and PEP. The magnesium concentration dependence for Pi and Mg precipitation, for adsorption of PEP onto solid Pi.Mg, and for PPi formation showed complex cooperative behavior. These results taken as a whole lead to the conclusion that the Pi.Mg surface not only provides a reactant for PPi formation but also catalyzes the reaction.

Diphosphates↗
PubMed1992

Withdrawal precipitation by benzodiazepine receptor antagonists in dogs chronically treated with diazepam or the novel anxiolytic and anticonvulsant beta-carboline abecarnil.

The effects of the benzodiazepine (BZ) receptor antagonists flumazenil (Ro 15-1788) and the beta-carboline ZK 93426 were compared in dogs before and after chronic treatment with diazepam or the novel BZ receptor ligand abecarnil (ZK 112119). Abecarnil, a beta-carboline, is thought to act as partial (low efficacy) and/or subtype selective agonist at central BZ receptors. Diazepam and abecarnil were administered at doses which, based on previous experiments on anticonvulsant activity, resulted in about equieffective drug concentrations during treatment. In dogs treated with diazepam, 6 mg/kg/day p.o., for 2 weeks, severe abstinence symptoms, including seizures, were precipitated in all animals by i.v. infusion of the BZ receptor antagonists, differences being found in the type of symptoms caused by flumazenil and ZK 93426. In dogs treated with abecarnil, 4 mg/kg/d s.c., for 6 weeks, only relatively mild abstinence symptoms were precipitated by infusion of flumazenil or ZK 93426, although pharmacologically active plasma concentrations of abecarnil had been maintained throughout the period of treatment. This suggests that BZ receptor ligands which act as partial and/or selective agonists might be more favourable than traditional agonists, such as diazepam, regarding the induction of physical dependence.

Animals↗
PubMed1976

Visualization of the retino-hypothalamic projection in the rat by cobalt precipitation.

The technique of cobalt sulfide precipitation combined with Timm's sulfide-silver method for intensification of heavy metals was used to delineate the retino-hypothalamic projection of the rat. Freshly isolated rat brains were dissected and a solution of cobaltous chloride was applied to one of the cut optic nerves. Sixteen hours later, after cobalt ions had passed into the brain along the entire length of the optic fibers, the preparation was treated with ammonium sulfide to precipitate the cobalt as cobalt sulfide. In thick light microscopic sections, cobalt-filled axons were visualized as black fibers against a light gold background. Such fibers were observed to leave the posterior medial portion of the optic chiasm and, after arching dorsally, to project into the posterior fifth of the suprachiasmatic nucleus (SCN), as well as into the rostral part of the arcuate nucleus. Neither bifurcation of these axons nor looping of the axons back to the chiasm was seen. Most fibers projected to the SCN contralateral to the filled nerve, but the projection represented less than 0.1% of the total number of fibers in one optic nerve. These observations are considered to be graphic evidence of a retino-hypothalamic projection. The interpretation of the cobalt method is discussed, as are the functions of the connections that have been observed.

Animals↗
PubMed1987

Calcium oxalate precipitation in urine following T.U.R. with glycine as irrigation fluid.

Precipitation of calcium oxalate was studied in a group of ten patients who underwent transurethral prostatectomy with glycine irrigation. Post operatively all patients showed hyperoxaluria; 60% with oxaluria higher than 10 times the critical concentration of calcium oxalate in urine. Other factors, known to favour crystallogenesis were modified during the same period: low urinary output, relative hypercalciuria and uraturia and hypomagnesuria. Thus, conditions for intraluminal precipitation of calcium oxalate were present post operatively. We suggest the use of a xanthine oxidase inhibitor to prevent hyperoxaluria.

Aged↗
PubMed1986

Necrotizing fasciitis precipitating diabetic ketoacidotic coma.

Necrotizing fasciitis is a rapidly spreading infection of the subcutaneous tissue and fascia; diabetes mellitus appears to be the most frequent underlying disease. Early diagnosis and immediate aggressive surgical therapy are paramount to curtail morbidity and mortality, but diagnosis is often difficult and unnecessarily delayed. We describe a case of necrotizing fasciitis precipitating diabetic ketoacidotic coma where correct diagnosis was not made until the 14th hospital day. We stress the fact that physicians caring for critically ill patients should be keenly aware of the possibility of necrotizing fasciitis when tending diabetic patients with unexplained fever; failure to recognize the disease can have devastating results. Finally, we believe this to be the first reported case of diabetic ketoacidotic coma precipitated by necrotizing fasciitis.

Adult↗
PubMed1976

Sites of action of morphine involved in the development of physical dependence in rats. I. Comparison of precipitated morphine withdrawal after intraperitoneal and intraventricular injection of morphine antagonists.

