DFT法研究HCOOH在Pd/WC(0001)上的分解机理（英文）

作为便携式电子设备的动力源,直接甲酸燃料电池(DFAFC)具有燃料跨界范围小、电动势大、甲酸无毒、低温下功率密度大等优点,因而引起了人们的极大兴趣.DFAFC商业化的主要挑战之一是阳极电催化剂材料的高成本和低CO耐受性.阳极通常需要高负载的贵金属电催化剂(Pt或Pd)氧化甲酸(HCOOH)以获得所需的电能.完全电氧化甲酸在Pt和Pd表面上会产生强吸附的CO,从而降低了Pt或Pd催化剂的活性.Pt和Pd储量少且价格昂贵,减少Pt和Pd含量且保持催化性能的燃料电池催化剂一直是研究者的奋斗目标.本文用周期性密度泛函理论(DFT)系统地研究了WC负载的单分子层Pd(Pd/WC(0001))催化剂对甲酸的分解机理,这可为所需的反应路径设计、筛选催化剂提供指导.Trans-HCOOH通过C–H, O–H, C–O键的活化发生分解.关于吸附,确定了可能反应中间体的最稳定吸附构型.trans-HCOOH, HCOO, mHCOO, cis-COOH, trans-COOH, CO, H₂O, OH和H的吸附过程是化学吸附,而cis-HCOOH和CO₂与Pd/...     

Iron(II) complex of 2-(1H-pyrazol-1-yl)pyridine-4-carboxylic acid (ppCOOH) suitable for surface deposition

Abstract

The synthesis, structural and magnetic characterization of the tris iron(II) complex of 2-(1H-pyrazol-1-yl)pyridine-4-carboxylic acid (ppCOOH) ligand are reported in [Fe(ppCOOH)₃](ClO₄)₂·0.5H₂O·2EtOH. Single crystal structure and magnetic characterization of the bulk compound show that the low-spin state is dominant from 2 to 400 K. ESI-MS and UV–Vis spectroscopy experiments indicate that acetonitrile solutions of this complex are stable with time. ESI-MS confirms the presence of the tris complex in solution. This complex can be deposited onto SiO₂ surfaces due to the presence of carboxylic acid groups by immersing the substrates into acetonitrile solutions of the complex. XPS spectra of the deposited complex are similar to those of the bulk sample. AFM images show a slight increase in roughness with respect to the naked substrate and the absence of aggregates. These results are consistent with the formation of a monolayer of the complex on the surface.     

Structures of Peptidic H‐wires at Mercury Surface: Molecular Dynamics Study

Biopolymer immobilization strategies, self‐assembly systems and adsorption phenomenon in general are crucial for the development of methods that work on the basis of the surface‐detection principle, including electrochemistry. A mechanistic view into the interaction of biopolymers with electrode surfaces is also important for studying fundamental and dynamic processes such as electron/proton transport. In this sense, the utilization of new approaches for investigating the interfacial behavior of immobilized biomolecular architectures is a permanent focus. Here we use a molecular dynamics (MD) approach to simulate the structural changes and metallic surface interactions of a model 21‐mer peptide of His (H) and Ala (A), A₃(HA₂)₆, a peptidic proton wire (H‐wire). This H‐wire was previously proposed for the electrochemical study of proton transfer at mercury electrodes (Langmuir, 2018, 34, 6997). The rigid solid mercury mono‐atomic layer (α‐mercury lattice model) was used systematically in all our simulations. The calculations were performed in a simulation box with 1, 16 and 32 H‐wire strands attached covalently to the mercury layer via the thiol group of a cysteinamide residue appended to the H‐wire C‐terminus. The internal alpha‐helical configuration of H‐wires was maintained by the presence of 2,2,2‐trifluoroethanol. It was shown that both the surface density of H‐wires and the protonation state of His residues play a decisive role in the structural stability and orientation of the peptide to the surface, whereas the applied voltage only has a mild effect on it, especially in case of 16 and 32 H‐wire strand configurations. The MD simulations presented here could be used for the further investigation of other peptides at metallic surfaces and for electrochemical analyses of structural changes of surface‐attached peptides that depend on their protonation states and other external factors.     

Highly ordered amphiphilic cyclopalladated arylimine self‐assembly films for catalyzing Heck and Suzuki coupling reactions

