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71.
Much recent attention has been given to molecules containing only nitrogen atoms. Such molecules N(x) can undergo the reaction N(x) --> (x/2)N(2), which is very exothermic. These molecules are potential candidates for high energy density materials (HEDM). However, many all-nitrogen molecules dissociate too easily to be stable, practical energy sources. It is important to know which nitrogen molecules will be stable and which will not. In the current study, a variety of N(12) cages with all single bonds are examined by theoretical calculations to determine which ones are the most thermodynamically stable. Calculations are carried out using Hartree-Fock (HF) theory, gradient-corrected density functional theory (DFT), and Moller-Plesset perturbation theory (MP2 and MP4). Relative energies among the various isomers are calculated and trends are examined in order to determine which structural features lead to the most energetically favorable molecules. 相似文献
72.
Joseph T. Repine Douglas S. Johnson Andrew D. White Michael A. Stier Trent Rankin Samarendra N. Maiti 《Tetrahedron letters》2007,48(31):5539-5541
A series of regioisomerically monofluorinated 1-(naphthalen-1-yl)piperazines is described. 相似文献
73.
A differential microcalorimetric study of whey proteins and their behaviour in oil-in-water emulsions 总被引:1,自引:0,他引:1
Oil-in-water emulsions (20% soya oil, 1% protein) have been prepared containing lysozyme or isolates of -lactalbumin and β-lactoglobulin from whey protein. The structural characteristics of these proteins adsorbed at an oil/water interface were determined by following their thermal transitions using differential scanning microcalorimetry. Thermograms of the proteins in the adsorbed state differed markedly from the corresponding transitions seen for the proteins in solution. This suggests that the proteins underwent substantial changes in secondary and tertiary structure upon adsorption. In general, for all the proteins studied, a net decrease in the total energy absorbed during denaturation was found when the proteins were in an adsorbed state. Both lysozyme and -lactalbumin were in part “surface denatured”, and they showed a certain degree of reversibility between solution and the adsorbed state. β-Lactoglobulin showed the highest degree of denaturation upon adsorption and the conformational change was irreversible. 相似文献
74.
Mohandas Devaki V. Whelan Douglas R. Panchal Chandra J. 《Applied biochemistry and biotechnology》1995,(1):307-318
Mutants resistant to comparatively high levels of acetic acid were isolated from the xylose-fermenting yeastsCandida shehatae andPichia stipitis by adapting these cultures to increasing concentrations of acetic acid grown in shake-flask cultures. These mutants were
tested for their ability to ferment xylose in presence of high acetic acid concentrations, in acid hydrolysates of wood, and
in hardwood spent sulfite liquor, and compared with their wild-type counterparts and between themselves. TheP. stipitis mutant exhibited faster fermentation times, better tolerance to acid hydrolysates, and tolerance to lower pH. 相似文献
75.
Klumpp DA Rendy R Zhang Y McElrea A Gomez A Dang H 《The Journal of organic chemistry》2004,69(23):8108-8110
A variety of aminoalkynes and related heterocycles are reacted in the Bronsted superacid CF(3)SO(3)H (triflic acid), and products are obtained in generally good yields (69-99%) from Friedel-Crafts-type reactions. The reactions are consistent with the formation of novel dicationic intermediates having a vinyl cationic site and an adjacent protonated N-heterocycle or ammonium cation. 相似文献
76.
