聚合物锂离子电池不同化成电压下产生气体的研究

应用气相色谱方法初步探讨了聚合物锂离子电池在首次充电过程中于不同化成电压下产生气体的原因和机理.结果表明,当电池电解液采用1mol/LLiPF6-EC～DMC～EMC(三者体积比1∶1∶1)时,于化成电压小于2.5V下,产生的气体主要为H2和CO2等;化成电压为2.5V时,电解液中的EC开始分解,电压在3.0～3.5V的范围内,由于EC的还原分解,产生的气体主要为C2H4;而当电压大于3.0V时,由于电解液中DMC和EMC的分解,除了产生C2H4气体外,CH4,C2H6等烷烃类气体也开始出现;电压高于3.8V后,DMC和EMC的还原分解成为主反应.此外,当化成电压处于3.0～3.5V之间,化成过程中产生的气体量最大;电压大于3.5V后,由于电池负极表面的SEI层已基本形成,因此,电解液溶剂的还原分解反应受抑制,产生的气体的数量也随之迅速下降.     

Six-dimensional quantum dynamics of dissociative chemisorption of H2 on Ru(0001)

Six-dimensional quantum dynamics calculations on dissociative chemisorption of H(2) on Ru(0001) are performed. The six-dimensional potential energy surface is generated using density functional theory. Two different generalized gradient approximations are used, i.e., RPBE and PW91, to allow the results to be compared. The dissociation probability for normally incident H(2) on a clean Ru(0001) surface is calculated. Large differences between the reaction probabilities calculated using the RPBE and PW91 are seen, with the PW91 results showing a much narrower reaction probability curve and a much higher reactivity. Using the reaction probabilities and assuming normal energy scaling reaction rates are generated for temperatures between 300 and 800 K. The rate generated using the PW91 results is higher by about a factor 5 than the rate based on the RPBE results in the range of temperatures relevant to ammonia production.     

Reactions of oxygen free radicals with copper complexes in pyridine: differentiation between superoxide and hydroxyl radicals

Superoxide radicals are generated in tetraalkylammonium hydroxide-pyridine-H₂O₂ and detected by spin trapping and by reduction of nitroblue tetrazolium. The addition of low-molecular-weight copper complexes (e.g., of anti-inflammatory drugs) decreases the concentration of superoxide. Depending on the solvent, different oxygen radicals are generated by the addition of hydrogen peroxide to solutions of the copper complexes; hydroxyl radicals are observed in aqueous solutions whereas superoxide is found in pyridine.     

Acylation of α-(N-carbamoyl)alkylcuprates and alkyl- or aryl(halo)cuprates

α-(N-Carbamoyl)alkylcuprates [R₂CuLi·LiX or RCuXLi (X=CN, Cl)] when prepared from THF soluble CuX·2LiCl (X=Cl, CN) undergo a reliable and generally high yield reaction with aroyl, alkanoyl, and alkenoyl chlorides to provide a rapid and efficient synthesis of α-carbamoyl ketones. Cuprates prepared from acyclic, cyclic, and a functionalized carbamate can be utilized. Although yields are a function of cuprate reagent and substrate structure, nearly quantitative yields can be obtained with reagents generated from 2RLi+CuCN·2LiCl. The use of reagents generated from CuCl·2LiCl are more efficient in the α-(N-carbamoyl)alkyl ligand, although yields are slightly lower. Acylation of alkyl(chloro)cuprates generated from one equivalent of CuCl·2LiCl and organolithium or Grignard reagents provides an efficient and high yield procedure for ketone synthesis.     

铜氧团簇负离子的产生

自Smalley等利用激光蒸发／超声分子束载带（ix／un）法产生c。。问起，这种方法逐渐成为形成高质量气相团簇的常用实验手段，其中分子束载带的主要作用是缓冲气体通过提供三体碰撞稳定动力学激发的团簇并促进高质量团簇的形成．但0’Keef6门和Cre。Sy同的实验发现无需利用缓冲     

Relationships between unfolded configurations of proteins and dynamics of folding to the native state

We compare folding trajectories of chymotrypsin inhibitor (CI2) using a dynamic Monte Carlo scheme with Go-type potentials. The model considers the four backbone atoms of each residue and a sphere centered around C^β the diameter of which is chosen according to the type of the side group. Bond lengths and bond angles are kept fixed. Folding trajectories are obtained by giving random increments to the φ and ψ torsion angles with some bias toward the native state. Excluded volume effects are considered. Two sets of 20 trajectories are obtained, with different initial configurations. The first set is generated from random initial configurations. The initial configurations of the second set are generated according to knowledge-based neighbor dependent torsion probabilities derived from triplets in the Protein Data Bank. Compared to chains with randomly generated initial configurations, those generated with neighbor-dependent probabilities (i) fold faster, (ii) have better defined secondary structure elements, and (iii) have less number of non-native contacts during folding. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3667–3678, 2006     

