About: Ether is a(n) research topic. Over the lifetime, 46286 publication(s) have been published within this topic receiving 572209 citation(s). The topic is also known as: ether.
01 Apr 1986-Journal of Computational Chemistry
TL;DR: An all atom potential energy function for the simulation of proteins and nucleic acids and the first general vibrational analysis of all five nucleic acid bases with a molecular mechanics potential approach is presented.
Abstract: We present an all atom potential energy function for the simulation of proteins and nucleic acids. This work is an extension of the CH united atom function recently presented by S.J. Weiner et al. J. Amer. Chem. Soc., 106, 765 (1984). The parameters of our function are based on calculations on ethane, propane, n−butane, dimethyl ether, methyl ethyl ether, tetrahydrofuran, imidazole, indole, deoxyadenosine, base paired dinucleoside phosphates, adenine, guanine, uracil, cytosine, thymine, insulin, and myoglobin. We have also used these parameters to carry out the first general vibrational analysis of all five nucleic acid bases with a molecular mechanics potential approach.
27 May 1980-Biochemistry
TL;DR: The compounds described are fluorescent Ca2+ indicators absorbing in the ultraviolet region; the very large spectral shifts observed on binding Ca2+, fit the prediction that complexation should hinder the conjugation of the nitrogen lone-pair electrons with the aromatic rings.
Abstract: A new family of high-affinity buffers and optical indicators for Ca2+ is rationally designed and synthesized. The parent compound is 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), a relative of the well-known chelator EGTA [ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid] in which methylene links between oxygen and nitrogen are replaced by benzene rings. BAPTA and its derivatives share the high (greater than 10(5)) selectivity for Ca2+ over Mg2+ of EGTA but are very much less affected by pH changes and are faster at taking up and releasing Ca2+. The affinity of the parent compound for Ca2+ (dissociation constant 1.1 x 10(-7) M in 0.1 M KCl) may be strengthened or weakened by electron-releasing or -withdrawing substituents on the aromatic rings. The Ca2+ and Mg2+ affinities may further be altered by replacing the ether oxygens by heterocyclic nitrogen atoms. The compounds described are fluorescent Ca2+ indicators absorbing in the ultraviolet region; the very large spectral shifts observed on binding Ca2+ fit the prediction that complexation should hinder the conjugation of the nitrogen lone-pair electrons with the aromatic rings. Derivatives with quinoline nuclei are notable for their high sensitivity of fluorescent quantum yield to the binding of Ca2+ but not of Mg2+. Preliminary biological tests have so far revealed little or no binding to membranes or toxic effects following intracellular microinjection.
15 Mar 2002-Journal of Membrane Science
Abstract: Novel biphenol-based wholly aromatic poly(arylene ether sulfone)s containing up to two pendant sulfonate groups per repeat unit were prepared by potassium carbonate mediated direct aromatic nucleophilic substitution polycondensation of disodium 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (SDCDPS), 4,4′-dichlorodiphenylsulfone (DCDPS) and 4,4′-biphenol. Copolymerization proceeded quantitatively to high molecular weight in N -methyl-2-pyrrolidinone at 190 °C. Tough membranes with a SDCDPS/DCDPS mole ratio up to 60:40 were successfully cast using N , N -dimethylactamide. An increase of sulfonate groups in the copolymer resulted in increased glass transition temperature, enhanced membrane hydrophilicity, and intrinsic viscosity; the 100% SDCDPS homopolymer was water soluble. The acid form membranes were successfully obtained by treating the sodium form of the membranes with dilute sulfuric acid solution. Thermogravimetric analysis shows that the sodium form materials have enhanced thermal stability relative to the acid form, as expected. Atomic force microscopy (AFM) phase images of the acid form membranes clearly show the hydrophilic domains, with sizes increasing from 10 to 25 nm as a function of the degree of sulfonation. A phase inversion could be observed for the 60% SCSDPS copolymer, which was consistent with a rapid increase in water absorption. Short-term aging (30 min) indicates that the desired acid form membranes are stable to 220 °C in air and conductivity values at 30 °C of 0.11 S/cm (SDCDPS/DCDPS=0.4) and 0.17 S/cm (SDCDPS/DCDPS=0.6) were measured, which are comparable to or higher than the state-of-the-art fluorinated copolymer Nafion 1135 control (0.12 S/cm). The conductivity is greatly influenced by ion exchange capacity, temperature, and water activity. The new copolymers, which contain ion conductivity sites on the deactivated positions of the aryl backbone rings, are candidates as new polymeric electrolyte materials for proton exchange membrane (PEM) fuel cells.
