Reactions of stabilized criegee intermediates from the gas‐phase reactions of O3 with selected alkenes

The gas‐phase reactions of O₃ with 1‐octene, trans‐7‐tetradecene, 1,2‐dimethyl‐1‐cyclohexene, and α‐pinene have been studied in the presence of an OH radical scavenger, primarily using in situ atmospheric pressure ionization tandem mass spectrometry (API‐MS), to investigate the products formed from the reactions of the thermalized Criegee intermediates in the presence of water vapor and 2‐butanol (1‐octene and trans‐7‐tetradecene forming the same Criegee intermediate). With H₃O⁺(H₂O)_n as the reagent ions, ion peaks at 149 u ([M + H]⁺) were observed in the API‐MS analyses of the 1‐octene and trans‐7‐tetradecene reactions, which show a neutral loss of 34 u (H₂O₂) and are attributed to the α‐hydroxyhydroperoxide CH₃(CH₂)₅CH(OH)OOH, which must therefore have a lifetime with respect to decomposition of tens of minutes or more. No evidence for the presence of α‐hydroxyhydroperoxides was obtained in the 1,2‐dimethyl‐1‐cyclohexene or α‐pinene reactions, although the smaller yields of thermalized Criegee intermediates in these reactions makes observation of α‐hydroxyhydroperoxides from these reactions less likely than from the 1‐octene and trans‐7‐tetradecene reactions. Quantifications of 2,7‐octanedione from the 1,2‐dimethyl‐1‐cyclohexene reactions and of pinonaldehyde from the α‐pinene reactions were made by gas chromatographic analyses during reactions with cyclohexane and with 2‐butanol as the OH radical scavenger. The measured yields of 2,7‐octanedione from 1,2‐dimethyl‐1‐cyclohexene and of pinonaldehyde from α‐pinene were 0.110 ± 0.020 and 0.164 ± 0.029, respectively, and were independent of the OH radical scavenger used. Reaction mechanisms are presented and discussed. © 2001 Wiley Periodicals, Inc. Int J Chem Kinet 34: 73–85, 2002     

Determination of 4-nonylphenol and 4-nonylphenol ethoxylates in river sediments by microwave assisted solvent extraction

The efficiency of Microwave Assisted Solvent Extraction (MASE) for the simultaneous determination of nonylphenol (NP) and nonylphenol ethoxylates (NPE) in river sediments has been evaluated. An optimisation study was carried out in order to identify the variables having the greatest influence on the extraction efficiency. The comparison between the solvents (methanol and acetone-hexane 1:1) shows that the more polar solvent (i.e. methanol) allows a more effective extraction of NP and NPE from sediments. Analytical results show that there is not a considerable improvement by doubling extraction time, while the increase of solvent volume is significant. The comparative study with Soxhlet and pressurised liquid extraction (PLE) methods demonstrates that Microwave Assisted Solvent Extraction is a suitable alternative extraction method for the 4-NP and 4-NPE determination in river sediments, showing an accuracy and precision comparable to those obtained with PLE and better than those obtained with Soxhlet.     

Capillary electrophoresis off-line matrix-assisted laser desorption/ionisation mass spectrometry of intact and digested proteins using cationic-coated capillaries

Capillary electrophoresis (CE) was coupled off-line with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) for the analysis of proteins and peptides. CE fractions were collected directly on a matrix-coated MALDI target, using a sheath-flow interface. Protein adsorption during CE separations was prevented by coating the capillaries with the physically adsorbed, cationic polymer PolyE-323. The CE/MALDI-MS system was used for the analysis of model proteins and peptides at physiological pH as well as analysis of proteins in tear fluid. Moreover, tryptic on-target digestion of the collected protein fractions, with subsequent MALDI-MS and MS/MS peptide analysis, was demonstrated.     

