A Comparative Study of Electrochemical Reduction of 4‐Nitrophenyl Covalently Grafted on Gold and Carbon

4‐Nitrophenyl layers were grafted on gold and glassy carbon surfaces by electrochemical reductive adsorption of the corresponding diazonium salt. Electrochemical conversion efficiencies of 4‐nitrophenyl moieties to 4‐aminophenyl moieties on gold versus on glassy carbon in a protic medium were investigated using X‐ray photoelectron spectroscopy (XPS). In total contrast to all previous comparative studies showing greater electrochemical reactivity of aryl diazonium salt‐derived layers on gold than on glassy carbon, a much lower rate of conversion to 4‐aminophenyl was observed on gold than on glassy carbon by both cyclic voltammetry (CV) and chronoamperometry (CA) methods. The lower electron transfer rate during conversion observed on gold versus glassy carbon was proposed to be due to a mechanism related to the molecular structure rearrangement of 4‐nitrophenyl during the process on glassy carbon. However, whilst complete conversion of 4‐nitrophenyl to 4‐aminophenyl on gold by chronoamperometry was achieved, on glassy carbon complete reduction could not be achieved under the same conditions.     

Determination of complex reaction mechanisms. Analysis of chemical, biological and genetic networks

We present several methods of determining, not guessing, complex chemical reaction mechanisms and their functions. One method is based on the theory of correlation functions of measured time series of concentrations of chemical species; another is on measurements of temporal responses of concentrations to various perturbations of arbitrary magnitude; a third deals with the analysis of oscillatory systems; a fourth is on the use of genetic algorithms to determine functions of chemical reaction networks. All methods are applicable to chemical, biochemical, and biological reaction systems and to genetic networks and systems biology. The methods depend on the design of appropriate experiments on the whole system and corresponding theories for interpretation that lead to information on the causal chemical connectivity of species, on reaction pathways, on reaction mechanisms, on control centers in the system, and on functions of the system. The first three methods require no assumption of a model or hypothesis, nor extensive calculations, unlike the interpretation of measurements made on a gene network at only one time.     

Different approaches to legal requirements on validation of test methods for official control of foodstuffs and of veterinary drug residues and element contaminants in the EC

 In order to ensure food consumer protection as well as to avoid barriers to trade and unnecessary duplications of laboratory tests and to gain mutual recognition of results of analyses, the quality of laboratories and test results has to be guaranteed. For this purpose, the EC Council and the Commission have introducedprovisions – on measures for quality assurance for official laboratories concerning the analyses of foodstuffs on the one hand and animals and fresh meat on the other, – on the validation of test methods to obtain results of sufficient accuracy. This article deals with legal requirements in the European Union on basic principles of laboratory quality assurance for official notification to the EC Commission and on method validation concerning official laboratories. Widespread discussions and activities on measurement uncertainty are in progress, and the European validation standards for official purposes may serve as a basis for world-wide efforts on quality harmonization of analytical results. Although much time has already been spent, definitions and requirements have to be revised and further additions have to be made.     

Status of Drug Discovery Research Based on Marine Organisms from Eastern Indonesia

Despite the vastness of Eastern Indonesian Waters (EIW), no review has been done on the status of drug discovery research based on marine organisms from this area. The aim of this paper is to briefly discuss the challenges and perspectives on drug discovery research based on marine organisms in these indigenous waters. The emphasis is on the last 20 year period (1993 to 2013). Research activities completed during this period suggest that marine organisms from EIW could be utilized as an important natural resource for future drug discovery and development. However, lack of facilities, as well as competent human resources, significantly hinder progress on drug discovery research. More in-depth study especially on deep-sea natural products needs to be carried out to solidify the research on the potential for marine organisms from EIW to contribute to the future of drug discovery.     

Role of the Fermi surface in adsorbate-metal interactions: an energy decomposition analysis

We present the result of a fragment-based energy decomposition analysis on some molecule-surface interactions. The analysis allows us to quantify the Pauli repulsion, its relief, and the attractive orbital interaction energy. In a metal, the existence of incompletely occupied energy bands causes significant relief of the Pauli repulsion due to escape of antibonding electrons to unoccupied states at the Fermi energy. This is the key electronic structure feature of metals that causes metal-molecule bond energies to be stronger and dissociation barriers of chemisorbed molecules to be much lower than those in comparable systems with no or one metal atom. As examples, we discuss the energy decomposition for the activated dissociation of hydrogen on the Cu surface and its unactivated dissociation on Pd, and for the (activated) chemisorption of N2 on W. We show that in all cases the relief of Pauli repulsion is of crucial importance for the chemisorption energy and for the low (or nonexistent) dissociation barriers. The barrier to the chemisorption well for nitrogen on tungsten is clearly related to a late relief of the Pauli repulsion. The relief of Pauli repulsion is important in lowering the barrier to dissociation of H2 on both Cu and Pd, but the difference in barrier heights for Cu and Pd appears to not be due to stronger relief of Pauli repulsion on Pd but primarily to the Pauli repulsion itself being stronger on Cu than on Pd, the relief energy being quite comparable on the two metals.     

