NOFBX新型绿色推进剂燃烧化学反应动力学模型

本文以具有绿色无毒、高性能、低成本等诸多优势的N_2O-C_2烃类燃料单元复合推进剂(即NOFBX)为对象,首先发展了包含52组分、325反应的燃烧化学反应机理模型。该机理不仅能够准确计算N_2O热解过程中重要组分的分布,而且能够在较宽的温度、压力、化学计量比范围内准确预测N_2O-C_2烃类燃料体系的着火延迟时间和层流火焰传播速度。鉴于本文提出的N_2O-C_2烃类燃料反应机理具有机理规模小、实验验证充分的特点,有望在NOFBX发动机的多维燃烧数值模拟中得到广泛应用。     

Electrical properties of niobium-doped titanium dioxide. 1. Defect disorder

The present work reports the electrical conductivity and thermoelectric power for Nb-doped TiO(2) at elevated temperatures (1073-1298 K) in the gas phase of controlled oxygen activity, 10(-14) Pa < p(O(2)) < 75 kPa. It is shown that in reduced conditions the Nb-doped TiO(2) exhibits metallic-type conductivity. This finding paves the way for the development of high-performance photoelectrodes with substantially reduced internal energy losses during charge transport. The present work also determined the equilibrium constant for the formation of oxygen vacancies and titanium vacancies for Nb-doped TiO(2).     

An AB initio molecular orbital study of the NF2 and N2F4 molecules,and ESR hyperfine coupling constants in NF2

In this publication, we present the results of gaussian type orbital calculations of ESR hyperfine coupling constants in NF₂. We also present electron density maps for the molecule, and the results of a calculation of ΔH⁰₂₉₈ for the reaction N₂F₄ → 2NF₂.     

Cell protection from Ca2+-overloading by bioactive molecules extracted from olive pomace

We are reporting in the present study that molecules extracted from olive pomace prevent cell death induced by Ca²⁺-overloading in different cell types. Exposure of cells to these molecules counteracts the Ca²⁺-induced cell damages by reducing the activation of the Ca²⁺-dependent protease calpain, acting possibly through the modification of the permeability to Ca²⁺ of the plasma membrane. The purification step by RP-HPLC suggests that effective compound(s), differing from the main biophenols known to be present in the olive pomace extract, could be responsible for this effect. Our observations suggest that bioactive molecules present in the olive pomace could be potential candidates for therapeutic applications in pathologies characterised by alterations of intracellular Ca²⁺ homeostasis.     

Vibrational analysis of tertiary alkyl chlorides

Vibrational spectra were obtained for 2-chloro-2-methylpentane, 3-chloro-3-methylpentane, 2-chloro-2-methylhexane, and 3-chloro-3-methylhexane. All four compounds exist in T_HHH and T_CHH conformations in the neat liquid, and the T_HHH' conformer of the last named compound also seems to be present. Only the T_HHH conformer is present in the crystalline state of the two pentanes, but the hexanes could not be made to crystallize and both conformers were present in the solid. A 44-parameter modified valence force field was used in normal coordinate calculations, with fifteen force constants being adjusted to fit 188 assigned frequencies below 1500 cm^?1 of six molecules (two conformers each of 2-chloro-2-methylbutane, 2-chloro-2-methylpentane, and 3-chloro-3-methylpentane). The resulting force constant values were used in zero-order calculations of the two hexanes as an aid in interpreting vibrational spectra for those compounds.     

Hydrogen adsorption on carbon-doped boron nitride nanotube

The adsorption of atomic and molecular hydrogen on carbon-doped boron nitride nanotubes is investigated within the ab initio density functional theory. The binding energy of adsorbed hydrogen on carbon-doped boron nitride nanotube is substantially increased when compared with hydrogen on nondoped nanotube. These results are in agreement with experimental results for boron nitride nanotubes (BNNT) where dangling bonds are present. The atomic hydrogen makes a chemical covalent bond with carbon substitution, while a physisorption occurs for the molecular hydrogen. For the H(2) molecule adsorbed on the top of a carbon atom in a boron site (BNNT + C(B)-H(2)), a donor defect level is present, while for the H(2) molecule adsorbed on the top of a carbon atom in a nitrogen site (BNNT + C(N)-H(2)), an acceptor defect level is present. The binding energies of H(2) molecules absorbed on carbon-doped boron nitride nanotubes are in the optimal range to work as a hydrogen storage medium.     

