Search

The modification of polyvinyltrimethylsilane under treatment by direct-current discharge at a reduced pressure has been investigated. Polymer films were placed at the anode and cathode, and filtered atmospheric air was used as a process gas. It has been found that the discharge treatment imparts the property of hydrophilicity to the surface of the samples. The chemical composition of the untreated and modified films was investigated by X-ray photoelectron spectroscopy, and their morphology was studied by atomic force microscopy. It has been shown that plasma treatment leads to the formation of a layer chemically close to silicon dioxide on the surface and increases the roughness of the surface of polyvinyltrimethylsilane.

This work considers new possibilities for the use of membrane gas separation technology for target control of the composition of synthesis gas. For this purpose, we propose using highly permeable modified disubstituted polyacetylenes with an improved combination of selectivity of separation of hydrogen, carbon monoxide, and carbon dioxide and a high level of transfer of hydrogen as the main component of synthesis gas. This work presents the description of the modification of polymers and key properties of membrane materials. The process of membrane separation of synthesis gas is modeled using both commercially available membranes and new laboratory membranes. The possibility of creating a combined membrane system providing the preparation of synthesis gas with a wide range of H2 : CO ratios (from 0.5 to 4) and a low residual concentration of CO2 (5 vol %) from biosyngas with the composition H2 (40 vol %)/CO (25 vol %)/CO2 (35 vol %) is also shown.

Platinum-based supported catalysts for hydrocarbon conversion are among the most effective for selective dehydrogenation and isomerization processes. However, high process temperatures and the poss...

The specifics of diffusion of water and methanol vapors in nonporous polymer films based on polyvinyltrimethylsilane (PVTMS) have been studied. The vapor diffusion coefficients have been determined by measuring the kinetics of unsteady flow through the membrane (differential method) and subsequent processing the results by functional scaling . The kinetic curves have been found to deviate from those described by classical Fick’s law. It has been theoretically shown that such deviations can be due to the formation of associates of penetrant molecules inside the membrane, and a modified method for calculating diffusion coefficients has been proposed for this case. The behavior of the diffusion coefficients of water and methanol vapors in PVTMS in the temperature range of 50–90°C and the vapor activity range of 0.3–0.9 has been studied. The activation energies of diffusion of water and methanol vapors in PVTMS have been determined to be 23 and 44 kJ/mol, respectively, and the effective kinetic diameters of the molecules have been calculated to be 0.29 and 0.37 nm, respectively. The proposed approach opens the possibility for systematic studies of the diffusion kinetics of vapors of different organic compounds with an assessment of their kinetic contribution to the membrane permselectivity.

This study examines the fundamental and practical aspects of C1-C4 hydrocarbons separation (pure or in binary or ternary mixtures), using highly permeable glassy 1,2-disubstituted polyacetylenes. Poly(4-methyl-2-pentyne) (PMP) was chosen as the main object of study. An attempt is made here to carry out a systematic comparative study of the PMP permeability target parameters using correlation detection and a thermodynamic gas/polymer model. A non-isothermal application method was used, which allowed us to work with each gas individually and with various mixtures to obtain an experimental value for the dependence on temperature of the permeability of C1, C3, C4 hydrocarbons. This is the first time that this method has been used for the study of glassy polymers with high free volume. An interesting phenomenon of an increase in non-additive separation selectivity α was shown (for a value of α of between ∼10 and ∼8000 units) with increase of butane activity (p/psat) from 0.02 to 0.94 in the feed gas mixture. In the current study, an explanation is given for the increase in non-additive selectivity for PMP membrane separation. Modelling was carried out of the separation process of a binary butane/methane mixture using this non-additive phenomenon, which gives rise to concentrated components.

A «green» method of obtaining gas separation composite membranes from cellulose solutions and its mixtures with chitosan in orthophosphoric acid is proposed for industrial use, and differs from the viscose method of producing cellophane and other known methods for producing cellulose gas separation membranes without gaseous emissions and wastewater. It is shown that new composite cellulose membranes on a viscose fabric substrate are characterized by high productivity and selectivity for O2/ N2 pairs, comparable to the values obtained for known membranes made of synthetic polymers, as well as increased mechanical strength. The developed composite membranes demonstrate an inverse selectivity for the CH4/CO2 pair, which is not typical for gas separation membranes described in the literature with cellulose-based selective layers.

Recent advances in organic surface sensitization of metal oxide nanomaterials focused on two-step approaches with the first step providing a convenient functionalized chemical "hook", such as an alkyne functionality connected to a carboxylic group in prop-2-ynoic acid. The second step then took advantage of copper-catalyzed click chemistry to deliver the desired structure (such as benzyl or perylene) attached to an azide to react with the surface-bound alkyne. The use of this approach on CuO not only resulted in a successful morphology preserving chemical modification but also has demonstrated that surface Cu(I) can be obtained during the process and promote a surface-catalyzed click reaction without additional copper catalyst. Here, it is demonstrated that this surface-catalyzed chemistry can be performed on a surface of the CuO nanomaterial without a solvent, as a "dry click" reaction, as confirmed with spectroscopic and microscopic investigations with X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, solid-state nuclear magnetic resonance, and scanning electron microscopy. Computational studies provided instructive information on the interaction between the surface prop-2-yonate and azide functional group to better understand the mechanism of this surface-catalyzed click reaction.

The structure and gas transport properties of polymer membranes prepared from commercial Lavsan™ (polyethylene terephthalate based material) films by irradiation of the polymer films with Ar ions, followed by etching in an NaOH solution, were studied. Analysis of the polymer structure by differential scanning calorimetry showed that irradiation of the Lavsan™ matrix with Ar ions (energy 2.4 MeV nucleon−1, fluence 6 × 107 cm−2) led to a 20–30% decrease in the degree of crystallinity. The permeability of the new membranes to He, H2, O2, Ar, N2, CH4, CO2, and H2/CH4 mixture was evaluated. UV sensitization allows a fourfold increase in the permeability of the Lavsan™-based films to the gases tested relative to the films etched without preliminary UV irradiation. The composition of the H2/CH4 gas mixture does not influence the separating properties of the membranes, and the mixture separation factor coincides with the ideal value of the gas selectivity.

A three-stage process for the production of motor fuel (MT) components from lignocellulosic raw materials is described. In the first, pretreatment stage, lignocellulose is subjected to hydrolysis with cellulases followed by fermentation of the resulting sugars into ethanol; then, dilute ethanol solutions are concentrated by membrane vapor separation to obtain 70–80% solutions. At the third stage, aqueous ethanol solutions (water content 0–50%) in the presence of a Pd–Zn/Al2O3/MFI catalyst at 350°C and a space velocity of 0.6 h−1 are converted into alkanes, and С3–С8 olefins and С6–C12 aromatic compounds (MT components). It has been found that water in an amount of up to 30% in ethanol solutions effectively inhibits the detrimental hydrocarbon cracking and catalyst coking processes, thereby leading to a decrease in the formation of undesirable C1 and C2 products and an increase in the catalyst on-stream time to 100 h wherein the yield of the desired fraction is reduced only by 10–15%. The subsequent treatment of the catalyst surface with steam and hydrogen completely restores its catalytic activity.

