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61.
Cheong KW Leow TC Rahman RN Basri M Rahman MB Salleh AB;Enzyme Microbial Technology Research Group 《Applied biochemistry and biotechnology》2011,164(3):362-375
A thermostable lipase from Geobacillus zalihae strain T1 was chemically modified using propionaldehyde via reductive alkylation. The targeted alkylation sites were lysines,
in which T1 lipase possessed 11 residues. Far-UV circular dichroism (CD) spectra of both native and alkylated enzyme showed
a similar broad minimum between 208 and 222 nm, thus suggesting a substantial amount of secondary structures in modified enzyme,
as compared with the corresponding native enzyme. The hydrolytic activity of the modified enzymes dropped drastically by nearly
15-fold upon chemical modification, despite both the native and modified form showed distinctive α-helical bands at 208 and
222 nm in CD spectra, leading us to the hypothesis of formation of a molten globule (MG)-like structure. As cooperative unfolding
transitions were observed, the modified lipase was distinguished from the native state, in which the former possessed a denaturation
temperature (T
m) in lower temperature range at 61 °C while the latter at 68 °C. This was further supported by 8-anilino-1-naphthalenesulfonic
acid (ANS) probed fluorescence which indicated higher exposure of hydrophobic residues, consequential of chemical modification.
Based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis, a small number
of lysine residues were confirmed to be alkylated. 相似文献
62.
63.
Shabi Abbas Zaidi Seung Mi Lee Zeid A. AL Othman Abdullah M. AL Majid Won Jo Cheong 《Chromatographia》2011,73(5-6):517-525
Some acidic chiral templates were used to prepare open tubular (OT) molecule imprinted polymer (MIP) capillary columns to explore the effects of molecular structures of templates on chiral recognition capabilities and to verify the feasibility of the general MIP preparation protocol introduced in the previous study. The templates are phenyl carboxylic acids and their derivatives. Optimization was carried out for chiral separation of template enantiomers for each MIP column through varying pH and composition of eluent. It was found that the preparation protocol can be successfully applied for the appropriate templates with functional groups fulfilling the three-points interaction rule. The chiral separation performances were quite satisfactory for MIPs of such templates although they are yet inferior to the separation performances of the MIP columns fabricated with the templates of profen drugs (2-arylpropionic acids with a large substituent on the phenyl ring). Subtle variations of the template molecular structures have been found to be critical to enhance chiral recognition ability of the resultant MIP column. 相似文献
64.
Antioxidant and antityrosinase activities of various extracts from the fruiting bodies of Lentinus lepideus 总被引:1,自引:0,他引:1
Yoon KN Alam N Lee KR Shin PG Cheong JC Yoo YB Lee TS 《Molecules (Basel, Switzerland)》2011,16(3):2334-2347
Lentinus lepideus is an edible mushroom currently available in Korea. The acetone, methanol and hot water extracts were prepared and assayed for their antioxidant and antityrosinase inhibitory activities. The hot water extract showed the strongest β-carotene-linoleic acid inhibition compared to the other extracts. At 8 mg/mL, the methanolic extract showed a high reducing power of 1.21. The acetone and methanol extracts were more effective in scavenging DPPH radicals than the hot water extract. The strongest chelating effect was obtained from the methanolic extract. Xanthine oxidase and tyrosinase inhibitory activities of the acetonic, methanol and hot water extracts increased with increasing concentration. Gallic acid, chlorogenic acid, vanillin, naringin, naringenin, formononetin, and biochanin-A were detected in the acetonitrile and hydrochloric acid (5:1) solvent extract. This study suggests that fruiting bodies of L. lepideus can potentially be used as a readily accessible source of natural antioxidants. 相似文献
65.
Shim YN Lee JK Im JK Mukherjee DK Nguyen DQ Cheong M Kim HS 《Physical chemistry chemical physics : PCCP》2011,13(13):6197-6204
The catalytic roles of ionic liquids (ILs) in the syntheses of 1,3-disubstituted ureas from the carboxylation of amines by CO(2) were experimentally and theoretically investigated. The carboxylation reaction of n-butylamine was greatly facilitated by the presence of an IL and the catalytic activity of the IL was strongly affected by the nucleophilicity of the anion. Computational study on the mechanistic aspects of the carboxylation with methylamine with or without the presence of an IL, 1-ethyl-3-methylimidazolium chloride, implies that the activation energies of the transition states and the intermediate ionic species could be lowered significantly through the multi-interactions of the carbonyl group of CO(2) with both cations and anions of the ILs. 相似文献
66.
