Experimental and density functional theory and ab initio Hartree-Fock study on the vibrational spectra of 2-(4-fluorobenzylideneamino)-3-(4-hydroxyphenyl) propanoic acid

2-(4-Fluorobenzylideneamino)-3-(4-hydroxyphenyl) propanoic acid (4-FT) was synthesized through the reaction of 4-fluorobenzaldehyde and l-tyrosine in refluxing EtOH. The structure of 4-FT was verified by measuring 1H NMR, FTIR and Raman. The ground-state geometries were optimized at B3LYP/6-31G**, B3LYP/6-31G*, HF/6-31G** and HF/6-31G* levels without symmetry constrains. The vibrational wavenumbers of 4-FT were calculated at same levels. The scaled spectra using B3LYP methods, which are in a good agreement with the measured spectra, are superior to those calculated using HF methods.     

Über die Wirkung verschiedener Oxydationsstufen des Nickels und Chroms bei der Heterogenen Austauschkatalyse

On the Effect of Different Oxidation States of Nickel and Chromium in Heterogenous Halogen Exchange Ni-doted AlF₃ catalysts and chromium oxide fluoride catalysts being used for production of C? Cl? F compounds from chlorocarbons by reaction with HF have been investigated by EPR. There are different oxidation states of Ni resp. Cr at the catalysts which show exchange behaviour. Extending the consumptions of mechanisms for heterogeneous Cl? F exchange the oscilation of oxidation state and therefore the exchange in donor-acceptor functions at the catalysts is said to be the cause for the effectiveness of the catalysts. It is presumed that this exchange of oxidation states is of general importance for catalytic processes with heterolytic bond cleavage.     

Experimental and density functional theory and ab initio Hartree-Fock study on the vibrational spectra of 2-(4-fluorobenzylideneamino)-3-mercaptopropanoic acid

2-(4-Fluorobenzylideneamino)-3-mercaptopropanoic acid (4-FC) was synthesized through the reaction of 4-fluorobenzaldehyde and l-cysteine in refluxing EtOH. Its structure was verified by (1)H NMR, FT-IR and Raman. The ground-state geometries were optimized at B3LYP/6-31G**, B3LYP/6-31G*, HF/6-31G** and HF/6-31G* levels without symmetry constrains, respectively. The vibrational wavenumbers of 4-FC were calculated at same level. The scaled theoretical spectra using B3LYP methods, which are in a good agreement with the experimental ones, are superior to those using HF methods.     

Oxygen removal from raw silicon powder by the HF‐ethanol solution etching

Silicon powder is vulnerable to oxidation due to its high surface activity. The as‐prepared Si powder is characterized by X‐ray photoelectron spectroscopy spectra coupled with an oxygen nitrogen analyzer, revealing that oxygen impurities mainly consist of Si oxides but with a small amount of free oxygen. The stable oxide films can deteriorate the properties of sintered materials since they cannot be removed during sintering process. The cleaning of these oxides by a single‐HF solution is not straightforward and efficient due to the large surface tension. To remove the oxygen, a more efficient way with the addition of ethanol to a HF solution has been proposed. The addition of a moderate percent of ethanol can decrease the water contact angle and then improve the cleaning efficiency. Importantly, the resulting Si powder possesses good dispersity, uniformity and fluidity. However, excess hydrofluoric acid suppresses oxide removal. Copyright © 2012 John Wiley & Sons, Ltd.     

Anchoring metal nanoparticles on hydrofluoric acid treated multiwalled carbon nanotubes as stable electrocatalysts

We attempted the treatment of multiwalled carbon nanotubes (MWCNTs) in hydrofluoric acid (HF) aqueous solution for depositing Pt nanoparticles as catalysts for methanol oxidation for the first time. The preliminary results revealed that the Pt nanoparticles could be well dispersed on HF treated MWCNTs and gave enhanced activity and stability for methanol oxidation. As demonstrated in this study, the Pt supported on HF treated MWCNTs catalyst gave over doubled current density than that of Pt supported on as-received MWCNTs for methanol oxidation at the same Pt loadings. The enhancement in the stability of the Pt supported on HF treated MWCNTs catalyst for methanol oxidation is believed due to the stronger interaction between Pt nanoparticles and MWCNTs. This study opens promising possibilities for anchoring metal nanoparticles on the walls of the MWCNTs uniformly and stably.     