A novel approach to the evaluation of the C 1 –C 4 hydrocarbon (pure and mixed-gas) permeability parameters in the thin film composite membranes with rubbery or glassy-like selective layers is presented. The permeability measurements are performed for the C 1 –C 4 hydrocarbons on the commercially available membranes MDK (based on polydimethylsiloxane (PDMS)) at the temperature range of −20° up to +40 °C under linear heating. The values of the gas permeability coefficients P and the apparent activation energy E P were measured during same experiment. The solubility data ( S and ΔH S ) were calculated using the Pierotti’s statistical-thermodynamic model. The diffusion coefficients were calculated indirectly using the permeability and solubility data assuming the solution-diffusion model for permeation. The equal data sets were obtained for the polyisoprene membranes and the polyvyniltrimethylsilane ones. It is concluded that the ideal C 1 –C 4 -hydrocarbon separation selectivity is controlled by the kinetic component (selectivity of diffusion). The article also describes the permeability increase of propane, butane (pure and in mixtures) under the temperature pull down in the PDMS (being consistent with the lower activation diffusion energy E D of those hydrocarbons in the typical rubber-like polymeric matrix which is a thin selective layer). The results of this study will be useful in understanding of the fundamental aspects of the membrane C 1 –C 4 separation phenomena, and for the fast separation parameters evaluation of the lower hydrocarbon mixtures using the polymeric membranes as well.

Chemical functionalization of ZnO surface with an alkyne functional group was successfully achieved by exposing ZnO nanopowder to gas-phase propiolic acid in vacuum, which left the alkyne group available for subsequent chemical modification via the azide-alkyne cycloaddition "click" reaction with benzyl azide. The highly selective formation of a bidentate carboxylate linkage and the reaction of benzyl azide were confirmed by solid-state nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Most importantly, scanning electron microscopy revealed that the surface morphology was perfectly preserved by this gas-phase modification, as opposed to the alternative protocols based on liquid phase processing. This simple and precise design can serve as a universal method for the modular functionalization of zinc oxide surface following the initial surface preparation and be further applied to thin films, nanostructures, and powders, where preserving surface morphology during chemical modification is especially important.

This chapter represents results of critical analysis of published and owned data on application and potential of polymeric membranes for hydrogen separation/purification. This paper considers the promising polymers for membranes, gas separation properties of commercially available and lab-scale membrane (hollow fibers [HF] and flat sheets), and results of correlation analysis for prediction of the permeance of attendant gases presented in multicomponent gaseous mixtures. The calculation of the membrane separation for hydrogen recovery (separation) using commercially available and lab-scale membranes is done as an example of the membrane technology application for hydrogen recovery from biomass treatment products (renewable sources) and from exhaust gas mixtures of technogenic origin. Critical aspects included (1) phenomenology and some regularities of the gas transfer through nonporous polymeric materials as basis for gas separation membranes; (2) membrane polymers with high selectivity in relation to hydrogen; (3) commercially available and lab-scale polymeric membranes for separation of H2 from mixtures with CO2, CO, N2, CH4, and H2S; and (4) calculation of standard one-stage membrane processes itself for hydrogen recovery from selected gaseous multicomponent mixtures of technogenic and biogenic origin. All studied gas-permeable polymeric materials can be divided in two classes: (1) Most glass-like polymers are hydrogen-selective polymers and can, in principle, be used for membranes with predominant hydrogen permeability. In this case, hydrogen enrichment (purification) occurs in permeate. The selectivity of H2/N2 separation by glass-like polymers is mainly 100–160, which is a key parameter for the separation of hydrogen-containing mixtures. (2) The second group of high permeable polymers includes rubberlike and glass-like polymers with a high free volume. Unfortunately, such polymers exhibit low selectivity of hydrogen separation. These polymers can be used for membranes when more permeable impurities need to be removed from hydrogen mixtures (e.g., CO2). Recommendations for the use of the polymeric membranes for the separation of hydrogen-containing multicomponent gas mixtures are formulated.

Leaching of polymetallic sulfides is often challenging due to the complexity of these systems. The main issues are related to the formation of surface by-products or to the presence of different metals that require a greater consumption of chemicals compared to that needed to extract the target metal during leaching. This latter case is followed in the present work using X-ray photoelectron spectroscopy (XPS) during the leaching of a silver-containing polymetallic (Mn-Fe-Pb) sulfide under three different cyanidation procedures: (1) conventional leaching, (2) ultrasound-assisted leaching, and (3) leaching of a sample pretreated in alkaline media. In all cases, leaching results in the build-up of Pb compounds (oxides/hydroxides) on the surface of the minerals, suggesting a mechanism in which Pb is first leached by hydroxide and cyanide and later is re-adsorbed as an external layer on the minerals. On the other hand, the effect of each process on Mn was quite distinct: 1) Conventional leaching leads to the oxidation of the sulfide (pyrite) surface and a slight increase of surface Mn species; 2) Ultrasound-assisted leaching decreases surface Mn by dissolving oxidized species, which exposes fresh sulfide surfaces and increases Ag extraction; and 3) An alkaline pretreatment at high temperature exposed fresh sulfide surfaces and decreased the surface concentration of Mn. The fact that ultrasound-assisted leaching and leaching after an alkaline pretreatment allow for a higher Ag extraction (60% and 75% of total Ag, respectively, as opposed to the 25% extracted via conventional leaching), indicates that leaching is more efficient if the surface is not oxidized and if Mn is removed from the samples, either before or during leaching.

The covalent attachment of nonfunctionalized and carboxylic acid-functionalized carbon nanotubes to amine-terminated organic monolayers on gold and silicon surfaces is investigated. It is well established that the condensation reaction between a carboxylic acid and an amine is a viable method to anchor carbon nanotubes to solid substrates. The work presented here shows that the presence of the carboxylic group on the nanotube is not required for attachment to occur, as direct attachment via the substrate amine and the nanotube cage can take place. Scanning and transmission electron microscopy and atomic force microscopy confirm the presence of carbon nanotubes in intimate contact with the surface. X-ray photoelectron spectroscopy is utilized to compare the surface chemistry of the functionalized and nonfunctionalized carbon nanotubes and is supported by a computational investigation. Ion fragments attributed to the direct attachment between the surface and carbon nanotube cage are detected by time-of-flight secondary ion mass spectrometry. The overall attachment scheme is evaluated and can be further used on multiple carbonaceous materials attached to solid substrates.

