用θ-2θ型衍射仪测定溶液结构的新方法

叙述了用θ－２θ型Ｘ射线衍射仪精确测定电解质溶液结构的新实验技术。设计制作了具有恒温功能的超厚液体样品池，并建立了样品池窗口强度的校正方法。优化了液体Ｘ射线衍射数据和结构参数精细化的计算机程序，获得了非常令人满意的实验结果。由θ－２θ型Ｘ射线衍射仪精确测定的径向分布函数与θ－θ型衍射仪自由散射比较，表明ＤＲＦ分辨率有所提高。     

Fabrication and characterization of stable ultrathin film micropatterns containing DNA and photosensitive polymer diazoresin

Stable, ultrathin DNA micropatterns were fabricated from photosensitive polymer diazoresin (DR) through a self-assembly technique. The micropatterns were achieved on LBL ultrathin film after UV exposure through a photomask. The patterns were characterized systematically with scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and fluorescence microscopy. All of the results indicate that the combined LBL self-assembly and photolithography technique is a promising method for constructing stable, well-defined micropatterns with a nanoscale thickness.     

Separation and determination of estrone in environmental and drinking water using molecularly imprinted solid phase extraction coupled with HPLC

Estrone has been identified as an important potential endocrine-disrupting compound, so that sensitive and reliable analytical methods are required for its determination and the assurance of human health. Using estrone as the template, acrylamide as the functional monomer, and methacryloxypropyltrimethoxysilane as the cross-linker, an organic-inorganic hybrid material has been synthesized by the molecular imprinting technique combined with a non-hydrolytic so-gel process. The synthesized polymer was characterized by FT-IR and static adsorption experiments, and the results showed that it had good recognition and selective ability for estrone. A novel method for separation and determination of trace estrone in water samples was developed using molecularly imprinted solid phase extraction coupled with HPLC. Under the selected experimental condition, the detection limit (S/N = 3) was 9.3 ng/L, and the RSD for five replicate extractions of 10 mug/L estrone was less than 5.0%. This method was employed for quantitative determination of estrone in river, lake, and tap water with recoveries ranging from 83.38 to 98.12%.     

Influence of electric field intensity, ionic strength, and migration distance on the mobility and diffusion in DNA surface electrophoresis

In order to increase the separation rate of surface electrophoresis while preserving the resolution for large DNA chains, e.g., genomic DNA, the mobility and diffusion of Lambda DNA chains adsorbed on flat silicon substrate under an applied electric field, as a function of migration distance, ionic strength, and field intensity, were studied using laser fluorescence microscope. The mobility was found to follow a power law with the field intensity beyond a certain threshold. The detected DNA peak width was shown to be constant with migration distance, slightly smaller with stronger field intensity, but significantly decreased with higher ionic strength. The molecular dynamics simulation demonstrated that the peak width was strongly related with the conformation of DNA chains adsorbed onto surface. The results also implied that there was no diffusion of DNA during migration on surface. Therefore, the Nernst-Einstein relation is not valid in the surface electrophoresis and the separation rate could be improved without losing resolution by decreasing separation distance, increasing buffer concentration, and field intensity. The results indicate the fast separation of genomic DNA chains by surface electrophoresis is possible.     

Chemical ionization mass spectrometry of nitrosamines

The mass spectra of eight nitrosamines have been recorded, with excitation by chemical ionization (CI) and electron impact (EI). Comparison of the intensities of the base peaks under CI and El conditions gives intensity ratios in the range 1.4-1.9 for low resolution measurements and up to 10 for high resolution measurements, confirming the enhanced sensitivity available in the CI mode.     

