Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 114-127).

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 181-212). Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 106-128).

Thesis (Ph. D.)(Botany)--University of Pretoria, 2001. / Acrobat Adobe Reder needed to open files.

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

The aim of this project was to investigate a range of medicinal herbs which have radical scavenging and antioxidant activities and then apply novel mass spectrometric techniques to investigate and analyse active components responsible for their pharmaceutical actions. A sensitive electron capture negative ionization of gas chromatography-mass spectrometry (ECNI-GC-MS) method was developed to assess hydroxyl radical production, as indicated by 3.4-dihydroxyphenylacetic acid (DOPAC) production, which allows excellent evaluation of hydroxyl radical scavenging and antioxidant activity of a number of medicinal Chinese herbs. Melatonin is an effective multiple radical scavenger and antioxidant and has been used in this study for the comparison of radical scavenging activity with medicinal herbs. To analyse active compounds from herbal extracts, mass spectrometric techniques were used to separate components that suppressed hydroxyl radical production from Dimocarpus longan Lour, determine known ginsenosides from ginseng extracts as well as to identify and quantify melatonin in ten herbal extarcts. The results obtained indicated that 1) the utilization of alumina in the ECNI-GC-MS method diminished interferences from ???noise??? products in a Fenton-type reaction, which allows obtaining pure final hydroxyl radical product and this method demonstrated optimal sensitivity and reliability; 2) Aqueous extracts of all herbs analysed showed different levels of hydroxyl radical scavenging activity. Dimocarpus longan Lour, Chrysanthemum morifolium Ramat, Lonicera hypoglauca Miq, Ginkgo biloba L, Rehmannia flutinosa and Libosch Cornus officinalis Sieb all exhibited stronger inhibitory effect on hydroxyl radical production than melatonin. 3) Aqueous extract of Dimocarpus longan Lour. showed the greatest inhibitory effect on hydroxyl radical production among the other herbs tested. The active fractions of this herb eluted just after the void volume using HPLC suggesting that the active compounds responsible for radical scavenging activity are polar and water soluble. They may belong to phenol group of chemicals. 4) Herbal extracts using non-polar solvents showed no effect on hydroxyl radical production suggesting active compounds in those herbs are water soluble. 5) Different species and origins of ginseng were compared for their radical scavenging activity. Chinese fresh ginseng (Oriental ginseng) showed higher activity than Korean ginseng tablet and American ginseng. Seven known active ginsenosides were identified using HPLC-MS-MS. 6) Melatonin was found at varying concentrations in ten herbs, which may contribute to the radical scavenging activity of herbs, on the other hand, it may provide the justification of clinical use and food resources, particularly for those herbs contain high level of melatonin.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 161-175).

Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (leaf 169-194) Also available in print.

Thesis (M. Phil.)--University of Hong Kong, 2008. / Includes bibliographical references (leaves 74-93) Also available in print.

Thesis (M.Sc. (Organic Chemistry)) -- Mahidol University, 1976. / Supported by University Development Commission.