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PubMed1999

The Structure of Amorphous Bulk and Silica-Supported Copper(II) Hydroxides.

The data obtained show that at pH 7 copper(II) ions are adsorbed on a SiO2 surface as polymeric species of hydroxide nature. The structure of these species is similar to that of the bulk amorphous copper hydroxide. The amorphous state of supported Cu(OH)2 is caused by a small (ca. 11 Å) size of the surface particles. In contrast, the overstoicheometric water molecules seem to act as "amorphizers" of the bulk copper hydroxide. The structures of the bulk and dispersed amorphous copper(II) hydroxide were determined. The amorphous Cu(OH)2 has a layered structure close to the structure of the crystalline hydroxide, but the layers in the amorphous hydroxide are shifted toward one another approximately for 14 of the "c" period of the lattice. Copyright 1999 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↗
PubMed1975

Reaction of tris(bipyridine)ruthenium(III) with hydroxide and its application in a solar energy storage system.

Irradiation of Ru(bipy)(3) (2+) (bipy = 2,2'-bipyridine) with light below 560 nm results in the formation of a charge-transfer excited state potentially capable of reducing water to dihydrogen with concomitant production of Ru(bipy)(3) (3+). The latter may be reduced by hydroxide [Formula: see text] to form dioxygen and regenerate the starting complex. The use of these reactions in a cell designed to bring about the photochemical decomposition of water is proposed.The stoichiometry, kinetics, and mechanism of the Ru(bipy)(3) (3+)-hydroxide reaction have been investigated by conventional and stopped-flow spectrophotometry. The dioxygen yield is a sharp function of pH, attaining its maximum value (about 80%) at pH 9. At low pH (3 and 4.8) the production of ruthenium(II) is first order with k(obsd) = (1.41 +/- 0.04) x 10(-4) sec(-1) (25 degrees , ionic strength mu = 1.00 M with sodium sulfate). In the intermediate pH range (7.9-10.0) complex kinetics are observed. In the hydroxide range 0.01-0.50 M, ruthenium(II) production is predominantly first order with k(obsd) = k(a)[OH(-)] + k(b)[OH(-)](2) sec(-1); k(a) = 148 M(-1) sec(-1) and k(b) = 138 M(-2) sec(-1) (25 degrees , mu = 1.00 M, sodium sulfate). For the k(a) term, the activation parameters are DeltaH(double dagger) = 15.3 +/- 1.0 kcal mol(-1) and DeltaS(double dagger) = 7 +/- 3 cal deg(-1) mol(-1) (1 cal = 4.184 J). An intermediate species (lambda(max) 800 nm) forms at the same rate as ruthenium(II) in this hydroxide range. It disappears with k(obsd) = 1.2 + 1.1 x 10(2) [OH(-)] sec(-1) at 25 degrees . Similarly absorbing (lambda(max) 750 to 800 nm) species are generated by the addition of hydroxyl radical to M(bipy)(3) (2+/3+) [M = Fe(II), Os(II), Ru(II), Cr(III), Ru(III)] in pulse radiolysis experiments. The kinetics above pH 7 are described in terms of rate-determining nucleophilic attack by hydroxide on the bound bipyridine ring. The hydroxide adduct so generated is tentatively identified with that observed in the pulse radiolysis experiments with Ru(bipy)(3) (2+).For reduction of Ru(bipy)(3) (3+) by hydrogen peroxide ruthenium(II) production is first order with k(obsd) = k(c)[HO(2) (-)] + k(d)[H(2)O(2)] where k(c) = 5.4 x 10(7) M(-1) sec(-1) and k(d) = 8.3 M(-1) sec(-1) (25 degrees , mu = 1.00 M, pH 3.5 to 9.7). This reaction produces dioxygen in 83 +/- 15% yield at pH 6.8 and in 1.0 N sulfuric acid.

Journal Article↗
PubMed1977

Aluminium hydroxide in bile-salt diarrhoea.

The treatment of choleraic diarrhoea remains a problem. Cholestyramine is effective but long-term treatment is often impracticable. In-vitro studies have shown that aluminium hydroxide has bile-acid-binding properties comparable with those of cholestyramine. The bile-acid-binding properties of aluminium hydroxide have now been investigated in vivo and applied to the treatment of patients with choleraic diarrhoea. Aluminium hydroxide increased the faecal bile-salt concentration of patients with a normal bowel habit whereas magnesium hydroxide had no effect. Eight patients with severe choleraic diarrhoea were treated with aluminium-hydroxide suspension: bowel motion became less frequent and daily faecal weight fell.

Adult↗
PubMed2005

Can a hydroxide ligand trigger a change in the coordination number of magnesium ions in biological systems?

