Molecular dynamics simulations of a poly(ethylene oxide) surface

Potentials developed earlier for crystalline and amorphous bulk PEO systems have been used for the MD simulation of a PEO surface model. The surface comprises the outer region of a 122 Å-thick sheet of PEO in which the PEO, -(CH₂-CH₂-O)_n- chains run obliquely across the cell, and are terminated by C₂H₅ ethyl groups. The atoms on one side of the sheet are tethered to facilitate a satisfactory Ewald summation. The sheet expands from its ‘crystalline’ width of 122 Å to 128 Å in the simulated model. Simulations were performed at three temperatures: 300 K, 400 K and 500 K. Different behaviour in the surface layer was found compared to that in the bulk. The structural and dynamical properties of the surface were analyzed at each temperature.     

Blocking of the silver catalyst surface in the conversion of ethylene to ethylene oxide

The conversion of ethylene oxide on silver catalysts of varying degree of oxidation has been studied. The formation of an adsorbed layer partially blocks the surface under catalytic conditions.

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Role of the surface hydroxyl groups of modified titanium oxide in catalytic ethylene oxide hydration

A quantum-chemical study of the mechanism of ethylene oxide hydration on titanium oxide (anatase) modified with phosphorus additives was performed. It was demonstrated that the hydroxyl groups of the anatase surface are of importance for the activation interaction of ethylene oxide with the catalyst surface. The activation of the ethylene oxide molecule and proton transfer occur with the participation of these hydroxyl groups. It was found that the modification of the titanium oxide surface with phosphorus additives plays a crucial role in proton transfer.     

Formation of ethylene from beta-halopropionic acids.

The reaction of beta-halopropionic acids with peroxydisulfate and Ag⁺ in aqueous solutions gives in high yield ethylene via the intermediate formation of beta-haloalkyl radicals and subsequent reductive elimination by Ag+.     

Influence of N-methylation on a cation-pi interaction produces a remarkably stable beta-hairpin peptide

The methylation of lysine in histone tails is a common posttranslational modification that functions in histone-regulated chromatin condensation, with binding of methylated lysine occurring in aromatic pockets on chromodomain proteins. We have synthesized a highly stable 12-residue beta-hairpin peptide that exploits the histone-related cation-pi interaction between a methylated lysine residue and a tryptophan residue. Thermodynamic analysis reveals significant entropic stabilization of the peptide due to methylation of the lysine residue. Chemical denaturation of the peptide demonstrates two-state behavior. In comparison to other reported, highly stable designed beta-hairpins, this peptide is the most thermally stable beta-hairpin reported to date. This study provides insight into the role of Lys methylation in histone proteins and more generally in mediating protein-protein interactions.     

Dynamic elasticity of triblock copolymer of poly(ethylene oxide) and poly(propylene oxide) on a water surface

Dilatational viscoelasticity of adsorbed and spread films of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer at the air-water interface is studied by the capillary waves and oscillating barrier techniques. At the surface pressure below 10 mN/m, dynamic surface properties of these films coincide with those of poly(ethylene oxide). At higher surface pressures, the results obtained indicate the desorption of poly(propylene oxide) segments from the monolayer and their interaction with poly(ethylene oxide) segments in an aqueous phase. At a surface pressure close to 19 mN/m, the behavior of adsorbed and spread poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) films becomes different. The real part of dynamic surface elasticity of spread films tends toward its maximum value (20 mN/m) and, upon further compression, films begin to dissolve. At the same time, the surface elasticity of adsorbed films decreases nearly twofold upon the achievement of the maximum value that testifies the formation of looser structure of the surface layer.     

Infrared spectra of matrix isolated and solid ethylene. Formation of ethylene dimers

Spectra of matrices with ethylene/argon ratios from 1/1 to 1/999 and a 1/24 ethylene/xenon matrix have been recorded in the temperature range 15–105 K. From relative i.r. intensities, frequency shifts and statistical calculations, the data are interpreted in terms of a monomer → dimer → aggregate → crystal scheme. It is proposed that the dimer, (C₂H₄)₂, has D_2d symmetry with a structure determined by quadruple hydrogen bonding and hydrogen-hydrogen repulsion. A method is described for calculation of the vibrational splitting due to interactions between the dimer molecular constituents.Solid ethylene has been studied between 15 and 85K. A transformation between two crystalline phases is characterized.     