Spectroscopic analysis of L-histidine adsorbed on gold and silver nanoparticle surfaces investigated by surface-enhanced Raman scattering

The adsorption of l-histidine on gold (Au) and silver (Ag) nanoparticle surfaces has been comparatively analyzed by means of surface-enhanced Raman scattering (SERS). The SERS spectra of l-histidine on Ag were found to be quite different from those on Au, indicating dissimilar adsorption structures depending on metal substrates. Most peaks of l-histidine on Ag appeared to be due to coordination via the carboxylate (COO(-)) group with an imidazole ring of fairly upright geometry, whereas on Au it was assumed to adsorb with a rather flat geometry. A density functional theory (DFT) calculation was performed at the level of B3LYP/LANL2DZ to estimate the energetic stability of the binding of the imidazole ring and the carboxylate group of l-histidine with the Ag and Au atoms, respectively. Based on the DFT calculation, the carboxylate group of l-histidine was predicted to bind more favorably to Ag than to Au, and this was in line with our SERS spectral analysis.     

溶菌酶蛋白在聚合物防污膜表面的吸附

采用分子动力学模拟方法比较了溶菌酶蛋白在两种典型聚合物防污材料聚乙二醇(PEG)和聚二甲基硅氧烷(PDMS)表面的吸附行为, 在微观上探讨了聚合物膜表面性质对蛋白质吸附的影响. 根据蛋白质与聚合物膜之间的相互作用、能量变化及表面水化层分子的动力学行为, 解释了PEG防污涂层相对于PDMS表面具有更佳防污效果的原因: (1) 相比PDMS涂层, 蛋白质与PEG涂层的结合能量较低, 使其结合更加疏松; (2) 蛋白质吸附到材料表面要克服表面水化层分子引起的能障, PEG表面与水分子之间结合紧密, 结合水难于脱附, 造成蛋白质在其表面的吸附需要克服更高的能量, 不利于蛋白质的吸附.     

溶菌酶蛋白在聚合物防污膜表面的吸附

采用分子动力学模拟方法比较了溶菌酶蛋白在两种典型聚合物防污材料聚乙二醇(PEG)和聚二甲基硅氧烷(PDMS)表面的吸附行为,在微观上探讨了聚合物膜表面性质对蛋白质吸附的影响.根据蛋白质与聚合物膜之间的相互作用、能量变化及表面水化层分子的动力学行为,解释了PEG防污涂层相对于PDMS表面具有更佳防污效果的原因:(1)相比PDMS涂层,蛋白质与PEG涂层的结合能量较低,使其结合更加疏松;(2)蛋白质吸附到材料表面要克服表面水化层分子引起的能障,PEG表面与水分子之间结合紧密,结合水难于脱附,造成蛋白质在其表面的吸附需要克服更高的能量,不利于蛋白质的吸附.     

Ionic reaction of halogens with terminal alkenes: the effect of electron-withdrawing fluorine substituents on the bonding of halonium ions

Ionic reactions of terminal alkenes with chlorine (Cl(2)), bromine (Br(2)), and iodine monochloride (ICl) are sensitive to the alkyl substituents, and the positions and number of vinyl fluorine atoms. These perturbations influence the symmetry of the halonium ion intermediates, which can be determined by the distribution of the Markovnikov to anti-Markovnikov products. A vinyl fluorine on the number-2 carbon favors an unsymmetrical intermediate with greater charge on the number-2 carbon unless the alkyl group is electron withdrawing. A vinyl fluorine on the terminal number-1 carbon favors positive charge development on that carbon unless a resonance stabilizing group is on the number-2 carbon. The symmetry of halonium ions with vinyl fluorines on both carbons-1 and -2 depends primarily on the characteristics of the alkyl substituent. Intermediates range from open-ions with the positive charge on carbon-2, to various bridged species, to open-ions on the terminal carbon.     

Advancements in internationally accepted standards for radiation processing

Three subcommittees of the American Society for Testing and Materials (ASTM) are developing standards on various aspects of radiation processing. Subcommittee E10.01 “Dosimetry for Radiation Processing” has published 9 standards on how to select and calibrate dosimeters, where to put them, how many to use, and how to use individual types of dosimeter systems. The group is also developing standards on how to use gamma, electron beam, and x-ray facilities for radiation processing, and a standard on how to treat dose uncertainties. Efforts are underway to promote inclusion of these standards into procedures now being developed by government agencies and by international groups such as the United Nations' International Consultative Group on Food Irradiation (ICGFI) in order to harmonize regulations and help avoid trade barriers.

