A Study on 4,4′-Diaminobenzene Sulfonanilide (DABSA) and the Properties of Dyes Derived from DABSA

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Quantum mechanics/molecular mechanics study of the catalytic cycle of water splitting in photosystem II

This paper investigates the mechanism of water splitting in photosystem II (PSII) as described by chemically sensible models of the oxygen-evolving complex (OEC) in the S0-S4 states. The reaction is the paradigm for engineering direct solar fuel production systems since it is driven by solar light and the catalyst involves inexpensive and abundant metals (calcium and manganese). Molecular models of the OEC Mn3CaO4Mn catalytic cluster are constructed by explicitly considering the perturbational influence of the surrounding protein environment according to state-of-the-art quantum mechanics/molecular mechanics (QM/MM) hybrid methods, in conjunction with the X-ray diffraction (XRD) structure of PSII from the cyanobacterium Thermosynechococcus elongatus. The resulting models are validated through direct comparisons with high-resolution extended X-ray absorption fine structure spectroscopic data. Structures of the S3, S4, and S0 states include an additional mu-oxo bridge between Mn(3) and Mn(4), not present in XRD structures, found to be essential for the deprotonation of substrate water molecules. The structures of reaction intermediates suggest a detailed mechanism of dioxygen evolution based on changes in oxidization and protonation states and structural rearrangements of the oxomanganese cluster and surrounding water molecules. The catalytic reaction is consistent with substrate water molecules coordinated as terminal ligands to Mn(4) and calcium and requires the formation of an oxyl radical by deprotonation of the substrate water molecule ligated to Mn(4) and the accumulation of four oxidizing equivalents. The oxyl radical is susceptible to nucleophilic attack by a substrate water molecule initially coordinated to calcium and activated by two basic species, including CP43-R357 and the mu-oxo bridge between Mn(3) and Mn(4). The reaction is concerted with water ligand exchange, swapping the activated water by a water molecule in the second coordination shell of calcium.     

偶氮苯衍生物Langmuir-Blodgett膜的结构与红外热释电性能

利用Langmuir-Blodgett(LB)方法,在镀有金属膜的盖玻片和CaF_2衬底上转移了双嗜性偶氮苯衍生物多层LB膜.用线性红外二向色性光谱方法研究了分子的各跃迁矩的取向和分子长轴的取向.利用X射线衍射方法研究了LB膜的有序周期结构,讨论了双周期结构与高热释电活性的关系.     

酯加氢反应中影响羧基活化的因素

通过浸渍法制备4%Ru-9%La/γ-Al2O3催化剂,采用X射线衍射(XRD),X射线光电子能谱(XPS)和透射电子显微镜(TEM)对其结构进行表征.将该催化剂用于丙酸甲酯的加氢反应,分别考察了溶剂、无机盐添加剂、底物空间因素及电子因素对酯加氢反应的影响.发现以水为溶剂以及添加Co(NO3)2对丙酸甲酯加氢都显示出明显的促进作用,底物的转化率及丙醇的选择性随之增加.这是由于水及适量Co2+的引入能极化底物分子的C=O键,有利于活化氢对羧基碳原子的进攻,改善催化剂的性能.此外,底物分子中吸电子基团能提高羧基碳原子的正电性,也有利于加氢反应的进行;而增大底物分子空间位阻,不利于底物在催化剂上的吸附,催化反应速率下降.     

Surface Anchoring Stabilized High Strength Disclinations in Smectic C Phase of a Schiff-base Liquid Crystal

The observation of disclination cores of high strength S= -2, -3, -4, -5, -6, -7, -8 in a smectic C phase of Schiff-base type liquid crystal (LC) is reported. The results of polarizing optical microscope (POM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) prove that the sample exhibits smectic C phase. It is suggested that the formation of the high strength disclination is mainly ascribed to the stronger anchoring of LC molecules on the substrate due to the formation of hydrogen bonds between the pendent hydroxyl of the LC molecule and the substrate.     