Density functional (B3LYP) calculations indicate that a hydroxide ligand is capable of triggering a reduction in the coordination number of Mg(2+) ions from 6 to 5. Since this could be quite relevant in the mode of action of magnesium-containing enzymes (especially hydrolases in which a metal-bound hydroxide species is believed to play a crucial role), we have performed a systematic deprotonation study of biologically relevant magnesium complexes. We explicitly calculated the preferred coordination number of [MgL(1)(x)L(2)(y)L(3)(z)](2)(-)(n) species at the B3LYP/aug-cc-pVTZ level of theory. L(1), L(2), and L(3) represent combinations of water, hydroxide, carboxylate (models Glu and Asp), ammonia ligands (models Lys and His residues), and fluoride ions. As expected, Mg(2+) exclusively prefers an octahedral coordination geometry with H(2)O, HCO(2)(-), or NH(3). Surprisingly, one hydroxide ligand triggers a change to a trigonal bipyramidal geometry. The isoelectronic fluoride ion behaves similarly. When two OH(-) are present, a tetrahedral coordination geometry is preferred. We postulate that a hydroxide (in addition to its role as an active nucleophile) could be employed by magnesium-containing enzymes to trigger a differential coordination behavior.

Ammonia↗
PubMed2000

The influence of sample dimensions on hydroxyl ion release from calcium hydroxide products.

The purpose of this study was to compare the rate of hydroxyl ion release from commercially available setting and non-setting calcium hydroxide products. The rate of hydroxyl ion release is important, as this has been suggested to be the main factor in the therapeutic activity of these products. In total, hydroxyl ion release was measured from 1104 samples of Dycal, Life, Calasept and Hypocal in solution using in vitro titration. The rate of hydroxyl ion release was measured for up to 14 days, using two sizes of sample surface area. The dimensions of the exposed sample surface area was found to be an important physical constraint to the hydroxyl ion release from non-setting calcium hydroxide products, whereas this was not found to be the case with setting products. The range in hydroxide activity between products was found to be 298%. In rank order of hydroxide ion release, from the most to the least active was: Hypocal, Calasept, Life and Dycal. The differences in the rate of hydroxyl ion release from these products may have some implications for their clinical applications. It is suggested that in cases where the oral healing responses have been poorer than expected, the size and seal of prepared cavities could have negatively influenced the therapeutic release of hydroxyl ions from non-setting calcium hydroxide products.

Analysis of Variance↗
PubMed1999

The elimination of sodium and potassium hydroxides from desiccated soda lime diminishes degradation of desflurane to carbon monoxide and sevoflurane to compound A but does not compromise carbon dioxide absorption.

UNLABELLED: Normal (hydrated) soda lime absorbent (approximately 95% calcium hydroxide [Ca(OH)2], the remaining 5% consisting of a mixture of sodium hydroxide [NaOH] and potassium hydroxide [KOH]) degrades sevoflurane to the nephrotoxin Compound A, and desiccated soda lime degrades desflurane, enflurane, and isoflurane to carbon monoxide (CO). We examined whether the bases in soda lime differed in their capacities to contribute to the production of these toxic substances by degradation of the inhaled anesthetics. Our results indicate that NaOH and KOH are the primary determinants of degradation of desflurane to CO and modestly augment production of Compound A from sevoflurane. Elimination of these bases decreases CO production 10-fold and decreases average inspired Compound A by up to 41%. These salutary effects can be achieved with only slight decreases in the capacity of the remaining Ca(OH)2 to absorb carbon dioxide. IMPLICATIONS: The soda lime bases used to absorb carbon dioxide from anesthetic circuits can degrade inhaled anesthetics to compounds such as carbon monoxide and the nephrotoxin, Compound A. Elimination of the bases sodium hydroxide and potassium hydroxide decreases production of these noxious compounds without materially decreasing the capacity of the remaining base, Ca(OH)2, to absorb carbon dioxide.

Absorption↗
PubMed1976

Structure of aluminum hydroxide gel I: initial precipitate.

The initial aluminum hydroxide gel precipitate resulting from the reaction of aluminum chloride or aluminum sulfate with ammonium hydroxide is shown by potentiometric titration, chemical analysis, and the ratio of bound hydroxide to aluminum to fit a polymer model described previously. The formation of polynuclear hydroxyaluminum particles is treated as a stepwise process involving a deprotonation-dehydration mechanism, which results in the formation of six-membered rings; these rings may further coalesce by the same mechanism. The aluminum hydroxide gel precipitated from aluminum chloride can be represented by the formula Al(OH)2.55(Cl)0.45 and probably exists as a polymer of 10 fused six-membered rings. The aluminum hydroxide gel precipitated from aluminum sulfate can be represented by the formula Al(OH)2.30(SO4)0.35. This species probably exists as a polymer of three fused six-membered rings.

