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131.
In this work, we present a complete study on He I photoelectron spectroscopy (PES) for the fluorocarbonyl mono-, di-, and trisulfur compounds FC(O)SCl, FC(O)SSCH(3), and FC(O)SSSC(O)F. After optimizations of the structure for stable conformers at different levels of theory, a complete theoretical study involving the calculation of the ionization energies using orbital valence Green's functional (OVGF) was performed. Calculations of radical-cationic forms were carried out in order to compare their properties with those of the neutral molecules. The first IP values are 10.7, 9.0, and 10.5 eV for FC(O)SCl, FC(O)SSCH(3), and FC(O)SSSC(O)F, respectively. The groups bonded to the S atom mainly influence the ionizations originating from the sulfur lone pairs. A wide electronic delocalization in the FC(O)S moiety can be deduced from experimental and theoretical results, which leads to a strong energetic stabilization of the n' '(S) (sulfur lone pair pi orbital). Other conclusions relate to effects on the substituents attached to the S atom and the importance of the molecular planarity in the orbital stabilization of the FC(O)S moiety for the neutral molecules. It is worthwhile mentioning that FC(O)SCl retains its planar structure after ionization, but drastic changes occur in the geometry of both FC(O)SSCH(3) and FC(O)SSSC(O)F. The FC(O)SSCH(3) molecule adopts a heavy atom planar structure after ionization. The FC(O)SSS moiety becomes a planar form after the ionization of the FC(O)SSSC(O)F molecule, whereas the second C(O)F group maintains its original conformation with respect to the SSS group. 相似文献
132.
V. V. Yushchenko Carlos J. Vanegas B. V. Romanovskii 《Reaction Kinetics and Catalysis Letters》1989,40(2):235-240
A new method to calculate the function of density distribution of adsorption centers according to the activation energies of desorption by using temperature-programmed desorption curves is suggested. The application of this method is exemplified by toluene desorption from ZSM-5 zeolite.
, . .相似文献
133.
Total synthesis of LFA-1 antagonist BIRT-377 via organocatalytic asymmetric construction of a quaternary stereocenter 总被引:1,自引:0,他引:1
A catalytic route for enantioselective total synthesis of cell adhesion inhibitor BIRT-377 is described. The quaternary stereocenter was constructed through l-proline-derived, tetrazole-catalyzed direct asymmetric alpha-amination of 3-(4-bromophenyl)-2-methylpropanal with dibenzyl azodicarboxylate. In the course of these studies, a one-pot trifluoro acetylation/selective benzyloxycarbonyl deprotection method was developed. [structure: see text] 相似文献
134.
Seghezzo L Trupiano AP Liberal V Todd PG Figueroa ME Gutiérrez MA Da Silva Wilches AC Iribarnegaray M Guerra RG Arena A Cuevas CM Zeeman G Lettinga G 《Applied biochemistry and biotechnology》2003,109(1-3):167-180
A pilot-scale sewage treatment system consisting of two upflow anaerobic sludge bed (UASB) reactors followed by five waste stabilization ponds (WSPs) in series was studied under subtropical conditions. The first UASB reactor started up in only 1 mo (stable operation, high chemical oxygen demand [COD] removal efficiency, low volatile fatty acids concentration in the effluent, alkalinity ratio above 0.7, biogas production above 0.1 Nm3/kg of CODremoved). Removal efficiencies up to 90% were obtained in the anaerobic steps at a hydraulic retention time of 6 + 4 h (80% removal in the first step). Fecal coliform removal in the whole system was 99.9999% (99.94% in anaerobic steps and 99.98% in WSPs). COD balances over UASB reactors are provided. A minimum set of data necessary to build COD balances is proposed. Intermittent sludge washout was detected in the reactors with the COD balances. Sludge washout from single-step UASB reactors should be monitored and minimized in order to ensure constant compliance with discharge standards, especially when no posttreatment is provided. The system combined high COD and fecal coliform removal efficiency with an extremely low effluent concentration, complying with discharge standards, and making it an attractive option for sewage treatment in subtropical regions. 相似文献
135.
