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PubMed1995

Dentinal diffusion of hydroxyl ions of various calcium hydroxide pastes.

The aim of this study was to analyze in vitro the dentinal diffusion of hydroxyl ions of calcium hydroxide pastes, prepared with different acid-base vehicles, in an inert nitrogen atmosphere. Sixty maxillary incisors with mature apexes were selected and after access and root canal preparation each root was filled with calcium hydroxide pastes prepared with different vehicles: saline solution, anesthetic and polyethylene glycol 400. The roots were then sectioned 2 mm from the apical vertex and the teeth mounted in the center of a round platform, filled with saline solution up to 2 mm from the root tip. The platforms remained inert in an atmosphere of nitrogen, completely sealed, in the absence of light and with a constant temperature of 36.5 degrees C. Diffusion analysis of the hydroxyl ions was carried out by a colorimetric method on days 7, 15, 30, 45 and 60. Calcium hydroxide pastes prepared with saline solution and anesthetic showed a pH change of 5-7 to 7-8 after 30 days, remaining at this level at 60 days. In the polyethylene glycol 400 group, the same alteration occurred at 45 days, and continued at 60 days.

Calcium Hydroxide↗
PubMed1996

Scanning electron microscopic evaluation of resin-dentin and calcium hydroxide-dentin interface with resin composite restorations.

Calcium hydroxide has been used as a liner in resin composite restorations to protect the pulp. Recent research has demonstrated that pulpal inflammation is caused by microleakage of restorations and by the subsequent passage of bacteria. The present study involved scanning electron microscopic observation of cross-sections of resin composite-dentin interfaces after the interposition of a layer of calcium hydroxide. A new-generation adhesive system that involves etching of the dentin was used. Ultrastructural analysis indicated that polymerization shrinkage of the resin composite caused the separation of the calcium hydroxide from the dentinal surface, forming 8- to 15-micron-wide interfacial gaps in 100% of the areas studied. Where the adhesive was applied directly to dentin, it adhered closely, forming a gap-free attachment with evidence of an acid-resistant hybrid layer (4 to 6 microns in thickness) and resin tags of various lengths that hermetically sealed the dentinal tubules.

Acid Etching, Dental↗
PubMedDate not supplied

Calcium hydroxide pulpotomy with a light-cured cavity-sealing material after two years.

In this follow-up study a light-cured glass ionomer lining cement was evaluated as a cavity-sealing material in calcium hydroxide pulpotomies in primary molars after one and two years. The pulpotomy dressing was a suspension of pure calcium hydroxide with either tap water or sterile saline. The success rate of the pulpotomies after one year was 87.7 percent and after two years 80.4 percent (clinically and radiographically). This result was only influenced by the type of restoration (amalgam versus stainless steel crown). The results of the present investigation compare favorably with those of other published studies of pulpotomy of primary molars using calcium hydroxide as the wound dressing.

Calcium Hydroxide↗
PubMed1998

Effect of aluminium hydroxide and meningococcal serogroup C capsular polysaccharide on the immunogenicity and reactogenicity of a group B Neisseria meningitidis outer membrane vesicle vaccine.

Three different formulations of an outer membrane vesicle (OMV) vaccine against group B meningococcal disease have been prepared and tested for immunogenicity and reactogenicity in adult volunteers. The vaccines were prepared with or without aluminium hydroxide and serogroup C-polysaccharide (C-ps). Doses from 12.5 to 100 micrograms protein were given twice at a six weeks' interval. All three formulations were well tolerated and highly immunogenic, inducing bactericidal and opsonizing antibodies in humans. Adsorption of OMVs to aluminium hydroxide reduced the pyrogenicity in rabbits. The differences in immunogenicity between the formulations were relatively small, but after the second dose a stronger booster response was observed when the vaccines were adsorbed. Thus, a formulation with OMVs and C-ps represents a safe and highly immunogenic vaccine, even without aluminium hydroxide.