Laplace-transformed diagonal Dyson correction to quasiparticle energies in periodic systems

We present a method to self-consistently evaluate quasiparticle energies of periodic systems within the diagonal approximation for solving Dyson's equation. Our method is based on the Laplace transform of the second-order M?ller-Plesset perturbation (MP2) theory kernel in the atomic basis formulation. The overhead computational cost of evaluating the fully self-consistent diagonal correction over the MP2 band energy calculation is negligible. We present numerical benchmark results for the band structure of trans-polyacetylene and compare it with MP2 and other approaches.     

Towards benchmark second-order correlation energies for large atoms: Zn2+ revisited

To provide very accurate reference results for the second-order M?ller-Plesset (MP2) energy and its various components for Zn(2+), which plays for 3d-electron systems a similar role as Ne for smaller atoms and molecules, we have performed extensive calculation by two completely different implementations of the MP2 method: the finite element method (FEM) and the variation-perturbation (VP) method. The FEM and VP calculations yield partial wave contributions up to l(max)=45 and 12, respectively. Detailed comparison of all FEM and VP energy components for l(max)=12 has disclosed an extraordinary similarity, which justifies using the present results as benchmarks. The present correlation energies are compared with other works. The dependability of an earlier version of FEM, already applied to very large closed-shell atoms, is confirmed. It has been found that for larger atoms the accuracy of the analytical Hartree-Fock results has an impact on the accuracy of the MP2 energies greater than for smaller atoms. Fields of applications of the present results in studies of various electron correlation effects in 3d-electron atoms and molecules are indicated.     

Decoding two-dimensional polyacrylamide gel electrophoresis complex maps by autocovariance function: a simplified approach useful for proteomics

This paper describes a mathematical approach applied for decoding the complex signal of two-dimensional polyacrylamide gel electrophoresis maps of protein mixtures. The method is helpful in extracting analytical information since separation of all the proteins present in the sample is still far from being achieved and co-migrating proteins are generally present in the same spot. The simplified method described is based on the study of the 2-D autocovariance function (2D-ACVF) computed on an experimental digitized map. The first part of the 2D-ACVF allows for the estimation of the number of proteins present in the sample (2D-ACVF computed at the origin) and of the separation performance (mean spot size). Moreover, the 2D-ACVF plot is a powerful tool in identifying order in the spot position, and singling it out from the complex separation pattern. This method was validated on synthetic maps obtained by computer simulation to describe 2-D PAGE real maps and reference maps retrieved from the SWISS-2DPAGE database. The results obtained are discussed by focusing on specific information relevant in proteomics: sample complexity, separation performance, and identification of spot trains related to post-translational modifications.     

Reflected shock tube studies of high-temperature rate constants for OH + C2H2 and OH + C2H4

The reflected shock tube technique with multi-pass absorption spectrometric detection of OH-radicals at 308 nm (corresponding to a total path length of approximately 4.9 m) has been used to study the reactions, OH + C(2)H(2)--> products (1) and OH + C(2)H(4)--> C(2)H(3) + H(2)O (2). The present optical configuration gives a S/N ratio of approximately 1 at approximately 0.5-1.0 x 10(12) radicals cm(-3). Hence, kinetics experiments could be performed at [OH](0) = approximately 4-20 ppm thereby minimizing secondary reactions. OH was produced rapidly from the dissociations of either CH(3)OH or NH(2)OH (hydroxylamine). A mechanism was then used to obtain profile fits that agreed with the experiment to within <+/-5%. The derived Arrhenius expressions, in units of cm(3) molecule(-1) s(-1) are: k(1) = (1.03 +/- 0.24) x 10(-10) exp(-7212 +/- 417 K/T) for 1509-2362 K and k(2) = (10.2 +/- 5.8) x 10(-10) exp(-7411 +/- 871 K/T) for 1463-1931 K. The present study is the first ever direct measurement for reaction (1) at temperatures >1275 K while the present results extend the temperature range for (2) by approximately 700 K. These values are compared with earlier determinations and with recent theoretical calculations. The calculations agree with the present data for both reactions to within +/-10% over the entire T-range.     