H.W. Choi C. Liu M.G. Cheong J. Zhang S.J. Chua 《Applied Physics A: Materials Science & Processing》2005,80(2):405-407
The effect of plasma exposure to n-type GaN surfaces has been examined. Etch pits are formed as a result of preferential sputtering at the sites of threading dislocations. Dark spots which are visible before plasma exposure can be attributed to screw dislocations, while those that emerge after plasma exposure are edge dislocations. The optimum condition for revealing defects clearly is derived, and has been adopted for the study of dislocations in a series of GaN epilayers grown under different conditions. A distinct trend in the dislocation density can be observed as the dopant concentration of the film varies. PACS 61.72.Ff; 68.37.Tj 相似文献
67.
F.C. Cheong C.H. Sow A.T.S. Wee P. Shao A.A. Bettiol J.A. van Kan F. Watt 《Applied physics. B, Lasers and optics》2006,83(1):121-125
We report the transport, funnelling and dynamic sorting of colloidal microspheres in an aqueous suspension using line optical
tweezers with asymmetrical intensity profiles. The line tweezers readily trapped and propelled the microspheres along the
length of the line tweezers. Using this simple technique, transporting and funnelling of microspheres within a microscopic
region were demonstrated. To illustrate the dynamic particle-sorting capability of the line tweezers, a binary colloidal system
comprising of microspheres with diameters of 1.1 μm and 3.2 μm were driven past the line tweezers by electrophoresis. As the
optical trapping force is dependent on the size of the microspheres, the line tweezers was able to change the path of the
larger spheres while exerting little influence on the smaller spheres thus sorting the two types of microspheres. At optimized
laser power and flow rate of microspheres, sorting efficiency greater than 90% has been achieved.
PACS 42.15.Eq; 87.80.Cc; 87.80.Fe; 82.70.Dd 相似文献
68.
Boris Aronov Mark de Berg Otfried Cheong Joachim Gudmundsson Herman Haverkort Michiel Smid Antoine Vigneron 《Computational Geometry》2008,40(3):207-219
Given a set S of n points in , and an integer k such that 0k<n, we show that a geometric graph with vertex set S, at most n−1+k edges, maximum degree five, and dilation O(n/(k+1)) can be computed in time O(nlogn). For any k, we also construct planar n-point sets for which any geometric graph with n−1+k edges has dilation Ω(n/(k+1)); a slightly weaker statement holds if the points of S are required to be in convex position. 相似文献
69.
Irradiation with approximately 10 keV x rays or medium-energy electrons destroys long-range order of Ir spin dimers in CuIr2S4 while preserving the dimers locally. We find that as the order is destroyed, a new type of incommensurate structural correlations appears. This represents an intriguing example of order from disorder phenomenon, in which a previously unknown incommensurate order appears in the radiation-induced disordered state. These results suggest that two competing instabilities, one of which can be suppressed by radiation, are present in the system. Otherwise unrealized structural or electronic states can, therefore, be revealed in correlated systems by x-ray or electron irradiation. 相似文献
70.
Microchip-based one step DNA extraction and real-time PCR in one chamber for rapid pathogen identification 总被引:1,自引:0,他引:1
Optimal detection of a pathogen present in biological samples depends on the ability to extract DNA molecules rapidly and efficiently. In this paper, we report a novel method for efficient DNA extraction and subsequent real-time detection in a single microchip by combining laser irradiation and magnetic beads. By using a 808 nm laser and carboxyl-terminated magnetic beads, we demonstrate that a single pulse of 40 seconds lysed pathogens including E. coli and Gram-positive bacterial cells as well as the hepatitis B virus mixed with human serum. We further demonstrate that the real-time pathogen detection was performed with pre-mixed PCR reagents in a real-time PCR machine using the same microchip, after laser irradiation in a hand-held device equipped with a small laser diode. These results suggest that the new sample preparation method is well suited to be integrated into lab-on-a-chip application of the pathogen detection system. 相似文献