Thesis (M.Ed.)--University of Hong Kong, 1988. / Includes bibliographical references (leaf 135-144). Also available in print.

Graduation date: 1996

La bio-transformation naturelle des médicaments peut produire des métabolites toxiques; l’identification de ces métabolites est essentielle dans la stratégie de choix de molécules thérapeutiques. En appliquant les technologies de fermentation en bioréacteur des cellules hétérologues (souches d’E. coli recombinantes exprimant une iso-enzyme de cytochrome P450 humain avec la réductase humain), la bioconversion du substrat (principe actif) en ses métabolites de dégradation, a été réalisée à grande échelle (g-g). Notre choix s’est porté sur le complexe hCYP3A4/HR fonctionnel produit par un hôte E. coli. Les cellules intactes ou les membranes cellulaires peuvent être exploitées comme biocatalyseur dans un système bioréacteur. Cependant, la faible solubilité des principes actifs dans des milieux de bioconversion aqueuse limitent le rendement. Un bioréacteur biphasique a été étudié. En solution, plusieurs combinaisons eau/solvants organiques conciliant la viabilité des cellules, la solubilité des principes actifs et produits de réaction et la catalyse des complexes enzymatiques ont conduit à l’établissement d’un mélange approprié. Cependant, ces combinaisons présentent toujours une inhibition importante du pouvoir catalytique des complexes enzymatiques. Pour minimiser un effet dénaturant possible des solvants sur le système enzymatique, ce dernier a été maintenu dans un environnement aqueux en immobilisant les cellules et/ou les membranes cellulaires dans une matrice hydrophile. L’alginate de calcium apparaît être une matrice d’immobilisation idéale pour les membranes assurant la fonctionnalité du complexe CYP/HR et permettant en outre un stockage à long terme des préparations. Par contre, l’immobilisation des cellules dans diverses matrices, si elle permet une viabilité et une conservation à long terme des souches recombinantes, ne permet aucune expression de l’activité enzymatique présente dans les cellules. La combinaison d’une localisation du complexe hCYP/HR fonctionnel dans la membrane interne et d’une perméabilité réduite des cellules d’E. coli (immobilisées) en est une explication possible mais non-démontrée. Entre-temps, cette technologie de bioréacteur homogène biphasique ou par immobilisation des membranes cellulaires a été utilisée plusieurs reprises pour produire des métabolites humains à partir de divers principes actifs. Ces métabolites ont été purifiés avec succès, démontrant que cette approche technologique est compétitive comparée aux procédures conventionnelles. Néanmoins, de nouvelles pistes de recherche seraient extrêmement intéressantes. La localisation des complexes enzymatiques recombinants en surface des cellules permettrait de concilier les propriétés hydrophobes des principes actifs et l’environnement hydrophile nécessaire aux enzymes. D’autre part une investigation de complexes enzymatiques résistant aux solvants pourrait remplacer avantageusement l’immobilisation.

Graduation date: 1992

The research addressed in this thesis is focused on the solubility and pseudo-polymorphic transition of L-serine in mixed water-methanol systems. Cooling re-crystallizations were carried out that varied both temperature and methanol concentration. Solubilities were measured with high-performance liquid chromatography. It is found that the solubility increased with increase in temperature and decreased drastically with methanol concentration. The effect of temperature at which there is a transition of L-serine crystals from the rod-shaped (anhydrous) form to hexagonal (monohydrate) form was confirmed and that transition temperatures decreased with methanol concentrations in a non-linear manner. The solubility data were correlated and plotted using the vant Hoff equation and the enthalpy and entropy of dissolution were determined. These values increased with increase in methanol concentration. The solid crystals were analyzed by optical microscopy and powder X-ray diffraction. The rod-shaped crystals were identified to be anhydrous L-serine, while the hexagonal crystals were L-serine monohydrate. Dehydration of the monohydrated crystals in their solid-state was examined and the onset of such phenomenon was known to start once the crystals were removed from the solutions.

The Electrolyte Nonrandom Two-Liquid Activity Coefficient model in Aspen PlusTM 2006.5 was used to develop a rigorous and consistent thermodynamic representation for the base sub-component systems associated with aqueous combinations of K₂CO₃, KHCO₃, MEA, and piperazine (PZ) in a mixed-solvent electrolyte system for the application of CO₂ absorption/stripping from coal fired power plants. We developed a new vapor-liquid equilibrium apparatus to measure CO₂, amine, and H2O vapor pressures at 40 and 60 oC. We found that the volatility of MEA and PZ can be approximated at 50 and 20 ppmv at 40°C for any solvent composition studied in this work, over the CO₂ partial pressure range from 0.01 to 0.1 kPa. Very few solvent compositions exhibited a greater differential capacity than 7 m MEA at 60°C; specifically 11 m MEA, 3.5 m MEA + 3.6 m PZ, 7 m MEA + 2 m PZ, 7 m MEA + 3.6 m PZ, and 5 m K+ + 7 m MEA + 3.6 m PZ. Piperazine exhibited a possible maximum differential capacity of 2.21 mole CO₂/kg-H₂O at a concentration of 7.3 m. At the Norwegian University of Science and Technology, Inna Kim determined the differential enthalpy of CO₂ absorption for aqueous combinations of K₂CO₃, KHCO₃, MEA, PZ, and CO₂, based on a consistent experimental method developed for MEA, from 40 to 120°C for use in this work. In addition, we developed a consistent method to measure the specific heat capacity for a number of similar solvent combinations. We found that the enthalpy of CO₂ absorption increased with temperature because the apparent partial heat capacity of CO₂ may be considered small. Finally, by using a differential scanning calorimeter, we determined the dissolution temperature for aqueous mixtures of unloaded piperazine, which inferred an effective operating range for solutions of concentrated piperazine, greater than 5 m PZ, over a loading range between 0.25 to 0.45 mole CO₂/2·mol PZ. Through unit cell x-ray diffraction, we were able to identify and characterize the presence of three solid phases (PZ·6H₂O, KHCO₃, and KvPZ(COO)₂) in aqueous mixture combinations of K₂CO₃, KHCO₃, PZ, and CO₂. / text

