Application of a Single-Wall Carbon Nano-Tube Film Electrode to the Determination of Trace Amounts of Folic Acid

Single-wall carbon nano-tubes were used to modify the surface of a glassy carbon electrode (GC) and applied in the determination of folic acid with voltammetry. The experiments demonstrated that the presence of a carbon nano-tube film on the electrode greatly increased the reduction peak current of folic acid. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used in a comparative investigation of the electrochemical reduction of folic acid with the film electrode. Effects of pH on the peak current and the peak potential were studied in the pH range of 4.0–8.0 with Britton-Robinson buffer solution. The reduction peak current was found to be linearly related to folic acid concentration over the range of 1 × 10⁻⁸ to 1 × 10⁻⁴ mol L⁻¹ with a detection limit of 1 × 10⁻⁹ mol L⁻¹ after 5 min accumulation. The film electrode provides an efficient way for eliminating interferences from some inorganic and organic species in the solution. The high sensitivity, selectivity and stability of the film electrode demonstrate its practical application from a simple and rapid determination of folic acid in tablets.     

镓(Ⅲ)-向红菲咯啉络合物极谱吸附波的研究及应用

在 ＰＨ＝４．２的 ０．０７ ｍｏｌ／Ｌ ＨＡｃ－ＮａＡｃ介质中，Ｇａ（Ⅲ）－向红菲咯啉络合物在单扫描极谱仪上于－０．９８ Ｖ（ｖｓ．ＳＣＥ）处产生一灵敏的吸附还原波，其二阶导数波灵敏度高，波形好，峰电流 Ｉｐ与 Ｇａ（Ⅲ）在 ８．０×１０－８～３．０× １０－６ｍｏｌ／Ｌ的浓度范围内呈现良好线性关系，检出限为７．０×１０－８ｍｏｌ／ＬＧａ（Ⅲ）。用该法对粮食中的镓进行了测定，并对电极过程进行了研究。     

Anhydrous Sol-Gel Synthesis of Titania-Doped Siloxane Polymer for Integrated Optics

Sol-gel synthesis of organic-inorganic hybrid materials for planar waveguides and devices has received growing interest due to its low-cost processing and good suitability for doping. Titania is an important optical dopant, but homogeneous incorporation of titania in silica is difficult to be achieved by the conventional sol-gel process (aqueous system) because of the significant difference between the hydrolysis rates of the precursors. In this paper, we report an anhydrous sol-gel process for synthesising titania-doped siloxane polymers. The process consists of a hydrolysis of 3-methacryloxypropyltrimethoxysilane (MPS) with boric acid under anhydrous conditions, and a condensation with dimethyldimethoxysilane (DMDMS), diphenyldimethoxysilane (DPhDMS) and titanium ethoxide (TET). Optical characterisations for the produced titania-doped polymer were performed, and results showed that TET doping is useful for reducing the OH concentration of the synthesised polymer and is also effective for improving the optical quality of spin coatings. DMDMS and DPhDMS are favourable in reducing the birefringence and in increasing the thermostability of the material, and the methacryl groups of MPS are UV-polymerizable, which is useful for low cost fabrication of waveguides by photolithographic process. The results of ellipsometry scanning measurements show that titania is homogeneously incorporated in the hybrid matrix, suggesting that the anhydrous sol-gel process is useful for preparation of UV-sensitive titania-doped siloxane polymers for optical applications.     

Theoretical study of molecular interaction between tirapazamine enzymatic catalysis metabolites and water

The weakly hydrogen‐bonded complexes, between tirapazamine enzymatic catalysis metabolites and water, have been investigated by density functional theory (DFT), using the B3LYP hybrid functional. The geometries of these complexes have been fully optimized at the B3LYP/6‐31G(d) and B3LYP/6‐311+G(d) levels. The stabilization energies and charge changes of some atoms have been calculated and analyzed. The results indicate that the catalysis metabolites and water can form stable hydrogen‐bonded complexes. Nine complexes are identified. It is important and necessary to add zero‐point vibrational energy (ZPVE) and basis set superposition error (BSSE) corrections for calculating stabilization energy. The results also reveal an important relationship between the relative stabilities of hydrogen‐bonded complexes and the final products of tirapazamine medication. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