Adjuvants, Immunologic↗
PubMed1998

[Magnesium hydroxide in idiopathic calcium nephrolithiasis].

BACKGROUND: While in vitro the protective effect of magnesium on calcium oxalate crystallization is well known, its clinical relevance in calcium nephrolithiasis is still debated. Therefore, the clinical and metabolic effects of magnesium hydroxide therapy were evaluated in calcium stone formers. METHODS: Nine patients (7 M, 2 F), selected for a low urinary magnesium excretion (uMg 56 +/- 12 mg/day), were given Mg hydroxide (500 mg/day), with clinical and metabolic controls at 3, 12 and 18 months. RESULTS: Urinary Mg/uCreat increased throughout the study; uOx/uCreat decreased significantly; uCa/uCreat increased but not significantly. The stone recurrence rate decreased from 0.75 to 0.11 stones/year/patient, throughout the study period. The decrease of uOx is considered a more important risk factor in calcium stone patients than a similar uCa change; it may be due to a reduced intestinal Ox absorption, for the formation of insoluble and not absorbed Mg oxalate. CONCLUSION: In conclusion, Mg hydroxide therapy was encouraging in patients with calcium nephrolithiasis and low uMg; nevertheless a longer period of treatment is needed to confirm these data.

Calcium↗
PubMed2001

The gas-phase reaction between hydroxide ion and methyl formate: a theoretical analysis of the energy surface and product distribution.

The potential energy surface for the prototype solvent-free ester hydrolysis reaction: OH- +HCOOCH3 --> products has been characterized by high level ab initio calculations of MP4/6-311 + G(2df,2p)//MP2/6-31 + G(d) quality. These calculations reveal that the approach of an OH- ion leads to the formation of two distinct ion-molecule complexes: 1) the MS1 species with the hydroxide ion hydrogen bonded to the methyl group of the ester, and 2) the MS4 moiety resulting from proton abstraction of the formyl hydrogen by the hydroxide ion and formation of a three-body complex of water, methoxide ion and carbon monoxide. The first complex reacts to generate formate anion and methanol products through the well known B(AC)2 and S(N)2 mechanisms. RRKM calculations predict that these pathways will occur with a relative contribution of 85% and 15% at 298.15 K, in excellent agreement with experimentally measured values of 87% and 13%, respectively. The second complex reacts by loss of carbon monoxide to yield the water-methoxide complex through a single minimum potential surface and is the preferred pathway in the gas-phase. This water-methoxide adduct can further dissociate if the reactants have excess energy. These results provide clear evidence that the preferred pathways for ester hydrolysis in solution are dictated by solvation of the hydroxide ion.

Journal Article↗
PubMed2004

Stabilization of p-block organoelement terminal hydroxides, thiols, and selenols requires newer synthetic strategies.

Metal hydroxides represent a very interesting and highly useful class of compounds that have been known to chemists for a very long time. While alkali and alkaline earth metal hydroxides (s-block) are commonplace chemicals in terms of their abundance and their use in a chemical laboratory as bases, the interest in Brønsted acidic molecular terminal hydroxides of p-block elements, such as aluminum and silicon, has been of recent origin, with respect to the variety of applications these compounds can offer both in materials science and catalysis. Moreover, these systems are environmentally friendly, relative to the metal halides, owing to their -OH functionality (resembling that of water). Design and conceptualization of the corresponding terminal thiols, selenols, and tellurols (M-SH, M-SeH, and M-TeH) offer even more challenging problems to synthetic inorganic chemists. This concept summarizes some of the recent strategies developed to stabilize these otherwise very unstable species. The successful preparation of a number of silicon trihydroxides a few years back resulted in the generation of several model compounds for metal-silicates. The recent synthesis of unusual aluminum compounds such as RAl(OH)(2), RAl(SH)(2), and RAl(SeH)(2) with terminal EH (E=O, Se, or Se) groups is likely to change the ways in which some of the well-known catalytic conversions are being carried out. The need for very flexible and innovative synthetic strategies to achieve these unusual compounds is emphasized in this concept.