Role of ion ligands in the attachment of poly(ethylene oxide) to a charged surface

Using a surface force balance we demonstrate unambiguously that high-molecular-weight poly(ethylene oxide) (PEO) does not adsorb onto mica from purified water with no added salt, a surprising observation in view of its strong adsorption on mica from aqueous 0.1 M KNO3 solution. Analysis of the force profiles, together with the known complexation of PEO with metal ions, suggests that the polymer attachment to the negatively charged surface is mediated by the hydrated potassium ion acting as a ligand.     

Reaction of ethylene with oxygen adsorbed on a silver film. Dependence of the selectivity to ethylene oxide on the ethylene pressure

Kinetics of the reaction of ethylene with oxygen adsorbed on a silver film was studied by a static method at 333 K, initial surface coverage with oxygen close to 0.8 and initial ethylene pressures of 1.1 and 4.4 Pa. The ethylene oxide selectivity was found to increase with increasing ethylene pressure.     

Selective adsorption of poly(ethylene oxide) onto a charged surface mediated by alkali metal ions

Using a surface force balance, we have measured normal and shear interactions between mica surfaces across pure water and across 0.1 M aqueous solutions of LiNO3, NaNO3, KNO3, and CsNO3, both prior to adding polymer and following addition of 1.5 x 10(-4) w/w poly(ethylene oxide) (PEO, Mw = 170 kD) and overnight incubation. Our results reveal that while the PEO adsorbs strongly from the KNO3 and CsNO3 solutions, unexpectedly it does not adsorb at all from the LiNO3 and NaNO3 salt solutions. We attribute this to the different nature of the hydration layers about the alkali metal ions: these favor liganding to the negatively charged mica surface of the etheric -O- group on the ethylene oxide monomer for the case of the more weakly hydrated K+ and Cs+, but not for the case of Na+ or Li+ with their more strongly bound water. A simple model relating the electrostatic energy changes occurring upon such liganding to the experimentally measured hydration energies of the different alkali metal ions supports this attribution.     

Reaction of oxazolidone-2 with ethylene oxide. XIV

The reaction of ethylene oxide with oxazolidone-2 under various conditions is investigated. A method of preparing 3--hydroxyethyloxazolidone-2 from ethylene oxide and oxazolidone-2 under pressure in an autoclave, at 72–75° in aqueous medium, is described.For Part XIII see [8].     

Poly[(methylene oxide) oligo(ethylene oxide)] vs. poly(ethylene oxide) as hosts for neodymium compounds

In view of the residual crystallinity in PEO found to limit the solubility of some Nd³⁺-compounds, amorphous PEO (aPEO) was synthesized for exploration as an alternative host. Complexation, solubility limit, morphology, and response to moisture absorption in the doped systems were investigated using FTIR, DSC, TGA, and WAXD techniques. Representing a perturbation to the structural regularity present in PEO, aPEO was found to present lower solubilities for dopants (Nd(act)₃ and Nd(acac)₃, both characterized by a weak Nd³⁺–ether oxygen interaction. On the other hand, no difference in solubility was observed for dopant Nd(NO₃)₃, characterized by a strong Nd³⁺–ether oxygen interaction. Laser interferometry was employed to assess film homogeneity of the Nd(NO₃)₃-doped systems across a 20-mm diameter, and the measured peak-to-valley distortion values were observed to be encouraging for practical applications. © 1994 John Wiley & Sons, Inc.     

Determination of the surface area of smectite in water by ethylene oxide chain adsorption

This study investigates the feasibility of using ethylene oxide (EO) chain adsorption to determine the surface area of smectite in water. Experimental results indicate that high-molecular-weight poly(ethylene oxide) (PEO) should be used to provide reasonable estimations for monolayer capacity of PEO on smectite. The surface areas of smectites in water are calculated from the monolayer capacity of PEO adsorbed on smectite by taking the area per EO unit as 8.05 A(2). The method measures the actual surface area of smectite exposed when dispersed in water, which is important to applications of smectite under aqueous conditions.     

