Theoretical Study of the C_(60)O_3 Isomers

WiththepreparationandisolationofC,,O.'moreandmoreattentionwaspaidtotheirstructuresandpropertiest').WooddetectedC,,O.firstwhentheypreparedC,,byvaporizinggraphite").Fromthenon,thelaboratoriesallovertheworldhavepreparedC6,O.byvariousmethodssuchasPhotoxidationt2-4),Electrochemicaloxi-dation[si,Ozonizationt7.83andChemicaladditiont6'12-14iandsoon.Accordingtothefollow-uptheoreticalstudiesforC,,O.,itisindicatedthattherearetwoisomersofC,,O:eithertheoxygenatomislocatedoverthe6/6bondtogeneratethe6/…     

As, Bi, Sb and Sn determination in atmospheric particulate matter by direct solid sampling-hydride generation-electrothermal atomic absorption spectrometry

A novel, rapid and simple method by hydride generation-electrothermal atomic absorption spectrometry (HG-ETAAS) after direct As, Bi, Sb and Sn hydrides generation from untreated filters of atmospheric particulate matter (PM₁₀ and PM_2.5) was optimised. PM₁₀ and PM_2.5 were not subjected to any pre-treatment: circular portions between 0.28 and 6.28 cm² were directly placed into the reaction vessel of a batch mode generation system. A 2⁸ × 3/64 Plackett–Burman design was used as a multivariate strategy for the evaluation of the effects of several variables affecting the hydride generation, trapping and atomisation efficiencies. Trapping temperature was the most statistically significant variable for As, Bi and Sn. Atomisation temperature was also statistically significant for Sb determination. Optimum values of significant variables were selected by using univariate optimisation approaches. An aqueous calibration method was used throughout. The developed method has been found to be precise with relative standard deviations of 6.2, 5.3, 9.1 and 7.5% for 11 determinations in a filter sample containing 0.7, 1.0, 1.4 and 1.7 μg l⁻¹ for As, Bi, Sb and Sn, respectively. Results obtained by direct solid sampling-HG-ETAAS have been found statistically comparable with those obtained after conventional method based on an acid digestion followed to ICP-MS. Absolute detection limits were 37, 15, 30, and 41 ng l⁻¹ for As, Bi, Sb and Sn, respectively. Detection limits referred to the air volume sampled (in the range of 0.020–0.050 ng m⁻³) were low enough for the determination of several hydride-forming elements from PM₁₀ and PM_2.5 samples collected in a non-polluted suburban area of A Coruña (NW Spain).     

Microwave digestion-ICP-MS for elemental analysis in ambient airborne fine particulate matter: rare earth elements and validation using a filter borne fine particle certified reference material

NIST standard reference material SRM 2783 was employed to validate a high temperature, high pressure, two-stage microwave assisted acid digestion procedure using HNO₃, HF and H₃BO₃ developed for the analysis of trace elements (including rare earths) in atmospheric fine particulate matter (PM_2.5) prior to inductively coupled plasma mass spectrometry (ICP-MS). This method quantitatively solubilized Na, Mg, Al, K, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sb, Cd, Cs, Ba, Pb, Th, U and several rare earth elements (REEs) (La, Ce, Pr, Nd, Gd, Dy, Er, Sm and Eu) from SRM 1648 and SRM 2783. A small amount of HF in the first stage was required to dissolve silicates necessitating the corresponding addition of H₃BO₃ in second stage to dissolve fluoride precipitates of Mg, La, Ce and Th. The optimized microwave dissolution—ICP-MS method detected Na, Mg, Al, K, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Cd, Mo, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Gd, Pb, Th and U at trace to ultra-trace levels in ambient airborne fine particles from three sites in North Carolina. La to light lanthanide signature ratios suggested that soil and motor vehicles are the dominant REE sources in SRM 2783 and PM_2.5 samples collected during this study.     

The role of C-centered radicals on the mechanism of action of artemisinin

Artemisinin is a sesquiterpene lactone with an endoperoxide function that is essential for its antimalarial activity. Endoperoxides are supposed to act on heme leading to the reduction of the peroxide bond and production of radicals, which can be responsible for killing the parasite. The geometries of artemisinin, radical anions and neutral species generated by rearrangement after reduction of the peroxide bond were fully optimized with the AM1 and PM3 semi-empirical methods, in order to characterize the intermediates formed during the process. Among the radicals calculated along the pathway for reductive decomposition of artemisinin, the secondary radical centered on carbon C₄ has the highest stability when compared to other radicals that can be achieved either by hydrogen migration to the original O-centered radical or by homolytic break of C–C bond. This suggests that the C₄-centered radical may be the species responsible for killing the parasite, as has been indicated previously in experimental studies.     

