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71.
[reaction: see text] Ester-containing nitrones, including 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide 5, have been reported to be robust spin traps for superoxide (O2*-). Using a chiral column, we have been able to isolate the two enantiomers of nitrone 5. With enantiomerically pure nitrone 5a and 5b we explored whether one of these isomers was solely responsible for the EPR spectrum of aminoxyl 6. Data obtained demonstrate that the spin trapping of O2*- by nitrone 5a and nitrone 5b affords the identical EPR spectra and lifetimes in homogeneous aqueous solution and exhibits the same ratio of cis and trans isomers. Quantum chemical modeling in vacuo also finds no difference, aside from the expected optical activity, arising from the difference in stereochemistry. 相似文献
72.
We report the separation of polycyclic aromatic hydrocarbons (PAHs) using 0.1% poly(ethylene oxide) (PEO) in micellar electrokinetic chromatography (MEKC). In the presence of PEO, adsorption of PAHs on the capillary wall was reduced, leading to better resolution and reproducibility. Effects of tetrapentylammonium iodide (TPAI), dextran sulfate (DS), methanol, and sodium lauryl sulfate (SDS) on the separation of PAHs were elucidated. In terms of resolution and speed, DS, compared to TPAI, is a better additive for separation of PAHs. When using 0.1% PEO solution containing 45% methanol, 50 mM SDS, and 0.02% DS, separation of 10 PAHs containing 2 to 5 benzene rings was accomplished in less than 12 min at 15 kV in a commercial CE system. The method has also been tested for separating seven PAHs with high quantum yields when excited at 325 nm using a He-Cd laser. Unfortunately, separation of the seven PAHs was not achieved and sensitivity diminished under the same conditions. To optimize sensitivity, resolution and speed, a stepwise technique in MEKC has been proposed. The seven PAHs were resolved in 35 min at 15 kV when separation was performed in 0.1% PEO solution containing 35 mM SDS, 40% methanol and 0.02% DS for 2 min, and subsequently in 0.1% PEO solution containing 20 mM SDS, 50% methanol, and 0.02% DS. 相似文献
73.
Synthesis and photochemistry of several title compounds 1-3 containing multiple chromophoric systems are described. The Diels-Alder reactions of 2,6,6-trimethylcyclohexa-2,4-dienone (5) with acetylenes 6a-d provided the adducts 7a-d, which upon hydrolysis furnished the desired bicyclo[2.2.2]octenediones 1a-d. Oximes 2a-d were prepared from diones 1a-d by treatment with hydroxylamine hydrochloride in pyridine. 5-Methylenebicyclo[2.2.2]oct-7-en-2-ones 3a-d were obtained via chemoselective Wittig reaction of the corresponding diones 1a-d. Bicyclo[2.2.2]octenediones 1a-c underwent chemoselective oxa-di-pi-methane rearrangement under sensitized conditions and suffered formal ketene extrusion upon direct irradiation. Direct irradiation of 1d afforded 11d via formal ketene extrusion but under sensitization it remained unchanged. Oximes 2a-d suffered ketene extrusion upon direct irradiation and E/Z isomerization under sensitized conditions. On the other hand, 5-methylenebicyclo[2.2.2]oct-7-en-2-ones 3a-d generally underwent 1,3-acyl shift. The plausible courses of all these photochemical processes are discussed. 相似文献
74.
Chun-Hao Su Dr. Meng-Jung Tsai Wei-Kai Wang Yi-Yun Li Prof. Dr. Jing-Yun Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(21):6529-6537
Through a dual-ligand synthetic approach, five isoreticular primitive cubic (pcu)-type pillared-layer metal–organic frameworks (MOFs), [Zn2(dicarboxylate)2(NI-bpy-44)] ⋅ x DMF ⋅ y H2O, in which dicarboxylate=1,4-bdc ( 1 ), Br-1,4-bdc ( 2 ), NH2-1,4-bdc ( 3 ), 2,6-ndc ( 4 ), and bpdc ( 5 ), have been engineered. MOFs 1 – 5 feature twofold degrees of interpenetration and have open pores of 27.0, 33.6, 36.8, 52.5, and 62.1 %, respectively. Nitrogen adsorption isotherms of activated MOFs 1′ – 5′ at 77 K all displayed type I adsorption behavior, suggesting their microporous nature. Although 1′ and 3′ – 5′ exhibited type I adsorption isotherms of CO2 at 195 K, MOF 2′ showed a two-step gate-opening sorption isotherm of CO2. Furthermore, MOF 3′ also had a significant influence of amine functions on CO2 uptake at high temperature due to the CO2–framework interactions. MOFs 1 – 5 revealed solvent-dependent fluorescence properties; their strong blue-light emissions in aqueous suspensions were efficiently quenched by trace amounts of nitrobenzene (NB), with limits of detection of 4.54, 5.73, 1.88, 2.30, and 2.26 μm , respectively, and Stern–Volmer quenching constants (Ksv) of 2.93×103, 1.79×103, 3.78×103, 4.04×103, and 3.21×103 m −1, respectively. Of particular note, the NB-included framework, NB@ 3 , provided direct evidence of the binding sites, which showed strong host–guest π–π and hydrogen-bonding interactions beneficial for donor–acceptor electron transfer and resulting in fluorescence quenching. 相似文献
75.