Journal Article↗
PubMed1977

Thermal decomposition of 1,3-dimethyl derivative of phenobarbital in trimethylanilinium hydroxide.

Extensive degradation of the 1,3-dimethyl derivative of phenobarbital occurs when it is injected with trimethylanilinium hydroxide in methanol into a gas chromatograph. The application of mass spectrometry demonstrated that the major products are N-methyl-2-phenylbutyramide, N,N-dimethyl-2-phenylbutyramide, methyl 2-phenylbutyrate, N,N,N'-trimethylethylphenylmalondiamide, and N,N,N',N'-tetramethylethylphenylmalondiamide. The methyl group of the ester arises from the methanol solvent, whereas the methyl groups of the substituted amides arise from the parent compound or the methylating reagent. Tetramethylammonium hydroxide causes much more degradation than trimethylanilinium hydroxide under comparable conditions.

Aniline Compounds↗
PubMed2000

Covalent Grafting of Ethylene Glycol into the Zn-Al-CO(3) Layered Double Hydroxide.

Zn-Al-CO(3) layered double hydroxide was synthesized at room temperature using a procedure reported elsewhere. After characterization, 0.5 g of the Zn-Al-CO(3) layered compound was reacted under air with 15 cm(3) of ethylene glycol at 80 degrees C for a period of 5 days. After washing with acetone and drying at 50 degrees C, the resulting white powder was characterized by X-ray powder diffraction, thermal analysis (simultaneous TG/DSC), elemental analysis (C, H, N, Al, and Zn content), and FTIR spectroscopy. All of the experimental data were consistent with the bidentade grafting of ethylene glycol into the interlayer surface of the Al-Zn double hydroxide. The stoichiometry obtained [Zn(0.66)Al(0.34)(OCH(2)CH(2)O)](OH)(0.34).0.4H(2)O] showed that all of the surface hydroxide groups were replaced by ethylene glycol through Al-(Zn)-O-C bonds. Carbonate could not be detected by FTIR, proving that OH(-) was probably the actual intercalated counteranion. Copyright 2000 Academic Press.

Journal Article↗
PubMed2001

Uptake of Au(III) Ions by Aluminum Hydroxide and Their Spontaneous Reduction to Elemental Gold (Au(0)).

The behavior of AuCl(4)(-) ions during the formation of aluminum hydroxide at pH 6 was examined. With an increase in NaCl concentration, the content of gold taken up by aluminum hydroxide decreased, suggesting that chloro-hydroxy complexes of Au(III) ion were taken up due to the formation of Al-O-Au bonds. It was found unexpectedly that the Au(III) ions taken up were spontaneously reduced to elemental gold without addition of a specific reducing reagent and then colloidal gold particles were formed. The mechanisms for the uptake of Au(III) ions by aluminum hydroxide and for their spontaneous reduction are discussed. Copyright 2001 Academic Press.

Journal Article↗
PubMed2001

In Situ Monitoring of Generation and Precipitation of Ferric Hydroxide Sol with a Piezoelectric Quartz Crystal Impedance Analyzer.

The piezoelectric quartz crystal (PQC) impedance technique was applied to monitor in situ generation and precipitation of the ferric hydroxide sol in aqueous solutions at 90 degrees C. Equivalent circuit parameters and resonant frequencies as well as the half-peak width of the electroacoustic conductance spectrum deltaf(G1/2) for the PQC resonance were obtained and analyzed. Three stages, sol generation and simultaneous adsorption, adsorption equilibrium, and precipitation of ferric hydroxide sol could be identified in the process of adding the ferric nitrate solution into the hot water. A scheme of two consecutive reactions occurring at the electrode/solution interface was used to analyze the adsorption kinetics of ferric hydroxide sol onto the Au electrode. In addition, the electrolyte-induced precipitation of the colloid was monitored and discussed. Temperature effect on the PQC resonance behavior in liquid was also investigated. Since the PQC impedance technique provides multidimensional piezoelectric information in situ, it is highly recommended for studying the process of sol-gel generation and precipitation. Copyright 2001 Academic Press.

