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PubMed1978

Factors affecting homogeneous precipitation of aluminum hydroxide gel.

The variables affecting homogeneous precipitation in the hydrolysis of aluminum nitrate by sodium carbonate were studied. Increased temperature, decreased concentration of reactants, and decreased rate of addition of titrant favor conditions that achieve homogeneous precipitation. During acid hydrolysis, the nitrate anion was the major anion associated with the gel and only small amounts of carbonate were observed. It is recommended that homogeneous conditions be achieved during the precipitation of aluminum hydroxide gel to improve reporducibility.

Aluminum↗

PubMed1984

Mechanism of freeze-thaw instability of aluminum hydroxycarbonate and magnesium hydroxide gels.

The effect of freeze-thaw cycles on the physical stability of aluminum hydroxycarbonate and magnesium hydroxide gels was studied. Coagulation following a freeze-thaw cycle, leading to the formation of visible aggregates, affected the content uniformity of both gels. The freeze-thaw cycles did not affect the crystal form or surface characteristics of the gels as determined by X-ray powder diffraction and point of zero charge, but caused a slight reduction in the rate of acid neutralization and a large increase in the rate of sedimentation. The greatest effect was observed after the first freeze-thaw cycle. While the duration of freezing was not a factor, the rate of freezing was important and was inversely related to the aggregate size. The aggregates which formed following a freeze-thaw cycle were not redispersed by shaking, but were reversed by ultrasonic treatment or homogenization. The adsorption of polymers or surface-active agents prior to freezing reduced and, in some cases, prevented the formation of aggregates. The physical instability produced by a freeze-thaw cycle was explained by the modified DLVO theory. The force exerted on the particles by the growing ice crystals forced the particles into the primary minimum, producing strong interparticle attraction. On thawing, simple agitation did not provide enough force to overcome the attractive force of the primary minimum. Adsorption of polymers or surface-active agents increased the steric repulsive force and prevented the particles from reaching the primary minimum.

Aluminum Hydroxide↗

PubMed1985

In vivo and in vitro evaluation of magnesium-aluminum hydroxide antacid tablets and liquid.

The effect of magnesium-aluminum hydroxide antacid tablets or liquid on food-stimulated gastric acidity was evaluated in vivo in eight duodenal ulcer patients. Experiments were performed also in vitro. Although in vitro neutralizing capabilities of the two preparations were the same (28.3 +/- 0.1 mmol/liter), the duration of effect of tablets was longer in vivo. For example, at 3 3/4 hr after an eaten meal, mean hydrogen ion concentration with three tablets was 29.8 +/- 9.9 mmol/liter while with 15 ml liquid it was 59.6 +/- 10.3 mmol/liter (P less than 0.05). Additional studies were performed in vitro to explain the longer duration of effect of tablets compared with liquid in vivo. These experiments suggested that tablets reacted more slowly with acid than did liquid and that saliva, which was mixed with tablets during chewing, also contributed to the prolonged duration of effect.

Aluminum Hydroxide↗

PubMed2002

Controlled release of a plant growth regulator, alpha-naphthaleneacetate from the lamella of Zn-Al-layered double hydroxide nanocomposite.

Formation of the so-called organic-inorganic nanohybrid material was exploited for the preparation of a controlled release formulation. The inorganic Zn-Al-layered double hydroxide (LDH) was used as a matrix, hosting an active agent or a guest, alpha-naphthaleneacetate (NAA), a plant growth regulator by self-assembly technique. The reverse process, i.e., the deintercalation or release of the guest, NAA was found to be rapid initially, followed by a more sustained release thereafter and this behavior was dependent on the pH of the release medium, the aqueous solution. The mechanism of release has been interpreted on the basis of the ion-exchange process between the NAA anion intercalated in the lamella host and nitrate or hydroxyl anions in the aqueous solution.

Aluminum Hydroxide↗

PubMed2006

Hydration phenomena of sodium and potassium hydroxides by water molecules.

The hydrated structures, dissociation energies, thermodynamic quantities, infrared spectra, and electronic properties of alkali-metal hydroxides (MOH, M = Na and K) hydrated by up to six water molecules [MOH(H(2)O)(n=1-6)], are investigated by using the density functional theory and Møller-Plesset second-order perturbation theory. Further accurate analysis based on the coupled cluster theory with singles, doubles, and perturbative triples excitations is more consistent with the MP2 results. NaOH shows a peculiar trend in dissociation: it begins to form a partially dissociated structure for n = 3, and it dissociates for n = 4 and 6, whereas it is undissociated for n = 5. However, for n = 5, the dissociated structure is nearly isoenergetic to the undissociated structure. For KOH, it begins to show partial dissociation for n = 5, and complete dissociation for n = 6.

