http://hdl.handle.net/10397/226 Search the Channel search http://repository.lib.polyu.edu.hk/jspui/simple-search http://hdl.handle.net/10397/5668 Title: Transition metal-catalyzed cyanation and isocyanation of aryl halides and sulfonates<br/><br/>Authors: Yeung, Pui-yee<br/><br/>Abstract: The mildest cyanation has been developed for aryl halides and sulfonates with environmental friendly cyanating source: K₄[Fe(CN)₆]3H₂O. In the presence of highly effective Pd/CMPhos catalyst, cyanation of aryl chlorides proceeds at 70 °C in general, which is the mildest reaction temperature achieved so far for this process. Moreover, sterically hindered non-activated ortho-ortho-disubstituted electrophile was also a feasible coupling partner in cyanation. In addition, palladium-catalyzed cyanation of aryl bromides was also achieved general application of aryl halides in cyanation. The reactions were completed at 50°C under mixed solvents (water/MeCN = 1:1). This result is the mildest temperature published so far for palladium-catalyzed aryl bromides cyanation. In order to further explore cyanation, the coupling of aryl mesylates was investigated. Interestingly, the use of water as the solvent or a co-solvent was found to be essential. Moreover, this system was also applicable to the cyanation of other aryl and alkenyl tosylates. The one-pot cyanationamination sequence demonstrated the suitability of the cyanation of aryl chlorides and tosylates for the introduction of a nitrile group and manipulation of a further functional group in a synthetic pathway without isolation of the initial nitrile-substituted intermediates. These palladium catalyst systems tolerated common functional-groups: nitriles, esters, ketos, aldehydes, free amines, and heterocyclic groups are found compatible. Lastly, a palladium-catalyzed decarboxylative coupling of potassium cyanoacetate with aryl bromides and chlorides was also described. The reaction conditions featured the absence of additional strong inorganic bases and provided ester functional group tolerance. With Pd(dba)₂ and XPhos ligand as the catalyst system, α-diaryl nitriles could be obtained in good yields.<br/><br/>Description: xviii, 368 p. : ill. ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577M ABCT 2012 Yeung http://hdl.handle.net/10397/5667 Title: Characterization of the estrogenic effects of ginsenoside Rg1 : mechanism involved in achieving tissue selectivity<br/><br/>Authors: Gao, Quangui<br/><br/>Abstract: Our previous study demonstrated that ginsenoside Rg1 was a unique class of phytoestrogens which activated estrogen-like activities without direct interaction with the estrogen receptor (ER). It could initiate activation of the estrogen response element (ERE) via phosphorylation of MEK1/2 and ERα in MCF-7 cells. The present study aims to investigate if Rg1 could exert tissue-selective estrogenic effects in ER-positive target tissues and the molecular mechanism involved in its tissue-selective estrogenic effects. The short-term and long-term estrogenic effects of Rg1 were investigated in 21-day-old immature female CD-1 mice and 6-month-old ovariectomized C57BL/6J mice, respectively. The signal transduction pathways that mediate the estrogenic actions of Rg1 were investigated in MCF-7 cells and rat osteoblastic UMR106 cells in comparison to that of 17β-estradiol and estren which was a novel pathway-selective ER ligand. Additionally, MCF-7 cells and SKBR-3 cells were used to evaluate the role of GPR30 in mediating the estrogenic actions of Rg1.; Our results demonstrated that the estrogenic actions of Rg1 were distinct from those of 17β-estradiol and its effects were tissue selective. The potent estrogenic effect of Rg1 was only observed in mammary gland in immature female CD-1 mice. Chronic administration of Rg1 did not result in bone protective effects and unwanted simulation of reproductive tissues in OVX mice model in a way that was distinct from 17β-estradiol which exerted bone protective effects and also the stimulatory effects in uterus. However, Rg1 exerted potential anti-apoptotic effects on cardiovascular tissues and estrogenic effects on brain tissues. In addition, we demonstrated that Rg1, but not estren, failed to exert stimulatory effects in UMR106 cells with expressed lower level of ER, suggesting that the estrogenic effects of Rg1 in bone may require higher abundance of ER. For the molecular mechanisms study, differential signaling pathways were involved in mediating the estrogenic actions of Rg1 in MCF-7 cells in comparison to 17β-estradiol and estren. 17β-estradiol decreased ERα protein expression in MCF-7 cells, but not Rg1 and estren. 17β-estradiol increased ERα Ser 118 phosphorylation both in the cytoplasm and nucleus, especially in the nucleus. Rg1 increased ERα Ser 118 phosphorylation pricipally in the cytoplasm. Estren increased ERα Ser 118 phosphorylation pricipally in the nucleus. For the estrogen-realted pS2 gene expression, both 17β-estradiol and Rg1 increased pS2 mRNA expression in MCF-7 cells, while estren decreased pS2 mRNA expression. Additionally, both 17β-estradiol and Rg1 induced the recruitment of co-activator SRC-1 to ERE-containing pS2 promoter, but not estren. Furthermore, we are the first to report the possible involvement of GPR30 pathway on the activation of MEK1/2 by Rg1 in MCF-7 cells. In conclusion, the estrogenic effects of Rg1 might be tissue selective. The rapid ER-dependent signaling pathway was involved in the tissue-selective estrogenic effects of Rg1. Differential ER-dependent signaling pathways were involved in the estrogenic effects of 17β-estradiol, Rg1 and estren in MCF-7 cells. Additionally, GPR30 pathway was involved in mediating the estrogenic actions of Rg1. The present study provides new insights to understand the molecular action of ginsenoside Rg1 and its potential application for management of postmenopausal symptoms.