Charge-transfer photochemistry of bis(diethyl-diselenocarbamato)copper(II)

The photochemical reactions of bis(diethyl-diselenocarbamato)copper(II), Cu(Et2dsc)2, complex have been studied in toluene, CH2Cl2, CHCl3 and chloroalkane/EtOH mixed solvents. Charge-transfer irradiation induces intramolecular oxidation of the ligand and reduction of copper(II) to copper(I) as evidenced by EPR and UV-Vis spectra of the complex as well as quantum yield results. When photolysis is carried out in CHCl3 or CH2Cl2 or in the solvent mixture CHCl3/EtOH resp. CH2Cl2/EtOH of lower than 1:1 EtOH content, the primary photoproduct CuI(Et2dsc) is further oxidised in a dark reaction with the chloroalkane producing the corresponding paramagnetic mixed-ligand CuII(Et2dsc)Cl complex in equilibrium with its chloride-bridged and EPR silent, dimeric form Cu2(Et2dsc)2Cl2. At low concentration of EtOH the equilibrium is shifted to the dimeric form whereas at higher than 1:1 EtOH content in the mixed solvent CHCl3/EtOH it is shifted to CuII(Et2dsc)Cl. A reaction mechanism is proposed and the role of ethanol is discussed.     

Plasma chemical synthesis and activation of heterogeneous catalysts gas treatment

Bulk and supported catalysts that are active in the CO oxidation reaction were obtained by the reaction of a low-temperature plasma with various catalyst materials Treating oxide catalysts with an HF discharge plasma results in an increase of their activity.Institute of General and Inorganic Chemistry, Ukrainian Academy of Sciences, Kiev. Translated from Teoreticheskaya in Eksperimental'naya Khimiya, Vol. 27, No. 6, pp. 641–646, November–December, 1991. Original article submitted August 27, 1991.     

Solvent effect on rate and mechanism of oxidation of chromium(III) by periodate

Summary The kinetics of chromium(III) oxidation by periodate were studied in various EtOH–H₂O solvent mixtures covering the 0.0 to 58.0 wt% EtOH range, at five different temperatures in the 15–35°C range. The rate of reaction increases with increasing EtOH content. Thermodynamic activation parameters have been calculated and an appropriate mechanism is suggested.     

Photoelectron spectroscopic and ellipsometric investigation of In0.53Ga0.47As surfaces after wet chemical etching

Summary The surface of (In, Ga)As has been investigated by photoelectron spectroscopy (XPS) and ellipsometry after different etching steps with a solution containing sulphuric acid to form an As rich surface layer. It was found that after rinsing the samples in a chloroform/acetone/methanol solution the native oxide consists mainly of As-oxide and In-hydroxide. The native oxide is almost completely removed by a short 1 s dip in buffered HF. The As rich surface formed after sulphuric acid etching oxidises quickly during exposure to air as can be seen from the XPS spectra. The etching causes a surface roughness of several nm. Taking into account surface roughness and oxidation the calculated ellipsometric angles fit well the data measured immediately after etching and after storage in air and Ar.     

优化金属辅助法腐蚀液组分制备多孔硅

金属辅助化学腐蚀法可以在无外加电路的条件下,在40%HF/30%H2O2/乙醇的混合溶液中完成多孔硅的制备,该方法简单快速。本文研究了金属辅助法腐蚀液体系各组分(HF、H2O2、乙醇)含量对多孔硅表面的SiHx成分和多孔层结构的影响,根据Si-H和Si-O的红外吸收峰强度的变化曲线优化了腐蚀液体系中各组分含量。在腐蚀液各组分体积比为V40%HF∶V30%H2O2∶V乙醇=2∶2∶1和腐蚀时间为4 min的条件下制备了形貌均匀、化学活性(SiHx成分)和多孔结构稳定性较好的多孔硅,并对金属辅助法与阳极蚀刻法制得的两种多孔硅进行比较,结果显示金属辅助法制备的多孔硅的化学活性和稳定性在后续的生物技术应用中具有明显的优越性。     

A study of gas-phase reactions of radical cations of mono- and dihaloethenes with alcohols by FT-ICR spectrometry and molecular orbital calculations: substitution versus oxidation

