Kim-Hung Lam

A COMPARATIVE INVESTIGATION ON THE BIOSORPTION OF LEAD BY FILAMENTOUS FUNGAL BIOMASS

The removal of lead from aqueous solutions by adsorption on filamentous fungal biomass was studied. Batch biosorption experiments were performed to screen a series of selected fungal strains for effective lead removal at different metal and biomass concentrations. Biosorption of the Pb2+ ions was strongly affected by pH. The fungal biomass exhibited the highest lead adsorption capacity at pH 6. Isotherms for the biosorption of lead on fungal biomass were developed and the equilibrium data fitted well to the Langmuir isotherm model. At pH 6, the maximum lead biosorption capacity of Mucor rouxii estimated with the Langmuir model was 769 mg/g dry biomass, significantly higher than that of most microorganisms. Biomass of Mucor rouxii showed specific selectivity for Pb2+ over other metals ions such as Zn2+, Ni2+ and Cu2+. This fungal strain may be applied to develop potentially cost-effective biosorbent for removing lead from effluents. The technique of scanning electron microscopy coupled with X-ray dispersion analysis shows that Pb2+ has exchanged with K+ and Ca2+ on the cell wall of Mucor rouxii, thereby suggesting ion exchange as one of the dominant mechanisms of metal biosorption for this fungal strain.

Asymmetric Hydrogenation of Quinoxalines with Diphosphinite Ligands: A Practical Synthesis of Enantioenriched, Substituted Tetrahydroquinoxalines†

The 1,2,3,4-tetrahydroquinoxaline ring system is an important structural unit in many bioactive compounds. Optically pure tetrahydroquinoxaline derivatives have shown great potential for pharmaceutical applications. For example, chiral compound A has been pursued as a potent vasopressin V2 receptor antagonists, and optically pure compound B is a promising inhibitor of cholesteryl ester transfer protein. In both cases, the chirality of the compounds was found to play a very important role in the relevant bioactivity of these compounds. The most convenient and straightforward route to chiral tetrahydroquinoxalines is the asymmetric hydrogenation of quinoxalines. Although several kinds of heteroaromatic compounds, such as quinolines, indoles, furans, pyridines, and pyrazines have been successfully hydrogenated with good to excellent enantioselectivities and yields in the presence of chiral transition-metal catalysts, the enantioselective hydrogenation of substituted quinoxaline derivatives has been less extensively studied. In 1987, Murata et al. first reported the rhodium-catalyzed asymmetric hydrogenation of 2-methylquinoxaline with only 3% ee. Later Bianchini et al. enantioselectively hydrogenated 2-methylquinoxaline with an orthomelated dihydride iridium complex to produce the product with up to 90% ee, but the reduction suffered from lower conversions. The performance of [RuCl2(diphosphine)(diamine)] complexes [3d,e] and Ir/PQphos (PQ-phos = (R)-[6,6-(2S,3S-butadioxy)]-(2,2’)-bis(diphenylphosphino)-(1,1’)-biphenyl) was also investigated, but only gave medium to low ee values. Given the importance of chiral tetrahydroquinoxalines and in view of the lack of efficient methods for the preparation of these compounds, the development of a practical and highly efficient catalytic asymmetric synthetic method appeared to be of great importance. Herein we describe the asymmetric hydrogenation of quinoxalines with an easily accessible Ir/diphosphinite catalyst. Good to excellent enantioselectivity (up to 98 % ee), unprecedented high catalytic activity (TOF up to 5620 h ), and productivity (TON up to 18 140) were observed for a wide range of substrates. Recently, the combination of transition metals and chiral phosphinite ligands has led to efficient catalysts for the asymmetric hydrogenation of prochiral olefins. In comparison with diphosphines, diphosphinites offer the advantages of easy preparation and derivatization. Recently, we have demonstrated that the easily accessible chiral diphosphinite ligands derived from (R)-H8-binol (binol = (1,1’-bi-2-naphthyl)) and (R)-1,1-spirobiindane-7,7-diol provided excellent catalytic activity and/or enantioselectivity in the Ir-catalyzed asymmetric hydrogenation of quinolines. Based on our previously optimized reaction conditions, we first investigated the performance of the [{IrCl(cod)}2] (cod = 1,5-cyclooctadiene)/(R)-H8-binapo or the (R)-sdpo/I2 catalyst system in THF for the asymmetric hydrogenation of 2-methylquinoxaline (1 a). To our delight, both catalysts worked efficiently with full conversions and good enantioselectivities (Table 1, entries 1 and 2), and (R)-H8-binapo gave the desired product in somewhat better enantiomeric excess. In sharp contrast to [*] Dr. W. Tang, J. Wang, Dr. B. Fan, Prof. Z. Zhou, Dr. K.-h. Lam, Prof. A. S. C. Chan Department of Applied Biology and Chemical Technology and Open Laboratory of Chirotechnology of the Institute of Molecular Technology for Drug Discovery and Synthesis The Hong Kong Polytechnic University, Hong Kong (China) E-mail: bcachan@polyu.edu.hk

Highly efficient and enantioselective hydrogenation of quinolines and pyridines with Ir-Difluorphos catalyst

The combination of the readily available chiral bisphosphine ligand Difluorphos with [Ir(COD)Cl](2) in THF resulted in a highly efficient catalyst system for asymmetric hydrogenation of quinolines at quite low catalyst loadings (0.05-0.002 mol%), affording the corresponding products with high enantioselectivities (up to 96%), excellent catalytic activities (TOF up to 3510 h(-1)) and productivities (TON up to 43000). The same catalyst was also successfully applied to the asymmetric hydrogenation of trisubstituted pyridines with nearly quantitative yields and up to 98% ee. In these two reactions, the addition of I(2) additive is indispensable; but the amount of I(2) has a different effect on catalytic performance.

