Self-assembly of l-tryptophan on Cu(111) studied by low-temperature scanning tunneling microscopy

The self-assembly of l-tryptophan on Cu(111) is investigated by an ultrahigh vacuum scanning tunneling microscope (STM) at 4.4 K. When deposited onto the substrate at around 120 K with a coverage of 0.1 monolayer, molecular trimers, tetramers, hexamers, and chains coexist on Cu(111). Then almost all molecules self-assemble into chiral hexamers after being annealed at room temperature. When increasing molecular coverage to the full layer, a new type of chain is observed on the surface. Based on the high-resolution STM images at sub-molecular level, we suggest that the l-tryptophan molecules are present in neutral, zwitterionic or anionic states in these structures.     

A new kind of single Li-ion polyelectrolyte based on triazolate in a polyurea matrix: syntheses and properties

In this work, a new class of single Li-ion polyelectrolyte (SLIP) based on a polyurea matrix was developed from triazolate salt and diisocyanates with an aliphatic or aromatic moiety. The structure and chemical information were checked by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses. The aggregate structure, thermal stability, phase behavior and morphology were examined via X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry and scanning electron microscopy, respectively. It was found that the obtained SLIPs were disordered pore materials with amorphous structures and high stability, and the influence of varied isocyanate monomers on their properties was associated with hydrogen bonding derived from urea linkage. Furthermore, the electrochemical properties for the SLIPs absorbing dimethyl sulfoxide were determined by cyclic voltammetry, linear sweep voltammetry and electrochemical impedance spectroscopy, and the results showed that the electrolytes could endure an oxidation potential up to 4.2 V (vs. Li⁺/Li) and exhibited a practicable conductivity (10^?4 S cm^?1) at 30 °C. The cycling performance for an Li|Li cell was also tested preliminarily. The obtained results indicated that the developed SLIPs could be used as potential polyelectrolytes in lithium batteries.     

White luminescence of Tm-Dy ions co-doped aluminoborosilicate glasses under UV light excitation

Tm³⁺ and Dy³⁺ ions co-doped aluminoborosilicate glasses were prepared in this study. The luminescence properties of the glasses were analyzed. A combination of blue, green, yellow, and red emission bands was shown for these glasses, and white light emission could be observed under UV light excitation. White light luminescence color could be changed by varying the excitation wavelength. Concentration quenching effect was investigated in this paper. Furthermore, the dependence of luminescence properties on glass compositions was studied. Results showed that the luminescence intensity changed with different network modifier oxides, while the white color luminescence was not affected significantly.     

STM studies of fusion of cholesterol suspensions and mixed 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/cholesterol vesicles onto a Au(111) electrode surface

Electrochemical scanning tunneling microscopy (EC-STM) has been applied to study the structure of the film formed by fusion of cholesterol suspensions and mixed dimyristoylphosphatidylcholine (DMPC)/cholesterol vesicles on a Au(111) electrode surface. It has been demonstrated that cholesterol molecules assemble at the gold support into several structures templated by the crystallography of the metal surface and involving flat or edge-on adsorbed molecules. Studies of the film formed by fusion of mixed DMPC/cholesterol vesicles revealed that ordered domains of either pure DMPC or pure cholesterol were formed. These results indicate that, at the metal surface, the molecules released by the rupture of a vesicle initially self-assemble into a well-ordered monolayer. The self-assembly is controlled by the hydrocarbon skeleton-metal surface interaction. In the case of mixed DMPC/cholesterol vesicles, the molecule-metal interactions induce segregation of the two components into single component domains. However, the molecule-metal interaction induced monolayer is a transient phenomenon. When more molecules accumulate at the surface, the molecule-molecule interactions dominate the assembly, and the monolayer is transformed into a bilayer.     

Isothermal crystallization of polypropylene/surface modified silica nanocomposites

In the present work, 3-methacryloxypropyltrimethoxy-silane silanized silica(SiO_2-WD70) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide immobilized silica(SiO_2-WD70-DOPO) nanoparticles were prepared. Silica, SiO_2-WD70 and SiO_2-WD70-DOPO were incorporated into polypropylene(PP) by melt compounding. Differential scanning calorimetry(DSC), X-ray diffraction(XRD) and polarized optical microscopy(POM) were employed to investigate the isothermal crystallization behavior of PP and PP/silica composites. The kinetic constant(kn), and half crystallization time(t1/2) were calculated by Avrami equation,while the surface free energy of folding was calculated by Lauritzen-Hoffman theory. The increased kn, decreased t1/2 and the surface free energy(σe) in the order of PP, PP/SiO_2, PP/SiO_2-WD70 and PP/SiO_2-WD70-DOPO nanocomposites were attributed to the surface modification of silica. XRD indicated that SiO_2-WD70-DOPO addition had no effect on PP crystal structure but accelerated the crystallization rate. POM determined that SiO_2-WD70-DOPO addition promoted the nucleation of PP by inducing a higher nucleation density during isothermal conditions. The surface modified nanoparticle SiO_2-WD70-DOPO might find possible application as a new type of inorganic nano-sized nucleation agent for PP.     

Electric-field-driven surface aggregation of a model zwitterionic surfactant

Electrochemical measurements, atomic force microscopy, and scanning tunneling microscopy have been combined to describe the electric-field-controlled surface aggregation of N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS), a model zwitterionic surfactant, at a Au(111) electrode surface. At concentrations below the critical micelle concentration (CMC), the monomer adsorbs and aggregates at the surface. The charge on the metal (sigmaM) controls the orientation of adsorbed molecules and consequently the film structure. At high negative (sigmaM < -5 microC cm-2) charge densities, a spongy, disordered film is formed in which the polar heads are turned toward the solution. At high positive (sigmaM > +5 microC cm-2) charge densities, a planar film with "blisters" is observed with the polar heads of DDAPS turned to the metal. Hemicylindrical aggregates are observed in the intermediate charge density range (-5 < sigmaM < +5 microC cm-2). At bulk concentrations higher than the CMC, micelles adsorb and the structure of these films is controlled by the fusion of the adsorbed micelles. STM and AFM images provided direct visualization of this field-driven surface aggregation of the zwitterionic surfactant.     

卡托普利在汞电极表面的电化学行为

用循环伏安法、阴极溶出伏安法和电毛细管曲线测量等方法研究了卡托普利在汞电极表面的电氧化机理。实验结果表明,酸性溶液中卡托普利比较稳定,而在中、碱性溶液中卡托普利不稳定。在酸性溶液中有质子参与电极过程,卡托普利在电极表面发生单电子转移,生成汞（Ｉ）－硫化合物,该化合物在电极表面有强吸附,并进一步转化成汞（Ⅱ）－硫化合物。按照实验结果,计算了卡托普利的扩散系数和电极反应速率常数,提出了卡托普利电化学氧     

维生素K3电化学反应机理的红外光谱电化学研究

用循环信安法及现场红外光谱电化学法研究了维生素Ｋ３在铂电极上,弱碱性水溶液介质中的电化学反应机理。循环伏安法实验结果显示ＶＫ３的电反应为两步电子准可逆电极过程,现场光谱电化学实验结果则从基团特征吸收频率的变化表明了ＶＫ３的电化学还原和氧化经历了从萘醌到萘酚的互变过程。据此进一步证实了ＶＫ３由萘醌到酚的电化学反应机理。