阴离子柱撑磁性镍铝水滑石的制备及表征

将磁性基质与镍铝类水滑石组装制备磁性镍铝水滑石。研究了磁性基质含量、焙烧温度对水滑石磁学性能及结构的影响。并采用SEM、XRD、FT-IR、DSC-TG及VSM(vibrating sample magnetometer)等测试技术对制备的水滑石的结构和磁学性能进行了表征。结果表明,磁性基质的引入赋予镍铝类水滑石以超顺磁性,磁性基质含量对样品的磁性能起决定性作用,磁性镍铝水滑石的比饱和磁化强度随磁性基质含量的增加而增加;XRD分析结果表明,磁性基质的引入没有改变水滑石的典型层状结构且随着磁性基质含量的增多,磁性镍铝水滑石的特征衍射峰的衍射强度有所降低,n(Ni2 )/n(Fe2 )达到20时,XRD谱图中开始出现Fe3O4晶相的衍射峰;前驱体经1073K焙烧后出现尖晶石晶相;DSC-TG分析结果表明,磁性基质的引入没有改变水滑石2个阶段吸热的特征,这与XRD的检测结果一致。     

A pi-stacking terthiophene-based quinodimethane is an n-channel conductor in a thin film transistor

A terthiophene-based quinodimethane, 3',4'-dibutyl-5,5' '-bis(dicyanomethylene)-5,5' '-dihydro-2,2':5',2' '-terthiophene (1) was synthesized and crystallized. Compound 1 has a planar quinoid geometry that is stabilized by dicyanomethylene groups at each end of the molecule. In the crystal each molecule is part of a dimerized face-to-face pi-stack, with intermolecular spacings of 3.47 and 3.63 A, respectively. Cyclic voltammetry showed that 1 could be reversibly reduced and oxidized in methylene chloride solution. Thin film transistors (TFTs) were prepared by vacuum evaporation of 1 onto SiO2(300 nm)/Si substrates, followed by evaporation of Ag source and drain contacts. The doped Si substrate served as the gate electrode. X-ray diffraction and atomic force microscopy indicate the films are polycrystalline, with the long axes of the molecules approximately perpendicular to the substrate. The TFT measurements revealed n-channel conduction in films of 1, with room-temperature electron field effect mobilities as high as 0.005 cm2/Vs. The butyl side chains give 1 appreciable solubility in a range of common solvents, and preliminary TFT results on films cast from chlorobenzene show electron mobility as high as 0.002 cm2/Vs. These results indicate that pi-stacked quinoidal thiophene oligomers are a promising new class of soluble n-channel organic semiconductors.     

Ellipsometric and neutron diffraction study of pentane physisorbed on graphite

High-resolution ellipsometry and neutron diffraction measurements have been used to investigate the structure, growth, and wetting behavior of fluid pentane (n-C(5)H(12)) films adsorbed on graphite substrates. We present isotherms of the thickness of pentane films adsorbed on the basal-plane surfaces of a pyrolytic graphite substrate as a function of the vapor pressure. These isotherms are measured ellipsometrically for temperatures between 130 and 190 K. We also describe neutron diffraction measurements in the temperature range 11-140 K on a deuterated pentane (n-C(5)D(12)) monolayer adsorbed on an exfoliated graphite substrate. Below a temperature of 99 K, the diffraction patterns are consistent with a rectangular centered structure. Above the pentane triple point at 143.5 K, the ellipsometric measurements indicate layer-by-layer adsorption of at least seven fluid pentane layers, each having the same optical thickness. Analysis of the neutron diffraction pattern of a pentane monolayer at a temperature of 130 K is consistent with small clusters having a rectangular-centered structure and an area per molecule of approximately 37 A(2) in coexistence with a fluid monolayer phase. Assuming values of the polarizability tensor from the literature and that the monolayer fluid has the same areal density as that inferred for the coexisting clusters, we calculate an optical thickness of the fluid pentane layers in reasonable agreement with that measured by ellipsometry. We discuss how these results support the previously proposed "footprint reduction" mechanism of alkane monolayer melting. In the hypercritical regime, we show that the layering behavior is consistent with the two-dimensional Ising model and determine the critical temperatures for layers n = 2-5.     

金衬底上阴、阳离子型硫醇分子的量子化学计算

采用量子化学程序Gaussian98从头计算方法，对用做金衬底离子化的2—巯基乙基—二甲基氯化铵和3—巯基丙磺酸钠两种硫醇分子进行了全优化计算，得到了这两种化合物的平衡几何构型、基态能量、分子轨道组成和电荷分布等，并分析讨论了其分子轨道作用性质以及自由硫醇分子和金表面的相互作用．研究发现，表面分子基团带有大部分的净电荷，说明利用金与硫醇分子的自组装可实现金衬底的离子化。     

A quantum chemical study of the catalysis for cytidine deaminase: contribution of the extra water molecule

