Ab initio study of the reaction of propionyl (C2H5CO) radical with oxygen (O2)

The reaction of propionyl radical with oxygen has been studied using the full coupled cluster theory with the complete basis set. This is the first time to gain a conclusive insight into the reaction mechanism and kinetics for this important reaction in detail. The reaction takes place via a chemical activation mechanism. The barrierless association of propionyl with oxygen produces the propionylperoxy radical, which decomposes to form the hydroxyl radical and the three-center alpha-lactone predominantly or the four-center beta-propiolactone. The oxidation of propionyl radical to carbon monoxide or carbon dioxide is not straightforward rather via the secondary decomposition of alpha-lactone and beta-propiolactone. Kinetically, the overall rate constant is almost pressure independent and it approaches the high-pressure limit around tens of torr of helium. At temperatures below 600 K, the rate constant shows negative temperature dependence. The experimental yields of the hydroxyl radical can be well reproduced, with the average energy transferred per collision -DeltaE=20-25 cm(-1) at 213 and 295 K (helium bath gas). At low pressures, together with the hydroxy radical, alpha-lactone is the major product, while beta-propiolactone only accounts for about one-fifth of alpha-lactone. At the high-pressure limit, the production of the propionylperoxy radical is dominant together with a fraction of the isomers. The infrared spectroscopy or the mass spectroscopy techniques are suggested to be employed in the future experimental study of the C2H5CO+O2 reaction.     

Simultaneous determination of malachite green, gentian violet and their leuco-metabolites in aquatic products by high-performance liquid chromatography-linear ion trap mass spectrometry

A method has been developed for the simultaneous determination of malachite green, gentian violet and their leuco-metabolites in various aquatic products using isotope dilution liquid chromatography-linear ion trap mass spectrometry without post-column oxidation. Sample was extracted with McIlvaine buffer and acetonitrile, followed by partitioning with dichloromethane, purified on basic alumina and OASIS MCX SPE column, and finally analyzed by LC-ESI-MS/MS with the select reaction monitoring (SRM) mode. Decision limits (CCalpha, alpha=0.01) and detection capability (CCbeta, beta=0.05) of the method were in the range of 0.02-0.09 and 0.04-0.13microg/kg for MG, GV, LMG and LGV in grass carp, eel, salmon, shrimp and shellfish, respectively, recoveries of MG, GV, LMG and LGV at all fortification levels (0.25-10microg/kg) were from 80.8% to 115.7%, inter-day relative standard derivations were from 1.9% to 18.4%. This method appeared suitable for the control of MG, GV, LMG and LGV residues in aquatic products.     

Thixotropic properties of aqueous suspensions containing cationic starch and aluminum magnesium hydrotalcite-like compound

The rheological properties of aqueous suspensions consisting of cationic starch (CS) and positively charged aluminum magnesium hydrotalcite-like compound (HTlc) were investigated. Special emphasis was placed on the thixotropic phenomena. With the increase of mass ratio (R) of HTlc to CS, the equilibrium viscosity (eta(eq)) and the consistency coefficient (m) values of the suspensions increase in the range of neutral and alkaline pH (higher than 6.5) while decrease in the range of acid pH (lower than 6.5). With the increase of pH value, the eta(eq) and m values of the suspensions in the R range of 0-0.08 studied increase initially and then decrease, appearing a maximum value at about pH 7.41+/-0.25. The CS/HTlc suspensions display viscid character and the yield point of the suspensions was not observed except the suspension with R=0.08 in the pH range of 7.66-9.70, which showed a yield point and viscoelasticity. The CS/HTlc suspensions may display different thixotropic types: negative, complex or positive thixotropy, depending on pH and R value. The thixotropic type of the CS/HTlc suspension may be transformed from negative (pure CS solution), through complex (R=0.02), into positive thixotropy (R=0.05 and 0.08) with the increase of R in the studied R range of 0-0.08, and the thixotropic strength of the suspensions increases initially and then decreases with pH value in the pH range studied. The mechanism of the thixotropic phenomenon is discussed.     

