Ozone source attribution during a severe photochemical smog episode in Beijing, China

Beijing,the capital of China,frequently suffers from the high levels of ozone in summer.A 3-D regional chemical transport model,the Comprehensive Air Quality Model with extensions(CAMx),has been used to simulate a heavy O3 pollution episode in Beijing during June 26―July 2,2000.Ozone Source Apportionment Technology(OSAT) and Geographic Ozone Assessment Technology(GOAT) were applied to quantify the contributions of the precursor emissions from different regions to O3 concentrations in Beijing,to identify the...     

ENHANCED MECHANICAL PROPERTIES OF POLYPROPYLENE/SILICA NANOCOMPOSITES WITH SURFACE MODIFICATION OF NANO-SILICA VIA IN SITU COPOLYMERIZATION OF METHYL METHACRYLATE AND BUTYL ACRYLATE

Nano-sized silica particles were modified with methacryloxy-propyltrimethoxysilane(MPS) followed by in situ copolymerization of methyl methacrylate(MMA) and butyl acrylate(BA).These modified nanoparticles were compounded with polypropylene(PP) to prepare PP/silica nanocomposites.PMMA grafted on nano-silica enhances the dispersion of the nanoparticles and interfacial adhesion,decreases the size of PP spherulites in nanocomposites and leads to increasing the Young's modulus and toughness of PP/silica nanoc...     

Electrochemical behavior and voltammetric determination of tryptophan based on 4-aminobenzoic acid polymer film modified glassy carbon electrode

Herein, a novel electrochemical method was developed for the determination of tryptophan based on the poly(4-aminobenzoic acid) film modified glassy carbon electrode (GCE). The electrochemical behaviors of tryptophan at the modified electrode were investigated. It was found that the oxidation peak current of tryptophan at the modified GCE was greatly improved compared with that at the bare GCE. The effects of supporting electrolyte, pH value, scan rate, accumulation potential and time were examined. The oxidation peak current of tryptophan was proportional to its concentration over the range from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹. The limit of detection was evaluated to be 2.0 × 10⁻⁷ mol L⁻¹. The proposed method was sensitive and simple. It was successfully employed to determine tryptophan in pharmaceutical samples.     

Theoretical study on the reaction of the Δ ground state of ZrO with CS2 in the gas phase

The mechanisms for the three products ZrS⁺, and ZrOS⁺ of the title reaction have been studied by using B3LYP/6-311+G* and CCSD(T)/SDD+6-311+G* methods. It is found that both ZrS⁺ and formations involve the same O/S exchange process via a four-center transition state TS12 to form an intermediate IM2. Exception of that IM2 can dissociate into the ZrS⁺ product, a favorable intramolecular rearrangement mechanism associated with the formation has been identified, which explains why ZrS⁺ was excluded as a precusor for the formation and why the lower efficiency of the ZrS⁺ formation was observed in experiment. For the formation of ZrOS⁺, two parallel channels (path A and B) yielding their corresponding product isomer have been identified. Path B involving an insertion–elimination mechanism with a calculated barrier underestimated by ca. 25.0 kJ/mol should be attributed to the threshold of 114.8 ± 12.5 kJ/mol assigned in the experiment. But path A should make some contributions to the formation of ZrOS⁺ at elevated energy.     

Study on the morphology, crystalline structure and thermal properties of yellow ginger starch acetates with different degrees of substitution

Yellow ginger starch acetates with different degrees of substitution (DS) were prepared by reacting native starch with glacial acetic acid/acetic anhydride using sulfuric acid as catalyst. X-ray diffraction (XRD) of acetylated starch revealed that the crystal structure of native starch was disappeared and new crystalline regions were formed. Their formation was confirmed by the presence of the carbonyl signal around 1750 cm⁻¹, as well as the reduced hydroxyl groups, in the Fourier transform infrared spectroscopy (FT-IR). The scanning electron microscopy (SEM) suggested most of the starch granules disintegrated with many visible fragments along with the increasing DS. The thermal behavior of the native starch and starch acetate were investigated using thermogravimetric analysis (TGA) and differential thermal analysis (DTA), it was observed that the thermal stability of acetylated starch depends on the degree of substitution. Thermal stability of high DS acetylated starch is much better than that of the original starch when DS reached to 2.67.     

环境中有机磷污染物碱性的理论研究

有机膦化合物的碱度对深入了解有机膦类污染物的降解有着重要的意义. 发展基于第一性原理的理论方法精确计算有机膦化合物的pKa值有重要意义. 本研究工作发展了精确计算有机膦阳离子化合物pKa值的方法: 用B3LYP/6- 31＋G(d)优化气相结构, PBEPBE计算单点能量, IEFPCM/Bondi (f＝1.0)计算溶剂化能. 理论值与实验值比较, 其平均偏差和均方根差分别为－0.6 pKa单位和0.7 pKa单位. 基于此方法, 我们研究了常见有机膦污染物阳离子的碱性, 定量计算其pKa值. 并进一步讨论了这类化合物的α取代效应和远程取代效应对其碱性的影响, 总结了影响杂环有机膦化合物阳离子酸性的因素.     