Tsai Chia-Wei Lin Jason Chiu Lung Yang Chun-Wei 《International Journal of Theoretical Physics》2021,60(9):3599-3608
International Journal of Theoretical Physics - Ma et al. [Int. J. Theor. Phys. (2021): 1328–1338] proposed a multi-party quantum key distribution (MQKD) protocol using Bell states, in which... 相似文献
76.
77.
Chuan-Pin Lee Ching-Yuan Liu Ming-Chee Wu Chun-Hua Pan Tsuey-Lin Tsai Hwa-Jou Wei Lee-Chung Men 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(2):1119-1125
The sorption capacity of cesium (Cs) and selenium (Se) in crushed mudrock was demonstrated in this study through a 2-site Langmuir model. To employ such a numerical analysis, batch tests were applied in this study in synthetic seawater and groundwater with sorption/desorption kinetic experiments (time-dependent) and different concentrations (10?2–10?7 M). The 2-site sorption models, which correspond to two rate constants (λ 1 and λ 2), might be more adequate than 1-site sorption models in characterizing Cs and Se sorption/desorption according to the least square errors between the numerical analysis and the results of the batch tests. The fitting results showed that a 2-site Langmuir model is capable of appropriately describing Cs and Se sorption in mudrock. Consequently, the sorption capacity was calculated at about 0.06 mol/kg for Cs and at 0.015 mol/kg for Se. 相似文献
78.
Yung-Sen Lin Tsung-Hsien Tsai Shih-Chan Hung Shih-Wei Tien 《Journal of Solid State Electrochemistry》2013,17(4):1077-1088
Enhanced lithium electrochromic performances of mixed organo-tungsten oxide (W x O y C z )/organo-molybdenum oxide (Mo x O y C z ) films by a rapid codeposition onto 40 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates at a short exposed duration of 23 s using an atmospheric pressure plasma jet (APPJ) at various mixed concentrations of hexacarbonyl precursors [W(CO)6 and Mo(CO)6] are investigated. The flexible organo-tungsten–molybdenum oxide (WMo x O y C z ) films demonstrated noteworthy electrochromic performance for 200 cycles of reversible Li+ ion intercalation and deintercalation in a 1 M LiClO4–propylene carbonate electrolyte by the switching measurements of potential sweep from ?1 to 1 V at a scan rate of 50 mV/s and the potential step at ?1 and 1 V, even after being bent 360o around a 2.5-cm diameter rod for 1,000 cycles. The optical modulation (ΔT) of 61.3 % for MoO y C z films at a wavelength of 795.6 nm was significantly improved up to 72.5 % for WMo x O y C z films cosynthesized with an APPJ. 相似文献
79.
80.
The present study used differential scanning calorimetry, thermogravimetric analysis, and UV spectrometry to examine: i) the encapsulation of an organic UV filter 1-(4-methoxyphenyl)-3-(4- tert-butylphenyl)propane-1,3-dione (avobenzone) within modified dextrin and ii) the characteristics of these inclusion complexes (MDA). The properties of avobenzone emulsions with and without encapsulation in modified dextrin, the in vitro UV protection factor, dissolution and release, and the skin penetrability of avobenzone were also examined. The presence of inclusion complexes significantly decreased the tendency of the UV filter to penetrate the skin. In addition, such inclusion complexes should effectively prevent skin damage from radiation extending from the UVA to the UVC. 相似文献