Picolinamide-Cu(Ac)2-imprinted polymer with high potential for recognition of picolinamide-copper acetate complex

In this report, with semi-empirical quantum method, we have studied the conformation and energy of supermolecule composed of picolinamide and its positional isomers with methacrylic acid. We tried to explore the reason why picolinamide was not likely to show imprinting effect when using methacrylic acid as functional monomer in our previous work. In order to produce imprinting effect, which was not achieved based on hydrogen bonding interaction, we have synthesized a molecular-imprinted polymer (MIP) based on copper ion coordination in prepolymerization. The complex in prepolymerization was composed of copper(II), acetate, picolinamide and 4-vinylpyridine (4-Vpy). Suprisingly, the MIP had high selectivity to picolinamide-copper acetate complex, and changes of either copper ion, picolinamide or acetate would result in decrease in the imprinting effect. This is also the first example where the high selective recognition of the MIP to its template was achieved mainly by inhibiting the binding of non-template rather than enhancing the binding of the template. And this report can be also looked upon as a first step towards the solution to the problem of imprinting of template that contains intramolecular hydrogen bond.     

Analysis of the effect of the electronic structure of the Cl atom in complexes of chlorides of group IV elements on Cl NQR frequency and asymmetry parameter

Analysis of changes in ³⁵Cl NQR frequency of complexes MCl₄.L and MCl₄.2L for M = Si, Ge, Sn and Ti was performed. The population of the atomic orbitals was calculated by the quantum chemistry methods PM3 and INDO. The results provided an explanation of the changes in ³⁵Cl NQR frequency and the asymmetry parameter upon complex formation. In the complexes of non-transition elements, a decrease in ³⁵Cl NQR frequency is first of all related to increasing population of p_z orbitals on Cl atoms. In the complexes of Ti, the increase in ³⁵Cl NQR frequency depends on a decrease in the p_π to d_π electron density transfer.     

木麻黄质膜离子泵在酸雨条件下对镧的响应

研究镧对酸雨(pH为4.5)胁迫下木麻黄幼苗早期生长和质膜离子泵ATP酶活性的影响。结果表明:较低浓度La3+浸种能使幼苗株高、根长、鲜重以及质膜质子泵活性明显增强,在200mg·L-1La3+处理时达到最高增强值,而高浓度的La3+浸种使之表现出抑制效应;幼苗质膜钙泵的活性受La3+抑制。质子泵活性与细胞的伸长生长呈显著正相关关系,镧对质子泵的活化作用有助于促进植物的生长,且适量的镧具有缓解酸雨胁迫下生长的植物细胞质酸化,维持细胞内环境稳定的间接作用。为抗酸雨和促生长,木麻黄经镧浸种8h的最适宜La3+浓度为50～200mg·L-1。     

Determination of polycyclic aromatic hydrocarbons (PAHs) in particulate matter collected with low volume samplers

The determination of polycyclic aromatic hydrocarbons (PAHs) contained in samples of particulate matter (PM), collected with low volume pumps, were carried out with an high sensitivity method that comes from several revisions of a previous method. The present work describes how, by using programmable temperature vaporization (PTV) and a mass selective detector with inert ionic source for the GC-MS analysis and the modifications of microwave-assisted extraction (MAE), the sensitivity of the method can be increased.The PAHs chosen for testing the method are: benzo[a]anthracene (BaA), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1,2,3-cd]pyrene (Ip) and dibenzo[a,h]anthracene (DbA). They, in fact, belong to that group of substances that are the most harmful for human health for their carcinogenicity.PAHs recoveries for spiked standard solutions at different concentrations were between 95 and 100% with relative standard deviation ranging from 1 to 3%. The revised method was validated using a 1649a urban dust standard reference material (SRM). The results obtained were in good agreement with certified values. The high sensitivity of the method allows to carry out analyses using only a half of the sampled filter (usually 47 mm diameter membranes). In this way, the other half can be used for the characterization of the other components of PM (heavy metals, organic carbon, ions, etc). The last step has been constituted by application of the optimized method on real samples collected in two cities located in Southern Italy (Bari and Taranto).     

环己硅烷类液晶化合物的量子化学研究

运用AM1和PM3两种SCF-MO方法，通过能量梯度全优化计算，给出20种环己硅烷类（苯基乙烷系）液晶化合物的稳定几何构型、电子结构和基本性质．联系有机电子结构理论进行了细致的讨论．     

Novel application of quantum chemical investigation in terms of substituent parameters: Statistical comparison of dual and single substituent parameter treatments

The correlation analysis of Mulliken charge (Q_M) calculated by using density functional theory (B3LYP/STO-3G) calculations of 1-(4-azido-5-hydroxymethyl-tetrahydro-selenophen-2-ylmethyl)-5-substituted-1H-pyrimidine-2,4-dione, were done by using mono substituent parameter (Hammett’s model), and dual substituent parameter (Taft’s, Reynolds’, and Swain’s models). The dual substituent parameter correlations of the Q_M data gave no significant improvement over single parameter correlations, the best correlation observed with the Taft’s Model as compared with the Swain’s and Reynolds’ Models, respectively. The correlation analysis of Mulliken charge can be used successfully to demonstrate the existence or absence of the interaction between the oxygen of the carbonyl group and selenium atom.