Synthesis, structure, and nonlinear optical properties of cross-conjugated perphenylated iso-polydiacetylenes

Monodisperse, cross-conjugated perphenylated iso-polydiacetylene (iso-PDA) oligomers, ranging from monomer 15 to pentadecamer 25, have been synthesized by using a palladium-catalyzed cross-coupling protocol. Structural characteristics elucidated by X-ray crystallographic analysis demonstrate a non-planar backbone conformation for the oligomers due to the steric interactions between alkylidene phenyl groups. The electronic absorption spectra of the oligomers show a slight red-shift of the maximum absorption wavelength as the chain length increases from dimer 17 b to pentadecamer 25, a trend that has saturated by the stage of nonamer 22. Fluorescence spectroscopy confirms that the pendent phenyl groups present on the oligomer framework enhance emission, and the relative emission intensity consistently increases as a function of chain length n. The molecular third-order nonlinearities, gamma, for this oligomer series have been measured via differential optical Kerr effect (DOKE) detection and show a superlinear increase as a function of the oligomer chain length n. Molecular modeling and spectroscopic studies suggest that iso-PDA oligomers (n>7) adopt a coiled, helical conformation in solution.     

Determination of alpha-tocopherol in the Traditional Chinese Medicinal preparation Sea buckthorn oil capsule by non-aqueous reversed phase-HPLC

A non-aqueous reversed phase HPLC was developed for determining alpha-tocopherol in Sea buckthorn oil capsule without the need for saponification. A reversed phase column (Alltima C(18), 4.6 x 250 mm, 5 microm) was used with a mobile phase of methanol-acetonitrile (95 : 5, v/v) and flow rate of 1 ml/min. The contents in capsule were extracted with n-hexane. Detection wavelength was set at 292 nm. Each analysis requires no longer than 20 min. The linearity range for alpha-tocopherol was 9.4-47.0 microg/ml. The detection limit was 0.94 microg/ml. The mean recovery was 95.82 (RSD 2.3%). This method is suitable for quantitative analysis of alpha-tocopherol in Sea buckthorn oil or its Traditional Chinese Medicinal preparation.     

钡A-偶氮氯膦Ⅲ络合物探针分光光度法测定蛋白质

在pH 1.0～ 1.5的酸性介质中 ,蛋白质与Ba 偶氮氯膦Ⅲ络合物发生作用 ,导致络合物溶液褪色 ,其最大吸收波长处吸光度的降低值与蛋白质的浓度成正比。基于此建立了以Ba 偶氮氯膦Ⅲ络合物为光谱探针 ,分光光度测定蛋白质含量的新方法。该法灵敏度高 ,选择性好。蛋白质 (以牛血清白蛋白为例 )的浓度在 0～ 4 0mg/L范围内服从比尔定律 ,表观摩尔吸光系数ε656=6 .4 7× 10 5L·mol-1·cm-1。生物体内常见物质均不产生干扰 ,直接应用于人血清样品中蛋白质总量的测定 ,结果满意     

Effect of temperature on the surface free energy of amorphous carbon films

Diamond-like carbon (DLC) and tetrahedral amorphous carbon (ta-C) have attracted much attention recently for biomedical and antifouling applications due to their excellent biocompatibility and inherent nonstick properties. It has been demonstrated that the solid surface free energy is a dominant factor in cellular or fouling adhesion. However, few data for the surface free energy of DLC and ta-C coatings at temperatures in the range 37-95 degrees C are available. In this study DLC and ta-C coatings on stainless steel 304 sheets were prepared using an unbalanced magnetron sputtering system and a filtered cathodic vacuum arc system, respectively. The contact angles of water, diiodomethane and ethylene glycol on the coated surfaces at temperatures in the range 20-95 degrees C were measured using a Dataphysics OCA-20 contact angle analyzer. The surface free energy of the coatings and their components (e.g., dispersion, polar or acid/base portions) were calculated using various methods. The experimental results showed that the total surface free energy and dispersive surface free energy of the ta-C coatings, DLC coatings, stainless steel 304 and titanium decreased with increasing surface temperature, while the acid-base SFE component increased with increasing temperature.     

Determining the folding and unfolding rate constants of nucleic acids by biosensor. Application to telomere G-quadruplex

Nucleic acid molecules may fold into secondary structures, and the formation of such structures is involved in many biological processes and technical applications. The folding and unfolding rate constants define the kinetics of conformation interconversion and the stability of these structures and is important in realizing their functions. We developed a method to determine these kinetic parameters using an optical biosensor based on surface plasmon resonance. The folding and unfolding of a nucleic acid is coupled with a hybridization reaction by immobilization of the target nucleic acid on a sensor chip surface and injection of a complementary probe nucleic acid over the sensor chip surface. By monitoring the time course of duplex formation, both the folding and unfolding rate constants for the target nucleic acid and the association and dissociation rate constants for the target-probe duplex can all be derived from the same measurement. We applied this method to determine the folding and unfolding rate constants of the G-quadruplex of human telomere sequence (TTAGGG)(4) and its association and dissociation rate constants with the complementary strand (CCCTAA)(4). The results show that both the folding and unfolding occur on the time scale of minutes at physiological concentration of K(+). We speculate that this property might be important for telomere elongation. A complete set of the kinetic parameters for both of the structures allows us to study the competition between the formation of the quadruplex and the duplex. Calculations indicate that the formation of both the quadruplex and the duplex is strand concentration-dependent, and the quadruplex can be efficiently formed at low strand concentration. This property may provide the basis for the formation of the quadruplex in vivo in the presence of a complementary strand.     

Large-scale fabrication of aligned single-walled carbon nanotube array and hierarchical single-walled carbon nanotube assembly

Aligned single-walled carbon nanotubes (SWNTs) and hierarchical SWNT assembly were fabricated by electrospinning. The high fiber elongation and high DC electric field applied during the electrospinning process result in the orientation of the SWNTs along the axial direction of the fiber. The alignment of the electropsun composite fiber transfers this local SWNT orientation to macroscopically aligned SWNTs. After removing the polymer component from the aligned composite fiber, we produced large area aligned SWNTs. The results show that the directional control of SWNT alignment and debundling of SWNTs into individual tubes can be simultaneously realized.     

A comparative study of quantitative structure-activity relationship methods based on gallic acid derivatives

By using hologram quantitative structure-activity relationship (HQSAR) and comparative molecular field analysis (CoMFA) methods, the relationships between the structures of 49 gallic acid derivatives and their analgesic activity have been investigated to yield statistically reliable models with considerable predictive power. The best HQSAR model was generated using atoms, bond and connectivity as fragment distinction parameters and fragment size 5-7 from a hologram length of 307 with 3 components. High conventional r2 (r2 = 0.825) and cross-validation r2 (r2(cv) = 0.726) values were obtained. CoMFA analyses varying lattice size and location, grid spacing, probe charges and using, Tripos standard and Indicator force field were performed. The best model was developed with 4 components using sp3-hybridized carbon atom with +1.0 charge as probe, grid spacing (2 A), lattice offset (1.0, 3.0, -2.5). The CoMFA model showed a conventional correlation coefficient r2 of 0.889 and across-validation r2(cv) equals to 0.633. The robustness and predictive ability of the HQSAR and CoMFA models have been validated by means of an external test set. The results indicate that both models possess high statistical quality in the prediction of analgesic potency of novel gallic acid analogs.