A series of new cyclopalladated arylimine compounds ( 3a , 3b , 3c , 4a , 4b , 4c ) were synthesized and characterized. Their catalytic properties for Heck and Suzuki coupling reactions in a homogeneous system were preliminarily investigated using water as solvent, in which no ligands, air isolation or assistant solvents were needed in cross‐coupling reactions. The optimization of the homogeneous system provided a basis for research on the heterogeneous catalytic reaction catalyzed by ordered self‐assembly films. Organized monolayers of 3a , 3b , 3c were prepared and utilized as C? C coupling catalysts. Monolayers of 3a , 3b , 3c were deposited using Langmuir–Blodgett techniques and analyzed using π–A isotherms, UV–visible and X‐ray photoelectron spectroscopies and atomic force microscopy, which showed near orientation on the surface and stability under the optimized experimental conditions suitable for exploring Heck and Suzuki coupling reactions. The activity of immobilized 3c monolayer is enhanced relative to homogeneous reaction, in which the ordered monolayers are efficient with a catalyst loading as low as 10^?5 mol%, turnover number as high as 79 200 and turnover frequency as high as 2640 h^?1. The catalytic efficiency is 100 times higher than that in the homogeneous case using the same amount and ratio of reagent. The increased activity of immobilized 3c monolayer is due to a combination of its structure and changes in conformation when deposited onto the substrate. The topographic changes of catalyst films, stability of films and catalytic activity were investigated with atomic force microscopy, cyclic voltammetry, X‐ray photoelectron spectroscopy and inductively coupled plasma atomic emission spectrometry, from which a heterogeneous catalytic mechanism for Suzuki coupling reaction is proposed. The study demonstrates that careful monolayer studies can provide useful models for the design and study of supported molecular catalyst systems. Copyright © 2016 John Wiley & Sons, Ltd.     

Fabrication of Au/Titania Composite Nanodot Arrays from Au‐Loaded Block Copolymer Micellar Films

Summary: A simple route to an ordered array of metal/semiconductor oxide composite nanodots is presented. Micellar monolayer films of polystyrene‐block‐poly(2‐vinyl pyridine) (PS‐b‐P2VP) loaded with HAuCl₄ in the P2VP nanodomains are used as templates. TiO₂ is generated selectively within the polar P2VP domains of PS‐b‐P2VP/HAuCl₄ films by chemical vapor deposition of TiCl₄. Subsequent removal of the organic matrix by oxygen plasma or UV light leads to an array of Au/TiO₂ composite nanoparticles on the substrate surface.

Schematic illustration of the process to fabricate an array of Au/titania composite nanodots.     

两种C60吡咯环多羧基衍生物自组装膜的制备及其光电转换性质研究

在ITO(indium-tin-oxide)透明电极和石英基片上,分别制备了两种C₆₀吡咯环多羧基衍生物的自组装膜,并用接触角、紫外光谱和电化学循环伏安进行表征.测定了这两种自组装膜体系的光电转换性质,研究了电子受体、偏压和光强等因素对它的影响.     

Calorimetric Investigation of the Monolayers Formed At Solid-liquid Interface

Heat capacity measurements have been made to investigate the formation of two solid monolayers each of n-pentane, n-heptane and n-dodecane adsorbed on graphite, one at submonolayer coverages and the other coexisting with the liquid. At submonolayer coverages the monolayers are found to melt respectively at 99.8, 151.6, and 217.3 K, well below the bulk melting points. The monolayers coexisting with the liquid melted at 205.6 for heptane and at 287.8 K for dodecane, whereas no evidence was obtained for pentane on the formation of such solid monolayer above the bulk melting point. The order persisting in the liquid near the interface depends upon the length of the molecules. The dodecane monolayers showed another transitions below the melting points both at submonolayer and multilayer coverages.This revised version was published online in November 2005 with corrections to the Cover Date.     

Structure and growth of self-assembling monolayers

The structural phases and the growth of self-assembled monolayers (SAMs) are reviewed from a surface science perspective, with emphasis on simple model systems. The concept of self-assembly is explained, and different self-assembling materials are briefly discussed. A summary of the techniques used for the study of SAMs is given. Different general scenarios for structures obtained by self-assembly are described. Thiols on Au(1 1 1) surfaces are used as an archetypal system to investigate in detail the structural phase diagram as a function of temperature and coverage, the specific structural features on a molecular level, and the effect of changes of the molecular backbone and the end group on the structure of the SAM. Temperature effects including phase transitions are discussed. Concepts for the preparation of more complex structures such as multi-component SAMs, laterally structured SAMs, and heterostructures, also with inorganic materials, are outlined. The growth and ways to control it are discussed in detail. Solution and gas phase deposition and the impact of various parameters such as temperature, concentration (in solution) or partial pressure (in the gas phase) are described. The kinetics and the energetics of self-assembly are analyzed. Several more complex issues of the film formation process including non-equilibrium issues are discussed. Some general conclusions are drawn concerning the impact of various molecular features on the growth behavior and concerning the relationship between growth and structural phase diagram. Finally, the potential of self-assembly as a route for the preparation of monolayers with pre-designed properties and SAMs as building blocks in heterostructures as well as application strategies are discussed.     

基于巯基自组装单层膜的日本血吸虫石英晶体微天平免疫传感器

应用自组装膜技术在压电石英晶振金电极表面自组装一带羧基的巯基丙酸单层膜,通过盐酸1-乙基-3-(3-二甲基氨基丙基)碳二亚胺及N-羟基琥珀酰亚胺共价固定32KD的日本血吸虫分子抗原(SjAg32),设计了石英晶振微天平免疫传感器,用于测定日本血吸虫抗体.比较了巯基自组装单层膜与HEMA-MMA共聚物涂层修饰的石英晶振在溶液中的振荡行为,发现巯基自组装单层膜修饰的石英晶振稳定快,且稳定性好.在优化条件下,测得IRS(49-2000)的滴度为1:1500.此外,对不同程度血吸虫感染的兔血清进行了测试,结果表明,该传感器能较好地定量区别血吸虫感染程度.