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991.
Young Seok Kim Yong Sun Won Nicol Omenetto Timothy J. Anderson 《Journal of Raman spectroscopy : JRS》2010,41(1):106-112
Computational chemistry has been widely used to understand homogeneous reactions and to support spectroscopy analysis. Thus, it is a useful tool to understand gas‐phase dynamics of metal organic chemical vapor deposition (MOCVD). In this study, we report that the basis set selection possibly results in unequivocal peak assignment in Raman spectroscopy, especially when an effective core potential (ECP) is employed. The basis set selection for the decompositionof dimethylcadmium (DMCd), for example, was examined using five different ECPs (i.e. CRENBS, CRENBL, SDD, LanL2DZ and SBKJC for Cd atom combined with STO‐3G, 3‐21G, 6‐31G(d), 6‐311G(d) and 6‐311++G(2d,2p) for C and H atoms). The analyses demonstrated that the SDD/STO‐3G/3‐21G combination for Cd/C/H atoms best reproduce the experimentally reported Cd C vibrational stretching modes of Cd(CH3)2 (DMCd) and •CdCH3 (MMCd). Although the SDD/STO‐3G/3‐21G combination consists of simple and basic basis sets, we found that a good potential balance between metal (Cd) and auxiliary (C) atoms is essential to estimate frequencies suitable for spectroscopy analysis computationally. The same combination of basis set was then used to examine other possible reaction steps, and Raman experiments successfully detected one of the suggested intermediates of (CdCH3)2. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
992.
UV resonance Raman spectra of the antimicrobial peptide (AMP) Anoplin (L ‐Anoplin‐NH2) and two of its derivatives (enantiomer D ‐Anoplin‐NH2 and C‐terminus deamidated L ‐Anoplin‐OH) were measured in aqueous buffer solution and in membrane‐mimetic environments including 2,2,2‐trifluoro ethanol (TFE), zwitterionic lipid dipalmitoylglycerophosphocholine (DPPC) and anionic lipid dipalmitoylglycerophosphoglycerol (DPPG) vesicle solutions. All three peptides were found to adopt random‐coil/β turn‐like conformation in aqueous solution over the temperature range of 1–60 °C. The conformation was found to become more α‐helical in membrane‐mimetic solutions such as TFE and DPPG but not in DPPC for all Anoplin derivatives. The data demonstrate that Anoplin preferentially binds to the anionic over the zwitterionic model cell membranes. Results also showed that deamidation does not change the conformation of L ‐Ano‐NH2 very significantly, but does alter membrane rupturing and antimicrobial activities thus confirming that it is the physicochemical properties rather than the peptide conformation that define the mechanism of AMP action. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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996.
Redundancy or standby is a technique that has been widely applied to improving system reliability and availability in system design. In this paper, a general method for modelling standby system is proposed and system performance measures are derived. It is shown that the proposed general standby system includes the cases of cold, hot and warm standby systems with units of exponential distribution, which were studied in the literature, as special cases. An optimal allocation problem for a standby system is also discussed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
997.