Hydroxides↗

PubMed2003

In vitro diffusion of hydroxyl ions through root dentine from various calcium hydroxide medicaments.

The purpose of this study was to determine diffusion of hydroxyl ions through dentine from different calcium hydroxide [Ca(OH)2] medicaments. Forty-five single-rooted teeth were instrumented and cavities (3 mm in diameter and 1 mm in depth) were prepared on the facial surface of each root. After smear layer was removed with 17% EDTA all surfaces of roots, except cavities, were coated with nail polish. Teeth were randomly divided into four experimental groups (each 10 samples) and a control group (five samples). They were filled with: group 1, Ca(OH)2 and distilled water mixture; group 2, TempCanal; group 3, Calasept; and group 4, Ca(OH)2 plus point. Control group, in which nothing was applied to the canals. All samples were immersed in distilled water maintained at 37 degrees C. pH values were measured at 1 h, 2 h, 3 h, 24 h, 48 h, 72 h, 4 days, 5 days, 6 days, 7 days and 14 days. Ca(OH)2-distilled water mixture and TempCanal showed highest pH values at 24 h. Calasept, Ca(OH)2 plus point and control showed highest pH values at 3 h. Time intervals after 24 h, Ca(OH)2-distilled water mixture, TempCanal and Calasept showed higher pH values than Ca(OH)2 plus point, with a statistically significant difference (P<0.05). The pH value of Ca(OH)2 plus point was lower than the values of other materials after 3 h. This study indicates that non-setting Ca(OH)2 based materials have an effective release of hydroxyl ions compared with Ca(OH)2 plus point.

Calcium Chloride↗

PubMed1994

Comparison of two calcium hydroxide pastes used for endodontic treatment of non-vital immature incisor teeth.

A proprietary calcium hydroxide paste, Reogan Rapid, that previously has been demonstrated to induce apical closure in non-vital immature incisor teeth, was becoming unavailable. A prospective clinical trial was conducted to compare Reogan Rapid with another proprietary paste, Hypo-cal. For teeth treated with Reogan Rapid apical closure was obtained in an average of 6.8 months involving 3.1 visits and the respective figures for teeth treated with Hypo-cal were 5.1 months and 2.4 visits. These results demonstrated that Hypo-cal was as effective as Reogan Rapid when used in a standardised technique for inducing apical closure.

Barium Sulfate↗

PubMed2005

Dentinal pH changes following electrophoretically activated calcium hydroxide ions in the root canal space of bovine teeth.

The aim of the study was to evaluate pH changes of external root dentin surface at different depths following electrophoretic activation of calcium hydroxide (CH) in the root canals. For the study, 60 cavities were drilled on three external root surfaces of 20 bovine teeth specimens to obtain remaining dentin thickness (RDT) of 0.3, 0.7 and 1.0 mm. CH paste was inserted in the lumens. In the experimental group (10 specimens) CH paste was electrophoretically activated. Microelectrode was used to measure pH changes in the cavities immediately after placement of CH, following electrophoretical activation, and after 30 days storage. A significant (P < 0.05) increase in pH following electrophoresis was found in all specimens in the experimental group. Cavities with 0.4 mm RDT showed a maximal pH increase to the value of 11.3 +/- 0.4. In the control group no change in pH was observed after 3 min. A similar increase in pH was observed in both groups after 30 days. The pH changes were significantly depended on the RDT (P < 0.05) in all groups. Electrophoretically activated CH could significantly increase dentinal pH of external root surface within minutes up to 30 days.

Analysis of Variance↗

PubMed1989

Influence of ranitidine, pirenzepine, and aluminum magnesium hydroxide on the bioavailability of various antibiotics, including amoxicillin, cephalexin, doxycycline, and amoxicillin-clavulanic acid.

