Thesis (M. Med. Sc.)--University of Hong Kong, 2006.

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Commercially available boron triiodide (stated to be 99.9% pure) was flash photolysed and found to contain a high level of impurity. After a lengthy purification procedure the sample was still too impure to be of use. Boron triiodide was, therefore, prepared by several methods and shown to be free of impurities by mass spectrometry. A detailed study of these preparative methods has removed many of the ambiguities present in the existing literature. The absorption spectrum of the water sensitive pure B13 vapour was recorded over the range 650-200nm and shown to consist of six absorption maxima ie. transitions to six electronic states of the B13 molecule were detected.

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Magister Scientiae Dentium - MSc(Dent) / Includes Bibliographical references (leaves 83- 94).Forty-three male athymic nude mice were implanted with human vaginal mucosal cysts under general anaesthesia with Ketamine [25mg/kg] and Medetomidine [0.5mg/kg]. Cysts in 37 mice were recovered after 9 weeks of growth. twenty three cyst linings had retained the original structure of the vaginal epithelium. No marked deifference was present between the thickness of 9 week old linings and donor vaginal epithelium. The contaminants isolated from the skin of mice before implantation were mainly normal commercals of healthy experimental animals. There was no distinct difference in the number of cases with intact cyst formation between the terramycin/vitamin cocktaik group. The frequency of poor wound healing and/ or murine epidermis ingrowth was three times higher in animals stitched with silk sutures that in those cases where nylon sutures were used. / South Africa

A study has been made of the potassium permanganate oxidation of three organic compounds: pivalaldehyde, p-nitrobenzaldehyde and p-nitrophenyltrifluoromethyl-carbinol. The permanganate-pivalaldehyde reaction has been investigated in the pH range 1 to 13. The results show that the reaction is first order in permanganate and aldehyde, that the oxidation by manganate is slower than that of permanganate by a factor of twenty five, and that the oxidation is general acid-catalyzed. The results in alkaline solution show some increase in rate but are not reproducible, which is most likely due to radical decomposition of the pivalaldehyde. Three mechanisms are discussed: Firstly, a typical general acid-catalysis scheme, secondly, one involving a tetragonal transition state and thirdly, one based on a hydride transfer. Of these, only the first two are able to accommodate the experimental evidence found earlier in the permanganate oxidation of benzaldehyde by Wiberg and Stewart (1). The autocatalysis exhibited by the permanganate benzaldehyde reaction has been studied at low pH. The autocatalysis has also been investigated with p-nitrobenzaldehyde in order to see if there is any substituent effect. Results show that the p-nitro aldehyde has a longer induction period. Moreover, it has been shown that overoxidation of the benzene ring rather than true autocatalysis has occurred. A radical chain mechanism has been put forward in an attempt to explain this observation. The permanganate oxidation of p-nitrophenyltri-fluoromethylcarbinol has been studied in 0.1 M sodium hydroxide in order to determine the mechanism of the reaction. A large enhancement in rate observed compared to rates found by Stewart and Van der Linden (2) in the permanganate oxidation of other substituted phenyltrifluoromethylcarbinols is good evidence for a reaction path involving hydrogen atom abstraction from the alkoxide to the permanganate ion. Such a mechanism is consequently favoured. / Science, Faculty of / Chemistry, Department of / Graduate

It is well-established that the presentation of a startling acoustic stimulus (SAS) simultaneous with the go-signal in a simple reaction time (RT) task results in significant RT reductions, while leaving movement kinematics essentially unaltered. While this phenomenon, termed the StartReact effect, has been extensively studied, cortical involvement in the neural mechanism underlying the RT-facilitation effects of a SAS remains widely debated. Applying sub-threshold TMS to motor areas results in increased cortical excitability and reductions in control RT. When this technique was used in a startle paradigm no RT benefits were seen, providing evidence that the cortex may not be involved in the StartReact effect; however, these results may also have been due to a floor effect of startle RT. It has been shown that RT in response to a SAS is significantly slower for complex movements, providing a possible method of distinguishing between these hypotheses. As such, the purpose of the experiments in this thesis was to determine if the application of sub-threshold TMS following a SAS when preparing to react with a complex movement would facilitate startle RT. If so, it would provide evidence for cortical involvement in the RT-facilitation effects of startle. The first experiment revealed that the task employed did not lead to an increase in RT in startle conditions, limiting the ability to make conclusions regarding the StartReact effect. In the second experiment the timing complexity of the task was increased, with the goal of increasing startle RT; however, startle RT was again not significantly slower for the complex movement than the simple movement. Furthermore, there was again no effect of TMS stimulation condition on startle RT. These results suggest that either the cortex does not play a role in the StartReact effect, or a floor effect of RT was reached in startle conditions; thus, alternative methods of investigating the neural mechanism underlying the RT-facilitation effects of startle are warranted.