<br/><br/>Description: xxxi, 288 p. : ill. (some col.) ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577P ABCT 2012 Gao http://hdl.handle.net/10397/5486 Title: Proteome changes in the somatosensory cortex of rats upon chronic exposure to low-dose methyl-mercury<br/><br/>Authors: Kong, Hang Kin<br/><br/>Abstract: Acute intake of high dose of MeHg through seafood consumption can cause severe neurotoxicity, including numbness of skin, loss of physical coordination, difficulty in speech, narrowing of the visual field and death. Thus, the possible harmful effects of chronic intake of low dose of MeHg from contaminated seafood became a public concern. However, the possible harmful effect is unknown. This current study was aimed to investigate the possible harmful effects using different proteomic techniques in a rat model. Results of this study inferred that the chronic exposure to low dose of MeHg causes the down-regulations of large number of proteins, which are involved in glycolysis, citrate cycle, Adenosine-5'-triphosphate (ATP) production, protein synthesis, cytoskeletal formation and synaptic transmission in the somatosensory cortex. Changes observed in the proteome are similar to the changes observed in the aging process, and some neurodegenerative diseases. Moreover, the decrease in calcium, pyruvate and ATP level are suspected to be the cause of the changes in the proteome after the chronic exposure. Decreased expression of these proteins invariably led to accelerate aging process and increase the risk of having neurodegenerative disease.<br/><br/>Description: xxiv, 377 p. : col. ill. ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577P ABCT 2012 Kong http://hdl.handle.net/10397/5485 Title: Development of a biosensing system from chloramphenicol acetyltransferase<br/><br/>Authors: Chow, Ka Yan<br/><br/>Abstract: Chloramphenicol is a low-cost and effective antimicrobial agent that binds to the bacterial ribosome and interferes with protein synthesis. It is commonly used in clinical treatments and veterinary practices. However, because of its harmful side effects such as bone marrow depression, the use of chloramphenicol in food production has been banned in many countries. Nevertheless, residual chloramphenicol is still found in some food products, such as in aqua organisms and honey in some countries. As a result, it is essential to develop rapid and sensitive methods for detecting and screening of chloramphenicol residues in food samples. In this project, we aimed to construct a fluorescent biosensor for chloramphenicol detection based on the enzyme chloramphenicol acetyltransferase (CAT). In the construction of chloramphenicol biosensor, a series of modified chloramphenicol were synthesized by connecting chloramphenicol base to fluorescein-5-isothiocyanate (FITC) through a short linker. The products were named as FITC-l-CM where l (l = 4, 5, 6, or 7) is the number of carbon atom present in the linker. In addition, the CAT gene was cloned and three amino acid residues of the enzyme (V28, F138 and E140) were mutated to tryptophan. These three sites were selected because they are close to the active site which can probably interact with the bound chloramphenicol. These two components, FITC-l-CM and CAT mutants were used together for chloramphenicol detection and determination.; Spectrophotometric assays indicated that chloramphenicol and FITC-l-CM can bind to the active site of those CAT mutants. Fluorescence measurements showed that only mutants V28W, V28W/F138W, V28W/E140W and V28W/F138W/E140W can quench FITC-l-CM. Addition of chloramphenicol can subsequently restore the fluorescence intensity of the quenched FITC-l-CM. The fluorescence change is attributed to the quenching effect exerted by the tryptophan residues on CAT mutants and competitive binding with chloramphenicol. When FITC-l-CM binds to the active site of CAT, the fluorophore interacts with the nearby tryptophan residues provided that the linker is of appropriate chain length. Since tryptophan is an effective quencher of the fluorophore, the bound FITC-l-CM is quenched through photo-induced electron transfer (PET). When chloramphenicol is added, it competes for the binding site with FITC-l-CM. Once FITC-l-CM is displaced from the active site, it is freed from the quenching effect of tryptophan. As a result, the fluorescence intensity increases again. Among different combinations of FITC-l-CM/CAT mutant, FITC-5-CM with the V28W mutant and FITC-6-CM with the V28W/E140W mutant exhibited the strongest change in fluorescence signals and therefore they were selected as the best candidates for biosensor fabrication. The fluorescence intensity of FITC-5-CM decreased about 40% after the addition of the V28W mutant and increased about 60% after addition of chloramphenicol while those of FITC-6-CM with the V28W/E140W mutant are about 60% and 70% respectively. For both FITC-5-CM and FITC-6-CM, the fluorescence intensities are mostly restored to that before quenching. The detection limits of chloramphenicol for FITC-5-CM with the V28W mutant and the FITC-6-CM with the V28W/E140W mutant are 0.1μM and 1μM respectively. Our results demonstrated the applicability of mutated CAT and fluorophore-linked chloramphenicol as a biosensing system for chloramphenicol determination. It is fast, simple and specific, though the sensitivity needs to be further improved before its application to real samples.<br/><br/>Description: xiii, 193 leaves : ill. (some col.) ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577M ABCT 2012 Chow