Jin Young Choi Soo Jung Lee Sung Joong Lee Semin Park Jung Han Lee Jae‐Han Shim A. M. Abd El‐Aty Jong‐Sung Jin Euh‐Duck Jeong Won Sup Lee Sung Chul Shin 《Journal of separation science》2010,33(9):1192-1197
The skin of Vitis coignetiae Pulliat (meoru) grown wild in the Republic of Korea was analyzed for anthocyanins via HPLC coupled to ESI‐MS/MS in positive ion mode. Chromatographic separation was conducted via RP HPLC using a C18 column, with a 50‐min gradient from 0 to 80% methanol in water containing 0.5% formic acid. A total of 18 anthocyanins were identified. Among them, nine compounds were newly determined by comparing the retention time (tR) and mass fragmentation patterns with those of the previously reported anthocyanins for other grape varieties: malvidin hexose, peonidin 3‐galactoside, malvidin 3‐galactoside, cyanidin, petunidin, petunidin 3‐(6″‐coumaroyl)‐5‐diglucoside, peonidin, malvidin, and malvidin 3‐(6″‐coumaroyl)‐5‐diglucoside. The antioxidant activity of the V. coignetiae Pulliat anthocyanins was determined via 2,2‐diphenyl‐2‐picrylhydrazyl radical scavenging and 2,2′‐azinobis‐(3‐ethylbenzothiazoline‐6‐sulfonic acid) radical cation assays in a range of concentration from 25 to 500 mg/L. The capacity increased with concentration. The IC50 values, defined as the concentration of sample required to scavenge 50% of free radicals, were calculated as follows: 189.63±11.31 mg/L and 141.29±6.70 mg/L for 2,2‐diphenyl‐2‐picrylhydrazyl and 2,2′‐azinobis‐(3‐ethylbenzothiazoline‐6‐sulfonic acid) radical cation, respectively. The antioxidant activity of the V. coignetiae Pulliat anthocyanins is substantially higher than that of ascorbic acid and is similar to the effects of the extracts obtained from other grape varieties. 相似文献
998.
Hyung Ju Kim Yong Seok Kim Min Ho Seo Sung Mook Choi Joungmo Cho George W. Huber Won Bae Kim 《Electrochemistry communications》2010,12(1):32-35
Electrochemical reduction of oxygen is studied over a novel nanowire network catalyst made of highly-dispersed Pt nanoparticles into electrospun Pt nanowire network architecture, which shows an excellent mass activity increase by 50% or higher per equal Pt mass than the conventional cathode electrocatalysts of Pt/C in polymer electrolyte membrane fuel cells. 相似文献
999.
Won Seok Lyoo Jin Woo Kwak Jeong Hyun Yeum Byung Chul Ji Chul Joo Lee Seok Kyun Noh 《Journal of polymer science. Part A, Polymer chemistry》2005,43(4):789-800
The particle size distributions of poly(vinyl pivalate) (PVPi) produced from low‐temperature suspension polymerization of vinyl pivalate (VPi) with 2,2′‐azobis(4‐methoxy‐2,4‐dimethylvaleronitrile) (AMDMVN) as an initiator have been studied. By controlling various synthesis parameters, near‐monodisperse PVPi microspheres from 100 to 400 μm were obtained that are expected to be precursors of near‐monodisperse syndiotactic poly(vinyl alcohol) (PVA) microspheres for biomedical embolic applications. The mean particle diameter follows the relationship: the volume average diameter, Dvad ∝ Y0.26[VPi]0.52[AMDMVN]?0.25[PVA]0.40T?8.35Rpm?0.67, where Y, [VPi], [AMDMVN], [PVA], T, and Rpm are the fractional conversion, concentrations of VPi, AMDMVN, and suspending agent, polymerization temperature, and agitation speed during the polymerization of VPi, respectively. The polydispersity of the particle size distribution of PVPi decreased with decreasing conversion, [AMDMVN], T, and Rpm and with increasing [VPi]. In the case of [PVA], optimization of the suspension stability led to a narrow particle size distribution. Ultrahigh‐molecular‐weights PVPi and PVA (number‐average degrees of polymerization of PVPi (25,000–32,000) and PVA (14,000–17,500), of high syndiotactic diad content (63%), and of high ultimate conversion of VPi into PVPi (85–95%) were obtained by suspension polymerization at 10 °C, followed by saponification. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 789–800, 2005 相似文献
1000.
Lattice dynamics in bis-(n-C16H37NH3)2SnCl6, where the hydrocarbon part is analogous to lipid membrane, was investigated by means of 200 MHz 1H nuclear magnetic resonance. As a result, critical fluctuations and molecular dynamics associated with the phase transitions, an order-disorder and a conformational phase transition, were distinguished in a wide temperature range. The dynamical origin of the critical fluctuations, observed in the long-chain compounds but not in the short-chain compounds, by the laboratory frame spin-lattice relaxation measurements, is revealed and discussed in this work. 相似文献