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At least 775 records · Page 43Linked to original sources
PubMed2006

Reduction in dentin permeability using a slurry containing dicalcium phosphate and calcium hydroxide.

Treatments that obdurate dentin tubules have been used for reducing dentin hypersensitivity. The purpose of this study was to determine the effect of a treatment with a slurry of micron sized calcium phosphate on the hydraulic conductance (L(p)) of etched dentin discs in vitro. The treatment slurry was prepared by mixing a powder mixture of dicalcium phosphate anhydrous and calcium hydroxide with a solution that contained sodium fluoride and carboxymethyl cellulose. The mean baseline L(p) (in mL cm(-2) s(-1) H(2)O cm(-1)) was 2.07 +/- 1.45 (mean +/- SD; n = 13)). After one treatment and 2, 4, and 7 days of incubation in a protein-free saliva-like solution (SLS), the mean relative L(p), presented as % of baseline, were 65 +/- 16, 42 +/- 27, 36 +/- 26, and 33 +/- 27 (n = 13), respectively. The L(p) values of the baseline and treatment after incubation in the SLS were significantly (p < 0.05) different. Scanning electron microscopic examination showed partial obturation of dentin tubules in the treated dentin. X-ray diffraction and chemical analyses indicated the major product formed from the slurry was a fluoride-containing hydroxyapatite. Treatment appeared effective in further reducing L(p) of dentin discs after incubation in the SLS.

Calcium Hydroxide↗
PubMed2007

Effects of airborne-particle abrasion, sodium hydroxide anodization, and electrical discharge machining on porcelain adherence to cast commercially pure titanium.

The aim of this study was to determine the effect of airborne-particle abrasion (APA), sodium hydroxide anodization (SHA), and electrical discharge machining (EDM) on cast titanium surfaces and titanium-porcelain adhesion. Ninety titanium specimens were cast with pure titanium and the alpha-case layer was removed. Specimens were randomly divided into three groups. Ten specimens from each group were subjected to APA. SHA was applied to the second subgroups, and the remaining specimens were subjected to the EDM. For the control group, 10 specimens were cast using NiCr alloy and subjected to only APA. Surfaces were examined by using scanning electron microscope and a surface profilometer. Three titanium porcelains were fused on the titanium surfaces, whereas NiCr specimens were covered with conventional porcelain. Titanium-porcelain adhesion was characterized by a 3-point bending test. Statistical analysis showed that the porcelain-metal bond strength of the control group was higher than that of the titanium-porcelain system (p < 0.05). There were no significant differences between the bond strengths of titanium groups (p 0.05), except the bond strengths of Noritake Super Porcelain TI-22 groups on which APA and SHA were applied (p < 0.05). SHA and EDM as surface treatment did not improve titanium-porcelain adhesion when compared to APA.

Chromium Alloys↗
PubMed2003

Preparation of 1-hydroxyethylidene-1,1-diphosphonic acid-intercalated layered double hydroxide and its physicochemical properties.

The intercalation of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), which is a drug for osteoporosis, in layered double hydroxide (LDH) was examined with the goal of developing a novel drug delivery system (DDS) of HEDP. To prevent side reactions, the intercalation reaction was carried out at 0 degrees C, and at pH 4-6. The uptake of HEDP was determined as 3.5 mmol x g(-1) of LDH, and the interlayer distance increased from 7.8 to 13 A. The HEDP-release profiles into K(2)CO(3) aqueous solution and into various buffer solutions were also examined.

Chemical Phenomena↗
PubMed2005

Immobilization of ibuprofen and copper-ibuprofen drugs on layered double hydroxides.

The immobilization of the NSAID ibuprofen (Hibp) and the Cu(II)-ibp compound on magnesium-aluminum layered double hydroxides (Mg3Al-LDH) is described. Ibuprofen was intercalated on LDHs by three routes (ion exchange, co-precipitation, and reconstruction). The organic drug and the Cu(II)-ibp were also immobilized by adsorption on LDH external surfaces. Materials were characterized by elemental analysis, UV/VIS, FTIR, and Raman spectroscopies, powder X-ray diffractometry (XRD), thermogravimetry, and electronic paramagnetic resonance (EPR). Mg3Al-(ibp)(cop) (30% w/w of drug/material) and Mg3Al-(ibp)(ie) (33%) materials exhibit bilayer arrangements of ibp anions intercalated between the host layers. Mg3Al-(ibp)(rec) and Mg3Al-(ibp)(ads) contain 13% and 6.2% of ibuprofenate, respectively. Mg3Al-(Cu-ibp)(ads) exhibits two Cu centers in different environments interacting with host layers. Pharmacological potential of materials are compared considering the amounts of immobilized drugs and their buffering properties. Mg3Al-(ibp)(ie) and Mg3Al-(ibp)(cop) exhibit poor buffering property, but contain high ibp amounts. Mg3Al-(ibp)(ads) despite having buffering property, contains low amount of ibuprofen. Mg3Al-(ibp)(rec) combines significant amount of immobilized ibp with good buffering property. Mg3Al-(Cu-ibp)(ads), due to the buffering property, may be an interesting new formulation aiming to decrease gastric irritation.