Pervaporation and vapor-phase membrane separation methods for the recovery of bioalcohols from dilute aqueous solutions have been critically compared. The importance of taking into account the liquid–vapor equilibrium diagram in studies on the separation of binary aqueous–alcoholic liquid media by these methods has been shown. Previously published experimental data on the transport of water, ethanol, and n-butanol vapors in hydrophobic membranes based on the glassy polymers poly(vinyltrimethylsilane) (PVTMS), poly(1-trimethylsilyl-1-propyne) (PTMSP), and poly(4-methyl-1-pentyne) (PMP) have been analyzed. Schemes of butanol and ethanol recovery by the vapor-phase membrane separation process from fermentation broths for the cases of application of water-selective and alcohol-selective membranes have been presented, as well as the results of mathematical simulation of the process and assessment of energy consumption.

Microtubule‐associated protein tau becomes abnormally phosphorylated in Alzheimer's disease and other tauopathies and forms aggregates of paired helical filaments (PHF‐tau). AT8 is a PHF‐tau‐specific monoclonal antibody that is a commonly used marker of neuropathology because of its recognition of abnormally phosphorylated tau. Previous reports described the AT8 epitope to include pS202/pT205. Our studies support and extend previous findings by also identifying pS208 as part of the binding epitope. We characterized the phosphoepitope of AT8 through both peptide binding studies and costructures with phosphopeptides. From the cocrystal structure of AT8 Fab with the diphosphorylated (pS202/pT205) peptide, it appeared that an additional phosphorylation at S208 would also be accommodated by AT8. Phosphopeptide binding studies showed that AT8 bound to the triply phosphorylated tau peptide (pS202/pT205/pS208) 30‐fold stronger than to the pS202/pT205 peptide, supporting the role of pS208 in AT8 recognition. We also show that the binding kinetics of the triply phosphorylated peptide pS202/pT205/pS208 was remarkably similar to that of PHF‐tau. The costructure of AT8 Fab with a pS202/pT205/pS208 peptide shows that the interaction interface involves all six CDRs and tau residues 202–209. All three phosphorylation sites are recognized by AT8, with pT205 acting as the anchor. Crystallization of the Fab/peptide complex under acidic conditions shows that CDR‐L2 is prone to unfolding and precludes peptide binding, and may suggest a general instability in the antibody. Proteins 2016; 84:427–434. © 2016 The Authors. Proteins: Structure, Function, and Bioinformatics Published by Wiley Periodicals, Inc.

Lignocellulose pretreated with dilute alkali and hydrolysed with cellulases was used as substrate for the processing of acetone–butanol–ethanol (ABE) clostridial fermentation followed by the vapour-phase membrane concentration of two alcohols and acetone with up to 99% degree of recovery. ABE concentrate was used for the catalytic synthesis of fuel components over a zeolite catalyst with aliphatic and aromatic hydrocarbons as the main products with up to 60% conversion. The zeolite catalyst was effectively regenerated from coking by hot steam treatment with up to 100% recovery in catalytic activity. The main novelties of the process are in demonstration the effectiveness of vapor-phase ABE concentration, its effective conversion to hydrocarbons followed by of catalyst’ regeneration. The process described paves the way to developing renewable technologies for the production of motor fuel components.

The appearance of gas (vapor) membrane separation technologies stimulates the expansion of the boundaries of the existing membrane material applications. One of these materials is commercially available poly(4-methyl-1-pentene) (PMP). This paper presents results of a theoretical and experimental study of selective gas transfer in PMP with varying degrees of crystallinity. In this study, the experimental measurements of selective gas transfer were carried out in the range of temperatures covering the glassy and high-elasticity state of the amorphous PMP phase. Pierotti's theory was used to estimate the solubility coefficients of ethane in the crystalline and amorphous PMP phases. The diffusion (D), solubility (S), and permeability (P) coefficients of the amorphous and crystalline PMP phase with respect to lower alkanes were determined for the first time. It was shown that the PMP crystalline phase is selectively permeable to gases with the properties, that are close to those of the amorphous phase below the Tg. It can be concluded that the crystalline phase “works” according to the solution–diffusion model and makes a significant contribution to the gas permeability of PMP. It is noted that the PMP crystalline phase has high selectivity for C1–C4 alkane separation.

Understanding the changes of a mineral during ore processing is of capital importance for the development of strategies aimed at increasing the efficiency of metal extraction. This task is often difficult due to the variability of the ore in terms of composition, mineralogy and texture. In particular, surface processes such as metal re-adsorption (preg-robbing) on specific minerals are difficult to evaluate, even though they may be of importance as the re-adsorbed material can be blocking the valuable mineral and negatively affect the extraction process. Here, we show a simple yet powerful approach, through which surface processes in individual minerals are identified by combining polarization microscopy (MP) and X-ray photoelectron spectroscopy (XPS). Taking as an example a silver-containing polymetallic sulfide ore from the Peruvian central Andes (pyrite-based with small amounts of galena), we track the changes in the sample during the course of cyanidation. While polarization microscopy is instrumental for identifying mineralogical species, XPS provides evidence of the re-adsorption of lead on a pyrite surface, possibly as lead oxide/hydroxide. The surface of pyrite does not show significant changes after the leaching process according to the microscopic results, although forms of oxidized iron are detected together with the re-adsorption of lead by XPS. Galena, embedded in pyrite, dissolves during cyanide leaching, as evidenced by PM and by the decrease of XPS signals at the positions associated with sulfide and sulfate. At the same time, the rise of a lead peak at a different position confirms that the re-adsorbed lead species cannot be sulfides or sulfates. Interestingly, lead is not detected on covellite surfaces during leaching, which shows that lead re-adsorption is a process that depends on the nature of the mineral. The methodology shown here is a tool of significant importance for understanding complex surface processes affecting various minerals during metal extraction.