Two randomized double-blind crossover studies and one randomized crossover study were performed to document possible drug-drug interactions between antacids (aluminum magnesium hydroxide, 10 ml per dose for 10 doses), antimuscarinic drugs (pirenzepine, 50 mg per dose for 4 doses), and H2-blockers (ranitidine, 150 mg per dose for 3 doses) and amoxicillin (1,000 mg), cephalexin (1,000 mg), doxycycline (200 mg), and amoxicillin-clavulanic acid (625 mg). Ten healthy volunteers participated in each study. Concentrations in serum and urine were measured by bioassay, and pharmacokinetic parameters were calculated by the usual open one- or two-compartment models (statistics were determined by the Wilcoxon test). The antacid, pirenzepine, and ranitidine had no influence on the bioavailability of amoxicillin, cephalexin, and amoxicillin-clavulanic acid. Only small differences could be observed in the pharmacokinetic parameters, but they are not of therapeutic importance. However, the antacid caused a significant (P less than 0.01) reduction in the gastrointestinal absorption of doxycycline (area under the concentration-time curve, 38.6 +/- 22.7 mg.h/liter, fasting; 6.0 +/- 3.2 mg.h/liter, with antacid), resulting in subtherapeutic levels of doxycycline.

Adult↗

PubMed1990

Effects of magnesium-aluminum hydroxide and calcium carbonate antacids on bioavailability of ofloxacin.

The effects of 15- and 5-ml doses of magnesium-aluminum hydroxide (MAH) and calcium carbonate (CC) antacids, respectively, on the bioavailability of ofloxacin after single oral 400-mg doses of ofloxacin were investigated in a 32-subject, randomized, crossover, open-label study. On four separate occasions, subjects received ofloxacin alone or antacid 24 h before, 2 h before, or 2 h after ofloxacin administration (n = 16 for each antacid). CC administration had no significant effect on the rate and extent of ofloxacin absorption regardless of the timing of antacid administration. A small but significant negative effect of MAH administration 2 h before ofloxacin administration was noted as evidenced by area under the curve and peak concentration in plasma data. Simultaneous administration of ofloxacin with either antacid was not investigated in this study. It appears that MAH and CC antacids in the doses used in this study generally do not interfere in a clinically significant manner with the bioavailability of ofloxacin, provided that an interval of at least 2 h separates the administration of these products.

Adolescent↗

PubMed2002

Ammonium hydroxide hydrolysis: a valuable support in the MALDI-TOF mass spectrometry analysis of Lipid A fatty acid distribution.

Lipid A is the lipophilic moiety of lipopolysaccharides (LPSs), the major components of the external membrane of almost all gram-negative bacteria. It is responsible for the toxicity of LPS and has a heterogeneous structure composed of a bis-phosphorylated glucosamine disaccharide backbone that is acylated at the positions 2, 3 of the GlcN I (proximal) and GlcN II (distal) residue with O- and N-linked 3-hydroxy fatty acids (primary substitution). These fatty acids are further acylated by means of their 3-hydroxy groups (secondary substitution). The toxicity of Lipid A is dependent on its primary structure; the number, the length, and the distribution of the fatty acids on the disaccharide backbone strongly influence the endotoxic activity. In this paper a general and easy methodology to obtain secondary fatty acid distribution, which is one of the most difficult issues in the structural determination of Lipid A, is proposed. The method combines ammonium hydroxide hydrolysis and matrix assisted laser desorption ionization (MALDI)-mass spectrometry analysis and has been successfully proven with five different Lipid A species. The procedure exploits the lower stability under mild alkaline conditions of acyl and acyloxyacyl esters with respect to that of the acyl and acyloxyacyl amides. The partially degraded Lipid A species obtained are analyzed by MALDI-MS. The generality of this approach was tested on five Lipid As, namely those arising from Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Pseudomonas reactans, and Burkholderia caryophylli.

Ammonium Hydroxide↗

PubMedDate not supplied

[Immobilizalion of extracellular glucose oxidase from penicillium funiculosum 46.1 on gels of aluminum or zinc hydroxides].

Different methods of immobilization of extracellular glucose oxidase (GO) from Penicillium funiculosum 46.1 on gels of aluminum or zinc hydroxides have been compared. GO from the culture liquid filtrate (CLF) associated with Zn(OH)2 but not Al(OH)3 gels. Preparation of samples of immobilized GO does not require isolation of the enzyme (CLF may be used). GO immobilized on Zn(OH)2 gels from CLF was 1.6 times more efficient in catalyzing D-glucose oxidation than the enzyme contained in the original culture liquid. Crosslinking of gel-adsorbed CLF proteins affected the properties of GO adversely and to a considerable extent. Various means of polymerization and immobilization of GO isolated from CLF have been studied. Optimum results were obtained when GO polymeric products were pre-synthesized in solution, followed by adsorption to Al(OH)3 but not Zn(OH)2 gels. The catalytic efficiency of GO immobilized on a Zn(OH)2 gel was significantly lower than that of the enzyme associated with Al(OH)3.