Adsorption↗
PubMed1975

Effect of dilution on reactivity and structure of aluminum hydroxide gel.

Aluminum hydroxide gel loses reactivity upon aging. However, a sharp decrease in reactivity occurs when the gel is diluted with double-distilled water. The loss of reactivity is directly related to the degree of dilution, but dilution with dioxane or the mother liquor has no effect on reactivity. It is hypothesized that dilution with water causes a change in the equilibrium between stabilizing ions incorporated in the gel structure and ions in solution. As the stabilizing ions leave the gel structure to reestablish the equilibrium, a loss of reactivity is observed until a new equilibrium is established.

Aluminum Hydroxide↗
PubMed1976

IR studies of development of order in aluminum hydroxide gels.

The usefulness of deuteration in detecting the development of order in aluminum hydroxide gel by IR spectra is demonstrated. By treatment of gel samples with deuterium oxide vapor at room temperature, the relative ease with which deuteroxyl-hydroxyl exchange takes place is determined as a function of the age of the gel. The use of scale expansion in conjunction with deuteration allows detection of IR absorbance characteristic of gibbsitic material long before such detection is possible by conventional IR analysis or X-ray diffraction.

Aluminum Hydroxide↗
PubMed1976

Kinetics of acid neutralization by aluminum hydroxide gel.

The rate of acid neutralization by an aluminum hydroxide gel prepared by the reaction of aluminum chloride solution and strong ammonia solution was studied. The decrease in acid-consuming capacity during aging as measured by the USP test is due to a decrease in the rate of reaction rather than to a decrease in equilibrium reactivity. The reactivity profile has three phases, which are shown to be related to the structure of the gel. The rate of loss of reactivity is directly related to the extent of washing.

Aluminum Hydroxide↗
PubMed1983

Complexation of procainamide with hydroxide-containing compounds.

The complexation of procainamide with hydroxide-containing compounds, ethanol, fructose, glucose, glycerin, lactose, maltose, propylene glycol, sorbitol, and sucrose, have been studied. Procainamide formed a complex with glucose, lactose, and maltose, all of which contain a hemiacetal group, whereas fructose and sucrose do not. The percent of complex formed was dependent on the pH of the solution, with an optimum range of approximately 4-5.2. As with glucose, the percent of complex formed was directly related to the concentration of lactose in the solution. In dry mixtures, procainamide did not form a complex with glucose or lactose. The complex formed with lactose or maltose could be completely reversed by adding hydrochloric acid. A similar observation with glucose was reported earlier. In the optimum pH range, equilibrium was established in approximately 24 hr, and the process of complexation followed the equation for reversible reactions.

Chemical Phenomena↗
PubMed1983

Stabilization of aluminum hydroxide gel by specifically adsorbed carbonate.

Ion-free aluminum hydroxide gel, prepared by the hydrolysis of aluminum tri-sec-butoxide, was observed by IR, X-ray analysis, and pH-stat titration to undergo rapid structural changes leading to the formation of pseudoboehmite and bayerite. The rate of development of order was directly related to the water-aluminum molar ratio. The Al--O bands at 625 and 470 cm-1 were the most sensitive indicators of the development of order in the gel structure. Direct evidence for the stabilizing effect of specifically adsorbed carbonate was obtained when carbon dioxide was introduced during the hydrolysis of aluminum tri-sec-butoxide. The resulting aluminum hydroxycarbonate gel possessed excellent antacid properties, retained its amorphous nature upon aging, and contained no cations other than aluminum. Hydrolysis of aluminum tri-sec-butoxide in the presence of stoichiometric amounts of sodium bicarbonate resulted in the immediate formation of crystalline sodium aluminum hydroxycarbonate (dawsonite).

Adsorption↗
PubMed1984

Adsorption of pepsin by aluminum hydroxide I: Adsorption mechanism.

