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Biomedical subjects

S L Hem

Publications and source records attributed to S L Hem.

At least 91 records · Page 5Linked to original sources
PubMed1978

Mechanism of adsorption of clindamycin and tetracycline by montmorillonite.

IR and X-ray analyses of the interaction of clindamycin with montmorillonite indicate that clindamycin is adsorbed by a cation-exchange mechanism under pH conditions favoring the cationic form of the drug and by physical adsorption when the unionized drug is present. This physical adsorption is relatively weak since the drug is readily desorbed by alkaline washing. Tetracycline is adsorbed by cation exchange at low pH values where the +00 species predominates. Complexation with divalent interlayer cations contributes significantly to adsorption at higher pH values where the +-0 and +-- species exist. In a strongly alkaline solution, the 0-- species was not adsorbed in the interlayer space of montmorillonite but rather produced an external calcium-tetracycline complex. This study illustrates the utility of X-ray and IR analyses in elucidating the mechanisms responsible for clay-drug interactions.

Adsorption↗
PubMed1978

Nature of amorphous aluminum hydroxycarbonate.

The titration of sodium carbonate with aluminum nitrate is shown to produce amorphous aluminum hydroxycarbonate. This compound is not stoichiometric, although the maximum carbonate to aluminum ratio appears to be 0.5. The pH conditions for achieving the maximum carbonate content are concentration dependent. A model for the particle surface at the solution interface is proposed. This model accounts for the presence of carbonate directly coordinated to the aluminum and carbonate adsorbed by electrostatic forces. Sodium is present in the diffuse layer and is, therefore, not an integral part of the structure.

Aluminum↗
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↗
PubMed1977

pH-stat titration of aluminum hydroxide gel.

The pH-stat titration of aluminum hydroxide gel was evaluated and was affected by pH, temperature, concentration, and ionic strength. Control of these parameters resulted in a highly sensitive and reproducible in vitro antacid test. The utility of the pH-stat test was illustrated by monitoring the aging of several carbonate-containing aluminum hydroxide gels and by comparing the antacid properties as measured by the pH-stat titration, the acid-consuming capacity, the Rossett-Rice test, and the test proposed by the food and Drug Administration Drug Evaluation Panel. The pH-stat titration also was useful for relatively nonreactive aluminum hydroxide gels. The use of sodium fluoride as the reaction medium extended the capability of the pH-stat titration to monitor the aging of chloride-containing gels. The pH-stat titrigram was interpreted in terms of a previously published polymer model of the structure of a chloride-containing aluminum hydroxide gel. The acid reactivity of relatively nonreactive gel is believed to be due totally to the chemical neutralization of acid, because the milliequivalents of aluminum ion appearing in solution is the same as the milliequivalents of acid neutralized throughout the ph-stat titration.

Adsorption↗
PubMed1977

Role of carbonate in acid neutralization of aluminum hydroxide gel.

The role of carbonate in the acid neutralization of a carbonate-containing aluminum hydroxide gel was studied. The pH-stat neutralization reaction was comprised of three phases: an initial, immediately reacting phase; a slow, zero-order phase; and a terminal, fast zero-order phase. The evolution of carbon dioxide and the appearance of aluminum ions were monitored during neutralization. Acid neutralization is believed to occur predominantly at the aluminum-carbonate bond during the slow phase of neutralization. The reaction of structural carbonate disrupts the gel structure and increases the porosity and surface area of the gel. The diffusion of acid into the gel structure is facilitated and accelerates the neutralization rate, as seen in the final phase of the pH-stat titrigrams. The behavior of carbonate is probably responsible for the rapid and complete neutralization of acid generally observed with carbonate-containing aluminum hydroxide gel.

Acids↗
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

Kinetic analysis of penicillin degradation in acidic media.

Degradation of penicillin in acidic media (pH 2.7) was monitored by high-pressure liquid chromatography and UV spectroscopy. The effects of temperature, buffer concentration, and ionic strength were examined. A degradation pathway is proposed, and the apparent first-order rate constant and energy of activation were calculated for each reaction. One or more degradation products containing a sulfhydryl group, a functional group often suggested as having a major role in eliciting allergic responses to penicillin therapy, were present throughout the degradation scheme.

Acids↗
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↗
PubMed1976

Structure of aluminum hydroxide gel II: aging mechanism.

The aging of aluminum hydroxide gel prepared by the reaction of aluminum chloride and ammonium hydroxide was studied by measurement of pH, acid-consuming capacity, hydroxide to aluminum ratio, chloride activity, and X-ray line broadening. The results were consistent with a polymer model involving particle growth by a deprotonation-dehydration mechanism. Anions inhibit this reaction by binding to the positively charged edges of the hydroxyaluminum polymers.

Aluminum Hydroxide↗
PubMed1976

Structure of aluminum hydroxide gel III: mechanism of stabilization by sorbitol.

The effect of sorbitol on the aging of aluminum hydroxide gel, prepared by the reaction of aluminum chloride solution with strong ammonia solution to a final pH of 7.0, was studied by potentiometric titration, acid-consuming capacity, pH, hydroxide to aluminum ratio, chloride activity, X-ray diffraction, and IR spectroscopy. Gels containing sorbitol lost less than 10% of their acid-consuming capacity during a 6-month aging period compared with a loss of more than 60% for an identical gel without sorbitol. The mechanism by which sorbitol stabilizes the gel appears to be inhibition of the secondary polymerization reaction which takes place upon aging. Another polyhydroxy compound, quercetin, also stabilizes aluminum hydroxide gel.

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↗
PubMed1976

Differential thermal analysis of aluminum hydroxide gel.

The development of order during the aging of aluminum hydroxide gel prepared by the reaction of aluminum chloride and ammonium hydroxide to a final pH of 7.0 can be monitored by differential thermal analysis. The loss of acid reactivity upon aging is accompanied by an increase in the temperature and intensity of the dehydroxylation endotherm and an accompanying decrease in the intensity of the water of hydration endotherm. With continued aging, the thermogram develops the characteristics of a crystalline aluminum hydroxide.

Aluminum Hydroxide↗
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↗
PubMed1975

Comparison of IR spectroscopic analysis and X-ray diffraction of aluminum hydroxide gel.

Data are presented which demonstrate the IR spectrophotometry is more sensitive than X-ray diffraction to structural changes occurring in aluminum hydroxide gel during aging. By examining changes in peak shape and position in the IR spectrum, evidence is seen for an increasing degree of order as the gel ages. The increased order may be responsible for the loss of acid reactivity observed during aging. IR analysis is also recommended for routine monitoring of aluminum hydroxide gels.

Absorption↗
PubMed1975

High-pressure liquid chromatographic analysis of penicillin G potassium and its degradation products.

An anion-exchange high-pressure liquid chromatographic system capable of separating penicillin G potassium from five of its degradation products was developed. The retention times were: penicillin G potassium, 17.5 min; DL-penicillamine, 4.5 min; benzylpenilloic acid, 7.0 and 8.0 min; benzylpenamaldic acid, 13.0 min; benzylpenicilloic acid, 19.5 min; and benzylpenillic acid, 22.0 min. In addition, the system permits quantification using linear calibration curves.

Benzyl Compounds↗