仿生聚合物材料用于糖肽的高选择性富集

蛋白质糖基化分析对深入认识其生物功能和发现生物标志物意义重大。由于生物样品中糖肽的丰度低，糖肽的富集至关重要。该文合成了一种以色氨酸为功能基团的新型仿生聚合物材料（简称Poly-Trp），并用于糖肽的高选择性富集。扫描电子显微镜、热分析仪和红外光谱仪等表征证明Poly-Trp已成功合成。通过考察溶液条件变化对糖肽在Poly-Trp保留的影响，发现糖肽在Poly-Trp上的保留分别随着溶液中乙腈浓度的降低和酸度的升高而变弱。且Poly-Trp对牛胎球蛋白糖肽的富集选择性高于商品化ZIC-HILIC和氨基硅胶，能抵抗物质的量倍数为100的牛血清白蛋白的干扰。该研究中仿生聚合物材料的设计为糖肽富集材料提供了新思路和新方法。     

Electrospun poly(l-lactide)-grafted hydroxyapatite/poly(l-lactide) nanocomposite fibers

Composite fibers composed of poly(l-lactide)-grafted hydroxyapatite (PLA-g-HAP) nanoparticles and polylactide (PLA) matrix were prepared by electro-spinning. Environmental scanning electron microscope (ESEM) and transmission electron microscopy (TEM) were employed to investigate the morphology of the composite fibers and the distribution of PLA-g-HAP nanoparticles in the fibers, respectively. At a low content (∼4 wt%) of PLA-g-HAP, the nanoparticles dispersed uniformly in the fibers and the composite fibrous mats exhibited higher strength properties, compared with the pristine PLA fiber mats and the simple hydroxyapatite/PLA blend fiber mats. But when the content of PLA-g-HAP further increased, the nanoparticles began to aggregate, which resulted in the deterioration of the mechanical properties of the composite fiber mats. The degradation behaviors of the composite fiber mats were closely related to the content of PLA-g-HAP. At a low PLA-g-HAP content, degradation may be delayed due to the reduction of autocatalytic degradation of PLA. When PLA-g-HAP content was high, degradation rate increased because of the enhanced wettability of the composite fibers and the escape of the nanoparticles from fiber surfaces during incubation.     

Preparation and characterization of pH- and temperature-responsive semi-IPN hydrogels of carboxymethyl chitosan with poly (<Emphasis Type="Italic">N</Emphasis>-isopropyl acrylamide) crosslinked by clay

A new kind of pH- and temperature-responsive semi-interpenetrating polymer network hydrogel based on linear carboxymethylchitosan (CMCS) and poly (N-isopropylacrylamide) (PNIPA) crosslinked by inorganic clay was prepared. The pH-and temperature-responsive behaviors, the deswelling kinetics, and the mechanical properties of the hydrogel were investigated. The hydrogels exhibited a volume phase transition temperature around 33 °C with no significant deviation from the conventional PNIPA hydrogels. The results of the influence of pH value on the swelling behaviors showed that the minimum swelling ratios of the hydrogels appeared near the isoelectric point (IEP) of CMCS, and when pH deviated from the IEP, the hydrogels behaved as polycations or polyanions. The novel hydrogels had much higher response rate than the conventional CMCS/PNIPA hydrogels. Moreover, the semi-IPN hydrogels crosslinked by clay could be elongated to more than 800% and the elongation could be recovered almost completely and instantaneously.     

Effect of secondary MO interaction on the regiospecificity in the reactions of tf-ionones with singlet oxygen

The ene reactions of a-ionones with singlet oxygen were examined to ascertain the effect of secondary MO interaction between the reactants on the reaction regiospecificity. Exclusive formation of 3-hydroxy-V-ionones found in the reactions reveals favorable interaction of singlet oxygen with the acyclic fl-hydrogen atom. On the other hand, no formation of 3-hydroxy-0-ionones implies that the steric requirement was not met for the bond formation between zwitterionic perepoxide with Ci-hydrogen in the process. The MMP21 and MNDO calculations indicate minus value of the secondary interaction energy for the acyclic a-hydrogen abstraction and a repulsion between the oxygen with C₁-hydrogen atom. Twisting tilting of the double bond may account for favorable attack of singlet oxygen on C3. An explanation of the excellent regiospecificity was addressed and placed in proper mechanic prospective.     

A note on constructing a symmetric matrix with specified diagonal entries and eigenvalues

A finite step algorithm is given such that for any two vectorsa, R ⁿ witha majorized by , it computes a symmetric matrixH R ^{n x n} with the elements ofa and as its diagonal entries and eigenvalues, respectively.Supported in part by NSF grant CCR-9308399.Supported in part by China State Major Key Project for Basic Researches.