Subcommittee F10.10 “Food Processing and Packaging” has completed standards on good irradiation practices for meat and poultry and for fresh fruits, and is developing similar standards for the irradiation of seafood and spices. These food-related standards are based on practices previously published by ICGFI.

Subcommittee E10.07 on “Radiation Dosimetry for Radiation Effects on Materials and Devices” principally develops standards for determining doses for radiation hardness testing of electronics. Some, including their standards on the Fricke and TLD dosimetry systems are equally useful in other radiation processing applications.     

甲醇与氧在银钯合金上的吸附和反应

本文运用UPS、超高真空程序升温反应谱(TPRS)研究了氧和甲醇在银钯合金上的吸附和反应。实验结果表明, 合金表面存在两种分别与Ag和Pd原子有关的活性位; 少量钯原子的存在, 一方面提供了甲醇分解反应的活性中心, 另一方面通过与银之间的电子相互作用, 削弱了氧与银的结合, 增强了表面吸附氧的反应活性, 从而改变了甲醇氧化反应的选择性。     

Dewetting of liquids on ceramic surfaces at high temperatures.

The influence of surface structure and chemistry on high-temperature dewetting of silicate liquids on ceramic surfaces has been investigated. Model systems based on well-defined crystallography and known chemistry have been used to illustrate the effect of surface roughness and chemistry on the dewetting process. Reconstructed ceramic surfaces provide ideal substrates to study effects of surface roughness. It has been shown that the morphology of dewet droplets depend on the length scale and the crystallography of the facets on the surface. Complex pattern formation due to solute redistribution during dewetting is illustrated in the case of SiO2 dewetting on (001) rutile substrates. The role of kinetics on the dewetting process has also been clarified.     

软模板印刷法制备超疏水性聚苯乙烯膜

首次利用软模板印刷的方法,以微米-亚微米-纳米复合结构的PDMS为软模板,在平滑聚苯乙烯表面上成功制备了同样具有微米-亚微米-纳米复合结构的超疏水表面,该表面与水的接触角高达161.2º。软模板印刷方法可以用在其它热塑性聚合物如聚丙烯、聚甲基丙烯酸甲酯和聚碳酸酯等材料上,是一种简单有效地制备超疏水性表面的方法。     

The electroreduction of formaldehyde on tin and indium

The electrochemical behavior of formaldehyde on tin and indium cathodes has been studied over a wide range of pH (0.4–13), concentrations (1×10^?3 to 6×10^?1M) and potentials. Potentiostatic, potentiodynamic, ac impedance and photoe mission techniques were used to determine the kinetics of the reaction and to postulate a mechanism. The behavior on indium is similar to that reported on mercury cathodes. Tafel slopes are about 65 to 80 mV/decade. This value indicates that protonation of a reaction intermediate is the rate determining step of the reaction. The value of the slope depends slightly on concentration and pH because of adsorption under Temkin conditions. The reaction order with respect to formaldehyde is close to 1 in the limiting current region, but smaller in the Tafel region. The effect of formaldehyde on tin in neutral and alkaline solutions is to decrease the hydrogen overpotential by about 0.5 V, without affecting the Tafel slope. The rate of formaldehyde reduction is very slow. An explanation for this catalytic effect is postulated, based on the adsorption of formaldehyde-related species on the electrode surface. Formation of bridge-type complexes is also postulated. The exact nature of the adsorbed species is unknown. Preliminary results indicate that the behavior of formaldehyde on lead is similar to that on tin. The influence of this species on the reduction of formic acid on tin and lead is discussed.     

Interfacial behavior of tetrapyridylporphyrin monolayer arrays

The behavior of monolayer films of free base 5,10,15,20-tetrapyridylporphinato (TPyP) and 5,10,15,20-tetrapyridylporphinato zinc(II) (ZnTPyP) on pure water, 0.1 M CdCl2, and 0.1 M CuCl2 subphases was investigated by surface pressure-area isotherms, specular X-ray reflectometry, and polarized total reflection X-ray absorption spectroscopy (PTRXAS). Surface pressure-area isotherms showed significant differences in the area per molecule on pure water compared to that on salt subphases, with a marked increase in the area observed on the salt solutions. This behavior was noted for both forms of the porphyrin and both salts investigated. Modeling of specular X-ray reflectometry data indicated that thinner and more electron dense layers on salt subphases best fit the observed profiles. These data suggest that the porphyrin macrocycle is oriented parallel to the interface on salt subphases and takes on a tilted conformation on pure water. In the case of ZnTPyP, PTRXAS was used to determine the orientation of the porphyrin moiety relative to the surface and to probe the coordination of the central Zn ion. In agreement with the pressure-area isotherms and reflectometry, the PTRXAS data indicate a change in orientation on the salt subphases.     