Ring-opening protonolysis of sila[1]ferrocenophanes as a route to stabilized silylium ions

The ring-opening reactions of a series of sila[1]ferrocenophanes with protic acids of anions with various degrees of noncoordinating character have been explored. Ferrocenyl-substituted silyl triflates FcSiMe2OTf (5 a) and Fc(3)SiOTf (5 b) (Fc=(eta5-C5H4)Fe(eta5-C5H5)) were synthesized by means of HOTf-induced ring-opening protonolysis of strained sila[1]ferrocenophanes fcSiMe2 (3 a) and fcSiFc2 (3 b) (fc=(eta5-C5H4)2Fe). Reaction of 3 a and 3 b with HBF4 yielded fluorosubstituted ferrocenylsilanes FcSiMe2F (6 a) and Fc3SiF (6 b) and suggested the intermediacy of a highly reactive silylium ion capable of abstracting F- from the [BF4]- ion. Generation of the solvated silylium ions [FcSiMe2THF]+ (7a+), [Fc3SiTHF]+ (7b+) and [FcSiiPr2OEt2]+ (7c+) at low temperatures, by reaction of the corresponding sila[1]ferrocenophanes (3 a, 3 b, and fcSiiPr2 (3 c), respectively) with H(OEt2)(S)TFPB (S=Et2O or THF; TFPB=tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) was monitored by using low-temperature 1H, 13C, and 29Si NMR spectroscopy. In situ reaction of 7a+, 7b+, and 7c+ with excess pyridine generated [FcSiMe2py]+ (8a+), [Fc3Sipy]+ (8b+), and [FcSiiPr2py]+ (8c+), respectively, as observed by 1H, 13C, and 29Si NMR spectroscopy. A preparative-scale reaction of 3 b with H(OEt2)(THF)TFPB at -60 degrees C and subsequent addition of excess pyridine gave isolable red crystals of 8b-[TFPB]CHCl3, which were characterized by 1H and 29Si NMR spectroscopy as well as by single-crystal X-ray diffraction.     

Rapid fabrication of a poly(dimethylsiloxane) microfluidic capillary gel electrophoresis system utilizing high precision machining

In this work, we demonstrate a rapid protocol to address one of the major barriers that exists in the fabrication of chip devices, creating the micron-sized structures in the substrate material. This approach makes it possible to design, produce, and fabricate a microfluidic system with channel features >10 microm in poly(dimethylsiloxane)(PDMS) in under 8 hours utilizing instrumentation common to most machine shops. The procedure involves the creation of a master template with negative features, using high precision machining. This master is then employed to create an acrylic mold that is used in the final fabrication step to cast channel structures into the PDMS substrate. The performance of the microfluidic system prepared using this fabrication procedure is evaluated by constructing a miniaturized capillary gel electrophoresis (micro-CGE) system for the analysis of DNA fragments. Agarose is utilized as the sieving medium in the micro-CGE device and is shown to give reproducible (RSD (n= 34) approximately 5.0%) results for about 34 individual separations without replenishing the gel. To demonstrate the functionality of the micro-CGE device, a DNA restriction ladder (spanning 26-700 base pairs) and DNA fragments generated by PCR are separated and detected with laser-induced fluorescence (LIF). The microchip is shown to achieve a separation efficiency of 2.53 x 10(5) plates m(-1).     

Electrochemical and coupled XPS studies on Langmuir–Blodgett mixed films of behenic acid and over-grafted platinum nanoparticles: Effect of the behenic acid removal

We report on the behavior of Pt nanoparticles functionalized with 4-mercaptoaniline over-grafted with 2-thiophenecarbonyl chloride. Stable Langmuir–Blodgett (LB) mixed films were built up from these particles with behenic acid (BHA). Such ultra-thin films were transferred onto gold substrates, which allowed the study of their electrochemical response towards Fe[(CN)₆]³⁻ and their XPS chemical analysis before and after the BHA removal. After washing, XPS analysis showed that the signals corresponding to the metal core and the capping agent were almost unchanged. Moreover, the layers became more compact, as shown by the Pt/Au intensity ratio decrease, because of the apparent decrease of length escape of electrons coming from gold, evidencing the removal of the fatty acid in the LB film structure. After BHA removal, the resulting electrochemical activity slightly increased. This result, in agreement with XPS analysis, showed the structural rearrangement within the film that facilitated the percolation between the particle domains.     

The preparation of 3‐substituted 1,2‐benzisothiazole 1,1‐dioxides from lithiated intermediates or grignard reagents and methyl 2‐(aminosulfonyl)benzoate

A polylithiated β‐ketoester, β‐diketone, or β‐ketoamide was condensed‐cyclized with lithiated methyl 2‐(aminosulfonyl)benzoate, to afford new 3‐substituted 1,2‐benzisothiazole 1,1‐dioxides. Some Grignard or organolithium reagents were also condensed‐cyclized with methyl 2‐(aminosulfonyl)benzoate to give 3‐substituted 1,2‐benzisothiazole 1,1‐dioxides.     