In rats made dependent on morphine by implantation of morphine pellets, withdrawal, as precipitated by intraventricular injection of morphine antagonists, was compared to withdrawal as precipitated by systemic antagonist application. The results, most clearly those obtained with a hydrophilic compound, diallyl-nor-morphinium-bromide, point to periventricularly located sites of action for the release of most withdrawal signs by antagonists. Jumping, reaching only low levels after i.ventr. injection of levallorphan and nalorphine, was very pronounced when the benzomorphane derivative SH 254, was used. In the case of writhing and diarrhea, the situation is more complicated. Possibly, central as well as peripheral mechanisms are involved in the expression of these signs.

Animals↗
PubMed1981

Evidence of a preferential role of brain serotonin in the mechanisms leading to naloxone-precipitated compulsive jumping in morphine-dependent rats.

Various drugs acting on brain serotonin or catecholamines were administered concurrently with morphine during the development of dependence or before naloxone-precipitated withdrawal syndrome. Of the various drugs only cyproheptadine, a serotonin antagonist, and piribedil, a dopamine agonist, reduced the frequency of jumping (but not of diarrhea or ptosis) when administered with morphine during development of dependence. When administered before naloxone, d-fenfluramine, a serotonin releaser, markedly reduced jumping, but not diarrhea and ptosis, and clonidine blocked these latter signs without affecting the frequency of jumping. Of the other drugs examined only phenoxybenzamine reduced diarrhea in morphine-abstinent rats. It is suggested that serotonin is involved in the mechanisms which lead to compulsive jumping during naloxone-precipitated withdrawal, whereas adrenergic sites on which clonidine acts are mainly involved in the expression of signs, such as ptosis and diarrhea. No clear evidence was obtained of a role for dopamine in the withdrawal signs studied.

Animals↗
PubMed1984

Koelle's copper thiocholine method performed with a low-pH phosphate buffer, followed by osmification of the precipitate: revival of two abandoned procedures.

Using a glutaraldehyde-fixed mouse neuromuscular junction, a fine precipitate of copper thiocholine was obtained with Koelle's medium prepared by a mixture of phosphate buffer (pH 5.6-5.9) and copper glycine solution (strongly acidic). The final pHs of these incubation media were very low, being situated between 3.8 and 4.2, respectively. It is well known that phosphate buffer, at such a low pH value, has no buffering effect on the acetic acid of enzymatic hydrolysis. This probably caused a sharp drop of the pH value in the vicinity of the enzymatic site and allowed a fine localization of copper thiocholine, the precipitation of which is pH dependent. Furthermore, the osmification of copper thiocholine in the same phosphate buffer provided a finely localized electron dense product. The chemical nature of the osmified copper thiocholine is discussed.

Animals↗
PubMed1978

The use of ultrasonication to remove non-specific precipitate.

The non-specific artifactual precipitate found in glycol methacrylate (GMA) embedded tissues, following acid phosphatase histochemical incubation, can now be eliminated with brief ultrasonication. A treatment of 1 to 2 min totally eliminated the artifactual residue, leaving the true histochemical reaction product and the physical integrity of the tissues intact. With this technique, most loosely bound precipitates, which clutter and mask GMA or conventionally embedded tissues, may now be treated and eliminated.

Acid Phosphatase↗
PubMed1975

Effects of depletion of brain catecholamines during the development of morphine dependence on precipitated withdrawal in rats.

The significance of long term depletion of brain catecholamines (CSs) for the development of morphine dependence and for the expression of morphine withdrawal was studied in rats which were implanted with morphine pellets for 10 days. CAs were depleted by inhibition of tyrosine-hydroxylase with alpha-methyl-tyrosine (AMT) or by destruction of catecholaminergic nerve terminals wit6-hydroxydopamine (6-OHDA). In the "acute" experiments these drugs were applied within 24 hrs before precipitation of withdrawal; in the "chronic" experiments drug administration was started before the first implantation and in the case of AMT, continued repeatedly thereafter. With either method, "acute" depletion of brain CAs resulted in reduced intensity of withdrawal. When CAs were kept low through the whole time of morphine exposure and also at the time of withdrawal, the intensity of withdrawal was normal in the case of 6-OHDA administration and only slightly decreased in the case of AMT. When AMT administration was discontinued 40 hrs before precipitation of withdrawal the withdrawal pattern occurred with unchanged intensity. Our experimental data are compatible with the assumption that long lasting depletion of brain CAs is compensated for by induction of neuronal supersensitivity for noradrenaline (NA) and dopamine (DA). While both CAs play an important role in the full expression of the withdrawal syndrome their possible involvement in mechanisms leading to dependence seems to be unlikely although final statements cannot be made by the presented experiments.

Animals↗