Evaluation of several versions of phenomenological theory of gas permeability in selective polymeric membranes is presented, along with the appropriate experimental methods for verification of these versions. The main focus is on a description of stationary mass transfer across membranes (films) containing dispersion inclusions of various shapes of one polymer in a matrix of another. Considering heterogeneous media as a membrane material, it was assumed that diffusion and sorption properties of inclusions are different from those of the dispersing medium. The problem of choosing optimal shape of inclusions is evaluated from the point of view of targeted permeability and selectivity of a membrane with respect to gases. To confirm this theoretical approach, the experimental results of the studies of diffusion (permeability) of permanent gases in polymeric membranes of different structures were used. The target gases included noble gases, hydrogen, nitrogen, oxygen, CO 2 , and methane. The target polymers included glassy polyvinyltrimethylsilane (PVTMS, T gl = 155–180 °C), rubberlike polydimethylsiloxane (PDMS, T gl = −120 °C), and two-phase block-copolymers based on these materials within a wide range of composition, including the region of phase inversion. In addition, available experimental literature data on gas permeation parameters for polyarylat–polysiloxane, polysulfon–polysiloxane, and polycarbonate–polysiloxane block-copolymers are utilized. In order to describe the stationary gas permeability for two-phase systems (from diluted dispersion of one polymer in another to concentrated dispersion and complete phase inversion) the empiric approaches based on modified Maxwell equations are offered. The requirements for two-phase systems with high permeability and selectivity parameters for gas separation are identified. The permeability parameters are predicted for C1–C4 hydrocarbons in block-copolymers based on PDMS dispersion in PVTMS, phase inversion, and PVTMS dispersion in PDMS. Thus, the perspectives of designing heterogeneous membranes based on block-copolymers with predetermined molecular-selective properties are demonstrated.

Background β-Amyloid (Aβ) peptide is believed to play a pivotal role in the development of Alzheimer’s disease. Passive immunization with anti-Aβ monoclonal antibodies may facilitate the clearance of Aβ in the brain and may thus prevent the downstream pathology. Antibodies targeting the immunodominant N-terminal epitope of Aβ and capable of binding both the plaques and soluble species have been most efficacious in animal models. Structural studies of such antibodies with bound Aβ peptides provided the basis for understanding the mechanisms of action and the differences in potency. To gain further insight into the structural determinants of antigen recognition and the preferential Aβ conformations, we determined the crystal structure of murine antibody C706 in complex with the N-terminal Aβ 1–16 peptide sequence. Methods The antigen-binding fragment of C706 was expressed in HEK293 cells and was crystallized in complex with the Aβ peptide. The X-ray structure was determined at 1.9-Å resolution. Results The binding epitope of C706 is centered on residues Arg5 and His6, which provide the majority of interactions. Unlike most antibodies, C706 recognizes a coiled rather than extended conformation of Aβ. Conclusions Comparison with other antibodies targeting the N-terminal section of Aβ suggests that the conformation of the bound peptide may be linked to the immunization protocol and may reflect the preference for the extended conformation in the context of a longer Aβ peptide as opposed to the coiled conformation in the isolated short peptide.

The results of a study of C1-C4 alkane gas permeability and C5-C6 alkane and methanol vapor permeability through pressed foil based on exfoliated graphite with a density of 1 g/cm3 are presented. It has been found that the permeability of the studied graphite foil to C4-C6 hydrocarbons is higher than calculated values; in particular, reverse selectivity for pairs such as H2/hydrocarbon and N2/hydrocarbon is observed. This can be due to a considerable effect of a surface flow on the total flow through the membrane.

Methods of estimation of molecular-selective gas transport parameters in polymeric membranes and explanation of separation selectivity evolution for ‘small’ and ‘large’ molecules up to inversed selectivity are proposed based on comparative analysis of diffusion and solubility of noble gases as isotropic diffusion probes in different classes of polymers and block copolymers on their basis. Two approaches are considered in this work: (1) analysis of diffusional migration of permanent gases, lower hydrocarbons, and alcohols (vapor) in glassy polymers and rubbers relative to the diffusion of noble gases including radon; (2) adaptation of the ‘hard sphere’ theory developed for gas solubility in liquids to the calculation of the solubility of gases in the polymer matrix. In the latter case, noble gases as isotropic probes are used for calculating the required fitting parameters of the polymer medium.

A reaction of 4-(2-mercaptophenyl)-1,2,3-thiadiazoles with an oxidant in the presence of 1.1 equiv of base afforded good yields of benzo[4,5]thieno[3,2-d][1,2,3]thiadiazoles via the intramolecular oxidative nucleophilic substitution of a hydrogen (ONHS) pathway. The reaction of 4-(2-mercaptophenyl)-1,2,3-thiadiazoles in the presence of ≥2 equiv of base gave 2-mercaptobenzo[b]thiophenes via an anionic ring-opening/ring-closure pathway.

The diluted organic-water solutions are convenient products of biomass treatment to biofuels (e.g., ABE fermentation). A continuous membrane-assisted method by example of butanol recovery from fermentation media is considered in present work. The method is based on combination of the gas stripping (convenient process) with membrane vapor separation (with preferable butanol vapor permeability). In comparison with known membrane pervaporation method the suggested one possesses such advantageousness as an expanded membrane module area and resistance to fouling. Main attention is put on fundamental aspects of separation: (1) the contribution of liquid/vapor phase transition and (2) vapor selective properties of organophilic membranes. Two polymers: poly-1-trimethylsilyl-1-propyne (PTMSP) and poly-4-methyl-2-pentyne (PMP), and two their block copolymers (with PTMSP–PMP ratio 60:40 and 25:75) are suggested as membrane materials for this purpose. Vapor permeability of water, butanol and butanol–water solutions are determined for selected polymers and block copolymers at different temperatures and butanol–water solution concentrations. Apparent activation energy and temperature parameter of permeability of water and butanol vapors in PTMSP and PMP membranes are obtained. The methodology of study can be used for the systematic research of the vapor permeability membrane properties influence on separation of liquid multi-component mixtures with taking into account of liquid/vapor equilibrium.

Alzheimer's disease is a progressive neurodegenerative disease characterized by extracellular deposits of β-amyloid (Aβ) plaques. Aggregation of the Aβ42 peptide leading to plaque formation is believed to play a central role in Alzheimer's disease pathogenesis. Anti-Aβ monoclonal antibodies can reduce amyloid plaques and could possibly be used for immunotherapy. We have developed a monoclonal antibody C706, which recognizes the human Aβ peptide. Here we report the crystal structure of the antibody Fab fragment at 1.7 A resolution. The structure was determined in two crystal forms, P21 and C2. Although the Fab was crystallized in the presence of Aβ16, no peptide was observed in the crystals. The antigen-binding site is blocked by the hexahistidine tag of another Fab molecule in both crystal forms. The poly-His peptide in an extended conformation occupies a crevice between the light and heavy chains of the variable domain. Two consecutive histidines (His4–His5) stack against tryptophan residues in the central pocket of the antigen-binding surface. In addition, they form hydrogen bonds to the acidic residues at the bottom of the pocket. The mode of his-tag binding by C706 resembles the Aβ recognition by antibodies PFA1 and WO2. All three antibodies recognize the same immunodominant B-cell epitope of Aβ. By similarity, residues Phe–Arg–His of Aβ would be a major portion of the C706 epitope. Copyright © 2010 John Wiley & Sons, Ltd.