The work summarizes the results of a studies conducted with six different flushing agents, i.e. two anionic surfactants (SDS and DOWFAX 8390), two complexing agents (cyclodextrins), a humid acid, and an alcohol (ethanol), for solubilizing and removing residual-phase immiscible liquid from porous media. Batch experiments were conducted to measure the degree of trichloroethene (TCE) and tetrachloroethene (PCE) solubilization induced by these agents. These studies revealed that the solubility of TCE and PCE was enhanced significantly. Column experiments were conducted to compare water and agent-enhanced flushing of Borden sand containing residual saturations of TCE and PCE. The results of these studies indicate that the total flushing volume necessary to remove the contaminant was reduced substantially in the presence of all applied agents. The relative effectiveness of the agents varied based on the method of evaluation. It was shown that a volatile contaminant, e.g. toluene, TCE, and PCE, can be separated from cyclodextrin solution by mean of air-sparging. The cyclodextrin solution was successfully reused for continuos flushing of a contaminated porous material. The simulation of selected experiments revealed that the mass transfer rate coefficients are generally increasing if evaluated based on the aqueous driving force approach. However, a relation based on the enhanced driving force approach was found to be less significant. Even though areas of additional research have been identified, this research contributes to a better understanding of the processes governing chemically enhance flushing of contaminated porous media.

Η συγκεκριμένη εργασία πραγματεύεται μία διδακτική προσέγγιση του φαινομένου της διάλυσης λευκών στερεών ουσιών σε δύο διαφορετικούς διαφανείς διαλύτες. Σαφέστερα, σκοπός της εργασίας είναι η μελέτη της ενδεχόμενης εννοιολογικής αλλαγής στη σκέψη παιδιών προσχολικής ηλικίας αναφορικά με το εν λόγω φαινόμενο μετά την υλοποίηση ενός εκπαιδευτικού προγράμματος. Τα αποτελέσματα της έρευνας έδειξαν ότι οι μαθητές προσχολικής ηλικίας μετά την εφαρμογή του εκπαιδευτικού προγράμματος είναι σε θέση να συγκροτήσουν συλλογισμούς συμβατούς με το σχολικό μοντέλο για το φαινόμενο της διάλυσης στερεών ουσιών σε υγρούς διαλύτες. / This paper deals with a teaching approach about the phenomenon of dissolution of white solids in two different transparent solvents. The aim of this paper is the study of the possible conceptual change in preschool children's thinking about this phenomenon after the implementation of an educational program. The results showed that preschool students are able to compose reasoning compatible with the school model about the effect of the dissolution of solids in liquid solvents after the implementation of the educational program.

No description available.

The biocatalytic activity of mushroom tyrosinase was optimized in chloroform medium, using five selected phenolic substrates, including catechin (CT), vanillin (VA), chlorogenic acid (CA), p-aminophenol (pAP) and hydroquinone (HQ). The specific activity (SA) of tyrosinase determined as the change in absorbance at the selected wavelength per $ mu$g protein per sec ($ delta$A/$ mu$g protein/sec) in chloroform was much higher than that obtained in aqueous media. The optimal amount of enzymatic protein for tyrosinase biocatalysis in chloroform was found to be 44.0 mg protein/L for CT and VA, 31.6, 180.5 and 90.3 mg protein/L, respectively, for CA, pAP and HQ. The optimal pH for the oxidative activity of tyrosinase in chloroform was 6.0 for all the substrates; however, the optimal temperature for enzymatic activity was 30$ sp circ$C for CT and 25$ sp circ$C for the other four substrates. The use of 1.25 and 6.65 mM catechol in chloroform medium activated the tyrosinase activity maximally by 56.2% and 267.2%, respectively for CT and CA as substrates; however, no effect from catechol (0 to 7 mM) was found with VA, pAP or HQ. In addition, the use of 4.25, 2.25 and 5.39 mM ethylenediamine tetraacetic acid (EDTA) in chloroform, with CT, VA and pAP as substrates, inhibited the tyrosinase activity maximally by 44.3, 84.7 and 67.0%, respectively; however, the use of 4.75 and 1.60 mM EDTA activated the enzyme by 101.9% and 115.9%, respectively, for CA and HQ. The use of high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) demonstrated the phenolic substrate bioconversion, whereas the spectrophotometric scanning showed the product formation during the enzymatic reaction. (Abstract shortened by UMI.)