Aluminum Hydroxide↗

PubMed2006

[Diffusion of hydroxyl ions from calcium hydroxide in the dentinal tubules].

The aim of this study was to compare hydroxyl ions diffusion from various calcium hydroxide forms: Hycal (1), Roeko points (2) and aqueous suspension placed in the pulpar chamber (3) or in the root canal (4). These experiments were conducted with bovine incisors in order to obtain quantitative evaluation. 540 lateral cavities, deep and superficial, were created in root dentin to measure the hydroxyl ions diffusion with a color indicator, the Blue epsilon With Hycal and aqueous suspension the diffusion of the OH- is obtained in the superficial cavities situated in the coronal part at 14 days (1 = 72%; 3 = 44%; 4 = 100%, (n=18)). In the apical part of the canal this phenomenon is never complete at 21 days (1 = 17%; 3 = 22%; 4 = 17%, (n=18)). No diffusion was observed with the Roeko points (the first generation).

Animals↗

PubMed1981

Double-blind clinical, endoscopic and histological comparison of hydrotalcite/dimethicone suspension and magnesium hydroxide/aluminum hydroxide suspension in the treatment of symptomatic gastritis.

A double-blind, randomized trial was undertaken to compare the clinical, endoscopic and histological response to 6-weeks' treatment with hydrotalcite/dimethicone suspension or magnesium hydroxide/aluminum hydroxide suspension in 36 patients with symptomatic gastritis. Significantly more patients (P less than 0.05) showed symptomatic improvement in the antacid-treated group than in the hydrotalcite/dimethicone-treated group and more had a reduction in histological inflammatory scores (P less than 0.01), although there was little correlation between histology and symptoms. There was no evidence from this study that the bile acid binding and anti-foaming properties of hydrotalcite/dimethicone suspension were of any benefit in the treatment of patients with symptomatic gastritis.

Adult↗

PubMed2001

Evaluation of carboxymethylcellulose, hydroxypropylmethylcellulose, and aluminum hydroxide as potential carriers for rhBMP-2.

Conventional iliac crest nonvascularized corticocancelous bone grafts and bone flaps have been used to treat bony defects. However, these treatments have some limitations, namely, the availability of donor tissue, donor site morbidity, difficulty to shape the bone flap to the defect, and complexity of the surgery. The bone morphogenetic protein (rhBMP-2) is osteoinductive. However, its implantation requires a matrix (carrier) in order to define the shape of the resulting bone and to retain the protein at the site for the time required for induction to occur. When the ideal carrier is found, an unlimited supply of material would be available for all applications where bone is needed. In this in vitro study, we evaluated the suitability of some potential carriers for rhBMP-2 by measuring the alkaline phosphatase (ALP) activity of fibroblast cultures. Either rhBMP-2 or sodium carboxymethylcellulose significantly increased the ALP activity, when used alone. When sodium carboxymethylcellulose was combined with rhBMP-2, there was an increase in the ALP activity, but lower than those obtained when the products were used alone. Hydroxypropylmethylcellulose alone did not affect ALP activity. However, the combination of rhBMP-2 with hydroxypropylmethylcellulose did not increase the ALP activity, despite the presence of rhBMP-2. Aluminium hydroxide proved to be an unsuitable rhBMP-2 adsorbent.

Alkaline Phosphatase↗

PubMed2003

Translational diffusion coefficient of cycloamylose in aqueous sodium hydroxide.

Seven cyclic (1 --> 4)-alpha-D-glucan (cycloamylose) samples ranging in weight-average molecular weight from 5 x 10(3) to 1.8 x 10(4) and gamma-cyclodextrin have been studied by sedimentation equilibrium in dimethylsulfoxide (at 25 degrees C) and by dynamic light scattering in 0.5 N aqueous sodium hydroxide (at 25 degrees C), a good solvent for linear amylose. The measured translational diffusion coefficients D in the aqueous NaOH agree fairly closely with previous Monte Carlo results for cyclic (1 --> 4)-alpha-D-glucan chains with excluded volume, when correction is made for the effects of bead diameter and fluctuating hydrodynamic interaction (HI) on the Kirkwood theory on which the computation of D was based. These D data are also explained almost quantitatively by Yamakawa and Fujii's expression for the associated KP ring (based on the Kratky-Porod wormlike chain) with the molecular parameters for linear amylose if the fluctuating HI and excluded-volume effects are taken into account. It is concluded that the translational diffusion behavior of cycloamylose in the aqueous NaOH is consistent with the conformational characteristics derived from the conformational energy of maltose and dilute-solution data for linear amylose.

