Investigation of Zn<Subscript>m</Subscript>Cd<Subscript>n</Subscript>X<Subscript>y</Subscript> (y = m + n; X = Te,Se and S) Clusters with TDDFT Method

Based on zinc blende and wurtzite structures of experimental ZnTe and CdTe nanocrystals, Zn_mCd_nX_y (X = Te, Se and S) clusters were investigated using DFT/B3LYP/LANL2DZ. From analyses of their characters of conformations, HOMO–LUMO gaps, Raman and absorption spectra, Mulliken charges and WBI (Wiberg Bond Index) values, we have discovered that Zn_mCd_nTe_y, Zn_mCd_nSe_y and Zn_mCd_nS_y molecules had similar characters. In this paper, characters of Zn_mCd_nTe_y were investigated in detail. First, we have found that HOMO–LUMO gaps, Raman spectra, absorption spectra, bond lengths and Mulliken charges of doping Zn₂CdTe₃, ZnCd₂Te₃, Zn₃CdTe₄, Zn₂Cd₂Te₄ and ZnCd₃Te₄ structures were in the scope of corresponding naked ZnTe and CdTe clusters. These characters of doping Zn_mCd_nTe_y molecules show that their stabilities are good. Second, comparing with ZnTe structures, the wavelengths of the absorption peaks of doping Zn_mCd_nTe_y clusters shift to red in water environment. Moreover, with increasing of the number of Cd atom, their wavelengths of the absorption peaks gradually shift to red. This conclusion is consistent with the experimental fact. Third, Raman spectra of pure ZnTe clusters have higher frequencies than corresponding naked CdTe structures. As for doping molecules, the frequencies of their Raman spectra gradually shift to low frequencies with increasing of Cd atoms’ number.     

固相微萃取-气相色谱-质谱联用测定水中酚类化合物

建立了固相微萃取与气相色谱－质谱联用技术（SPME－GC－MS）测定水中酚类化合物的新方法，探讨了萃取时间、搅拌速度、离子强度、pH值和解吸时间等条件对萃取量的影响。结果表明：65μm PDMS/DVB涂层对水中的酚类化合物有较好的萃取效果，用于水中酚类化合物的测定，结果满意。     

Giant extended pi-conjugated dendrimers containing the 10,15-dihydro-5H-diindeno[1,2-a;1',2'-c]fluorene chromophore: synthesis, NMR behaviors, optical properties, and electroluminescence

This paper reports the facile synthetic strategy of a series of novel pi-conjugated dendrimers (G0 and G1) based on 10,15-dihydro-5H-diindeno[1,2-a;1',2'-c]fluorene (truxene) in which the benzene cores are generated "in-situ" from acetyl aromatics by the acid-promoted cyclotrimerizations. The unique NMR behaviors, physical properties, and electroluminescence device applications are also presented. Besides the purity, the structure, and the confirmation of the successful formation and isolation of desired compounds by clear assignments of every molecule by (1)H and (13)C and 2D NMR characterizations, several astonishing NMR behaviors have been observed in various solvents. For 1, chemical shift values belonging to H-2' of hexyl substituents move to the most upfield; however, such chemical shift values move from 0.48 to 0.85 ppm when pyridine-d(5) or benzene-d(6) is used as solvent. Our dendrimers as the emissive layers in organic light-emitting diodes gave blue-green light with an external quantum efficiency up to 0.16% both for G0 and for G1 in nitrogen, respectively, which exhibit unique electroluminescence spectra in comparison with their corresponding photoluminescence ones.     

Synthesis and characterization of the non-Kekulé, singlet biradicaloid Ar'Ge(micro-NSiMe(3))(2)GeAr' (Ar' = 2,6-Dipp(2)C(6)H(3), Dipp = 2,6-i-Pr(2)C(6)H(3))

Reaction of Ar'GeGeAr' (1) with an excess of Me3SiN3 gives the non-Kekulé, biradicaloid Ar'Ge(mu-NSiMe3)2GeAr' (3, Ar' = 2,6-Dipp2C6H3, Dipp = 2,6-i-Pr2C6H3) which has a planar Ge2N2Si2 array and pyramidal geometry at the germaniums. DFT calculations for the model MeGe(mu-NSiH3)2GeMe indicate no Ge-Ge bonding and a singlet ground state. The calculated energy difference between the optimized singlet and triplet states is 17.51 kcal/mol.     