Stabilization and rovibronic spectra of the T-shaped and linear ground-state conformers of a weakly bound rare-gas-homonuclear dihalogen complex: He...Br2

Laser-induced fluorescence spectra of Br(2) entrained in a He supersonic expansion have been recorded in the Br(2) B-X, 8-0, 12-0, and 21-0 spectral regions at varying downstream distances, and thus different temperature regimes. Features associated with transitions of the T-shaped and linear He...Br(2)(X,nu(") = 0) complexes are identified. The changes in the relative intensities of the T-shaped and linear features with cooling in the expansion indicate that the linear conformer is energetically more stable than the T-shaped conformer. A He + Br(2)(X,nu(") = 0) ab initio potential-energy surface, computed at the coupled cluster level of theory with a large, flexible basis set, is used to calculate the binding energies of the two conformers, 15.8 and 16.5 cm(-1) for the T-shaped and linear complexes, respectively. This potential and an excited-state potential [M. P. de Lara-Castells, A. A. Buchachenko, G. Delgado-Barrio, and P. Villareal, J. Chem. Phys. 120, 2182 (2004)] are used to calculate the excitation spectra of He...(79)Br(2)(X,nu(") = 0) in the Br(2) B-X, 12-0 region. The calculated spectra are used to make spectral assignments and to determine the energies of the excited-state intermolecular vibrational levels accessed in the observed transitions. Temperature-dependent laser-induced fluorescence spectra and a simple thermodynamic model [D. S. Boucher, J. P. Darr, M. D. Bradke, R. A. Loomis, and A. B. McCoy, Phys. Chem. Chem. Phys. 6, 5275 (2004)] are used to estimate that the linear conformer is 0.4(2) cm(-1) more strongly bound than the T-shaped conformer. Two-laser action spectroscopy experiments reveal that the binding energy of the linear He...(79)Br(2)(X,nu(") = 0) conformer is 17.0(8) cm(-1), and that of the T-shaped He...(79)Br(2)(X,nu(") = 0) conformer is then 16.6(8) cm(-1), in good agreement with the calculated values.     

Organocatalytic regio- and asymmetric C-selective S(N)Ar reactions-stereoselective synthesis of optically active spiro-pyrrolidone-3,3'-oxoindoles

The first example of catalytic enantioselective nucleophilic aromatic substitution of beta-dicarbonyl compounds is presented. An O-benzoylated cinchona alkaloid derivative catalyst gave a selective C-arylation reaction compared to, e.g., the corresponding benzylated catalyst which provided a 1:1 mixture of the C- and O-arylation products. The reaction proceeds well for various aromatic compounds with different 1,3-dicarbonyl compounds, and the optically active products are obtained in very high yields and with up to 92% ee. One further scope of the organocatalytic enantioselective nucleophilic aromatic substitution reaction is demonstrated by the synthesis of the optically active spiro-pyrrolidone-3,3'-oxoindole structure.     

Quaternary ammonium substituted agarose as surface coating for capillary electrophoresis

A novel positively charged polymer of quaternary ammonium substituted agarose (Q-agarose) has been synthesized and explored for use as a coating in capillary electrophoresis. The fast and simple coating procedure is based on a multi-site electrostatic interaction between the polycationic agarose polymer and the negatively charged fused-silica surface. By simply flushing fused-silica capillaries with hot polymer solution a positively charged, hydrophilic deactivation layer is achieved. The polymer surface provides an intermediate electroosmotic flow of reversed direction, over a range of pH 2-11, compared to unmodified fused-silica. The coating procedure was highly reproducible with an RSD of 4%, evaluated as the electroosmotic flow mobility for 30 capillaries prepared at 10 different occasions. The application of Q-agarose coated capillaries in separation science was investigated using a set of basic drugs and model proteins and peptides. Due to the intermediate electroosmotic flow generated, the resolution of basic drugs could be increased, compared to using bare fused-silica capillaries. Moreover, the coating enabled separation of proteins and peptides with efficiencies up to 300.000 plates m(-1).