Cyclodextrins↗

PubMed2005

Mononuclear, dinuclear, and pentanuclear [[N,S(thiolate)]iron(II)] complexes: nuclearity control, incorporation of hydroxide bridging ligands, and magnetic behavior.

The mixed N3S(thiolate) ligand 1-[bis[2-(pyridin-2-yl)ethyl]amino]-2-methylpropane-2-thiol (Py2SH) was used in the synthesis of four iron(II) complexes: [(Py2S)FeCl] (1), [(Py2S)FeBr] (2), [(Py2S)4Fe5II(mu-OH)2](BF4)4 (3), and [(Py2S)2Fe2II(mu-OH)]BF4 (4). The X-ray structures of 1 and 2 revealed monomeric iron(II)-alkylthiolate complexes with distorted trigonal-bipyramidal geometries. The paramagnetic 1H NMR spectra of 1 and 2 display resonances from delta = -25 ppm to +100 ppm, consistent with a high-spin iron(II) ion (S = 2). Spectral assignments were made on the basis of chemical shift information and T1 measurements and show the monomeric structures are intact in solution. To provide entry into hydroxide-containing complexes, a novel synthetic method was developed involving strict aprotic conditions and limiting amounts of H2O. Reaction of Py2SH with NaH and Fe(BF4)2.6 H2O under aprotic conditions led to the isolation of the pentanuclear, mu-OH complex 3, which has a novel dimer-of-dimers type structure connected by a central iron atom. Conductivity data on 3 show this structure is retained in CH2Cl2. Rational modification of the ligand-to-metal ratio allows control over the nuclearity of the product, yielding the dinuclear complex 4. The X-ray structure of 4 reveals an unprecedented face-sharing, biooctahedral complex with an [S2O] bridging arrangement. The magnetic properties of 3 and 4 in the range 1.9-300 K were successfully modeled. Dinuclear 4 is antiferromagnetically coupled [J = -18.8(2) cm(-1)]. Pentanuclear 3 exhibits ferrimagnetic behavior, with a high-spin ground state of S(T) = 6, and was best modeled with three different exchange parameters [J = -15.3(2), J' = -24.7(3), and J'' = -5.36(7) cm(-1)]. DFT calculations provided good support for the interpretation of the magnetic properties.

Ferric Compounds↗

PubMed2007

Enhancement of relaxivity rates of Gd-DTPA complexes by intercalation into layered double hydroxide nanoparticles.

In this paper we report the preparation and characterization of [Gd(dtpa)](2-) intercalated layered double hydroxide (LDH) nanomaterials. [Gd(dtpa)](2-) (gadolinium(III) diethylene triamine pentaacetate) was transferred into LDH by anionic exchange. The intercalation of [Gd(dtpa)](2-) into LDH was confirmed by X-ray diffraction for the new phase with the interlayer spacing of 3.5-4.0 nm and by FTIR for the characteristic vibration peaks of [Gd(dtpa)](2-). The morphology of the nanoparticles was influenced by the extent of [Gd(dtpa)](2-) loading, in which the poly-dispersity quality decreased as the [Gd(dtpa)](2-) loading was increased. Compared with the morphology of the original Mg(2)Al-Cl-LDH nanoparticles (hexagonal plate-like sheets of 50-200 nm), the modified LDH-Gd(dtpa) nanoparticles are bar-like with a width of 30-60 nm and a length of 50-150 nm. LDH-Gd(dtpa) was expected to have an increased water proton magnetic resonance relaxivity due to the intercalation of [Gd(dtpa)](2-) into the LDH interlayer that led to slower molecular anisotropic tumbling compared with free [Gd(dtpa)](2-) in solution. Indeed, LDH-nanoparticle suspension containing approximately 1.6 mM [Gd(dtpa)](2-) exhibits a longitudinal proton relaxivity r(1) of approximately 16 mM(-1) s(-1) and a transverse proton relaxivity r(2) of approximately 50 mM(-1) s(-1) at room temperature and a magnetic field of 190 MHz, which represents an enhancement four times (r(1)) and 12 times (r(2)) that of free [Gd(dtpa)](2-) in solution under the same reaction conditions. We have thus tailored LDH-nanoparticles into a novel contrast agent with strong relaxivity, promising for great potential applications in magnetic resonance imaging.

Aluminum Chloride↗