Novel Lewis-base ionic liquids replacing typical anions 总被引:1,自引:0,他引:1
Masahiro Yoshizawa-Fujita Katarina Johansson Douglas R. MacFarlane 《Tetrahedron letters》2006,47(16):2755-2758
We have synthesized two kinds of new Lewis-base ionic liquids (ILs); one is based on the relatively strong Lewis basic acetate anion, and the other is a salt composed of a mono-alkylated diamine such that the Lewis base site is incorporated in the cation. 1-Octyl-4-aza-1-azonia-bicyclo[2.2.2]octane bis(trifluoromethanesulfonyl)amide, [C8dabco]TFSA, and N-butyl-N-methylpyrrolidinium acetate, [p1,4]OAc, melted into fluid liquids at 26 and 81 °C, respectively. The thermal decomposition of [p1,4]OAc started at around 150 °C, whereas the thermal stability of [C8dabco]TFSA was almost equal to that of typical TFSA-based ILs in spite of the Lewis base site. This suggests that if the Lewis base site is incorporated into the cation the IL can maintain higher thermal stability. In addition, as a further result of the presence of the basic nitrogen, [C8dabco]TFSA can dissolve hydrated Cu(NO3)2 whereas the other TFSA-based ILs cannot. 相似文献
77.
Grotjahn DB Van S Combs D Lev DA Schneider C Incarvito CD Lam KC Rossi G Rheingold AL Rideout M Meyer C Hernandez G Mejorado L 《Inorganic chemistry》2003,42(10):3347-3355
Inter- and intramolecular hydrogen bonding of an N-H group in pyrazole complexes was studied using ligands with two different groups at pyrazole C-3 and C-5. At C-5, groups such as methyl, i-propyl, phenyl, or tert-butyl were present. At C-3, side chains L-CH(2)- and L-CH(2)CH(2)- (L = thioether or phosphine) ensured formation of chelates to a cis-dichloropalladium(II) fragment through side-chain atom L and the pyrazole nitrogen closest to the side chain. The significance of the ligands is that by placing a ligating side chain on a ring carbon (C-3), rather than on a ring nitrogen, the ring nitrogen not bound to the metal and its attached proton are available for hydrogen bonding. As desired, seven chelate complexes examined by X-ray diffraction all showed intramolecular hydrogen bonding between the pyrazole N-H and a chloride ligand in the cis position. In addition, however, intermolecular hydrogen bonding could be controlled by the substituent at C-5: complexes with either a methyl at C-5 or no substituent there showed significant intermolecular hydrogen bonding interactions, which were completely avoided by placing a tert-butyl group at C-5. The acidity of two complexes in acetonitrile solutions was estimated to be closer to that of pyridinium ion than those of imidazolium or triethylammonium ions. 相似文献
78.
Copper(II) halides, CuX2 (X = Br?, Cl?), have been combined in non-aqueous medium with various α,-β-dione dioxime (α,β-dodoH) ligands to produce new 1:1 adducts, the di-μ-halo-bis[halo(α,β-dodoH)copper(II)] dimers. These are: Di-μ-bromo-bis[bromo(ethanedialdioxime)copper(II)]; di-μ-bromo-bis[bromo(diphenylethanedione dioxime)copper(II)]; di-μ-bromo-bis-[bromo(9,10phenanthrenedione dioxime)copper(II)]; di-μ-chloro-bis-[chloro(9,10-phenanthrenedione dioxime)copper(II)]. The materials were characterized by conventional methods. The results clearly indicate that the compounds crystallize in discrete dimers, quite consistent with the results of closely related dimers studied earlier. 相似文献
79.
Journal of Algebraic Combinatorics - We define a new type of Golomb ruler, which we term a resolvable Golomb ruler. These are Golomb rulers that satisfy an additional “resolvability”... 相似文献
80.
Let A be a C*-algebra. For a A let D(a, A) denote the innerderivation induced by a, regarded as a bounded operator on A,and let d(a, Z(A)) denote the distance of a from Z(A), the centreof A. Let K(A) be the smallest number in [0, ] such that d(a,Z(A)) K(A)||D(a, A)|| for all a A. It is shown that if A isnon-commutative and has an identity then either K(A) = , or K(A) = 1 / 3, or K(A) 1. Necessaryand sufficient conditions for these three possibilities aregiven in terms of the primitive and primal ideals of A. If Ais a quotient of an AW*-algebra then K(A) . Helly's Theorem is used to show that if A is aweakly central C*-algebra then K(A) 1. 相似文献