Designing a well-defined and stable interface between biomolecules and semiconductor surfaces is of great importance for current and future biosensing and bioelectronic applications. The well-characterized chemistry, stability, and easily tunable electronic properties of silicon substrate make it a practical platform for this type of interface. It has been established in our previous work that a robust, covalent attachment between thiol-DNA molecules of a pre-designed geometrical shape and a modified silicon surface can be achieved. This work focuses on using this binding model and altering the distance between the DNA molecules and silicon surface by strategically placing thiol linkers within the pre-determined geometric design of the rectangularly shaped DNA. The statistical analysis of the height profiles of DNA molecules attached to the surface, as determined by AFM, provides specific insight into how the construction of the DNA molecules affects the binding distance. A comparison between two thiol-DNA molecules with different numbers of thiol groups placed either within the rectangular shape or anchored to the free loop of the same geometric design suggest that the average distance of these molecules to the functionalized silicon surface can be changed by approximately 0.5 nm.

Extracellular matrix metalloproteinase inducer (EMMPRIN), also known as Hab18G, CD147, Basigin, M6, and neurothelin, is a membrane glycoprotein expressed on the surface of various cell types and many cancer cells. EMMPRIN stimulates adjacent fibroblasts and tumor cells to produce matrix metalloproteinases and plays an important role in tumor invasion and metastasis, angiogenesis, spermatogensis and fertilization, cell-cell adhesion and communication, and other biological processes (reviewed in Ref. 1 and references therein). It was demonstrated that the EMMPRIN extracellular domain (ECD), which structurally belongs to the IgG superfamily, can form homo-oligomers in a cis dependent manner and the N-terminal domain 1 (residues 22-101) was necessary and sufficient to mediate this interaction. The crystal structure of the ECD of recombinant human EMMPRIN (Hab18G/CD147) expressed in E. coli was reported at 2.8 {angstrom} resolution (Yu et al. 2008). The construct consists of residues 22-205 of the mature protein and has both an N-terminal IgC2 domain (ND1, residues 22-101) and a C-terminal IgC2 domain (ND2, residues 107-205). The two domains are joined by a five amino acid residue linker that constitutes a flexible hinge between the two domains. The crystal form has four copies of the molecule in the asymmetric unit, each of which hasmore » a different inter-domain angle that varies from 121{sup o} to 144{sup o}. The two domains each have a conserved disulfide bridge and both are comprised of two {beta}-sheets formed by strands EBA and GFCC, and DEBA and AGFCC for ND1 and ND2, respectively. Based on the crystal packing in this structure, the authors proposed that lateral packing between the two IgG domains of EMMPRIN ECD represents a potential mechanism for cell adhesion. Here we report the 2.0-{angstrom} crystal structure of the N-terminal domain of EMMPRIN ECD (ND1) expressed in mammalian cells. The overall structure of the domain is very similar to that in the full length ECD. Quite unexpectedly, ND1 forms a dimer mediated through the exchange of its last {beta}-strand (strand G). {beta}-strand swapping, which is a subset of 3D domain swapping, has been found to mediate cell-cell adhesion by cadherins. 3D domain swapping has been proposed to be a mechanism of protein oligomerization, aggregation, evolution of oligomeric proteins from single domains and amyloidogenesis. In domain swapped proteins, the same structural elements are involved in the final 3D structure, and so there is little overall energetic difference between the monomer and the swapped oligomers. However, there is often a high energy barrier for the conversion as it often goes through an unfolded state. It is also possible that strand-swapping occurs during folding of nascent polypeptide chains. Frequently, the exchange hinges contain proline-rich motifs which are often in high strain conformations. Domain swapping appears to be a strategy to resolve such local structural strain. The exchange hinge of ND1 contains a Pro-Glu-Pro tripeptide motif. Both of the proline residues adopt extended trans conformations, when compared with cis in the full-length ECD structure. Proline cis-trans isomerization may be the driving force for this exchange. Strand-exchanged dimerization may be a mechanism for the oligomerization of EMMPRIN ECD and its cis-dependent homophilic interactions in cell-cell adhesion.« less

In designing modern microelectronic and sensing devices based on biological molecules, the underlying scientific questions focus on the ability to form a well-defined and stable interface between biological molecules and the base of electrical devices. This manuscript addresses the ability to form such an interface between silicon and various DNA molecules placed on a chemically modified self-assembled monolayer (SAM). More importantly, this work explores the possibility of designing biochemical binding sites located at a predetermined distance from the solid semiconductor surface utilizing shape-restricted DNA molecules with strategically placed functional groups that can serve as anchors. Here, for the first time we combine microscopic and spectroscopic analytical techniques with the design of geometrically-restricted thiol-DNA molecules not only to prove the selective covalent binding of these molecules to the Si(1 1 1) surface modified with the 11-amino-1-undecene self-assembled monolayers but also to analyze the geometry of produced structures. Thus, a sharp and well-defined interface with a specific distance between the potential binding site and semiconductor surface for a biochemical sensor can be built. The binding between the thiol-DNA and the amino-groups terminating the monolayer is achieved by using a sulfo-succinimidyl 4-(N-maleimidomethyl)-cyclohexane-1-carboxylate (SSMCC) crosslinker molecule. The shape-restricted thiol-DNA is anchored to the surface via the formation of covalent bonds, as confirmed by combining biochemical investigation with X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary-ion mass spectroscopy (ToF-SIMS). Atomic force microscopy (AFM) is used to compare the well-defined but non-specific binding of the designed DNA on mica with that of selective covalent binding on SAM-covered Si(1 1 1). This approach allows for unambiguous assignment of the nature of chemical interaction between the DNA molecules and the surface and for the design of covalently bound geometrically defined biointerfaces for future applications.

Glucosamine 6-phosphate synthase converts fructose-6P into glucosamine-6P or glucose-6P depending on the presence or absence of glutamine. The isomerase activity is associated with a 40-kDa C-terminal domain, which has already been characterized crystallographically. Now the three-dimensional structures of the complexes with the reaction product glucose-6P and with the transition state analog 2-amino-2-deoxyglucitol-6P have been determined. Glucose-6P binds in a cyclic form whereas 2-amino-2-deoxyglucitol-6P is in an extended conformation. The information on ligand-protein interactions observed in the crystal structures together with the isotope exchange and site-directed mutagenesis data allow us to propose a mechanism of the isomerase activity of glucosamine-6P synthase. The sugar phosphate isomerization involves a ring opening step catalyzed by His504 and an enolization step with Glu488 catalyzing the hydrogen transfer from C1 to C2 of the substrate. The enediol intermediate is stabilized by a helix dipole and the epsilon-amino group of Lys603. Lys485 may play a role in deprotonating the hydroxyl O1 of the intermediate.