Protective effects of cyclooxygenase-2 inhibitors on narrow-band ultraviolet B-irradiated epidermal Ia+ Langerhans cells and Thy-1+ dendritic epidermal T cells in mice

Cyclooxygenase (COX)-2 inhibitors are known to be used as chemopreventative agents against certain malignancies. Thus far, there has been very limited information on whether COX-2 inhibitors protect against chronic narrow-band UVB (NB-UVB)-induced immunosuppression. The present study investigated the effect of nonselective and specific COX-2 inhibitors, indomethacin and celecoxib, on epidermal Ia+ Langerhans cells (LCs) and Thy-1+ dendritic epidermal T cells (DETCs) in mice irradiated with NB-UVB. Sixty female BALB/c mice were divided randomly into the control group (sham) and the experimental groups (irradiated with NB-UVB for 17 weeks, further divided into five groups according to the diets containing different concentrations of either COX-2 inhibitors). Alterations in the density and morphology of epidermal Ia+ LCs and Thy-1+ DETCs in mice were documented using fluorescence microscopy. Chronic NB-UVB irradiation substantially decreased the density and altered the morphology of the epidermal Ia+ LCs and Thy-1+ DETCs in control mice. The dietary supplementation of both COX-2 inhibitors displayed a dosage-dependent protective effect on the murine dendritic cells irradiated by NB-UVB. In conclusion, COX-2 inhibitors protected against chronic NB-UVB-induced density and morphologic changes in epidermal Ia+ LCs and Thy-1+ DETCs in mice.     

Ultraviolet Raman study of thymine on the Au electrode

We record the potential-dependent Raman spectra of thymine adsorbed on the roughened Au electrode by ultraviolet (UV) excitation at 325 nm, and we find that the surface-enhanced Raman spectra of thymine changed intensely with the negative shift of the applied potential. When the vibrational mode changes, the resonance potential (potential of maximum intensity) varies accordingly, indicating that the thymine molecules were chemisorbed on the roughened Au surface. The charge transfer (CT) mechanism could probably explain the experiment results in the present work.     

Synthesis of biphenyl-2-carbonitrile derivatives via a palladium-catalyzed sp2 C-H bond activation using cyano as a directing group

Pd(II)-catalyzed aromatic C-H bond activation using cyano as a directing group was carried out in TFA medium. Biphenyl-2-carbonitrile derivatives were therefore synthesized from aryl nitriles and aryl halides in moderate to good yields.     

A fluorescence-based method for direct measurement of submicrosecond intramolecular contact formation in biopolymers: an exploratory study with polypeptides.

A fluorescent amino acid derivative (Fmoc-DBO) has been synthesized, which contains 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) as a small, hydrophilic fluorophore with an extremely long fluorescence lifetime (325 ns in H2O and 505 ns in D2O under air). Polypeptides containing both the DBO residue and an efficient fluorescence quencher allow the measurement of rate constants for intramolecular end-to-end contact formation. Bimolecular quenching experiments indicated that Trp, Cys, Met, and Tyr are efficient quenchers of DBO (k(q) = 20, 5.1, 4.5, and 3.6 x 10(8) M(-1) x s(-1) in D2O), while the other amino acids are inefficient. The quenching by Trp, which was selected as an intrinsic quencher, is presumed to involve exciplex-induced deactivation. Flexible, structureless polypeptides, Trp-(Gly-Ser)n-DBO-NH2, were prepared by standard solid-phase synthesis, and the rates of contact formation were measured through the intramolecular fluorescence quenching of DBO by Trp with time-correlated single-photon counting, laser flash photolysis, and steady-state fluorometry. Rate constants of 4.1, 6.8, 4.9, 3.1, 2.0, and 1.1 x 10(7) s(-1) for n = 0, 1, 2, 4, 6, and 10 were obtained. Noteworthy was the relatively slow quenching for the shortest peptide (n = 0). The kinetic data are in agreement with recent transient absorption studies of triplet probes for related peptides, but the rate constants are significantly larger. In contrast to the flexible structureless Gly-Ser polypeptides, the polyproline Trp-Pro4-DBO-NH2 showed insignificant fluorescence quenching, suggesting that a high polypeptide flexibility and the possibility of probe-quencher contact is essential to induce quenching. Advantages of the new fluorescence-based method for measuring contact formation rates in biopolymers include high accuracy, fast time range (100 ps-1 micros), and the possibility to perform measurements in water under air.