Adsorption of pepsin by gibbsite and boehmite, non-acid-reactive forms of aluminum hydroxide, was observed and related to the surface area of the adsorbent. Adsorption was pH dependent, with maximum adsorption occurring between pH 2.7-3.3 for gibbsite and pH 2.7-4.3 for boehmite. Electrostatic attraction was an important adsorption mechanism at the pH conditions encountered in the GI tract; the isoelectric point of pepsin was approximately 1, giving it a negative charge, and the point of zero charge for the adsorbents was greater than 9, giving them a positive charge. However, the pH-adsorption profile can not be fully explained by electrostatic considerations. Desorption studies indicate the importance of specific adsorption because pepsin was not desorbed by washing with acidified water, but was partly desorbed by exchange with phosphate. The IR spectrum of adsorbed pepsin also suggested that specific adsorption of pepsin occurred through anionic ligand exchange involving carboxylate groups of pepsin and surface aluminum ions.

Adsorption↗
PubMed1986

Effect of shear on the apparent viscosity of amorphous carbonate ion containing aluminum hydroxide suspensions.

The application of shear to carbonate ion containing aluminum hydroxide suspensions caused a change in the apparent viscosity by two possible mechanisms: change in the surface charge because of desorption of specifically adsorbed carbonate ion, and aggregate dispersal and formation of more extensive particle networks. The desorption of specifically adsorbed carbonate ion is related to the expansion of the air-liquid interface during shear. Shear-inducing processing equipment which generates a minimal amount of new air-liquid interface was found to produce the least change in pH and, consequently, in surface charge. However, viscosity increases caused by aggregate dispersal and formation of more extensive particle networks may occur without a shear-induced change in surface charge.

Aluminum Hydroxide↗
PubMed2001

Successful molecular dynamics simulation of two zinc complexes bridged by a hydroxide in phosphotriesterase using the cationic dummy atom method.

I report herein two 2.0 ns (1.0 fs time step) MD simulations of two zinc complexes bridged by a hydroxide in phosphotriesterase (PTE) employing the nonbonded method and the cationic dummy atom method that uses virtual atoms to impose orientational requirement for zinc ligands. The cationic dummy atom method was able to simulate the four-ligand coordination of the two zinc complexes in PTE. The distance (3.39 +/- 0.07A) between two nearby zinc ions in the time-average structure of PTE derived from the MD simulation using the cationic dummy atoms matched that in the X-ray structure (3.31 +/- 0.001A). Unequivocally, the time-average structure of PTE was able to fit into the experimentally determined difference electron density map of the corresponding X-ray structure. The results demonstrate the practicality of the cationic dummy atom method for MD simulations of zinc proteins bound with multiple zinc ions. In contrast, a 2.0 ns (1.0 fs time step) MD simulation using the nonbonded method revealed a striking difference in the active site between the X-ray structure and the time-average structure that was unable to fit into the density map of PTE. The results suggest that caution should be used in the MD simulations using the nonbonded method.

Algorithms↗
PubMed2002

Chemical, structural, and thermal properties of Zn(II)-Cr(III) layered double hydroxides intercalated with sulfated and sulfonated surfactants.

Zn(II)-Cr(III)-LDHs (layered double hydroxides) containing sulfated or sulfonated surfactants as the interlamellar anion were synthesized by the coprecipitation method. The syntheses were conducted under various different experimental conditions, such as the Zn : Cr ratio, pH, and aging time. In each of the prepared materials, unlike previously reported data, the interlayer anion arrangement did not change, being consistent with a perpendicular monolayer. The thermal decomposition process of the prepared materials was studied by a set of analysis methods, such as TG/DTA, TG/MS, PXRD, and FT-IR. From the results obtained it was possible to conclude that, in an air atmosphere, the anions decomposed by a partial combustion, leading to the formation of sulfide. The results also showed that sulfonated surfactants containing LDHs are much more stable than those containing sulfated surfactants. A mechanism was proposed for the thermal decomposition of such LDHs based on the experimental results.

Benzenesulfonates↗
PubMed1994

Frog striated muscle is permeable to hydroxide and buffer anions.