Analysis of ethylene oxide sequences of the acetal copolymer from trioxane and ethylene oxide

An NMR method for the analysis of the ethylene oxide sequence of the acetal copolymer from trioxane and ethylene oxide has not yet been established. We found three novel cyclic compounds composed of 1 mol of ethyelene oxide and 1 mol of trioxane, 2 mol of ethylene oxide and 1 mol of trioxane, and 3 mol of ethylene oxide and 1 mol of trioxane. These compounds gave only one consecutive oxyethylene unit, two consecutive oxyethylene units, and three consecutive oxyethylene units in three consecutive oxymethylene units, respectively, and gave different ¹H NMR spectra for each oxyethylene unit. Considering these data, we synthesized three polymeric model compounds that have one consecutive oxyethylene sequence, two consecutive oxyethylene sequences, and three consecutive oxyethylene sequences in an oxymethylene main chain. By a linear combination of the ¹H NMR spectrum of each oxyethylene unit of the three polymeric model compounds, we succeeded in determining the ethylene oxide sequence by the ¹H NMR method for the copolymer from trioxane and ethylene oxide. Good agreement was observed between the ¹H NMR method and the hydrolysis method for the analysis of the ethylene oxide sequences. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3239–3245, 2001     

Structure of poly(ethylene oxide) complexes. II. Poly(ethylene oxide)–mercuric chloride complex

The structure of the crystalline complex of poly(ethylene oxide) with mercuric chloride, whose composition is (CH₂CH₂O)₄ · HgCl₂, has been determined by x-ray diffraction. The unit cell is orthorhombic with the dimensions of a = 13.55 Å, b = 8.58 Å, and c (fiber axis) = 11.75 Å, and the unit cell contains 4 HgCl₂ molecules and 16 CH₂CH₂O units. Four chains pass through the lattice and four monomeric units are contained in the fiber identity period. The space group is Ccmm–D_2h¹⁷, Ccm2¹–C_2v¹², Cc2m–C_2v¹⁶ or C222₁–D₂⁵. The positions of Hg and Cl atoms have been determined by the Patterson function synthesized by the use of intensity data of the fiber sample, and the molecular conformation of poly(ethylene oxide) has been determined by examining the space not occupied by mercuric chloride molecules in the crystal lattice. The conformation of polyethylene oxide in the complex has been found to be the form of T₅GT₅G ; that is, where G and G mean the right- and left-handed gauche forms, respectively. This molecular structure has been confirmed further by the results of the Fourier syntheses by using the more accurate data refined by the intensity measurements with a diffractometer on the powder sample. The bond length between Hg and Cl in the complex (2.30 Å) is a little longer than that of HgCl₂ in the crystal (2.25 Å). This is consistent with the fact that the infrared absorption band associated with the antisymmetric stretching vibration of HgCl₂ shifts to 353 cm^?1 in the complex from 367 cm^?1 in the crystal. It was also found that another type of complex, giving a different infrared spectrum and x-ray diffraction pattern, was obtained when the original complex was soaked much longer in a saturated ether solution of HgCl₂.     

Crystallinity of ethylene oxide oligomers

Nonaethylene glycol and pentadecaethylene glycol and their dimethyl ethers have been prepared and characterized, with respect to crystallinity by wide- and small-angle X-ray scattering, Raman scattering, i.r. spectroscopy and differential scanning calorimetry. Wide-angle X-ray scattering is similar to that from high molecular weight poly(ethylene oxide). The crystal habit is lamella. The lamellae are highly crystalline and the surface layers are ordered. Comparison with crystalline poly(ethylene oxide) prepared conventionally, and having a distribution of chain lengths, shows that such samples crystallize into lamellae with disordered surface layers.     

Reaction of alkenyldichlorophosphines with ethylene oxide and ethylene sulfide

Conclusions In contrast to ethylane oxide, ethylene sulfide reacts with the styryl- and isobutenyldichlorophosphines only in the presence of catalysts. The course of the discussed reactions is facilitated by solvents with a high electron-donor capacity. The obtained results are discussed from the standpoint of primary donor-acceptor interactions of the reactants.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 457–461, February, 1976.     

Vibrational relaxation of ethylene oxide and ethylene oxide-rare-gas mixtures

The collision-induced vibrational energy relaxation of ethylene oxide (C₂H₄O) was studied by means of laser-induced fluorescence. The time-dependent population of the vibrational modes v₃ and v₅/v₁₂ was measured after excitation of CH-stretching vibrations near 3000 cm^?1. Rate constants for the vibrational energy transfer by collisions with C₂H₄O and the rare gases are deduced, and a simplified model for the vibrational relaxation of C₂H₄O is discussed.