A comparison of 2-D chromatography separations using UV and (18)O quantification of proteins in similar proteomes

Proteins present in two mitochondria preparations were separated by 2-D chromatography using the ProteomeLab PF-2D Protein Fractional System, protein fractionation in two dimensions (PF-2D). The proteins in each first-dimension fraction were determined by trypsinization and LC-MS/MS. Chromatography peaks were quantified by UV detection using the "Mapping Tools" software (Beckman). The proteins present in UV detected peaks were trypsinized and identified by automated MS/MS sequencing. Relative amounts of the proteins present in the equivalent peak for each sample were assessed by comparison of the intensities of the constituent peptides and a predicted PF-2D value was calculated from the total ion count (TIC) for each peptide. Relative quantification for (18)O labeled peptides was performed using the ZoomQuant (v1.43b) software [1, 2]. We found that the chromatography peaks detected by UV generally contained several proteins. Using (18)O labeling we determined that in each peak the ratios of the constituent proteins were different. When these ratios were normalized using the TIC to account for abundance, the resulting ratio corresponded to that determined by UV. The predicted value for the PF-2D score corresponded to the observed value for each peak irrespective of the number or proteins detected.     

Steric and electronic contributions to conformational effects on chemical shifts of acyclic alcohols

Our calculations on bi- and polycyclic alcohols reveal that the Mulliken charge distribution and chemical shift patterns due to hyperconjugation of lone pairs on oxygen with neighboring groups break down or are attenuated for certain spatial relationships of the hydroxyl group. Since in strained ring systems other effects on these parameters may be present, we applied a similar analysis to acyclic alcohols. Calculations at the B3LYP/6-31G^* level on conformers of methanol, ethanol, 1- and 2-propanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 2-butanol, 2-methyl-2-butanol, 1- 2- and 3-pentanol and 2-methyl-3-pentanol, where hyperconjugation may be present, reveal steric effects as modifiers of hyperconjugative patterns affecting carbon-13 chemical shifts in such alcohols. Contrary to what is observed in bi- and policyclic systems, where electrostatic effects interfere with effects due to hyperconjugation, these steric effects may be the main cause for the attenuation of deshielding of nuclei that are subject to hyperconjugation. Electrostatic effects are also present but they do not interfere with hyperconjugation by lone pairs. Conformational effects fall off sharply after the third carbon in the chain.     

Rapid analysis of polyolefin antioxidants and light stabilisers by supercritical fluid chromatography

Nineteen commercial antioxidants and light stabilisers, with a wide range of relative molecular masses and boiling-points, present in polyolefins were analysed by packed column supercritical fluid chromatography on four different phases with CO2 or 10% MeOH-CO2 as the mobile phase and with UV detection. The technique is shown to yield short analysis times and sufficient resolution for a number of additives present in a given polyolefin.     

Conformational analysis of 1-chloro-4-iodobutane and 1-chloro-5-iodopentane

Infrared spectra were obtained for Cl(CH₂)₄I and Cl(CH₂)₅I in the liquid and solid states. Zero-order normal coordinate calculations were made for the five conformers of each compound that have all the carbon atoms coplanar. Comparison of the observed and calculated wavenumbers led to the conclusion that all five conformers of Cl(CH₂)₄I are present in the liquid and solid states. For Cl(CH₂)₅I, the TT, TG and GT conformers are present in the liquid state. No evidence was obtained that indicated either the presence or absence of the GG and GG' conformers. Only the TT conformer is present in the solid. Vibrational assignments were made for both compounds.     