The ion-molecule reactions of the radical cations of vinyl chloride (1), vinyl bromide (2), 1,2-dichloroethene (3), 1,2-dibromoethene (4), 1,1-dichloroethene (5), and 1,1-dibromoethene (6) with methanol (MeOH) and ethanol (EtOH) have been studied by FT-ICR spectrometry. In the case of EtOH as reactant the oxidation of the alcohol to protonated acetaldehyde by a formal hydride transfer to the haloethene radical cation is the main process if not only reaction observed with the exception of the 1,2-dibromoethene radical cation which exhibits slow substitution. In secondary reactions the protonated acetaldehyde transfers the proton to EtOH which subsequently undergoes a well known condensation reaction of EtOH to form protonated diethyl ether. With MeOH as reactant, the 1,2-dihaloethene radical cations of 3.+ and 4.+ exhibit no reaction, while the other haloethene radical cations undergo the analogous reaction sequence of oxidation yielding protonated formaldehyde. Generally, bromo derivatives of haloethene radical cations react predominantly by substitution and chloro derivatives by oxidation. This selectivity can be understood by the thermochemistry of the competing processes which favors substitution of Br while the effect of the halogen substituent on the formal hydride transfer is small. However, the bimolecular rate constants and reaction efficiencies of the total reactions of the haloethene radical cations with both alcohols exhibit distinct differences, which do not follow the exothermicity of the reactions. It is suggested that the substitution reaction as well as the oxidation by formal hydride transfer proceeds by mechanisms which include fast and reversible addition of the alcohol to the ionized double bond of the haloethene radical cation which generates a beta-distonic oxonium ion as the crucial intermediate. This intermediate is energetically excited by the exothermic addition and fragments either directly by elimination of a halogen substituent to complete the substitution process or rearranges by hydrogen migration before dissociation into the protonated aldehyde and a beta-haloethyl radical. Reversible addition and hydrogen migrations within a long lived intermediate is proven experimentally by H/D exchange accompanying the reaction of the radical cations of vinyl chloride (1) and 1,1-dichloroethene (5) with CD3OH. The suggested mechanisms are substantiated by ab initio molecular orbital calculations.     

DSA-type anode based on conductive porous p-silicon substrate

Porous silicon (PS) thin films have been prepared by electrochemical anodization of p-Si in HF–H₂O–EtOH solution and they have been used as substrate material for the preparation of iridium oxide based electrodes (PS/IrO₂) using the thermal decomposition technique. The morphology and the electrochemical behaviour of the PS/IrO₂ have been studied and the results have been compared with IrO₂ electrodes deposited on a sandblasted p-silicon (p-Si/IrO₂). SEM analyses have revealed that the PS/IrO₂ electrodes are porous, rough and IrO₂ appears to be deposited within some silicon pores, while the p-Si/IrO₂ present a ‘mud-cracked’ surface. Cyclic voltammetries in 1 M HClO₄ have shown that the PS/IrO₂ presents higher surface area than p-Si/IrO₂.     

Renewable Pencil Electrodes for Highly Sensitive Anodic Stripping Voltammetric Determination of 3‐Hydroxyflavone and Morin in Bulk Form and in Biological Fluids

An electrochemical anodic adsorptive stripping procedure for ultra‐trace assay of 3‐hydroxyflavone (3HF) and Morin at a renewable pencil electrode (PGE) in bulk form and in biological fluids is described. The nature of the oxidation process of 3HF and Morin taking place at the PGE was characterized by cyclic voltammetry. The results show that the determination of the oxidation peak current is the basis of a simple, accurate and rapid method for quantification of 3HF by square‐wave anodic stripping voltammetry. Determination of Morin was achieved by square‐wave anodic adsorptive stripping voltammetry of the formed Morin? Cu(II) complex at a PGE. Factors influencing the trace measurements of 3HF and the Morin? Cu (II) complex at a PGE are assessed. The limits of detection and quantitation for the determination of 3HF and Morin in bulk form and in biological fluids were determined. The statistical analysis and the calibration curve data for trace determination of 3HF and Morin are reported.     

Efficient CO oxidation at low temperature on Au(111)

The rate of CO oxidation to CO2 depends strongly on the reaction temperature and characteristics of the oxygen overlayer on Au(111). The factors that contribute to the temperature dependence in the oxidation rate are (1) the residence time of CO on the surface, (2) the island size containing Au-O complexes, and (3) the local properties, including the degree of order of the oxygen layer. Three different types of oxygen--defined as chemisorbed oxygen, a surface oxide, and a bulk oxide--are identified and shown to have different reactivity. The relative populations of the various oxygen species depend on the preparation temperature and the oxygen coverage. The highest rate of CO oxidation was observed for an initial oxygen coverage of 0.5 monolayers that was deposited at 200 K where the density of chemisorbed oxygen is maximized. The rate decreases when two-dimensional islands of the surface oxide are populated and further decreases when three-dimensional bulk gold oxide forms. Our results are significant for designing catalytic processes that use Au for CO oxidation, because they suggest that the most efficient oxidation of CO occurs at low temperature--even below room temperature--as long as oxygen could be adsorbed on the surface.     

In situ studies of oxide nucleation,growth, and transformation using slow electrons

Surface processes such as metal oxidation and metal oxide growth invariably influence the physical and chemical properties of materials and determine their interaction with their surroundings and hence their functionality in many technical applications. On a fundamental level, these processes are found to be governed by a complex interplay of thermodynamic variables and kinetic constraints, resulting in a rich variety of material-specific phenomena. In this review article, we discuss recent results and insights on transition metal oxidation and rare-earth oxide growth acquired by low-energy electron microscopy and related techniques. We demonstrate that the use of in situ surface sensitive methods is a prerequisite to gaining a deeper understanding of the underlying concepts and the mechanisms responsible for the emerging oxide structure and morphology. Furthermore, examples will be provided on how structural and chemical modifications of the oxide films and nanostructures can be followed in real-time and analyzed in terms of local reactivity and cooperative effects relevant for heterogeneous model catalysis.     

