Browsing by Author "Chen, HF"

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Isomers of OCS2: IR absorption spectra of OSCS and O(CS2) in solid ar
(2004-12-22)
Lo, WJ
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Chen, HF
;
Chou, PH
;
Lee, YP
;
應用化學系
Irradiation of an Ar matrix sample containing O-3 and CS2 with a KrF excimer laser at 248 nm yielded new lines at 1402.1 (1404.7), 1056.2 (1052.7), and 622.3 (620.5) cm-1; numbers in parentheses correspond to species in a minor matrix site. Secondary photolysis at 308 nm diminished these lines and produced mainly OCS and SO2. Annealing of this matrix to 30 K yielded a second set of new lines at 1824.7 and 617.8 cm-1. The first set of lines are assigned to C=S stretching, O-S stretching, and S-C stretching modes of carbon disulfide S-oxide, OSCS; and the second set of lines are assigned to C=O stretching and OCS bending modes of dithiiranone, O(CS2), respectively, based on results of S-34- and O-18-isotopic experiments and quantum-chemical calculations. These calculations using density-functional theory (B3LYP/aug-cc-pVTZ) predict four stable isomers of OCS2: O(CS2), SSCO, OSCS, and SOCS, listed in order of increasing energy. According to calculations, O(CS2) has a cyclic CS2 moiety and is the most stable isomer of OCS2. OSCS is planar, with bond angles angleOSCcongruent to111.9degrees and angleSCScongruent to177.3degrees; it is less stable than SSCO and O(CS2) by similar to102 and 154 kJ mol-1, respectively, and more stable than SOCS by similar to26 kJ mol-1. Calculated vibrational wave numbers, IR intensities, S-34- and O-18-isotopic shifts for OSCS and O(CS2) fit satisfactorily with experimental results. (C) 2004 American Institute of Physics.
Molecular elimination in photolysis of o- and p-fluorotoluene at 193 nm: Internal energy of HF determined with time-resolved Fourier transform spectroscopy
(2005-12-08)
Yang, SK
;
Liu, SY
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Chen, HF
;
Lee, YP
;
應用化學系
Following the photodissociation of o-fluorotoluene [o-C6H4(CH3)F] at 193 nm, rotationally resolved emission spectra of HF(1 <= v <= 4) in the spectral region of 2800-4000 cm(-1) are detected with a step-scan Fourier transform spectrometer. HF(v <= 4) shows nearly Boltzmann-type rotational distributions corresponding to a temperature similar to 1080 K; a short extrapolation from data in the period of 0.5-4.5 mu s leads to a nascent rotational temperature of 1130 +/- 100 K with an average rotational energy of 9 +/- 2 kJ mol(-1). The observed vibrational distribution of (v=1):(v=2):(v=3)=67.6: 23.2: 9.2 corresponds to a vibrational temperature of 5330 +/- 270 K. An average vibrational energy of 25 +/-(12)(3) kJ mol(-1) is derived based on the observed population of HF(1 <= v <= 3) and estimates of the population of HF (v=0 and 4) by extrapolation. Experiments performed on p-fluorotoluene [p-C6H4(CH3)F] yielded similar results with an average rotational energy of 9 +/- 2 kJ mol(-1) and vibrational energy of 26 +/-(12)(3) kJ mol(-1) for HF. The observed distributions of internal energy of HF in both cases are consistent with that expected for four-center elimination. A modified impulse model taking into account geometries and displacement vectors of transition states during bond breaking predicts satisfactorily the rotational excitation of HF. An observed vibrational energy of HF produced from fluorotoluene slightly smaller than that from fluorobenzene might indicate the involvement of seven-membered-ring isomers upon photolysis. (c) American Institute of Physics.
Mutations on CaENO1 in Candida albicans inhibit cell growth in the presence of glucose
(2006-05-01)
Yang, YL
;
Chen, HF
;
Kuo, TJ
;
Lin, CY
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生物科技學系
Enolase ( 2- phospho- (D)- glycerate hydrolase) is an enzymatic component of the glycolytic pathway and is conserved through evolution. The TR- CaENO1/ Caeno1 stain, of which the expression of CaENO1 is under control of the tetracycline- regulatable ( TR) expression system, is utilized for elucidating the functions of CaENO1 in Candida albicans. As expected, there was no detectable CaENO1 mRNA when the TR- CaENO1/ Caeno1 cells grew on media containing doxycycline repressing the expression of TR- CaENO1. The TR- CaENO1/ Caeno1 cells were arrested in media containing doxycycline in the presence of glucose but not in non- fermentable carbon sources, such as glycerol. Furthermore, the TR- CaENO1/ Caeno1 cells were also arrested in media containing 4% serum. In this study, we have showed that CaENO1 is required for the cell growth of C. albicans in the presence of glucose. Our findings may help us to design new and more effective antifungal agents for preventing and treating bloodstream fungal infections by blocking the function( s) of enolases.