Mikkelsen LM Hernáiz MJ Martín-Pastor M Skrydstrup T Jiménez-Barbero J 《Journal of the American Chemical Society》2002,124(50):14940-14951
The conformational properties of the C-glycosyl analogue of the core trisaccharide alpha-D-Man-(1 --> 3)-[alpha-D-Man-(1 --> 6)]-D-Man in solution have been carefully analyzed by a combination of NMR spectroscopy and time-averaged restrained molecular dynamics. It has been found that both the alpha-1,3- and the alpha-1,6-glycosidic linkages show a major conformational averaging. Unusual Phi ca. 60 degrees orientations for both Phi torsion angles are found. Moreover, a major conformational distinction between the natural compound and the glycomimetic affects to the behavior of the omega(16) torsion angle around the alpha-1 --> 6-linkage. Despite this increased flexibility, the C-glycosyl analogue is recognized by three mannose binding lectins, as shown by NMR (line broadening, TR-NOE, and STD) and surface plasmon resonance (SPR) methods. Moreover, a process of conformational selection takes place, so that these lectins probably bind the glycomimetic similarly to the way they recognize the natural analogue. Depending upon the architecture and extension of the binding site of the lectin, loss or gain of binding affinity with respect to the natural analogue is found. 相似文献
136.
Branco LC Serbanovic A da Ponte MN Afonso CA 《Chemical communications (Cambridge, England)》2005,(1):107-109
The combination of ionic liquids (ILs) as solvents in the asymmetric Sharpless dihydroxylation (AD) with the use of scCO(2) in the separation process allows a very simple, efficient, clean and robust system for the reuse of the AD catalytic system, which also does not need the use of organic solvents either for the reaction or for the separation of products and allows the isolation of the diol, in high yield and enantiomeric excess and basically without contamination with osmium. 相似文献
137.
Determination of rotenone residues in raw honey by solid-phase extraction and high-performance liquid chromatography 总被引:8,自引:0,他引:8
Jiménez JJ Bernal JL del Nozal MJ Novo M Higes M Llorente J 《Journal of chromatography. A》2000,871(1-2):67-73
A method for determining residues of the insecticide rotenone in raw-honey by high-performance liquid chromatography (HPLC) is described. To extract the residues, organic solvents such as ethyl acetate, n-hexane/dichloromethane and solid-phase extraction with octadecylsilane cartridges or Florisil packed columns were tested. Determination was carried out by reversed-phase HPLC using acetonitrile-buffer phosphate (pH 7) (60:40, v/v) as mobile phase and detection at 210 nm. Although the data showed that the two extraction methods were able to isolate the pesticide residues, the extraction on octadecylsilane cartridges was preferred due to its simplicity and higher recovery. Recoveries depended strongly on the fortification level for the two extraction procedures. Practical determination limits of 0.015 mg/kg were obtained. In the analysis of honeys, from beehives treated with rotenone at therapeutical doses for 1 month, residual amounts below 0.2 mg/kg were found. 相似文献
138.
Two families of mixed finite elements for second order elliptic problems 总被引:32,自引:2,他引:30
Summary Two families of mixed finite elements, one based on triangles and the other on rectangles, are introduced as alternatives to the usual Raviart-Thomas-Nedelec spaces. Error estimates inL
2
() andH
–5
() are derived for these elements. A hybrid version of the mixed method is also considered, and some superconvergence phenomena are discussed. 相似文献
139.
Naert C De Saeger S Van Peteghem C 《Rapid communications in mass spectrometry : RCM》2004,18(19):2317-2322
A combined gas chromatographic mass spectrometric (GC/MS/MS) method for the determination of seven polybrominated diphenyl ethers (PBDEs) and seven marker polychlorinated biphenyls (PCBs) in adipose tissue has been developed. Adipose tissue was melted and filtered through anhydrous sodium sulphate to obtain pure fat. Clean-up was performed using a glass column containing acidified silica, deactivated alumina and anhydrous sodium sulphate. Polybrominated biphenyl (PBB) 155 and Mirex were added as internal standards for PBDEs and PCBs, respectively. Injection standards, PBB 103 and PCB 143, for PBDEs and PCBs, respectively, were added before analysis with GC/MS/MS. The developed GC/MS/MS method has the advantage of being more selective than single MS methods because matrix effects are largely eliminated. Validation of this method was conducted according to Commission Decision 2002/657/EC. Decision limits for PBDEs and PCBs ranged from 0.06-0.15 ng g(-1) and from 0.35-1.22 ng g(-1), respectively. Detection capabilities were all between 0.23-0.55 ng g(-1) for PBDEs and between 0.98-2.29 ng g(-1) for PCBs. Precision, recovery, bias and selectivity were tested, with satisfactory results. 相似文献
140.
Fused pyrazolopyrimidines. I. Pyrazolo[4,3-e]-v-triazolo[1,5-a]pyrimidine. A new heterocyclic system
Misbahul Ain Khan Antonio Carlos Carreira Freitas 《Journal of heterocyclic chemistry》1980,17(7):1603-1604
5-Azido-4-cyano-1-phenylpyrazole reacts with benzylcyanide in the presence of sodium methoxide to give the title ring system. 相似文献