Visible light photoredox catalysis: generation and addition of N-aryltetrahydroisoquinoline-derived α-amino radicals to Michael acceptors

The photoredox-catalyzed coupling of N-aryltetrahydroisoquinoline and Michael acceptors was achieved using Ru(bpy)(3)Cl(2) or [Ir(ppy)(2)(dtb-bpy)]PF(6) in combination with irradiation at 455 nm generated by a blue LED, demonstrating the trapping of visible light generated α-amino radicals. While intermolecular reactions lead to products formed by a conjugate addition, in intramolecular variants further dehydrogenation occurs, leading directly to 5,6-dihydroindolo[2,1-a]tetrahydroisoquinolines, which are relevant as potential immunosuppressive agents.     

Automation of fluorous solid-phase extraction for parallel synthesis

An automatic fluorous solid-phase extraction (F-SPE) technique is developed by using FluoroFlash SPE cartridges on the RapidTrace workstation. A 10-module workstation has the capability to complete a maximum of 100 SPEs each round in 1-2 h. Another important feature of the RapidTrace system is that it has the capability to load slurry samples onto the F-SPE cartridges. The F-SPE cartridge charged with 2 g of fluorous silica gel is used to purify up to 200 mg of crude sample. Sample loading, elution solvent, cartridge reuse, and SPE reproducibility are evaluated. The automatic SPE system is used for purification of a small urea library generated from amine-scavenging reactions using fluorous dichlorotriazine, a 96-membered amide library generated using 2-chloro-4,6-bis[(perfluorohexyl)propyloxy]-1,3,5-triazine as the coupling agent, and another 96-membered library generated from fluorous Mitsunobu reactions. Approximately 90% of the products have > 90% purity after F-SPE.     

Electride characteristics of M2(η5-E5)2 (M = Be,Mg; E = Sb5-)

Structural Chemistry - Ab initio computation is performed on the binuclear sandwich complexes, M2(η5-Sb5)2. Eclipsed and staggered conformations are generated due to the η5 mode of...     

活性氮反应产生激发态卤化氮实验研究

A new method for producing electronically excited nitrogen monohalides NX(b) (X=F,Cl,Br) is reported. The strong emission spectra of NBr(b1Σ+→X3Σ–) are observed when alkyl bromides (CHBr3, CH2Br2, C2H5Br, and C4H9Br) are added to a stream of active nitrogen, generated by a hollow-cathode discharge of N2, in a flowing afterglow system. Some tentative experiments show that the electronically excited NBr(b) is formed by means of metastable N2(A3Σu+) Electronic-to-Electronic energy transfer to NBr(X), which is from the reaction of N(4S) with alkyl bromides. The emission spectra of NCl(b1Σ+→X3Σ–) are obtained when CCl4 or SOCl2 is admitted into a flow of active nitrogen, but neither CHCl3 nor CH2Cl2 addition results in such an emission. It has been proposed that the origin of the excited NCl(b) is an energy transfer from N2 (A) to NCl(X), generated by the reaction of N(4S) with CCl3 (or SOCl2). Similar experiments are also carried out with SF6 as reagent of active nitrogen, or as mixture with N2 in the discharge. By recording fluorescence it was found that excited NF(b) is produced only under discharge through N2/SF6 mixture. The NF(b) state presumably arises from the energy transfer from N2(A) to NF(X), and the latter is generated from the abstraction of fluorine by N(4S) from SF5.     

Oxidation Catalysis by an Aerobically Generated Dess–Martin Periodinane Analogue

Hypervalent iodine(V) reagents, such as Dess–Martin periodinane (DMP) and 2‐iodoxybenzoic acid (IBX), are broadly useful oxidants in chemical synthesis. Development of strategies to generate these reagents from dioxygen (O₂) would immediately enable use of O₂ as a terminal oxidant in a broad array of substrate oxidation reactions. Recently we disclosed the aerobic synthesis of I(III) reagents by intercepting reactive oxidants generated during aldehyde autoxidation. In this work, aerobic oxidation of iodobenzenes is coupled with disproportionation of the initially generated I(III) compounds to generate I(V) reagents. The aerobically generated I(V) reagents exhibit substrate oxidation chemistry analogous to that of DMP. The developed aerobic generation of I(V) has enabled the first application of I(V) intermediates in aerobic oxidation catalysis.     