Interactions between Nafion resin and protonated dodecylamine modified montmorillonite: a solid state NMR study

A series of nanocomposites have been prepared from perfluorosulfonylfluoride copolymer resin (Nafion) and layered montmorillonite (MMT) modified with protonated dodecylamine by conventional sol-gel intercalation. The structure of these nanocomposite materials have been characterized using FT-IR, elemental analysis, XRD and solid state NMR techniques, including 19F magic-angle spinning (MAS) NMR, 19F NMR relaxation time measurements, 29Si MAS, 1H MAS, 1H-13C cross-polarization magic-angle spinning (CPMAS), and 1H-13C heteronuclear correlation (HETCOR) 2D NMR. The results showed that thermal stability of Nafion was improved moderately by the addition of dodecylamine modified MMT without intercalation. FT-IR and 29Si MAS NMR results indicated that dodecylamine modification did not result in obvious changes in the MMT lattice structure. The XRD results showed that the protonated dodecylamine has been embedded and intercalated into the MMT interlayers, whereas Nafion was not. Elemental analysis results also suggested that some dodecylamine was adsorbed on the surface of MMT. 1H-13C HETCOR 2D NMR experiment clearly indicated that strong electrostatic interactions were present between the NH+3 group of dodecylamine and the fluorine-containing groups (CF3, OCF2, and SCF2) of Nafion resin. Such electrostatic interactions are probably the major contributors for the improved thermal stability of the resultant composite materials.     

Synthesis and structure of upper-rim 1,3-alternate tetraoxacalix[2]arene[2]triazine azacrowns and change of cavity in response to fluoride anion

The upper-rim 1,3-alternate tetraoxacalix[2]arene[2]triazine azacrowns were constructed effectively by macrocyclic condensation reaction of diamines with dichlorinated tetraoxacalix[2]arene[2]triazine intermediates that were synthesized from the stepwise fragment coupling reactions of 3,5-dihydroxybenzoic acid esters with cyanuric chlorides. Because of the formation of conjugation of amino groups with triazine rings, tetraoxacalix[2]arene[2]triazine azacrowns existed in a mixture of syn- and anti-isomeric forms. Both fluorescence titration and 1H NMR spectroscopic study showed that tetraoxacalix[2]arene[2]triazine azacrowns interacted with fluoride anion, leading to cavity changes of the host molecules.     

Formation of 4,5,6,7-tetrahydroisoindoles by palladium-catalyzed hydride reduction

Substituted 1,3-dihydro-2H-isoindoles (2, isoindolines) were prepared and subjected to palladium-catalyzed formate reduction. Alkyl isoindolines were reduced to 4,5,6,7-tetrahydro-2H-isoindoles (1). Only partial reduction was observed for 5-methoxyisoindoline, and 4-methoxy-, 5-carbomethoxy-, amino-, and amidoisoindolines were inert to the reaction. Halogen-substituted isoindolines were dehalogenated and reduced to 4,5,6,7-tetrahydro-2H-isoindoles. Isoindole 24 was also reduced to a mixture of an isoindoline and a 4,5,6,7-tetrahydro-2H-isoindole. In contrast, 2,3-dihydro-1H-indoles 21 underwent dehydrogenation to give thermodynamically stable indoles. Theoretical calculations show the significant difference in aromaticity between isoindoles and indoles, corresponding to the observed differences in reactivities. Tetrahydro-2H-isoindoles 1 were oxidized to 4,5,6,7-tetrahydroisoindole-1,3-diones in the presence of NBS and air.     

Completed and incompleted stochastic webs

In this paper,the completed stochastic web and incompleted stochastic web producedby the perturbed saddle separatrix net are given.The structural properties of two kinds ofweb are discussed by means of the dynamical system theory.     

连续函数与p幂可和函数的Jackson算子逼近

对f∈X是(X是G2x或D2x.1≤p< ∞)以及Jackson算子证明了如下不等式‖J.（f）-f‖x≤1+2π/3-3/（4π）+89π/24（2n2+1）ω（f·1/n）x,从而改进和推广了文献[1]的工作。     

正则变换的一种群表示

经典力学中的哈密顿正则变换所涉及的4个母函数F₁(q,Q),F₂(q,P),F₃(p,P),F₄(p,Q)和4种正则变量q,p,Q,P之间所有的关系,可以由7个基本关系式经线性变换而得到,这些变换是勒让德变换,变换是由32个8×8的变换矩阵来实现的,而这32个矩阵以4:1的关系与具有8个群元的D₄点群同态。热力学中的4个状态函数G(P,T),H(P,S),U(V,S),F(V,T)和4个热力学变量P,V,T,S之间的变换关系恰好与正则变换关系相同。热力学状态方程是源于宏观测量的实验结果的概括,而哈密顿正则变换是经典力学的理论性总结,它们的群表示是相同的,即它们的数学结构是相同的, 这种共性表明热力学变换是一维哈密顿正则变换的实例。     

气相色谱法测定榄香烯含量

以正己醇为内标,用气相色谱法测定榄香烯及其制剂,方法简便、快速,结果准确,可作为控制质量的方法。