Electron attachment induced proton transfer in a DNA nucleoside pair: 2'-deoxyguanosine-2'-deoxycytidine

To elucidate electron attachment induced damage in the DNA double helix, electron attachment to the 2'-deoxyribonucleoside pair dG:dC has been studied with the reliably calibrated B3LYP/DZP++ theoretical approach. The exploration of the potential energy surface of the neutral and anionic dG:dC pairs predicts a positive electron affinity for dG:dC [0.83 eV for adiabatic electron affinity (EAad) and 0.16 eV for vertical electron affinity (VEA)]. The substantial increases in the electron affinity of dG:dC (by 0.50 eV for EAad and 0.23 eV for VEA) compared to those of the dC nucleoside suggest that electron attachment to DNA double helices should be energetically favored with respect to the single strands. Most importantly, electron attachment to the dC moiety in the dG:dC pair is found to be able to trigger the proton transfer in the dG:dC- pair, surprisingly resulting in the lower energy distonic anionic complex d(G-H)-:d(C+H).. The negative charge for the latter system is located on the base of dC in the dG:dC- pair, while it is transferred to d(G-H) in d(G-H)-:d(C+H)., accompanied by the proton transfer from N1(dG) to N3(dC). The low energy barrier (2.4 kcal/mol) for proton transfer from dG to dC- suggests that the distonic d(G-H)-:d(C+H). pair should be one of the important intermediates in the process of electron attachment to DNA double helices. The formation of the neutral nucleoside radical d(C+H). is predicted to be the direct result of electron attachment to the DNA double helices. Since the neutral radical d(C+H). nucleotide is the key element in the formation of this DNA lesion, electron attachment might be one of the important factors that trigger the formation of abasic sites in DNA double helices.     

Discrimination of transgenic tomatoes based on visible/near-infrared spectra

VIS-NIR spectroscopy combined with multivariate analysis after the appropriate spectral data pre-treatment has been proved to be a very powerful tool for judgment of the relative pattern of the objects that have very similar properties. In this study, seventy transgenic tomatoes with antisense LeETR2 and 94 of their parents, non-transgenic ones were measured in VIS-NIR diffuse reflectance mode. Principal component analysis (PCA), discriminant analysis (DA) and partial least-squares discriminant analysis (PLSDA) were applied to classify tomatoes with different genes into two groups. Calibrations were developed using PLS regression with the leave-one-out cross-validation technique. The results show that differences between transgenic and non-transgenic tomatoes do exist and excellent classification can be obtained after optimizing spectral pre-treatment. The correct classifications for transgenic and non-transgenic tomatoes were both 100% using PLSDA after derivative spectral pre-treatment. The raw spectra with PLSDA model after the second derivative pre-treatment had the best satisfactory calibration and prediction abilities, with r_c = 0.97964, root mean square error of calibration (RMSEC) = 0.099, r_cv = 0.97963, root mean square error of cross-validation (RMSECV) = 0.0993 and a factor. The results in the present study show VIS-NIR spectroscopy together with chemometrics techniques could be used to differentiate transgenic tomato, which offers the benefit of avoiding time-consuming, costly and laborious chemical and sensory analysis.     

The 39K(2) 2(3)Sigma(g)+ state: observation and analysis

The (39)K(2) 2 (3)Sigma(g) (+) state has been observed by perturbation-facilitated infrared-infrared double resonance spectroscopy and two-photon excitation. Resolved fluorescence spectra into the a (3)Sigma(u) (+) state have been recorded. The observed vibrational levels have been assigned as the v=23-25, 27, 28, 31-33, 38-45, 47, and 53 levels by comparing the observed and calculated spectra of the 2 (3)Sigma(g) (+)-->a (3)Sigma(u) (+) transitions. Molecular constants have been obtained using a global fitting procedure with a comprehensive set of experimental data. Fine and hyperfine splittings have been resolved in the excitation spectra. Perturbations between the 2 (3)Sigma(g) (+) and 2 (3)Pi(g) states were observed. The hyperfine patterns of the 2 (3)Sigma(g) (+) levels are strongly affected by the perturbation. The perturbation-free and weakly perturbed levels follow the case b(betaS) coupling scheme, while the perturbed levels follow case b(beta J) coupling. A Fermi contact constant, b(F)=65+/-10 MHz, has been obtained. Intensity anomalies of rotational lines appeared both in the 2 (3)Sigma(g) (+) approximately 2 (3)Pi(g)<--b (3)Pi(u) excitation spectra and in the 2 (3)Sigma(g) (+) approximately 2 (3)Pi(g)-->a (3)Sigma(u) (+) resolved fluorescence spectra. These intensity anomalies can be explained in terms of a quantum-mechanical interference effect.