02 Sep 2010-Recueil des Travaux Chimiques des Pays-Bas
Abstract: Propargyl ethers HCCCH2OR [R = alkyl or-CH(CH8)(OC2H5)] have been isomerized with good yields into the corresponding allenyl ethers CH2CCHOR by warming with potassium tert.-butoxide at 70°. These allenyl ethers can be metallated with butyllithium in ether or alkali amides in liquid ammonia. In ether, subsequent alkylation with alkyl halides R′Hal affords α-substituted allenyl ethers CH2CC(R′)OR. Alkylation in liquid ammonia produces a mixture of this same compound and the γ-substituted product R′CHCCHOR. In both cases reasonable yields are obtained. Sodamide and potassium amide quickly convert allenyl ethers CH2CCHOR into metallated propargyl ethers MCC-CH2OR (M = Na or K). If alkylation is not performed almost simultaneously with the metallation with sodamide or potassium amide, the only alkylation product obtained is R′CCCH2OR.
05 Sep 2011-Angewandte Chemie
TL;DR: It is demonstrated that ether-based electrolytes are not suitable for rechargeable Li–O2 cells, although the ethers are more stable than the organic carbonates, the Li2O2 that forms on the first discharge is accompanied by electrolyte decomposition, to give a mixture of Li2CO3, HCO2 Li, CH3CO2Li, polyethers/ esters, CO2, and H2O.
Abstract: The rechargeable Li–air (O2) battery is receiving a great deal of interest because theoretically it can store significantly more energy than lithium ion batteries, thus potentially transforming energy storage. Since it was first described, a number of aspects of the Li–O2 battery with a non-aqueous electrolyte have been investigated. The electrolyte is recognized as one of the greatest challenges. To date, organic carbonate-based electrolytes (e.g. LiPF6 in propylene carbonate) have been widely used. However, recently, it has been shown that instead of O2 being reduced in the porous cathode to form Li2O2, as desired, discharge in organic carbonate electrolytes is associated with severe electrolyte decomposition. As a result it is very important to investigate other solvents in the search for a suitable electrolyte. In this regard much attention is now focused on electrolytes based on ethers (e.g. tetraglyme (tetraethylene glycol dimethyl ether)). Ethers are attractive for the Li–O2 battery because they are one of the few solvents that combine the following attributes: capable of operating with a lithium metal anode, stable to oxidation potentials in excess of 4.5 V versus Li/Li, safe, of low cost and, in the case of higher molecular weights, such as tetraglyme, they are of low volatility. Crucially, they are also anticipated to show greater stability towards reduced O2 species compared with organic carbonates. Herein we show that although the ethers are more stable than the organic carbonates, the Li2O2 that forms on the first discharge is accompanied by electrolyte decomposition, to give a mixture of Li2CO3, HCO2Li, CH3CO2Li, polyethers/ esters, CO2, and H2O. The extent of electrolyte degradation compared with Li2O2 formation on discharge appears to increase rapidly with cycling (that is, charging and discharging), such that after only 5 cycles there is little or no evidence of Li2O2 from powder X-ray diffraction. We show that the same decomposition products occur for linear chain lengths other than tetraglyme. In the case of cyclic ethers, such as 1,3dioxolane and 2-methyltetrahydrofuran (2-Me-THF), decomposition also occurs. For 1,3-dioxolane, decomposition forms polyethers/esters, Li2CO3, HCO2Li, and C2H4(OCO2Li)2, and for 2-Me-THF the main products are HCO2Li, CH3CO2Li; in both cases CO2 and H2O evolve. The results presented herein demonstrate that ether-based electrolytes are not suitable for rechargeable Li–O2 cells. A Li–O2 cell consisting of a lithium metal anode, an electrolyte, comprising 1m LiPF6 in tetraglyme, and a porous cathode (Super P/Kynar) was constructed as described in the Experimental Section. The cell was discharged in 1 atm O2 to 2 V. The porous cathode was then removed, washed with CH3CN, and examined by powder X-ray diffraction (PXRD) and FTIR. The results are presented in Figure 1 and Figure 2. The PXRD data demonstrate the presence of Li2O2, consistent with previous PXRD data for a Li–O2 cell with a tetraglyme electrolyte at the end of the first discharge. However, examination of the FTIR spectra, Figure 2, reveals that, in addition to Li2O2, other products form. Although the FTIR spectra provide clear evidence of electrolyte decom-