Cytidine deaminase is known as an important enzyme responsible for the hydrolytic deamination of cytidine, which is applied as a key step to the conversion of the precursor of the cancer drug to an active form in the living body. Cytidine with water is efficiently converted to uridine with ammonia in the cleft of cytidine deaminase. In this work, the catalysis of cytidine deaminase for the hydrolytic deamination was examined using cytosine as a model of cytidine and the model molecules for the active site of cytidine deaminase by means of the quantum chemical method. We especially investigated the contribution of the water molecule from the solvent to the catalysis, because the X-ray diffraction analysis of a crystal structure has revealed the existence of the water molecule in the vicinity of the substrate bound to the active site inside the cleft. Our computations showed that the extra water molecule from the solvent has a possibility to support the catalysis of cytidine deaminase.     

Molecular orientation and film morphology of pentacene on native silicon oxide surface

The growth morphology and mechanism of pentacene films on native Si oxide surface have been studied by using high-resolution electron energy loss spectroscopy (HREELS), X-ray diffraction (XRD), and atomic force microscopy (AFM). Despite the good agreement between our own and the reported XRD results, the previous XRD interpretation that the pentacene molecules are tilt-standing on the substrate cannot explain our HREELS data. The HREELS results show that a substantial portion of the first two layers of pentacene molecules are tilted-standing or randomly oriented, whereas the upper-layer molecules are mostly lying flat to the substrate. AFM reveals that the first two layers of molecules form a flat and smooth surface, but the upper layers show a rough terrace structure with a mean-square roughness equal to the average thickness (without counting the first two layers). This relationship is explained by a theoretical model which assumes the pentacene molecules to remain on a particular molecule layer after arrival. The observed film growth morphology may have significant implication on the performance of electronic devices based on pentacene thin films. A plausible explanation was proposed for the discrepancy between the HREELS-indicated and the XRD-derived molecular orientations.     

ChemInform Abstract: Molecular Structure of Chromium Tetrafluoride in the Gas Phase

is determined by electron diffraction at 195-220 °C. The diffraction patterns are completely consistent with a molecule of tetrahedral (Td) symmetry.     

Synthesis of 2‐Aminothiazole Derivatives in Easy Two‐Step,One‐Pot Reaction

Condensation of brominated ethyl acetoacetate with thiourea gives 2‐amino‐5‐ethoxycarbonyl‐4‐methylthiazole ( 1 ) and ethyl α‐(2‐amino‐4‐thiazolyl)acetate ( 2 ), indicating that bromination of the substrate occurs on both sides of the carbonyl group. X‐ray diffraction studies indicate weak hydrogen bonds of the amino groups, which are not observed in the IR spectra. The 1 molecule adopts planar S,O‐anti conformation in the crystal lattice, whereas the methylene group, insulating thiazole ring and the ester group in 2 molecule, makes it more flexible and makes the ester group nearly perpendicular to the thiazole ring. The small deviations of the bond lengths and angles indicate mesomeric interaction between complementary substituents across the thiazole ring.     

PVP-coated iron nanocrystals: Anhydrous synthesis, characterization, and electrocatalysis for two species

We report the synthesis of Fe nanocrystals (approximately 9 nm) in an anhydrous media, formamide, using poly(N-vinyl-2-pyrrolidone) (PVP) as a protecting agent. The morphology, structure, and composition of the PVP-coated Fe nanocrystals are studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and FT-Raman spectroscopy. The surface properties of the PVP-coated Fe nanocrystals are studied by electrochemistry and micro-surface-enhanced Raman scattering (mSERS) using pyridine as a probing molecule. The PVP-coated Fe nanocrystals, when immobilized on an electrode substrate, display very good electrocatalytic activities in the selective reduction of H2O2 in the presence of oxygen and in the oxidation of NO.     

Substrate-induced phases: transition from a liquid-crystalline to a plastic crystalline phase via nucleation initiated by the substrate

The presence of substrate-induced phases in thin films is an intriguing phenomenon with the physical and chemical factors responsible for their formation are not yet clearly understood. In this article, we present the structure and morphological changes associated with a substrate-induced phase in a discotic liquid crystal. The thin films of the discotic molecule are characterised by a combination of various X-ray diffraction methods to investigate the structural properties. Atomic force microscopy and polarised optical microscopy are used to determine the thin film morphologies. This is the first experimental proof of the presence of a substrate-induced phase in discotic liquid crystal, although they are known in thin films of molecular crystals. Moreover, we sought to decipher how the substrate-induced phase behaves with the evolution of time, temperature and changes at the interfaces. This work gives a unique example where the two-dimensional liquid-crystalline phase converts to a three-dimensional crystal plastic phase because of nucleation caused by the solid substrate over a time scale of a month or longer.     