Surface tension-induced gel fracture. Part 2. Fracture of gelatin gels

The spreading of surfactants on gel layers has been found to be accompanied by an intriguing instability which involves the formation of crack-like patterns on the surface of the gel. In an attempt to extend the findings on the spreading on agar gels presented in part 1 of this series, this paper examines the case of surfactant spreading on gelatin, which is a characteristic example of a protein-based gel. Aqueous solutions of Silwet L-77 of varying concentrations were spread on thick gelatin layers of varying concentrations. The resulting pattern formation was found to have many similarities to the corresponding phenomenon on agar. In terms of spreading dynamics, the values of the spreading exponent, n, of the power law L(t) ~ kt(n), which describes the temporal evolution of the cracks, are similar to those of the agar case, within the predicted limits for surface tension gradient-induced spreading on thick films, highlighting the dominant presence of Marangoni stresses. However, the values of the spreading coefficient, k, are much smaller compared to those measured during the spreading on agar. Further observations are linked with the rheological properties of gelatin, which are also measured in detail.     

NiO nanocone as a CO sensor: DFT investigation

Adsorption properties of CO molecule on NiO nanocone were investigated using density functional approach in terms of adsorbed energy, structural, and electronic properties. The results of the present study reveal that the favorable adsorption site for CO molecule is to the oxygen atom on the apex of NiO nanocone. The adsorbed energy on the apex of oxygen atom in nanocone is found to be ?8.432 eV. The average variation in the energy gap is found to be 50 % for CO adsorption on apex of oxygen atom. The Mulliken population analysis and density of states also confirm the adsorption of CO on to the oxygen atom in the apex of nanocone. The present result provides the insight to fine-tune the sensing properties of CO on to the NiO nanocone and enhance the sensing properties.     

Grafting of Polymers onto a Crosslinked Polymer Carrying Carboxyl Groups as a Model Compound for Carbon Black

Abstract

A cation-exchange resin (a crosslinked polymer carrying carboxyl groups) was used as a model compound for carbon black, and the grafting of several polymers to the resin was investigated. Reaction of acyl chloride groups that had been placed on the ion-exchange resin with polymers having hydroxyl or amino groups, such as polypropylene glycol, polyethylene glycol, polybutadiene glycol, polyvinyl alcohol, silicone diol, silicone diamine, and polyethyleneimine, resulted in grafting to the ion-exchange resin. In further experiments, primary amino groups were placed on the cation-exchange resin by reaction of acyl chloride groups with ethylenediamine. It was found that ring-opening polymerization of γmethyl L-glutamate N-carboxyanhydride is initiated by the amino groups on the resin, and polypeptide was grafted from the cation-exchange resin. Therefore, the reactivity of carboxyl groups on the resin was found to be similar to that on carbon black. However, carboxyl groups on the resin failed to initiate the cationic polymerization of vinyl monomers, in contrast to those on carbon black. This suggested that the acidity of carboxyl groups on carbon black is greater than on the cation-exchange resin.     

CO adsorption on Ag(100) and Ag/MgO(100)

Theoretical studies of CO adsorption on a two-layer Ag(100) film and on a two-layer Ag film on a MgO(100) support are reported. Ab initio calculations are carried at the configuration interaction level of theory using embedding methods to treat the metal-adsorbate region and the extended ionic solid. The metal overlayer is considered in two different structures: where Ag-Ag distances are equal to the value in the bulk solid, and for a slightly expanded lattice in which the Ag-Ag distances are equal to the O-O distance on the MgO(100) surface. The calculated adsorption energy of Ag(100) on MgO(100) is 0.58 eV per Ag interfacial atom; the Ag-O distance is 2.28 A. A small transfer of electrons from MgO to Ag occurs on deposition of the silver overlayer. CO adsorption at an atop Ag site is found to be the most stable for adsorption on the two-layer Ag film and also for adsorption on Ag deposited on the oxide; CO adsorption energies range from 0.12 to 0.19 eV. The CO adsorption energy is reduced for the Ag/MgO system compared to adsorption on the unsupported metal film thereby providing evidence for a direct electronic effect of the oxide support at the metal overlayer surface. Expansion of the Ag-Ag distance in the two-layer system also reduces the adsorption energy.