Determination of residual levels of unsaturation in partially hydrogenated poly(2,3-diphenyl-1,3-butadiene) using TG

The thermal degradation characteristics of head-to-head poly(styrene) [HHPS] should provide insight with respect to the impact of head-to-head placement on the thermal stability of traditional atactic head-to-tail polymer [HTPS]. The synthesis of head-to-head poly(styrene) must be accomplished indirectly. The head-to-head polymer is most satisfactorily obtained by dissolving metal reduction of poly(2,3-diphenyl-1,3-butadiene) [PDBD] generated by radical polymerization of the corresponding diene monomer. Full saturation of the polymer mainchain requires several iterations of the reduction procedure. Since the decomposition of poly(2,3-diphenyl-1,3-butadiene) is prominent at 374°C and that for head-to-head poly(styrene) is similarly facile at 406°C, it seemed feasible that TG of partially hydrogenated PDBD might be utilized as a convenient means of monitoring the extent of hydrogenation. This has been demonstrated for various levels of unsaturation remaining - from approximately 90 to less than 10%. Within this range the peak areas from the DTG plots of the partially hydrogenated polymer provide a good reflection of the ratio of unsaturated to saturated units in the polymer. Even low levels of unsaturation in the polymer may be detected by the asymmetry of the decomposition peak for the polymer. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and characterization of novel even-odd nylons based on undecanedioic acid

A series of novel even-odd nylons were synthesized through step-heating melting-polycondensation of undecanedioic acid with various diamines. The synthesized polyamides were characterized comprehensively by means of elements analysis, intrinsic viscosity, Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), Raman spectra, thermogravimetry analysis (TGA) and differential scanning analysis (DSC). The obtained products except nylons 4 11 and 2 11 have intrinsic average molecular weights ranging from 1.3 × 10⁴ to 2.5 × 10⁴. Nylons 4 11 and 2 11 have intrinsic average molecular weights of 8400 and 7200, respectively. The melting temperatures of this series of even-odd nylons decrease with declining the concentration of hydrogen bonds. Furthermore, the dynamic mechanical analysis (DMA) was performed for nylons 12 11, 10 11, 8 11 and 6 11. The glass transition temperatures of nylons 12 11, 10 11, 8 11 and 6 11 are in the range of 40.1-45.7 °C.     

The effect of micro-morphology of Bi2O3 on catalytic properties of Co/Bi catalyst for wet air oxidation of acetic acid

The novel phase transfer catalysts S-8 [4-(dimethyloctylammonium) propansultan] and DB-X [1,4-bis(triethylmethylammonium)benzene dibromide] were synthesized and employed for high conversion synthesis of dichlorocyclopropane from various olefins.This revised version was published online in December 2005 with corrections to the Cover Date.     

Study on the Superhydrophilicity of the SiO2-TiO2 Thin Films Prepared by Sol-Gel Method at Room Temperature

Nanoscale SiO₂-TiO₂ composite thin films with the thickness of about 100 nm were prepared by sol-gel method at room temperature in air. The chemical states of the elements on the surface and near the surface were measured by XPS. The results showed that the Ti on/near the surface of the thin films existed not only as TiO₂ but also as Ti₂O₃. Part of the TiO₂ was changed to Ti₂O₃ after UV irradiation. The crystalline structure of the TiO₂ in the SiO₂-TiO₂ thin films was anatase with the crystallite size of 14–20 nm. It was found that the thin film prepared at room temperature in air has good superhydrophilic property and has strong adherence to the substrate.     

A novel approach to the synthesis of 6-amino-7-hydroxy-flavone

A novel approach to the synthesis of 6-amino-7-hydroxyflavone (1) is described. Reaction in acetone of 2',4'-dihydroxy-5'-nitroacetophenone and benzoyl chloride in the presence of potassium carbonate affords 3-benzoyl-7-hydroxy-6-nitroflavone, which is cleaved in 5% ethanolic potassium hydroxide to give 1-(2,4-dihydroxy-5-nitrophenyl)-3- phenyl-1,3-propanedione. The 1,3-diketone thus formed is then transformed into 7-hydroxy- 6-nitroflavone, followed by reduction to afford the title compound.     

A QM/MM study of a nucleophilic aromatic substitution reaction catalyzed by 4-chlorobenzoyl-CoA dehalogenase

Calculated using a QM/MM method, the free energy profile for the conversion of 4-chlorobenzoate to 4-hydroxybenzoate catalyzed by 4-chlorobenzoyl-CoA dehalogenase indicates the existence of a stable Meisenheimer complex.