Aluminum↗
PubMed1979

Effect of interaction of aluminum hydroxycarbonate gel and magnesium hydroxide gel on acid neutralization.

Acid neutralization by mixtures of aluminum hydroxycarbonate gel and magnesium hydroxide gel differs from the sum of the acid neutralization of each gel. Acid neutralization by magnesium hydroxide gel in the mixture is not observed until after a substantial portion of the aluminum hydroxycarbonate gel has reacted with acid, even though magnesium hydroxide gel is the faster reacting of the two gels. It is hypothesized that amorphous aluminum hydroxycarbonate forms a coating on the crystalline magnesium hydroxide particles due to electrostatic attraction. This coating prevents protons from reaching the highly reactive magnesium hydroxide until the coating is dissolved by the acid neutralization of aluminum hydroxycarbonate.

Acids↗
PubMed1984

Microstructure of aluminum hydroxides and the formation of aluminum dye lakes.

The effect of processing variables on the type of aluminum hydroxide and the dye content of the resultant lakes were investigated. The solid-state structure of aluminum lakes in conjunction with the associated aluminum hydroxide was studied by electron microscopy, X-ray diffraction, and IR spectroscopy. The conditions under which the aluminum hydroxide was prepared were shown to govern the amorphous/crystalline character of the product, which was reflected in changes in particle size and surface area. A hypothesis for the interaction of the dye and aluminum hydroxide is formulated in which the amount of dye adsorbed on the aluminum hydroxide is dependent on the surface area of the microstructures present.

Alum Compounds↗
PubMed1993

Preventive effect of magnesium hydroxide on carcinogen-induced large bowel carcinogenesis in rats.

Preventive effect of magnesium hydroxide on carcinogen-induced, large bowel carcinogenesis was examined in three experiments using F344 rats. Experiment I: Rats received dietary administration of magnesium hydroxide at concentrations of 500 or 1,000 ppm after treatment with methylazoxymethanol (MAM) acetate (25 mg/kg, 3 times). These rats had a lower incidence of large bowel neoplasms than animals given MAM acetate alone. Reduction of the tumor incidence was especially significant at a dose of 500 ppm. Experiment II: Rats given magnesium hydroxide (250, 500, or 1,000 ppm) together with 1,2-dimethylhydrazine (DMH) (20 mg/kg, 10 times) showed a lower multiplicity of large bowel tumors than those given DMH alone. Experiment III: The labeling indices of the cryptal cells of the large bowel (cecum or proximal colon or distal colon) or rates given magnesium hydroxide for 4, 6, or 8 weeks after treatment with MAM acetate (25 mg/kg, 3 times) were smaller than those of animals given MAM acetate alone, indicating that magnesium hydroxide suppressed, carcinogen-induced epithelial cell (large bowel) proliferation. The results of the three experiments suggest that magnesium, one of the essential metals, is a promising chemopreventive agent in humans.

Adenocarcinoma↗
PubMed1999

A comparative infrared spectroscopic study of hydroxide and carbonate absorption bands in spectra of shark enameloid, shark dentin, and a geological apatite.

The purpose of the present work was to investigate the infrared (IR) spectrum of shark enameloid, especially with regard to hydroxide and carbonate bands. With thin sections placed directly in the IR beam it was possible to get high concentrations of ions without interfering effects from a dispersion medium (e.g., alkali halides). For comparison, spectra of shark dentin and a geo-apatite were also recorded. In spectra of shark enameloid and geo-apatite medium strong hydroxide absorption bands were found around 3535 cm(-1), and in shark dentin and geo-apatite spectra weak shoulders were observed at about 3570 cm(-1). Hydroxide libration bands at about 740 cm(-1) were found in shark enameloid and geo-apatite spectra; in the latter, also a band at 680 cm(-1). Carbonate bands were found in shark enameloid spectra at 1480 (weak shoulder), 1453, 1423, and 868 cm(-1). In shark dentin spectra there were carbonate bands at 1452, 1417, and 875 cm(-1), and probably also a carbonate band at about 1530 cm(-1) overlapped by an amide II band. Weak carbonate bands were also found in the spectra of the geo-apatite at 1452 cm(-1), and at about 1425 and 880 cm(-1). The relative intensities of the bands at 1453 cm(-1) (contributed from A and B sites) and around 1420 cm(-1) (B sites) changed from shark enameloid to shark dentin, and also from shark enameloid to the geo-apatite. More A sites seem to be occupied by carbonate in shark dentin than in shark enameloid, supposedly owing to fluoride occupation of A sites in shark enameloid. In geo-apatite and shark enameloid there are hydroxide ions hydrogen bonded to fluoride. Both shark enameloid and the geo-apatite are fluoride rich, and geo-apatite seems to have the highest fluoride concentration. There are, however, indications that the hydroxide concentration is also higher in the geo-apatite than in shark enameloid. This can be explained by the much higher carbonate content, and partly also by the higher water content in shark enameloid. There are A sites in geo-apatite and probably also in shark enameloid which are occupied by carbonate, but the proportion of occupied A sites relative to occupied B sites is greater in geo-apatite than in shark enameloid. This difference can be explained by the preference of A sites when the carbonate concentration is very low. On the other hand, for greater amounts of carbonate such as we have in shark enameloid, B sites are preferred.

