Chester S. Ho

Simultaneous measurement of oxygen diffusion coefficients and solubilities in electrolyte solutions with a polarographic oxygen electrode

Abstract The objective of this paper is to present a reliable yet convenient method of measuring simultaneously oxygen diffusion coefficients and solubilities in aqueous electrolyte solutions with a membrane-covered oxygen electrode. Measurements have been conducted in solutions of sodium chloride, potassium chloride, sodium sulfate, and magnesium sulfate over wide ranges of salt concentrations. The experimental results on oxygen diffusion coefficients and solubilities in test electrolyte solutions show an excellent accord with the literature data.

BIOCONVERSION WITH WHOLE CELL PENICILLIN ACYLASE IN AQUEOUS TWO-PHASE SYSTEMS

Abstract The deacylation of Pen G was carried out by using recombinant E. coli in an aqueous two-phase system consisting of polyethylene glycol and potassium phosphate solution, which partitions the cells to the bottom phase and the products to the top phase. Bioconversion and product separation were carried out in the same reactor. Repeated batch conversion was employed ten times and enzymic activity showed only a slight decline. When pure enzyme was used for bioconversion in an aqueous two-phase system, the decline was fast and bioconversion using whole cell penicillin acylase was better than that obtained using the pure acylase.

The effect of dissolved carbon dioxide on penicillin production: Mycelial morphology

Abstract The effect of carbon dioxide on the morphology of Penicillium chrysogenum was examined. The scanning electron microscopic (SEM) study indicated that the morphology of P. chrysogenum was subject to change when exposed to various dissolved CO2 concentrations in the medium. At low influent carbon dioxide partial pressures between 0% and 8%, the predominant morphological form of P. chrysogenum was filamentous. At higher influent carbon dioxide partial pressures of 15% and 20%, the appearance of swollen and stunted hyphae predominated, and a significant quantity of spherical or yeast-like cells were observed. It was evident that for production subject to high dissolved CO2 concentrations the inhibition of cell growth and penicillin production related strongly to the concomitant morphological changes of P. chrysogenum.

The measurement of oxygen diffusion coefficients in polymeric solutions

Abstract The objective of this paper is to present a new method of measuring oxygen diffusion coefficients with membrane-covered polarographic oxygen electrodes and to assess its applicability to viscous polymeric solutions of sodium carboxymethylcellulose (CMC), dextran and polyethylene glycol (PEG). The results indicate that, except in CMC solutions, the oxygen diffusion coefficient decreases with an increase in polymer concentration. In the CMC solutions, however, oxygen diffusion coefficients first decrease with an increased polymer concentration, then increase while the polymer concentration exceeds a critical value. Possible explanations for this phenomenon are explored.

Morphological Alterations of Penicillium ckrysogenum Caused by Carbon Dioxide

Summary: Scanning electron microscopic studies showed that the morphology of Penicillium chrysogenum Thom in fermentation cultures changed in response to changes in COz concentration. At influent COz partial pressures between 0.03% (air) and 8 %, the predominant morphological form was filamentous, whereas at 15% CO2, swollen and stunted hyphae predominated, and a significant quantity of spherical or yeast-like cells was observed.

ON DISSOLVED CARBON DIOXIDE IN PENICILLIN FERMENTATIONS

The behavior of dissolved carbon dioxide in penicillin fermentations was studied. It is demonstrated that the partial pressure of carbon dioxide in the offgas and of that dissolved in the fermentation medium were not in equilibrium. Excessive dissolution of carbon dioxide occurs during the course of the fermentation and can be attributed to the slower rate of CO2 desorption from the fermentation medium compared to the rate of CO2, absorption from the cell respiration.

Effective diffusivity of oxygen in microbial pellets

In a typical submerged aerobic fermentation with microbial pellets, the effective diffusivity of oxygen in the pellets is probably the most important, yet most difficult transport property to characterize experimentally. Its values directly indicate the efficiency or deficiency of oxygen to individual cells, and thus the biological activity of the microorganisms. In the past, it was not possible to assess reliably the effective diffusivity of oxygen in pellets due to several reasons. Firstly, most oxygen electrodes available were coarse, and hence not suitable for in situ measurements. Secondly, there was a lack of methods rigorous enough to characterize the structure of the microbial pellets. A state-of-the-art review of the literature relating to the feature subject is presented. Emphasis is laid upon development and evolution of the means for quantitative characterization of the effective diffusivity of oxygen in microbial pellets.

Oxygen Diffusion Coefficients in Commonly Used Topical Semisolid Creams

The objective of this paper is to determine oxygen diffusion coefficients, permeabilities, and solubilities in a commonly used o/w topical ointment (similar to USP XXI hydrophilic ointment) and four commercial 1% anthralin creams. A new method developed by Ju and Ho in 1986 by applying a coupled steady-state and unsteady-state analysis for oxygen diffusion through a thin layer of test material on the surface of a membrane-covered polarographic oxygen electrode was used in the study. The results indicate that oxygen diffusion coefficients decrease with an increasing petrolatum concentration in o/w topical creams. The oxygen diffusion coefficients in four commercial creams containing 1% of extremely oxygen-sensitive anthralin were also determined using the same method. The information generated in this study can lead to a better understanding of the diffusion transport mechanism of oxygen in the topical creams and, thus, be useful to the formulation design of oxygen-sensitive drugs in semisolid dosage forms intended for topical, ophthalmic, and parenteral use.