Observation and quantification of ultraviolet-induced reactive oxygen species in ex vivo human skin

Two-photon fluorescence imaging is used to detect UV-induced reactive oxygen species (ROS) in ex vivo human skin in this study. ROS (potentially H202, singlet oxygen or peroxynitrite [or all]) are detected after reaction with nonfluorescent dihydrorhodamine-123 (DHR) and the consequent formation of fluorescent rhodamine-123 (R123). The cellular regions at each epidermal stratum that generate ROS are identified. R-123 fluorescence is detected predominately in the lipid matrix of the stratum corneum. In contrast, the strongest R123 fluorescence signal is detected in the intracellular cytoplasm of the viable epidermal keratinocytes. A simple bimolecular one-step kinetic model is used for estimating the upper bound of the number of ROS that are generated in the skin and that react with DHR. After ultraviolet-B radiation (280-320 nm) (UVB) equivalent to 2 h of noonday summer North American solar exposure (1600 J m(-2) UVB), the model finds that 14.70 x 10(-3) mol of ROS that react with DHR are generated in the stratum corneum of an average adult-size face (258 cm(-2)). Approximately 10(-4) mol are potentially generated in the lower epidermal strata. The data show that two-photon fluorescence imaging can be used to detect ROS in UV-irradiated skin.     

Two coupled enzymes perform in parallel the 'AND' and 'InhibAND' logic gate operations

The coupled activation of two enzymes: glucose dehydrogenase (GDH) and horseradish peroxidase (HRP), is used to construct the parallel-operating AND and InhibAND logic gates. The added substrates for the respective enzymes, glucose and H(2)O(2), act as the gate inputs, while the biocatalytically generated NADH and gluconic acid provide the output signals that follow the operations of the gates. The two gates are generated in the same vial, thus allowing the logic operations to take place in parallel, and the simultaneous readout of the functions of the gates.     

Collisionally induced dissociative ionization of neutral products from ion fragmentations. 2—Collision gas effects and related phenomena

The ion retardation method (whereby an ion beam is prevented from entering a collision gas cell by means of a voltage applied thereto) for permitting the examination of the neutral products of unimolecular ion fragmentations has been extended to include observations of neutral products generated by collisions before the gas cell and their related phenomenology. Observations obtained using an ion beam deflection electrode, an alternative method of preventing the ion beam from entering the collision cell, are also reported. When low collision gas pressures are employed (<2×10^?7 Torr He), this latter method provides collisionally induced dissociative ionization (CIDI) mass spectra of unimolecularly generated neutral fragmentation products, free of complications arising from events induced by collisions occurring outside the collision cell. The CIDI mass spectra of CH₃˙, C₂H₄, CH₃?O, CH₃OH and C₂H₆ generated from positive ion precursors and CH₃˙, CH₃O˙ and C₆H₅NO₂ generated by electron loss from negative ions are described.     

Amination of Cyclohexane by Dielectric Barrier Discharge Processing in a Continuous Flow Microreactor: Experimental and Simulation Studies

A miniaturized flow device has been developed to combine microfluidics technology and plasma process. In this microreactor, atmospheric pressure dielectric barrier discharges are generated in a gas in contact with a liquid phase. This study was conducted with plasma generated in ammonia in contact with a flow of liquid cyclohexane. Cyclohexylamine was synthesized with a good selectivity, and the process can be implemented to improve conversion and effectiveness. Numerical simulations confirmed that NH₂ radicals are generated in the plasma and react with cyclohexyls radicals to achieve the reaction, giving a selectivity of 50% and a total molar conversion of 20% of cyclohexane. The effects of voltage and frequency on the selectivity and the experimental conversion rate were studied and discussed.

     

Q-band EPR spectroscopy of photogenerated quartet state organic nitreno radicals

Q-band 34 GHz EPR spectra are reported for quartet state 2-(para-nitrenophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl and 3-(para-nitrenophenyl)-1,5,6-triphenylverdazyl reactive intermediates generated from the corresponding azido precursors under frozen matrix photochemical conditions, in situ in a Q-band resonator. Comparison of the Q-band spectra to those generated under conventional X-band (9-10 GHz) conditions shows the much superior resolution of transitions in the g > 2 region of the former. Spectral transitions assigned by line shape simulation yield the zero field splittings for the nitreno-radical species.     

Absorption Spectra and Termination Kinetics of Transient Free Radicals in Solution Observed by UV./VIS. Spectroscopy with modulated excitation

Free radicals are generated in liquid solutions by harmonically modulated photolysis of suitable substrates. Harmonic analysis of the absorbance as functions of wavelength and modulation frequency yields the optical spectra and the decay kinetics of the transient species. The experimental technique and the analysis are described in detail. Results on t-butyl, 2-propyl and benzyl radicals generated by photolysis of the corresponding dialkyl resp. dibenzyl ketones are reported. They confirm previous spectral assignments and show that the termination reactions are diffusion controlled.     

Direct formation of hydrogen peroxide from H2/O2 using a gold catalyst

Supported Au catalysts are very selective for the direct formation of hydrogen peroxide from H2/O2 mixtures at 2 degrees C; the rate of H2O2 synthesis is markedly increased if Au-Pd alloy nanoparticles are generated by the addition of Pd.