Animals↗
PubMed1991

The hypocholesterolemic effect of an antacid containing aluminum hydroxide.

STUDY OBJECTIVE: To evaluate the efficacy, safety, and hypocholesterolemic effect of an aluminum hydroxide-containing antacid in hypercholesterolemic individuals. DESIGN: A prospective, randomized, double-masked, placebo-controlled phase of 2 months' duration, followed by an open-design treatment phase of 2 months' duration and a washout phase of 2 months' duration. SETTING: Family practice clinics of two rural communities (kibbutzim) in Israel. PATIENTS: Fifty-six men and women with hypercholesterolemia (type IIa or IIb). Fifty individuals completed the study. INTERVENTION: After 2 months of dietary modification (low-fat, low-cholesterol diet), the participants were randomized into two matched groups. Group 1 (28 participants) was treated for 2 months with a chewable antacid tablet containing simethicone, magnesium hydroxide, and 113 mg of aluminum hydroxide per tablet, at a dose of two tablets four times daily. Group 2 (22 participants) was given a similar number of placebo tablets for 2 months. During the following 2 months, both groups received the antacid at the above dose. MEASUREMENTS AND MAIN RESULTS: Lipoprotein levels were evaluated at baseline and every 2 months thereafter for 6 months. Compared with pretreatment levels, Group 1 experienced a decrease in low-density lipoprotein cholesterol (LDL-C) of 9.8% after 2 months (p less than 0.001) and 18.5% after 4 months (p less than 0.001). Compared with Group 2, the decrease in LDL-C in Group 1 was 6.2% at the end of the 2-month double-masked, placebo phase. Although the high-density lipoprotein cholesterol (HDL-C) was also reduced in Group 1 at the end of 4 months of therapy (10.2%), the HDL-C/LDL-C ratio increased by 13% during the same interval (p less than 0.05). The treatment was well tolerated, with minimal side effects. CONCLUSIONS: An aluminum hydroxide-containing antacid reduces LDL-C in hypercholesterolemic individuals. Although HDL-C was also reduced to a lesser extent, the overall atherogenic index was improved. Further studies should be conducted to evaluate the long-term safety and efficacy of antacids containing aluminum hydroxide in hypercholesterolemic patients.

Adult↗
PubMed1982

Comparison of calcium hydroxide and zinc oxide and eugenol pulpectomies in primary teeth of dogs.

The purpose of this investigation was to compare calcium hydroxide with zinc oxide and eugenol (ZOE) as root canal obturants in the pulpectomy procedure for irreversibly inflamed primary pulps of dogs. Clinical, radiographic, and histologic comparisons of calcium hydroxide and ZOE root canal filling materials were made in forty-two primary premolars of seven mongrel puppies. When the animals were 6 weeks of age, the pulps of all samples teeth were extirpated and the canals left open to the oral environment. The root canals were assigned to calcium hydroxide, ZOE, and control groups, instrumented, and filled 2 weeks later. The animals were killed 1 day, 1 week, 4 weeks, and 12 weeks after filling. Statistical analysis of all categories for comparison at 4 weeks indicated that calcium hydroxide gave significantly more favorable results than ZOE. Canals treated with calcium hydroxide exhibited less inflammation, less resorption, and more hard-tissue apposition than ZOE-treated and control groups.

Animals↗
PubMed1991

Evaluation of various forms of calcium hydroxide in the monitoring of microleakage.