The adsorption of tetrakis(dimethylamido)titanium, TDMAT, on ammonia-saturated Si(100) surfaces at 300 K is followed by infrared (IR) spectroscopy, temperature-programmed desorption (TPD), and density functional calculations. Experimental observations suggest the occurrence of a surface transamination reaction, where an approaching TDMAT molecule reacts with a surface NHX site, eliminating dimethylamine and attaching Ti to the surface N atom. Density functional calculations show that the reaction is thermodynamically possible, and the comparison of predicted vibrational frequencies to spectroscopic features further supports a surface transamination process. The reaction of TDMAT with Si−H surface sites is not found experimentally in agreement with calculations predicting a process less favorable thermodynamically. Since the transamination reaction investigated here can be viewed as the first step in the atomic layer deposition of TiN on silicon, the conditions required for this first step toward the forma...

Bacterial transport of many sugars, coupled to their phosphorylation, is carried out by the phosphoenolpyruvate (PEP):sugar phosphotransferase system and involves five phosphoryl group transfer reactions. Sugar translocation initiates with the Mg 2+ -dependent phosphorylation of enzyme I (EI) by PEP. Crystals of Escherichia coli EI were obtained by mixing the protein with Mg 2+ and PEP, followed by oxalate, an EI inhibitor. The crystal structure reveals a dimeric protein where each subunit comprises three domains: a domain that binds the partner PEP:sugar phosphotransferase system protein, HPr; a domain that carries the phosphorylated histidine residue, His-189; and a PEP-binding domain. The PEP-binding site is occupied by Mg 2+ and oxalate, and the phosphorylated His-189 is in-line for phosphotransfer to/from the ligand. Thus, the structure represents an enzyme intermediate just after phosphotransfer from PEP and before a conformational transition that brings His-189∼P in proximity to the phosphoryl group acceptor, His-15 of HPr. A model of this conformational transition is proposed whereby swiveling around an α-helical linker disengages the His domain from the PEP-binding domain. Assuming that HPr binds to the HPr-binding domain as observed by NMR spectroscopy of an EI fragment, a rotation around two linker segments orients the His domain relative to the HPr-binding domain so that His-189∼P and His-15 are appropriately stationed for an in-line phosphotransfer reaction.

Expression of the PSR132 protein from Dianthus caryophyllus(carnation, clover pink) is induced in response to ethylene production associated with petal senescence, and thus the protein is named petal death protein (PDP). Recent work has established that despite the annotation of PDP in sequence databases as carboxyphosphoenolpyruvate mutase, the enzyme is actually a C-C bond cleaving lyase exhibiting a broad substrate profile. The crystal structure of PDP has been determined at 2.7 A resolution, revealing a dimer-of-dimers oligomeric association. Consistent with sequence homology, the overall R/‚ barrel fold of PDP is the same as that of other isocitrate lyase/PEP mutase superfamily members, including a swapped eighth helix within a dimer. Moreover, Mg 2+ binds in the active site of PDP with a coordination pattern similar to that seen in other superfamily members. A compound, covalently bound to the catalytic residue, Cys144, was interpreted as a thiohemiacetal adduct resulting from the reaction of glutaraldehyde used to cross-link the crystals. The Cys144-carrying flexible loop that gates access to the active site is in the closed conformation. Models of bound substrates and comparison with the closed conformation of isocitrate lyase and 2-methylisocitrate lyase revealed the structural basis for the broad substrate profile of PDP. The glyoxylate cycle was discovered in bacteria (1 )a s a means of converting two-carbon compounds for synthesis of other cell constituents. The same cycle was subsequently found in plants to convert acetyl-CoA from fat degradation into succinate to fuel the tricarboxylic acid cycle ( 2). The glyoxylate cycle operates in all cells that have the capacity to convert acetate to carbohydrates, including bacteria, plants, fungi, and animals. A key enzyme of the glyoxylate cycle is isocitrate lyase (ICL) 1 which cleaves isocitrate into succinate and glyoxylate. A reaction analogous to that catalyzed by ICL occurs in the metabolism of propionyl-CoA via the 2-methyl isocitrate cycle (3). The corresponding 2-methyl- isocitrate lyase (MICL) cleaves 2-methylisocitrate into suc- cinate and pyruvate. The amino acid sequences of the two enzymes are homologous and belong to a protein superfamily that also includes phosphoenolpyruvate mutase (PEPM)

Fundamental features and industrial applications of the direct fluorination of polymers are reviewed. Fundamental features of the direct fluorination of a set of polymers, such as polystyrene, polyethyleneterephthalate, poly(2,6-dimethyl-1,4-phenylene oxide), PMMA, LDPE (two types), HDPE (six types), polyvinyltrimethylsilane, poly(4-methyl-pentene-1), polyimide Matrimid 5216®, polysulfones, polyetheretherketone, polycarbonatesiloxane, polysulphone–polybuthadiene block-copolymers, polypropylene, PVF, PVDF, etc. are described. Influence of composition of the fluorinating mixture (F2–He–N2–O2–HF), fluorine partial pressure, temperature and fluorination duration, on the rate of formation of the fluorinated layer and the chemical composition, density, refraction index, surface energy, gas separation properties and friction coefficient of fluorinated layer have been investigated. Processes of formation and termination of long-living and short-living radicals and grafting of acrylonitrile to fluorinated polymers have been studied. Industrial applications of the direct fluorination to enhance the commercial properties of polymeric goods, such as separation factor of polymeric membranes for gas separation, barrier properties of polymer vessels, pipes and packagings, adhesion, printability, wetting and transparency in visible and IR are reviewed.

The application area of existing gas separation membranes is limited by commercially available polymers for their preparation. In many cases the separation selectivity of these polymers is not sufficient for effective separation processes. One of the ways to improve the separation effectivity of existing membranes from glassy polymers is gas phase fluorination. It is very important to note that this method can be successfully used for modification of polymeric films, different types of membranes (flat sheet and hollow fiber) and membrane modules. The hollow fibers produced from Matrimid 5218 in Twente University and a flat-sheet membrane from polyvinylthrimethilsilane (PVTMS) produced in Russia were investigated. The treatment of samples by fluorination was carried out in closed reactor at 20–22 °C with gaseous mixtures of F2/He of different composition. A gas mixture of different concentrations (2–10 vol.% of F2) at 1 atm was used The time of fluorination was from 2 min to 265 min. The dependence of the structure of the PVTMS and Matrimid 5218 on gas phase fluorination by IR-spectroscopy and the influence of modification on membrane structure by SEM were studied. The productivity of He, CO2, N2 and CH4 through the membranes modified at different conditions of fluorination was measured, and it was shown that it is possible to achieve a significant increase of He/CH4, CO4/CH4 and He/N2 selectivity at high level He and CO2 productivity by this type of modification. Thus, modified membranes and membrane modules can be successfully used for separation of components of biogas in membrane contactors and selective membrane valves for extraction of He/Ne fraction from waste in the metallurgy industry and separation of natural gas components.