Journal Article↗
PubMed1990

Dysprosium (165Dy) hydroxide macroaggregates for radiation synovectomy--animal studies.

This paper reports the development of a new chemical formulation, Dy-HMA, to utilise the advantages of dysprosium 165 in radiation synovectomy of certain forms of arthritis. Dy-HMA is a sterile suspension of dysprosium hydroxide macroaggregates (approximately 6 mg Dy/ml) in saline with the majority of particles in the 3-5 microns range. The absence of ferric hydroxide and a higher concentration of dysprosium in the formulation offer advantages over dysprosium ferric hydroxide macroaggregates, Dy-165-FHMA. Biodistribution studies in rats and rabbits with Dy-HMA show less leakage than with Dy-FHMA and considerably less leakage than with yttrium silicate colloid. Rabbits treated with intra-articular injections of Dy-HMA equivalent to 10-30 times the typical clinical dose showed no signs of any toxic effects.

Animals↗
PubMed1987

Flameless atomic absorption spectrophotometric determination of platinum in tissues solubilized in hyamine hydroxide.

Processing biological samples by solubilization in Hyamine hydroxide (methylbenzethonium hydroxide) as an alternative to wet ashing with concentrated nitric acid for atomic absorption determination of platinum has been explored. The concentrations of platinum in tissues removed from rats 2 h after they had received the antitumor drug Carboplatin (60 mg/kg, iv) were comparable using either of the procedures, indicating the utility of tissue solubilization. Limits of detection were also comparable between the Hyamine hydroxide (0.25 microgram platinum/g) and nitric acid (0.15 microgram/g) procedures. The solubilization method, however, has advantages over wet digestion because of its simplicity and greater safety.

Animals↗
PubMed1990

Adsorption-desorption behaviour of zinc(II) at iron(III) hydroxide-aqueous solution interface as influenced by pH and temperature.

Batch studies were carried out to investigate the adsorption of zinc(II) from fresh waters on an iron(III) hydroxide surface maintained at the pH of zero point of charge of hydroxide (ZPC, 6.85) and also on both the acidic (5.5) and alkaline (8.2) sides of pH of ZPC, at 15 and 35 degrees C. Zinc(II) adsorption on iron(III) hydroxide increased with an increase in pH. The rise in temperature from 15 to 35 degrees C increased zinc(II) adsorption at pH 5.5 and 6.85, but decreased it at alkaline pH (8.2). In none of the cases did adsorption attain a maximum adsorption density. The results indicate the presence of heterogeneous sites of varying affinity on the adsorbent. Zinc(II) adsorption followed Langmuir behaviour only at small adsorption densities (less than 10(-2.95) M Zn/kg at pH 5.5) and at higher adsorption densities, the availability of strongest binding sites decreased. Nonspecifically adsorbed zinc(II) (reversible to Ba(II)) decreased with the increase in pH and temperature. Sequential desorption experiments also revealed that desorption of adsorbed zinc(II) decreased with an increase in pH.

Journal Article↗
PubMed2004

Adsorption of three azo reactive dyes by metal hydroxide sludge: effect of temperature, pH, and electrolytes.