Calcium hydroxide has been shown to be an effective medium for the in vivo microleakage testing of amalgams. The purpose of this study was to determine the relative effectiveness of several forms of calcium hydroxide in the measurement of this clinical problem. It was also the purpose of this study to determine whether a relationship exists between the pH of the Ca(OH)2 liner and its ability to detect microleakage. Standardized Class V preparations were generated on the buccal surfaces of extracted molars. The axial walls of the preparations were based either with Dycal, Dycal VLC, Pulpdent Liquid, or pure Ca(OH)2. A series of teeth without a calcium hydroxide base served as the negative control. All teeth were restored with a spherical amalgam and kept in de-ionized water. The surfaces of the restorations were then subjected to 20 mL of 2 degrees C water for a period of one min. After three min, a color-indicating pH paper was positioned over the restored area for detection of the presence of hydroxyl ions at the amalgam/tooth interface. Regardless of the form of calcium hydroxide, all indicated extensive microleakage immediately after insertion of the restoration. In all cases, the number of samples generating positive results for leakage decreased over a period of time. The rate of decrease, however, was substantially dependent upon the form of calcium hydroxide used as well as its pH. The reagent grade of Ca(OH)2 generated the greatest percentage of positive results for the longest duration.

Calcium Hydroxide↗
PubMed1993

Inhibitory effects of magnesium hydroxide on c-myc expression and cell proliferation induced by methylazoxymethanol acetate in rat colon.

The effects of magnesium hydroxide were examined on methylazoxymethanol (MAM) acetate-induced c-myc expression and cell proliferation of colonic mucosal epithelium in rats. Rats were divided into four groups and treated as follows: MAM acetate alone (25 mg/kg i.p. injection, five times, once a week for 5 weeks), MAM acetate and feeding of 0.2% magnesium hydroxide in diet, magnesium hydroxide alone and non-treatment. At 4, 8 and 16 weeks after the start of experiment, 10 rats in each group were sacrificed. Magnesium hydroxide inhibited the MAM-induced expression of c-myc proto-oncogene, and also suppressed the increased bromodeoxyuridine (BrdU) and proliferating cell nuclear antigen (PCNA) labelling indexes induced by MAM acetate in colon mucosa in initiation and post-initiation phase. These results suggest that the anti-carcinogenic effect of magnesium hydroxide on rat colon carcinogenesis induced by MAM acetate may be related to the inhibition of the carcinogen-induced expression of c-myc proto-oncogene and cell proliferation.

Animals↗
PubMed2005

Determination of trace concentrations of bromate in municipal and bottled drinking waters using a hydroxide-selective column with ion chromatography.

The International Agency for Research on Cancer determined that bromate is a potential human carcinogen, even at low micro/l levels in drinking water. Bromate is commonly produced from the ozonation of source water containing naturally occurring bromide. Traditionally, trace concentrations of bromate and other oxyhalides in environmental waters have been determined by anion exchange chromatography with an IonPac AS9-HC column using a carbonate eluent and suppressed conductivity detection, as described in EPA Method 300.1 B. However, a hydroxide eluent has lower suppressed background conductivity and lower noise compared to a carbonate eluent and this can reduce the detection limit and practical quantitation limit for bromate. In this paper, we examine the effect of using an electrolytically generated hydroxide eluent combined with a novel hydroxide-selective anion exchange column for the determination of disinfection byproduct anions and bromide in municipal and bottled drinking water samples. EPA Methods 300.1 B and 317.0 were used as test criteria to evaluate the new anion exchange column. The combination of a hydroxide eluent with a high capacity hydroxide-selective column allowed sub-microg/l detection limits for chlorite, bromate, chlorate, and bromide with a practical quantitation limit of 1 microg/l bromate using suppressed conductivity detection and 0.5 microg/l using postcolumn addition of o-dianisidine followed by visible detection. The linearity, method detection limits, robustness, and accuracy of the methods for spiked municipal and bottled water samples will be discussed.

Bromates↗
PubMed2006

Removal efficiency of calcium hydroxide intracanal medicament with two calcium chelators: volumetric analysis using spiral CT, an in vitro study.

The vehicles used to carry calcium hydroxide intracanal medicament are many and may affect the retrieval. Access cavities were prepared in 40 single rooted anterior teeth, cleaning and shaping was done and filled with either Metapex or pure calcium hydroxide powder in distilled water. After 7 days the calcium hydroxide was retrieved using either 17% EDTA or 10% citric acid in combination with ultrasonic agitation. Volume analysis was done using spiral computed tomography. The percentage difference was calculated and statistically analyzed using Kruskal-Wallis and Mann-Whitney U test. 10% citric acid showed better removal efficiency than 17% EDTA for Metapex (p = 0.003). The 17% EDTA showed excellent removal efficiency of powder form of calcium hydroxide in distilled water than Metapex (p < 0.001). Ten percent citric acid removed powder form of calcium hydroxide in distilled water better than Metapex (p = 0.05).

Calcium Hydroxide↗