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Biomedical subjects

W H Streng

Publications and source records attributed to W H Streng.

8 recordsLinked to original sources
PubMed1989

Dextrose adduct formation in aqueous teicoplanin solutions.

The interaction of Teicoplanin, a glycopeptide antibiotic, with dextrose in aqueous solution has been investigated. The equilibrium concentrations of the adduct formed by the interaction of the dextrose aldehyde and the Teicoplanin amino group is shown to be directly related to the concentration of the dextrose and is thought to be inversely proportional to the hydrogen ion concentration. It was also found that phosphate ion catalyzed the reverse reaction. Approximately 30 days were required to reach equilibrium a 4 degrees C, while equilibrium was established in about 7 days at room temperature. The reaction is reversed with dilution and the rate of the reverse reaction is two to three times faster than expected when phosphate ion is present at 0.05 M. From the temperature dependence of the rate constants, the activation energies for the various reactions were determined to be in the range 67-80 kjoules (16-19 kcal)/mol.

Anti-Bacterial Agents↗
PubMed1979

Osmolality of parenteral solutions.

Osmolality-concentration profiles for individual and mixed solute systems are presented. Linear relationships between osmolality and concentration held true in all systems examined at concentrations below 0.2 molal levels. At higher concentrations, linearity existed only in select systems. Deviations from linearity can be greater or less than extrapolated values. In view of the need to determine an osmolarity conversion factor for each parenteral formulation and the many errors possible in the use of these values, adoption of osmolality values for labeling parenteral products rather than osmolarity, as stipulated in USP XIX-NF XIV third supplement, strongly recommended.

Chemical Phenomena↗
PubMed1978

Relationship between osmolality and osmolarity.

Since the compendia require the osmolarity of certain parenterals to be labeled and since experimentally only the osmolality can be measured, it is necessary to obtain the relationship between these two quantities. This relationship was determined by considering fundamental physical-chemical definitions. The osmolality of a solution was found to be simply related to the osmotic coefficient. The conversion to osmolarity requires the use of the partial molal volume(s) of the solute(s). A single conversion factor is required for a particular solute system; i.e., the conversion factor is independent of the solution concentration.

Chemical Phenomena↗
PubMed1978

Microionization constants of commercial cephalosporins.

The equilibrium constants of five commercial cephalosporins were determined. Two are monoacidic and possess one Ka while three are amphoteric and have four microconstants. Although several assumptions were made in the calculations, good agreement was found between the compounds and with previously reported macroionization constants. By utilizing the microionization constants, the ratios of zwitterion to unchanged species were calculated to be in the 900-50,000 range and to have a maximum concentration between pH 3.5 and 5.

Cephalosporins↗
PubMed1976

Ionization constants of cephalosporin zwitterionic compounds.

The microionization constants for two zwitterionic compounds were determined by incorporating two experimental techniques. These compounds have chromophoric changes dependent upon the solution pH. By combining the spectrophotometric measurements with potentiometric mmeasurements, all four microionization constants were calculated. The method used is completely general and is applicable to all diprotic compounds that exhibit this spectrophotometric behavior. The observed pKa's had differences of at most 1.2 units for either compound and were in the 1-4 range. A comparison of the results with each compound and similar compounds indicates that the values are resonable.

Cephalosporins↗
PubMed1975

Nonisothermal kinetic studies III: rapid nonisothermal-isothermal method for stability prediction.

A continuous nonisothermal-isothermal method for stability prediction was developed. The approach yields all necessary parameters for prediction, including reaction order. The experimental procedure involves changing the temperature of the samples being studied until degradation is rapid enough to proceed at a convenient isothermal rate for a sufficient number of half-lives with adequate analytical sensitivity so that the reaction order can be unambiguously determined. The analytical information obtained during the nonisothermal and isothermal portions of the experiment is utilized without curve matching in calculating the activation energy and determining the reaction order, reaction rate, and stability prediction at any desired temperature. Model experiments include the acid-catalyzed hydrolysis of acetylcholine bromide and the inversion of sucrose.

Acetylcholine↗
PubMed1975

Diffusion model for fluidized-bed drying.

A sucrose-lactose-starch granulation was used to study particulate motion and attrition in a fluid bed dryer. There is some classification of material in the dryer as drying proceeds; fine particles are dried faster and become less dense, and the less dry but denser large particles show some (although not great) accumulation tendencies in the lower central area. Unlike countercurrent rotary drying, fluid bed drying cannot be accounted for by water diffusion inside the granule as the rate-limiting step. In its place, a model of external water vapor diffusion is proposed and is supported by vapor-concentration curves and by the linear dependence of the rate constants on the linear air velocities. The dried granulation exhibits the same trend as does countercurrent dried material in that larger particles have higher moisture contents than do smaller particles. Quantitative relationships between content of moisture and size were developed and are supported by experimental data. The granulation, upon storage, does not equilibrate, indicating that this type of water distribution is a problem in batch process granulations as well as in the earlier reported case of granulations for continuous production.

Diffusion↗