Adsorption of azo reactive dyes by metal hydroxide sludge were investigated using CI Reactive Red 2 (RR-2), CI Reactive Red 120, (RR-120), and CI Reactive Red 141 (RR-141). The adsorption isotherms, including the Langmuir constants (Q degrees and b) and the Freundlich constant (K(f)), for RR-2 decreased with increasing temperature, but this was reversed for RR-120 and RR-141. This behavior implied an exothermic process for RR-2 but an endothermic process for RR-120 and RR-141. The enthalpy value of adsorption for RR-2, RR-120, and RR-141 was -5.56, 2.77, and 6.41 kJ/mol, respectively, indicating that the adsorption of the less charged dyes (RR-2) was mainly physical, but that of the more charged dyes (RR-120 and RR-141) was chemical. The optimum system pH of 8.6+/-0.3 was maintained even when the solution pH was varied from 3 to 10. Higher concentration or more valence of anions of electrolytes in dye solution caused decreasing dye adsorption efficiency of metal hydroxide sludge. A higher dosage of sludge is required for real textile wastewater (>1% w/v) than for the synthetic dye solution (0.2% w/v). The leachates of heavy metals from metal hydroxide sludge to the environment are very low, which are within the standard limit of industrial effluent and leachable substances.

Journal Article↗
PubMed2005

Adsorptive bubble separation of zinc and cadmium cations in presence of ferric and aluminum hydroxides.

The adsorptive bubble separation of zinc and cadmium cations from solution in the presence of ferric and aluminum hydroxides was carried out by means of Tween 80 (nonionic surfactant), and sodium laurate and stearate (anionic surfactants). The mechanism of metal removal is different depending on the nature of the surfactant used. The removal of zinc cations by adsorbing colloid flotation is higher than that of cadmium cations. It increases with increases in the amount of hydroxide precipitate and the concentration of Tween 80. The removal of zinc cations by ion flotation is lower than that of cadmium cations. It does not change with increases in the hydroxide amount. It increases, however, with increased sodium laurate or stearate concentration. Both separation methods turned out to be helpful for studying both the solution's structure and the interactions at the solution-solid interface.

Journal Article↗
PubMed2006

Surface properties of kaolin and illite suspensions in concentrated calcium hydroxide medium.

The adsorption behaviour of calcium hydroxide onto illite and kaolin clay minerals was investigated by monitoring with atomic emission spectroscopy and pH measurements the amounts of ions left in solution after exposing clay minerals to calcium hydroxide solutions of various concentrations. Both clay minerals can adsorb calcium and hydroxyl ions. Rather than just considering proton exchanges at the clay mineral surfaces, the adsorption is explained by an approach based on Lewis description of molecules. With this approach, a mechanism for calcium hydroxide adsorption not only at the edges of the clay particles but also onto the faces is proposed. In order to gain a better insight onto the active groups at the surface of the studied clay minerals, adsorption of pyridine and ammonia on illite and kaolin was followed by FTIR spectroscopy. These measurements gave the signature of edges, which are marginally involved in interactions with calcium ions.

Journal Article↗
PubMed2002

Combined effects of anions on arsenic removal by iron hydroxides.

Batch experiments were conducted to investigate the combined effects of phosphate, silicate, and bicarbonate on the removal of arsenic from Bangladesh groundwater (BGW) and simulated groundwater by iron hydroxides. The apparent adsorption constants indicated that the affinity of the anions for iron hydroxide sites decreased in the following order arsenate>phosphate>arsenite>silicate>bicarbonate. Phosphate, silicate, and bicarbonate decreased the removal of As(III) even at relatively low concentrations and low surface site coverage. Phosphate (0-0.08 mM), silicate (0-0.8 mM), and bicarbonate (0-14 mM) in separate solutions had none to moderate effects on As(V) removal in a solution containing 6.7 mg/l Fe and 0.3 ppm As(V). In the presence of bicarbonate and silicate the adverse effect of phosphate on As(V) adsorption was magnified. The residual As(V) concentration after iron hydroxide treatment increased from less than 13 microg/l in separate bicarbonate (2.2 mM) and phosphate (0.062 mM) solutions to 110 microg/l in the solution containing both anions. The results suggested the combined effects of phosphate, silicate, and bicarbonate caused the high mobility of arsenic in Bangladesh water.

Adsorption↗