Double proton transfer behavior and one-electron oxidation effect in double H-bonded glycinamide-formic acid complex

The behavior of double proton transfer occurring in a representative glycinamide-formic acid complex has been investigated at the B3LYP/6-311 + + G( * *) level of theory. Thermodynamic and, especially, kinetic parameters, such as tautomeric energy, equilibrium constant, and barrier heights have been discussed, respectively. The relevant quantities involved in the double proton transfer process, such as geometrical changes, interaction energies, and intrinsic reaction coordinate calculations have also been studied. Computational results show that the participation of a formic acid molecule favors the proceeding of the proton transfer for glycinamide compared with that without mediate-assisted case. The double proton transfer process proceeds with a concerted mechanism rather than a stepwise one since no ion-pair complexes have been located during the proton transfer process. The calculated barrier heights are 11.48 and 0.85 kcal/mol for the forward and reverse directions, respectively. However, both of them have been reduced by 2.95 and 2.61 kcal/mol to 8.53 and -1.76 kcal/mol if further inclusion of zero-point vibrational energy corrections, where the negative barrier height implies that the reverse reaction should proceed with barrierless spontaneously, analogous to that occurring between glycinamide and formamide. Furthermore, solvent effects on the thermodynamic and kinetic processes have also been predicted qualitatively employing the isodensity surface polarized continuum model within the framework of the self-consistent reaction field theory. Additionally, the oxidation process for the double H-bonded glycinamide-formic acid complex has also been investigated. Contrary to that neutral form possessing a pair of two parallel intermolecular H bonds, only a single H bond with a comparable strength has been found in its ionized form. The vertical and adiabatic ionization potentials for the neutral complex have been determined to be about 9.40 and 8.69 eV, respectively, where ionization is mainly localized on the glycinamide fragment. Like that ionized glycinamide-formamide complex, the proton transfer in the ionized complex is characterized by a single-well potential, implying that the proton initially attached to amide N4 in the glycinamide fragment cannot be transferred to carbonyl O13 in the formic acid fragment at the geometry of the optimized complex.     

自由体积与亲水性对环氧涂层防护性能的影响

报道了涂层聚合物自由体积和亲水性对涂层腐蚀防护性能影响的初步研究结果.实验表明,相对于自由体积,树脂的亲水性是决定树脂吸水率的更主要因素.低亲水性涂层腐蚀防护性能的提高主要源自到达涂层/金属界面的水量的显著降低.但由于采用活性酯固化的环氧树脂涂层中水通道的尺寸相对较大,水合离子扩散较容易,因此该类涂层覆盖下的金属基体被润湿部分的腐蚀趋势反而较一般涂层为大.     

Determination of lutetium by fluorimetry, using BPMPHD and CTMAB

Lutetium(III) forms an association compound with a new synthetic reagent, 1,6-bi(1-phenyl-3-methyl-5-pyrazolone-4)hexandione (BPMPHD), and cetyltrimethylammonium bromide (CTMAB). The compound enhances the natural fluorescence of BPMPHD remarkably, upon which a new fluorescence method was developed for determining lutetium in rare earth (RE) samples. The determination range was 1.80 × 10^–7–8.8 × 10^–6 g/ml. The determination limit was 29 ng/ml. The composition of the ion associate was [Lu(BPMPHD)₂]–CTMAB⁺.     

应变速率和电位对应力腐蚀裂纹扩展的影响

以滑移-溶解-再钝化模型为基础,推导出应力腐蚀裂纹扩展速率与裂尖应变速率和电位之间的理论公式.计算表明,在裂纹扩展速率与裂尖应变速率的关系曲线中有两个特征区域.裂纹扩展速率在区域I随裂尖应变速率增加而增大,而在区域II不随裂尖应变速率的改变而变化.用慢应变速率拉伸技术（SSRT）测量了304L不锈钢的裂纹增长速率.当电位控制在区域II的阳极区时,理论计算的裂纹扩展速率与实验得到的结果比较吻合.     

