A revised quantum chemistry-based potential for poly(ethylene oxide) and its oligomers in aqueous solution

We have conducted a high-level quantum chemistry study of the interactions of 1,2-dimethoxyethane (DME) with water for complexes representing both hydrophilic and hydrophobic hydration. It was found that our previous quantum chemistry-based force field for poly(ethylene oxide) (PEO) and its oligomers in aqueous solution did a poor job in describing the hydrophobic binding of water to the ether, consistent with our recent calculations of the excess free energy and entropy of hydration of DME. Our original force field was revised to more accurately reproduce the interaction of water with the carboneous portions of DME. Molecular dynamics simulations of aqueous DME solutions using the revised quantum chemistry-based potential yielded good agreement with experiment for excess free energy, enthalpy, and volume as well as excess solution viscosity and the self-diffusion of water. Comparison with our original potential revealed that the relatively hydrophobic ether-water interactions in the new potential strongly reduced the favorable excess free energy and enthalpy but have relatively little influence on the excess entropy for dilute DME solutions. Other properties of DME and PEO solutions including conformational populations and dynamics, solution viscosity, hydrogen bonding, water translational and rotational diffusion and neutron structure factor as a function of solution composition were found to be largely unchanged from those obtained using the original potential.     

Molecular structure of ThBr4(DME)2 (DME = 1,2-dimethoxyethane)

The molecular structure of ThBr₄(DME)₂ (DME = 1,2-dimethoxyethane), the first structurally characterized thorium complex containing a simple bidentate ether ligand, is described. The eight-coordinate complex presents a distorted dodecahedral geometry, with Th—Br and Th—O bond lengths in the ranges 2.8516(13)–2.8712(13) Å and 2.564(8)–2.620(8) Å, respectively. ThBr₄(DME)₂ is monoclinic, space group P2₁/n, a = 7.672(1), b = 14.581(1), c = 15.847(2) Å, = 102.24(1)°, V = 1732.4(3) ų, and Z = 4.     

SmCl3（DME）·2THF的晶体结构

我们曾测定NdCl_3·4THF的晶体结构,并研究了它对双烯烃聚合的活化作用.本文报导含二甲氧基乙烷(Dimethoxyethane,简称DME)的SmCl_3(DME)·2THF的制备及其单晶结构,以利于对稀土催化双烯烃聚合反应机理作出更好的解释.     

DME构象的ADF研究

用ＡＤＦ方法对游离状态下的１,２－二甲氧基乙烷（ＤＭＥ）的构象进行了研究。结果表明,能量最低的３种构象ｔｇｇ,’ｔｇｔ,ｔｔｔ的能量相近,其中ｔｔｔ不是能量最低的构象,而且说明ＤＭＥ在气态、液态、固态和游离状态下分别采用哪种构象为最优构象,除了与构象的能量有关外,还受分子间相互作用及分子的对称性是否适合于紧密堆积的影响。     

A LiNi0.8Co0.15Al0.05O2/Ge electrochemical system for lithium-ion batteries

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Ion solvation in lithium battery electrolyte solutions. 1. Apparent molar volumes

Apparent molar volumes, V(MX), of seven electrolytes (NaClO₄, NaCF₃SO₃, NaBPh₄, LiClO₄, LiAsF₆, Ph₄AsCF₃SO₃ and KCF₃SO₃) have been determined by vibrating-tube densimetry in nonaqueous solvent mixtures of propylene carbonate (PC) with acetonitrile (AN), dimethoxyethane (DME) and tetrahydrofuran (THF). V(MX) was measured at an electrolyte concentration of 0.05M over the entire solvent composition range wherever possible. Ionic apparent molar volumes of transfer, _tV(ion), were obtained via the tetraphenylarsonium tetraphenylborate (TATB) assumption. _tV(ion) from PC to the mixed solvents are generally strongly negative for both cations and anions consistent with the greater compressibilities and lower dielectric constants of the cosolvents. In PC/AN mixtures cations and anions have similar values of _tV(ion) but in PC/DME and PC/THF mixtures they differ considerably. Cationic volumes show the expected dependence on ion-size but the differences among the anion volumes are much greater than expected at high cosolvent compositions. These effects are discussed in terms of preferential solvation and other solvent interactions. The implications of these findings for lithium batteries are briefly discussed.     

Conductimetric study of cesium chloride in isodielectric aqueous tetrahydrofuran, 1,2-dimethoxyethane and dioxane mixtures from 0 to 35°C

CsCl in nearly isodielectric aqueous mixtures with tetrahydrofuran, 1,2-dimethoxyethane and dioxane has been studied at temperatures between 0° and 35°C. The conductance data are analyzed for the limiting conductance ₀ and the association constant K _A by means of the Justice-Ebeling conductance equation. By application of the Bjerrum equation an apparent distance of closest approach á is evaluated. This parameter is generally close to the crystallographic radius, 35Å. The deviations are attributed to solvation effects and are interpreted in terms of the Friedman-Rasaiah-Gurney cosphere overlap model. The variations of the effect with temperature permits an evaluation of enthalpy and entropy solvation parameters.     

Catalytic Oxidation of Dimethyl Ether to Hydrocarbons over SnO2/MgO and SnO2/CaO Catalysts

A novel reverse microemulsion method was used to prepare SnO2/MgO and SnO2/CaO catalysts. It was found that both the catalysts were active for the reaction of catalytic oxidation of dimethyl ether (DME) in the temperature range of 275 to 300℃. SnO2/CaO catalyst exhibits much higher activity than SnO2/MgO. On SnO2/CaO catalyst, DME conversion of 21.8% was obtained at 300℃, while selectivities to methyl formate (MF) and dimethoxyethane (DMET) of 19.1% and 59.0% respectively were obtained at 275℃.