Hydroxide, bicarbonate and buffer anion permeabilities in semitendinosus muscle fibers of Rana pipiens were measured. In all experiments, the fibers were initially equilibrated in isotonic, high K2SO4 solutions at pHo = 7.2 buffered with phosphate. Two different methods were used to estimate permeabilities: (i) membrane potential changes were recorded in response to changes in external ion concentrations, and (ii) intracellular pH changes were recorded in response to changes in external concentrations of ions that alter intracellular pH. Constant field equations were used to calculate relative or absolute permeabilities. In the first method, to increase the size of the membrane potential change produced by a sudden change in anion entry, external K+ was replaced by Cs+ prior to changes of the anion under study. At constant external Cs+ activity, a hyperpolarization results from increasing external pH from 7.2 to 10.0 or higher, using either CAPS (3-[cyclohexylamino]-1-propanesulfonic acid) or CHES (2-[N-cyclohexylamino]-ethanesulfonic acid) as buffer. For each buffer, the protonated form is a zwitterion of zero net charge and the nonprotonated form is an anion. Using reported values of H+ permeability, calculations show that the reduction in [H+]o cannot account for the hyperpolarizations produced by alkaline solutions. Membrane hyperpolarization increases with increasing total external buffer concentration at constant external pH, and with increasing external pH at constant external buffer anion concentration. Taken together, these observations indicate that both OH- and buffer anions permeate the surface membrane. The following relative permeabilities were obtained at pHo = 10.0 +/- 0.3: (POH/PK) = 890 +/- 150, (PCAPS/PK) = 12 +/- 2, (PCHES/PK) = 5.3 +/- 0.9, and (PNO3/PK) = 4.7 +/- 0.5. PNO3/PK was independent of pHo up to 10.75. At pHo = 9.6, (PHCO3/PK) = 0.49 +/- 0.03; at pHo = 8.9, (PCl/PK) = 18 +/- 2 and at pHo = 7.1, (PHEPES/PK) = 20 +/- 2. In the second method, on increasing external pH from 7.2 to 10.0, using 2.5 mM CAPS (total buffer concentration), the internal pH increases linearly with time over the next 10 min. This alkalinization is due to the entry of OH- and the absorption of internal H+ by entering CAPS- anion. The rate of CAPS- entry was determined in experiments in which the external CAPS concentration was increased at constant external pH. Such increases invariably produced an increase in the rate of internal alkalinization, which was reversed when the CAPS concentration was reduced to its initial value.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1980

Oral aluminum and neuropsychological functioning. A study of dialysis patients receiving aluminum hydroxide gels.

Nine dialysis patients with significantly increased serum-aluminum levels due to chronic ingestion of aluminum hydroxide gels and eleven dialysis patients with normal serum-aluminum levels were tested neuropsychologically for generalized functions (intelligence, reasoning, memory) and for more specific abilities (visual memory, verbal and reading fluency, manual dexterity). All tests did not reveal any significant difference in neurophyscholigical functioning between the two groups. This finding seems to indicate that oral aluminum is not neurotoxic for man, even under circumstances of renal failure. This contradicts the idea that oral aluminum plays a role in etiology of dialysis dementia. However, the possibility cannot be excluded that aluminum overload in the present sample was not sufficient to induce changes in CNS functioning. Thus, until the importance of oral aluminum has been decided, it seems wise to keep all sorces of aluminum overload as low as possible.

Aluminum↗
PubMed1988

Immunogold localization of peroxisomal enzymes in Epon-embedded liver tissue. Enhancement of sensitivity by etching with ethanolic sodium hydroxide.

Epon-embedded biological materials exhibit well preserved ultrastructure but generally weak antigenicity. Brief etching of ultrathin Epon sections with resin solvent, ethanolic sodium hydroxide, brought about a nearly 2-fold increase in the immunogold labeling density of rat and human hepatic peroxisomes after incubation with antisera against catalase and 3 enzymes of lipid beta-oxidation: acyl-CoA oxidase, bifunctional protein (enoyl-CoA hydratase-3-hydroxyacyl-CoA dehydrogenase) and 3-ketoacyl-CoA thiolase. The etching was superior to pretreatment with an oxidant, sodium metaperiodate. Despite some deterioration of the cellular ultrastructure, the obtained enhancement of the sensitivity of the protein A-gold method may be helpful in cases when the antigenicity to be detected is strongly inhibited by epoxy resin embedding.

Acetyl-CoA C-Acyltransferase↗
PubMed1978

Iron hydroxide: model for enzymes that oxidize proteins.

The particles of an iron hydroxide sol were found to be a suitable model for protein-oxidizing enzymes such as peroxidase and polyphenol oxidase. In addition to small molecules such as pyrogallol, human serum proteins, albumin and gamma-globulin, are shown to be substrates of the oxidizing model. The activity is markedly increased by the addition of small amounts of copper to the iron in the particles of the sol. The size and molecular weight of the enzyme model, as well as the number of active centers were determined.

Blood Proteins↗
PubMed1989

Mixed-valence hydroxides as bioorganic host minerals.

A range of naturally occurring divalent-trivalent metal cation hydroxides and modified artificial analogs have been synthesized and characterized. Structural and chemical properties of these minerals, determining their capability to selectively concentrate, order and alter molecules of prebiotic interest, include their anion exchange capacity and specificity, photochemical reactivity, production of nascent hydrogen, and catalytic efficiency. Properties relevant to these functions have been investigated and are discussed.

Aluminum↗