The permeation process of hexane and heptane (nearest homologs) through poly(1-trimethylsilylpropyne) synthesized with catalytic system NbCl 5 and TaCl 5 was investigated. Dependencies of permeability coefficients on vapor activity were obtained. It was shown that the dependencies are nonlinear, and their character depends on conditions of polymer synthesis, namely which catalytic system used and nature ofthe vapor/polymer interaction. The influence of film thickness and storage time on dependencies of permeability coefficient on vapor activity was studied as well.

In contrast to common glassy polymers, poly(1-trimethylsilyl-1-propyne) (PTMSP), a high free volume glassy polymer, shows a preferable permeation of large condensable organic vapors in comparison to permanent gases. In order to investigate this phenomenon, a systematic permeability study over a large activity range has been performed on PTMSP with three types of volatile organic compounds (VOCs) as diffusing probes: toluene, dimethylketone and dichloromethane. PTMSP was synthesized with different catalytic systems (Nb or Ta based) able to induce controlled sub-molecular cis–trans structures. Whereas dimethylketone and dichloromethane permeability can be correctly described by a classical dual-mode equation, a peculiar bell shaped pattern was obtained for toluene, with a minimum permeability located at an activity value around a=0.3–0.4. In that case, only a dual-mode expression taking into account a concentration dependent diffusion coefficient can account for the results. On the other hand some apparent conflicting data recorded from PTMSP brand new films were related to the microstructure of the polymer main chain thanks to 13 C NMR spectroscopy analysis showing importance of cis- and trans-forms of the main chain of PTMSP. cis-Structure is more flexible and can be responsible for the creation of a higher density physical network (HDN) in polymeric matrix; conversely, trans-structure is more rigid and can provide lower density physical network (LDN). The higher permeability recorded for several probes through PTMSP synthesized with TaCl5/Al(i-Bu)3 catalytic system compared to those of NbCl5 based polymer can be explained by the geometric difference of the macromolecule networks.

Composite films based on the polyvinyltrimethylsilane (PVTMS) with polyaniline (PANI) coating were obtained by borderline polymerization of aniline. The obtained coating was shown to differ from the polymer forming in the reaction mixture bulk both in chemical structure and morphology. Ratio and concentration of the reagents, mixing rate, reaction time, and condition of support surface were among the investigated factors affecting the growth and quality of PANI coating. The gas separation characteristics of composite membranes, as affected by the process conditions and the type of PANI, were investigated. It is shown that the proposed method provides a means for obtaining composite membranes that combine high selectivity, especially in O2/N2, He/CH4, and CO2/CH4 separation, with permeability higher than that of known composite materials. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1379–1384, 2003

Temperature programmed desorption (TPD) studies have been performed to determine the influence of functionalization on the desorption of n-alkanes from inert substrates. Monolayer and multilayer desorption was investigated for a set of six 1-bromoalkanes, six alkanoic acids, and four 2-bromoalkanoic acids adsorbed on the basal plane of highly-oriented pyrolytic graphite (HOPG). Full activation of the substrate surface for monolayer adsorption required annealing temperatures of approximately 700 K. Molecular desorption from physisorbed mono- and multilayers was found to exhibit first- and zeroth-order kinetics, respectively, with no measurable dependence of the activation energy on coverage. A Redhead analysis of monolayer desorption signals uncovered a profound influence of alkane functional groups on the desorption barrier. As compared with the case of unfunctionalized n-alkanes, the desorption energies of all derivative species studied here exhibit a reduced chain length dependence in conjunction with a...

Membrane methods of vapor mixture separation proposed in the 1990s are now practically considered as reagent- or adsorbent-free technologies possessing higher energy efficiency in comparison with traditional ones. Many practical problems demand the separation (recovery) of organic vapors from different gas streams. Polymeric membranes with organic-selective properties can solve this task. Water-selective membranes can provide recovery of water vapor from the water–organic vapor phase. Moreover, membrane vapor permeation (MVP) is suitable for recovery of bioalcohols (bioorganics) from fermentation media. In many cases MVP efficiency is improved by a positive deviation of vapor–liquid equilibrium (VLE) from Raoult's law. The modern approach to vapor separation involves consideration of integrated membrane systems. Actually, the type (or operation scheme) of integrated system depends on the properties of the membrane involved in the separation process. Membrane materials such as high permeable hydrophobic glassy polymers with organic/water selectivity >1, medium permeable hydrophobic glassy polymers with organic/water selectivity

Dephospho-coenzymeA kinase catalyzes the final step in CoA biosynthesis, the phosphorylation of the 3′-hydroxyl group of ribose using ATP as a phosphate donor. The protein from Haemophilus influenzae was cloned and expressed, and its crystal structure was determined at 2.0-A resolution in complex with ATP. The protein molecule consists of three domains: the canonical nucleotide-binding domain with a five-stranded parallel β-sheet, the substrate-binding α-helical domain, and the lid domain formed by a pair of α-helices. The overall topology of the protein resembles the structures of nucleotide kinases. ATP binds in the P-loop in a manner observed in other kinases. The CoA-binding site is located at the interface of all three domains. The double-pocket structure of the substrate-binding site is unusual for nucleotide kinases. Amino acid residues implicated in substrate binding and catalysis have been identified. The structure analysis suggests large domain movements during the catalytic cycle.

The adsorption and chemical transformation of iodoethane were studied on a Si(100)-2×1 surface using multiple-internal reflection Fourier-transform infrared spectroscopy (MIR-FTIR). The C–H and Si–H stretch vibrations served as fingerprints of all surface transformations. Although ethyl groups are stable on the Si(100)-2×1 surface at room temperature, thermal annealing studies suggest the reaction-limited formation of ethylene, a major hydrocarbon reaction product, accompanied by the loss of hydrogen, which is left on the surface until the temperature of recombinative H2 desorption is reached. Variable temperature studies indicate that ethyl groups are the only hydrocarbon entities on a surface up until the hydrogen elimination temperature. The positions of Si–H stretching bands suggest that a mixture of surface sites is formed at temperatures between 300 K and 600 K. However, the majority of surface hydrogen forms SiH–SiI surface species as the surface temperature reaches 700 K.