Knoevenagel condensation catalysed by poly（vinyl chloride） supported tetraethylenepentamine （PVC-TEPA）

Poly(vinyl chloride) supported tetraethylenepentamine (PVC-TEPA) has been found to be an efficient catalyst for the Knoevenagel condensation. A wide range of aromatic aldehydes easily undergo condensations with ethyl cyanoacetate and malononitrile in the commercial 95% ethanol in refluxing using PVC-TEPA as catalyst to afford the desired products of good purity in moderate to excellent yields. A recycling study confirmed that the catalyst could be reused, the yield of the desired condensation product were not reduced. The merits of this protocol are environmentally benign, simple operation, convenient work-up and good yields. Furthermore, the catalyst can easily be recovered and reused at five times with comparable yields.     

1-氟代糖在化学-酶法合成糖类中的应用

化学-酶法合成糖类具有立体选择性和区域选择性, 逐渐成为糖类合成的主流. 1-氟代糖作为糖基供体应用于化学-酶法合成反应, 显示出越来越重要的作用, 综述了1-氟代糖在糖基转移酶和糖苷酶催化的糖类合成中的应用.     

Na2Ta2O6光催化剂的制备与性能研究

采用固相反应与水热法相结合制得了钽酸盐光催化剂. 对其在紫外光区降解刚果红溶液的行为进行了研究. 实验结果表明, 其具有光催化活性.     

铬(Ⅵ)与谷胱甘肽作用及其中间态配合物形成的电化学表征

本文采用电化学方法，对谷胱甘肽(GSH)与重铬酸钾的相互作用及其中间态配合物的形成过程进行研究。结果表明：在pH=5.6的HAc-NaAc缓冲溶液中，GSH浓度为Cr(Ⅵ)浓度5倍以上时，Cr(Ⅵ)与GSH作用完全并形成一新的中间态配合物，该中间态配合物于+0.21 V和+0.36 V(vs SCE)处产生一对新的氧化还原峰，UV-Vis的吸收光谱进一步证明了中间态配合物的形成。该配合物不稳定，在一定时间内缓慢分解，其电化学与UV-Vis光谱动力学信息同步。进一步探讨了GSH与Cr(Ⅵ)作用的电极反应机理。当Zn(Ⅱ)存在于该体系时，Zn(Ⅱ)对中间态配合物的生成和分解过程起着双向催化作用。     

A new capillary electrophoresis end-column amperometric detection system without the need for capillary/electrode alignment

A self-aligning end-column amperometric detection system for capillary electrophoresis was constructed. In this system, the electrode and capillary were exchanged easily and the capillary/electrode alignment procedure is not required. Gold, gold/mercury amalgam, copper and carbon fiber could be used as the working electrode. The principle is in the use of two disk holders with the capillary and the electrode in the center, so that by inserting the disk holders into a groove in the working electrode port, the capillary and the electrode are automatically aligned and the distance between the capillary and the electrode is assured at 0.24 mm. The relative standard deviation obtained using five different gold/mercury amalgam microdisk electrodes for determination of cysteine was 1.5% for the migration time and 3.3% for the electrophoretic peak current. The simple and convenient system was attractive for the routine analysis by capillary electrophoresis with electrochemical detection. The system was applied to the determination of promethazine hydrochloride in human serum.     

Direct spectrophotometric determination of Nd in mixed rare earths with semi-xylenol orange and cetylpyridinium chloride

The derivative absorption spectra of the neodymium complex with Semi-Xylenol Orange and cetylpyridinium chloride has been investigated. The characteristic absorption of the complex is approximately 350 times that of neodymium chloride. The fourth-order derivative spectrum has been used to eliminate the interference of the other lanthanides, and to increase the sensitivity by a further factor of 6. Beer's law is obeyed for 0-7.5 microg of Nd in 25 ml of solution. The relative standard deviation for 7 determinations of 1.8 microg/25 ml neodymium was 1.3%. The detection limits were 5.8 ng/ml in the absence of lanthanum and 11.2 ng/ml in the presence of 44 ng/ml lanthanum (or 36 ng/ml yttrium). The method has been used for the determination of neodymium in mixed rare earths, with satisfactory results.