Estimation of Pigment Stoichiometries in Photosynthetic Systems of Purple Bacteria: Special Reference to the (Absence of) Second Carotenoid in LH2

Abstract— In this short communication we present the stoichiometric ratio of bacteriochlorophyll, bacteriopheophytin and carotenoids in a few photosynthetic purple bacteria complexes (whose two-dimensional or three-dimensional structures are well known) determined using the spectrum-reconstruction method (SRCM). An important conclusion of our pigment stoichiometric analysis is the evidence for the absence of the second carotenoid in the light-harvesting complex 2 (LH2). In the process, we also highlight the useful application of SRCM in determining the molar extinction coefficients of carotenoids present in LH1, LH2 or reaction centers for which these values are not known due to isolation problems and/or stability.     

氮化硼纳米管气敏特性的理论研究

采用密度泛函理论计算研究了氮化硼纳米管及碳掺杂氮化硼纳米管对CH4, CO2, H2, H2O, N2, NH3, NO2, O2, F2等十余种气体小分子的气敏特性. 研究结果表明: 氮化硼纳米管对CH4, CO2, H2, H2O, N2, NH3等气体分子不敏感, 而对O2, NO2, F2等气体分子比较敏感. 虽然碳掺杂氮化硼纳米管可以明显地改变其表面的化学反应活性, 增强了气体分子与氮化硼纳米管之间的相互作用, 但是并不能明显地改变其对所研究气体分子的敏感性.     

Liquid chromatographic determination of alcohols in food and beverages with indirect polarimetric detection using a beta-cyclodextrin mobile phase.

An indirect polarimetric detection method for the determination of alcohols has been proposed in liquid chromatography (LC). Optically active mobile-phase additives, such as beta-cyclodextrin (beta-CD), could be used to visualize optically inactive alcohols in reversed-phase LC. The visualization of alcohols is based on a perturbation of the partition of beta-CD caused by the alcohols. The detection limits of the present system at a signal-to-noise ratio of 3 were 0.031, 0.019, 0.018, 0.013, 0.011, 0.008 and 0.008% (v/v) for ethanol, 2-propanol, 1-propanol, 2-methyl-2-propanol, 2-butanol, 2-methyl-1-propanol and 1-butanol, respectively. The method was successfully applied to the determination of ethanol present in food and beverage samples.     

Photochemistry studied with ab initio orbital-correlation and state-correlation plots: Classic cyclobutene ring opening, and the reaction of N2 with photoexcited O2

Pericyclic reaction theory arose from ideas presented in 1965, based on orbital-energy correlation diagrams (Woodward and Hoffmann) and state-energy correlation diagrams (Longuet-Higgins and Abrahamson). Here we have used ab initio complete-active-space self-consistent field (CASSCF) calculations to generate such diagrams. First we present diagrams for the classic case of cyclobutene ring opening, to demonstrate agreement between the CASSCF results and the classic diagrams of both Woodward/Hoffmann and Longuet-Higgins/Abrahamson. Then we present diagrams for the more difficult cases of N(2) + photoexcited O(2), to produce either 2 NO or NNO + O. These N(2) + O(2) cases feature significant electron reorganization, for which elementary pencil-and-paper diagrams are less accurate. Finally, the benefits and limitations of such diagrams for predicting photochemistry are briefly discussed.     

电拓扑状态预测多氯二苯并噻吩及噻吩砜化合物的气相色谱保留指数

以原子类型电拓扑状态指数(ETSI)有效表征了135 个多氯二苯并噻吩(PCDT)和135 个多氯二苯并噻吩砜(PCDTO₂)的分子结构, 应用基于预测的变量选择与模型化(VSMP)方法建立PCDT 和PCDTO₂ 化合物在DB-5 气相色谱柱上的气相色谱保留指数(RI)与分子结构(ETSI)的定量相关模型, 模型的相关系数r² 分别为0.9939 和0.9729, LOO 交叉验证相关系数 q² 分别为0.9921 和0.9692. 为验证模型稳定性和预测能力, 应用17 个PCDT 和PCDTO₂ 训练集样本构建的QSRR 模型的r² 分别为0.9959 和0.9783, LOO 交叉验证相关系数 q² 分别为0.9921 和0.9740, 说明模型具有良好的稳定性. 以此模型预测外部8 个检验集及110 个预测集的RI 值, 8 个检验集样本的结果表明训练集模型具有良好预测能力.