A new chiral dipyridylphosphine ligand Xyl-P-Phos and its application in the Ru-catalyzed asymmetric hydrogenation of β-ketoesters

Abstract A new chiral dipyridylphosphine ligand Xyl-P-Phos has been synthesized and the structure of (S)-Xyl-P-Phos oxide has been characterized by single crystal X-ray diffraction. The ruthenium complex of this ligand, Ru(R-Xyl-P-Phos)(C6H6)Cl2, has been found to be a highly active, enantioselective and air-stable catalyst for the asymmetric hydrogenation of β-ketoesters and shows good potential for industrial applications.

Flow pattern and velocity field distribution of cross-flow around four cylinders in a square configuration at a low Reynolds number

Abstract The flow around four cylinders in a square configuration with a spacing ratio of 4 and at a Reynolds number of 200 were investigated using laser-induced fluorescence (LIF) visualization and particle image velocimetry (PIV) for angles of incidence ranging from α=0° to 45° at a 5° interval. Several distinct flow patterns were observed. Dependent on α, the flow was classified into three basic flow regimes. Each regime has its own dominant flow pattern and could lead to different problems. Two distinct flow patterns, which could lead to strong flow-induced vibration, were observed in this experiment. One is the impingement of oncoming vortices on the cylinders directly. The other is the formation of a jet flow between the near wake (or alternatively known as stagnation wake) of the upstream cylinder and downstream cylinder and such a jet flow is most prominent at α=15°. These experimental results can be used to validate numerical simulation methods developed to investigate flows around cylinder arrays.

Synthesis of 8-hydroxyquinoline derivatives as novel antitumor agents

This letter describes the preparation of quinoline derivatives and their cytotoxic potentials toward human carcinoma cell lines. Among the selected compounds, 8-hydroxy-2-quinolinecarbaldehyde (3) showed the best in vitro cytotoxicity against the human cancer cell lines, including MDA231, T-47D, Hs578t, SaoS2, K562, SKHep1 (with a MTS50 range of 12.5-25 μg/mL) and Hep3B (with a MTS50 range of 6.25±0.034 μg/mL). The in vivo antitumor activity of compound 3 on subcutenaous Hep3B hepatocellular carcinoma xenograft in athymic nude mice was then studied. The results showed that the dose of 10 mg/kg/day of compound 3 with intraperitoneal injection for 9 days totally abolished the growth of the xenograft tumor of Hep3B with no histological damage on vital organs as compared with the control. The experimental results suggested that compound 3 has a good potential as an antitumor agent.

Antitumor activity of diethynylfluorene derivatives of gold(I)

A list of diethynylfluorenes and their gold(I) derivatives have been studied for their antitumor activity as a function of their structure-activity relationships. End-capping the fluoren-9-one unit with gold(I) moieties could significantly strengthen the cytotoxic activity in vitro on three human cancer cell lines with induction of reactive oxygen species generation on Hep3B hepatocellular carcinoma cells and exhibit attractive antitumor activity from in vivo nude mice Hep3B xenograft model with limited adverse effects on vital organs including liver and kidney.

In vivo anti-tumour activity of corilagin on Hep3B hepatocellular carcinoma

We have investigated the potential in vivo anti-tumour activity of corilagin using the Hep3B hepatocellular carcinoma cell line and an athymic nude mice xenograft model. The purity of corilagin was confirmed by high performance liquid chromatographic analysis. Corilagin was administrated intraperitoneally for a continuous period of 7 days at a concentration of 15 mg/kg of body weight per day. A significant inhibition of tumour growth was observed when treated mice are compared with control groups. Furthermore, analysis of enzymes markers of liver function, including alanine aminotransferase and asparate aminotransferase, suggested that current therapeutic dosage of corilagin did not exert adverse effect on liver. Our observations support the view that corilagin is considerably effective to retard the in vivo growth of xenografted Hep3B hepatocellular carcinoma.

Air-stable Ir-(P-Phos) complex for highly enantioselective hydrogenation of quinolines and their immobilization in poly(ethylene glycol) dimethyl ether (DMPEG)

An air-stable catalyst system Ir-(P-Phos) catalyst was found to be highly effective in the asymmetric hydrogenation of quinoline derivatives. The catalyst immobilized in DMPEG was efficiently recovered and reused eight times, retaining reactivity and enantioselectivity.

Recent advances in research of natural and synthetic bioactive quinolines

Many natural products that consist of quinoline core are found to be bioactive and the versatility of quinoline and its derivatives have attracted great attention in the field of drug development. As a result, in recent years, many green and sustainable synthetic approaches for the synthesis of structurally diverse quinolines have been developed. This review covers four main aspects, namely bioactive quinoline alkaloids, the biological activity and mechanism of action of quinoline-based compounds as well as various quinoline syntheses.