Nonequilibrium molecular transport photoinduced by potential energy fluctuations

The mechanism of directed substrate-parallel motion of molecules caused by photoinduced potential energy fluctuations is investigated. Unlike simplistic models (e.g., an on-off ratchet), the approach suggested implies that the necessary asymmetry of the potential energy can arise not only from the asymmetry of the substrate potential but also from an asymmetric distribution of the fluctuating charge density in the molecule. The thus induced asymmetry of the potential energy governs the direction motion and enables, under certain conditions, its reversal at some frequencies of resonant laser pulses or temperature. These inferences are exemplified by the model charge distributions in the molecule and substrate, and the charge density fluctuations which are obtained by quantum chemical calculations for the realistic molecule of a substituted phenylpyrene compound on a model substrate.     

Study on the Model for Regulation of the Allosteric Enzyme Activity

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Water adsorption on a p(2x2)-Ni(111)-O surface studied by surface x-ray diffraction and infrared reflection absorption spectroscopy at 25 and 140 K

The adsorption of water molecules on an oxygen-predosed p(2x2)-Ni(111)-O surface was studied by surface x-ray diffraction and infrared reflection absorption spectroscopy (IRAS) at temperature of 25 and 140 K. Precise structures including adsorbed water, predosed oxygen, and substrate nickel atoms at these two temperatures were determined by x-ray structural analysis. It was found that water molecules adsorb on oxygen additive sites, forming a hydrogen bond at 25 K. A predosed 2x2 oxygen atom appears to accommodate one, two, or three water molecules at positions relating to threefold rotation symmetry. When the surface temperature was raised to 140 K, water molecules appear at an atop site of Ni. The distance between Ni and the oxygen atoms of a monomer water molecule was found to be 0.2241(22) nm. The adsorbed water molecule induces buckling and a lateral shift of the substrate nickel. The IRAS results provided evidence regarding the existence of two distinct adsorption sites. Water molecules in the low-temperature phase exhibit bands from both hydrogen-bonded nuOD and free OD stretchings, while those in the high-temperature phase lie flat with a molecular plane parallel to the surface.     

High-performance field-effect transistors based on Langmuir-Blodgett films of cyclo[8]pyrrole

We demonstrate the field-effect transistors (FETs) made of cyclo[8]pyrrole thin films prepared by the Langmuir-Blodgett (LB) method. The cyclo[8]pyrrole molecule possesses a 30-pi-electron system and narrower highest-occupied molecular orbital-lowest-unoccupied molecular orbital energy gap (0.63 eV), forms a stable, reproducible monolayer at the air-water interface, and transfers onto a substrate with a nearly unity transfer ratio and face-to-face configuration due to its strong pi-pi interaction. The LB films are uniform characterized by atomic force microscopy and in ordered form confirmed by X-ray diffraction. The FET exhibited high performances with one of the highest hole mobilities (0.68 cm2 V(-1) s(-1)) for thin-film transistors and a high on/off ratio, implying a promising material in the FET family.     

Structure and bonding of large aromatic molecules on noble metal surfaces: The example of PTCDA

Recent efforts to understand the interaction of large aromatic molecules with metal surfaces are discussed. We focus exclusively on work involving the model molecule 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) and the noble metal surfaces of Cu, Ag, and Au. Using this material system as an example, salient features of the (chemical) bond between an extended π-conjugated electron system and a metallic substrate are illustrated. Interface structures are a valuable indicator of the metal–molecule interaction strength. Consistent with the trend observed for small molecule adsorption, they indicate that the interaction strength of PTCDA with the metal substrate decreases in the order Cu–Ag–Au. The interfaces of PTCDA with the Au(1 1 1) and Ag(1 1 1) surfaces have been studied in particular detail. The interaction of Au(1 1 1) with PTCDA is weak, leading to point-on-line coincidence between the lattices of the substrate and the molecular overlayer. Experimental results on this surface are generally consistent with a predominantly physisorptive bonding of PTCDA. The situation is different on Ag surfaces, and in particular on Ag(1 1 1), where clear signs of PTCDA chemisorption are observed in many ensemble averaging and single molecule spectroscopies. Issues of electronic and geometric structure as well as electron–vibron interaction, and their relation to the chemical molecule–substrate interaction, are discussed in detail.