Study of Aluminum–Oxygen Binary Systems: Determination of Partial Interatomic Distances

This paper reports on an Auger-electron study of the oxidation of the perfect surface of polycrystalline Al in residual gas atmosphere at a partial pressure of oxygen of 10 ^-10 torr. Under supervacuum conditions, layer-by-layer oxidation of the aluminum surface takes place along with stabilization of the chemical composition of the oxide film. Oxygen can penetrate into the oxidation region not only by deposition from the residual atmosphere but also by other mechanisms. After the chemical composition of the oxide film was stabilized, its local atomic structure was studied by Al and O K-edge extended electron energy loss fine structure (EELFS) spectroscopy. The estimated partial interatomic distances for Al–Al, Al–O, O–Al, and O–O atomic pairs permitted us to conclude that an oxide-like phase is formed in the subsurface layers of aluminum oxidized under supervacuum conditions and to construct a model of the local atomic structure of this oxide-like phase.     

Formation of titanium oxide nanogrooves island arrays by anodization

In the present work, titanium oxide nanogrooves island arrays (NGIAs) surface is formed by anodization of Ti foil in the high HF content electrolyte. The influences of anodization voltage and HF concentration of electrolyte on the formation of NGIAs are studied to control the depth and the distribution of nanogrooves. The formation mechanism of NGIAs is discussed. The strategy derived from the results is expected to apply to the NGIAs formation of other oxides which share the similar anodization behavior as titanium oxide.     

Correlation of global electrophilicity with the activation energy in single-step concerted reactions

The experimental energy of activation (Ea) of the single-step concerted oxidation process of aliphatic primary alcohols by quinolinium bromochromate (QBC) are correlated with the theoretically evaluated global electrophilicity values (w) [as proposed by Parr et al. (J. Am. Chem. Soc. 1999, 121, 1922)]. Conceptual justification in favor of correlating w of the substrate with Ea involved in a single-step concerted reaction is also discussed. The evaluated w values at HF/cc-pVTZ and MP2/6-31G(d,p) methods are found to be as expected (when we consider structural aspects), although there are some inconsistencies in other methods [e.g., HF/6-31G(d,p), B3LYP/cc-pVTZ, BLYP/dnp, PW91/dnp, PWC/dnp, VWN/dnp]. The reasons for the inconsistencies, even with a superior B3LYP/cc-pVTZ method, are discussed thoroughly. It is observed that the higher the value of w, the more the value of Ea involved in the process of oxidation of primary alcohols by QBC. The present study also reveals that the apparent success of insignificant (i.e., much smaller) local electrophilicity values (S+O(OH)), evaluated using Hirshfeld population analysis (HPA), in explaining observed trend of experimental Ea values turns out to be ambiguous when more significant (i.e., much larger) local nucleophilicity values (S-O(OH)) are also compared. This is evident from the corresponding correlation coefficient values.     

Relationships between strain,microstructure and oxide growth at the nano‐ and microscale

In the present article, the relationships between oxidation processes, surface strains and the microstructure of duplex stainless steels were investigated. Specimens were oxidized at 500 °C under secondary vacuum for 1 h to form a thin oxide film (thickness in the range of 20–50 nm). Such specimens were considered as the model system for developing novel methods of analysis in understanding the behavior of passive films. The interfacial strain field after oxidation was measured experimentally at the microscale using the point grid method. On the other hand, the chemical composition of the oxide film was determined at the submicroscopic scale by means of local scanning Auger spectroscopy (with a spot diameter of 50 nm). Local variations of the chemical composition of the oxide film were analyzed according to the specimen microstructure and the strain field. Copyright © 2008 John Wiley & Sons, Ltd.     

相转移催化合成香料烟酮及中间体异佛尔酮

报道了香料烟酮（2-羟基-3，5，5-三甲基-2-环戊烯酮）及中间体异佛尔酮的合成，首先用4-甲基-3-戊烯-2-酮与乙酰乙酸乙酯，在相转移催化剂Et3N^ CH2PhCl^-和EtONa/EtOH条件下合成中间体异佛尔酮，异佛尔酮在碱性条件下被H2O2氧化成2,3-环氧异佛尔酮，2，3-环氧异佛尔酮在酸性条件下反应生成烟酮，对烟酮的IR，^1H NHR谱进行了分析。