The wealth of kinetic and structural information makes inorganic pyrophosphatases (PPases) a good model system to study the details of enzymatic phosphoryl transfer. The enzyme accelerates metal-complexed phosphoryl transfer 10 10 -fold: but how? Our structures of the yeast PPase product complex at 1.15 Å and fluoride-inhibited complex at 1.9 Å visualize the active site in three different states: substrate-bound, immediate product bound, and relaxed product bound. These span the steps around chemical catalysis and provide strong evidence that a water molecule (O nu ) directly attacks PPi with a p K a vastly lowered by coordination to two metal ions and D117. They also suggest that a low-barrier hydrogen bond (LBHB) forms between D117 and O nu , in part because of steric crowding by W100 and N116. Direct visualization of the double bonds on the phosphates appears possible. The flexible side chains at the top of the active site absorb the motion involved in the reaction, which may help accelerate catalysis. Relaxation of the product allows a new nucleophile to be generated and creates symmetry in the elementary catalytic steps on the enzyme. We are thus moving closer to understanding phosphoryl transfer in PPases at the quantum mechanical level. Ultra-high resolution structures can thus tease out overlapping complexes and so are as relevant to discussion of enzyme mechanism as structures produced by time-resolved crystallography.

Silicalite-1 membranes were prepared on a TiO 2 coated porous stainless steel support. Different thicknesses of the membranes were achieved by changing the synthesis temperature. Increasing the crystallization temperature resulted in the formation of a monolith-type layer, which is close to a perfect microporous phase (without pores between crystals forming the layer). The silicalite-1 membranes were characterized by permeation measurements using single gases and a mixture of n -butane and i -butane in a Wicke–Kallenbach set-up. A direct relationship between the membrane thickness and the selectivity of n -butane to iso-butane was observed; the selectivity improved with an increase in the membrane thickness. The improvement in the selectivity was correlated with decreasing the intercrystalline spaces between the crystals forming the membrane. The best performing membranes were synthesized in the temperature range of 453–463 K. The competitive adsorption of the butanes at 303 K was governing the separation properties of the membranes. The selectivity for n -butane in a 50:50 n -butane/iso-butane mixture was as high as 55, and the flux equal to 2.75 mmol/m 2 per s (WK method at 101 kPa, 303 K). The ideal selectivities, calculated from the single component measurements towards n -butane, were between 33–48 and n -butane fluxes between 7–12 mmol/m 2 per s (WK method at 101 kPa, 303 K). Small variations in the selectivity performance of the membranes synthesized under the same conditions show that the optimized preparation method was highly reproducible.

Fluorinated poly(vinyl trimethylsilane) (FPVTMS) unlike virgin PVTMS is able to participate in electrochemical reactions and undergoes direct and indirect electrochemical reductive degradation. Specifically, its perfluorinated units are reduced irreversibly at a glass carbon electrode in a 0.05-M (C4H9)4ClO4 solution in dimethylformamide with subsequent splitting of C–F bonds and formation of conjugated double bonds in macromolecules at the polymer surface. On the other hand, the incompletely fluorinated units at the FPVTMS surface interact with the previously electrochemically reduced background solution to be dehydrofluorinated. This is accompanied by the formation of conjugated double bonds and dissolution of the dehydrofluorinated layer also. The data obtained allowed distinguishing the incompletely fluorinated units from the perfluorinated ones in the fluorinated layer of FPVTMS. Moreover, the quantity of the incompletely fluorinated units in FPVTMS can be determined. It was found that the strengthening of fluorination conditions led to an enhancement of the electrochemically induced FPVTMS transformations.

Here we report the remarkable chemistry exhibited by 6-bromo-1-hexene on a Cu3Pt(111) surface. The dehydrocyclization reaction leading to the formation of benzene takes place at very low coverage; as the surface fills up, decomposition becomes a predominant pathway. Further increase of the surface concentration of 6-bromo-1-hexene leads to the hydrogenation of 5-hexenyl formed on a surface as a result of C−Br bond dissociation. This reaction produces 1-hexene, which is stable on the surface until the molecular desorption of this compound commences at 230 K. Molecular desorption of 6-bromo-1-hexene from the monolayer becomes significant at even higher exposures. All these processes occur very cleanly within a specific coverage range, making the 6-bromo-1-hexene on the Cu3Pt(111) surface extremely attractive for analysis of kinetics of coverage-dependent reactions. Steric requirements for each of the processes described here and the availability of the adsorption sites on the alloy surface are believed to g...

The modification of polyvinyltrimethylsilane (PVTMS) has been carried out using the radiation-induced graft polymerization. PVTMS is applied as a basis for gas-separating membranes. Acrylonitrile, acrolein, ethyl acrylate, acrylic acid and acrylamide were used as monomers. The grafting was performed both from vapour and liquid phase of monomers and their solutions by the direct radiation method. Some kinetic regularities of radiation graft polymerization of monomers and the character of distribution of grafted polymers along the thickness of PVTMS films were studied. It was shown that grafting improves the chemical resistance, the selective permeability of gases and some mechanical properties of PVTMS films.

Fundamental features of the direct fluorination of poly(vinyl trimethylsilane) (PVTMS) and poly(phenylene oxide) (PPO) have been investigated. The influence of the fluorination conditions (fluorinating mixture composition, treatment duration) and polymer molecular weight on the rate of formation of the fluorinated layer and on physical–chemical properties (chemical composition, density, refractive index, absorption spectra in the visible and UV, surface energy) was investigated.

Radiation-induced crosslinking of homogeneous glassy polyvinyltrimethylsilane was carried out either by the γ -irradiation of the polymeric films containing 3–20 wt% of ethylene glycol dimethacrylate or by the radiation-induced grafting of allyl methacrylate from vapour phase onto films made of pure polymer. The dependence of grafting value on the absorbed γ -irradiation dose and film thickness was investigated. The modified films were analyzed for the sol/gel content and the dependence of gel fraction yield of crosslinked polymer on absorbed dose, concentration of the crosslinking agents and film thickness. The radiation-chemical yields of crosslinking and degradation as well as gelation doses were calculated. The permeability of oxygen and nitrogen through the crosslinked films was determined.

Benzene adsorption on Si(100)-(2×1) is investigated at 100 and 300 K by vibrational infrared (IR) spectroscopy, thermal desorption and near-edge X-ray absorption fine structure (NEXAFS) studies. At cryogenic temperatures (100 K), benzene is found to be predominantly physisorbed on this surface, whereas at room temperature benzene chemisorbs on Si(100)-2×1. IR studies show vibrational features at 2945 and 3044 cm−1 corresponding to sp3 and sp2 C–H stretching modes, respectively, and NEXAFS indicates the absence of conjugated double bonds in chemisorbed benzene. Two possible chemisorption structures are indicated, consistent with previous studies of this system. The majority structure is consistent with Diels–Alder type addition of benzene to the dimer of the Si(100)-2×1 surface and is described as 1,4-cyclohexadiene-like. The presence of another structure of chemisorbed benzene is suggested by a splitting in the π* transitions in the NEXAFS spectra of chemisorbed benzene. The energy difference is inconsistent with conjugation of double bonds, and the two features have different angular dependencies. The angular dependence for both π* transitions was studied and gave an angle between the double bond and the silicon surface of ∼30° for the primary 1,4-cyclohexadiene-like adduct and ∼43° for the second structure.