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101.
In the density-functional theory of the ground state of an electronic system there arise the concepts of softness, hardness, local softness, and local hardness. Definitions of these quantities are reviewed, and then local softness and local hardness are discussed in some detail. The local softness of a species, the derivative , is a measure of the chemical reactivity of a site in the molecule. From it can be obtained the total global absolute softness in the sense of Pearson and a normalized chemical reactivity index of frontier type. Several formulas for s( r ) are obtained, including new fluctuation formulas, and its determinative role in chemisorption, catalysis, and frontier-controlled charge-transfer processes is briefly discussed. Local hardness is a corresponding appropriately defined functional derivative η(r) = [δμ/δp(r)]v(r). Difficulties associated with ambiguities in this definition are discussed and resolved. It is concluded that for most purposes the best working formula for local hardness is , where η(r, r′) is the hardness kernel; , where F[p] is the usual Hohenberg-Kohn functional and f(r) is the Fukui function. With this definition, η(r) = η, a constant which is the global hardness. Just as the chemical potential equalizes in the ground state, so does the hardness. It is demonstrated that hardness can be taken to be an average of orbital contributions. 相似文献
102.
Sijtze Stob Ruud M. Scheek Rolf Boelens Klaas Dukstra Robert Kaptein 《Israel journal of chemistry》1988,28(4):319-327
Photo-CIDNP is a useful technique to identify surface residues in proteins and to assign resonances in their 1H NMR spectra by the spectral simplification that is obtained. In spite of this simplification, conventional photo-CIDNP spectra can be quite complex due to spectral overlap. For this reason two-dimensional (2D) methods are welcome. We present combinations of photo-CIDNP with 2D J-correlated spectroscopy (CIDNP-COSY) and with 2D NOE spectroscopy (CIDNP-NOESY). In these experiments we insert a saturation pulse sequence and a short laser-irradiation period at the beginning of the preparation period to generate CIDNP, leaving the remaining of the pulse scheme essentially unaltered. The CIDNP-COSY and CIDNP-NOESY spectra of a hen egg-white (HEW) lysozyme are presented. The CIDNP-NOESY spectrum of lysozyme is compared with the results from 1D cross-polarisation experiments on the same protein. CIDNP-NOESY spectra of lysozyme with and without inhibitor NAG are compared. 相似文献
103.
Fumonisin B1 is a sphingolipid-like compound that enhances the accumulation of yeast sphingolipids and 2-hydroxy fatty acids. These lipids
occur both as freely extractable and cell bound components in yeast fermentations. Both free and bound 2-hydroxy fatty acids
produced byPichia sydowiorum NRRL Y-7130 were increased when fumonisin B1 (50 mg/L) was added to the usual growth medium containing yeast extract/malt extract/peptone/glucose. Fumonisin-treated cultures
contained 38 mg/L more 2-hydroxyhexadecanoic and 15 mg/L more 2-hydroxyoctadecanoic acids than did untreated cultures. By
contrast, fumonisin inhibited the accumulation of free 8,9,13-trihydroxydocosanoic acid inRhodotorula sp. YB-2501 cultures, leading to 240 mg/L lower trihydroxy acid production than by untreated cultures. 相似文献
104.
Daniela M. Bonafede Lawrence J. Macala Martha Costantine-Paton Robert K. Yu 《Lipids》1989,24(8):680-684
Bovine buttermilk contains a unique ganglioside, 9-O-acetyl-GD3. In order to isolate large quantities of this ganglioside, a simplified isolation scheme which consists of several ion-exchange
and silica gel column chromatographic procedures was devised. The isolated 9-O-acetyl-GD3 was characterized on the basis of its thin-layer chromatographic behavior, its immunoreactivity with a specific monoclonal
antibody, JONES, and by conversion to authentic GD3 by mild base treatment. 相似文献
105.
Phosphatidylcholine acyltransferase (lecithin:cholesterol acyltransferase or LCAT; EC 2.3.1.43) activity was found to be present
in pig ovarian follicular fluid (POFF), in addition to pig serum (PS). The cholesterol esterification rate in both POFF and
PS is linear with incubation time up to 2 hr. The mean absolute rate of POFF-cholesterol esterification was 8.1±0.4 nmoles
per ml per hr approximately one-fourth of that in PS. However, the fractional rate (percent of labeled cholesterol esterified
per hr) of POFF-cholesterol esterification was similar to that observed in PS. There was little variation of absolute rate
of cholesterol esterification in the fluid obtained from different sizes of follicles. Fatty acid or triacylglycerol did not
participate in the reaction of cholesterol esterification in POFF. No appreciable change in enzymatic activity was found from
storing POFF at 4 C for periods of time up to 24 hr or at −70 C up to 2 months, but activity was lost thereafter. On the other
hand, PS showed a much longer period of stability (5 days at 4 C and 9 months at −70 C). A discrepancy between the fatty acid
composition of cholesteryl esters formed by the LCAT reaction and the fatty acid composition at the C-2 position of phosphatidylcholine
led us to propose a two-step mechanism for the LCAT reaction. It is concluded that the LCAT of POFF, as well as that of plasma,
is specific for individual fatty acids rather than for the fatty acid composition of phosphatidylcholine. The fatty acid concentration
of lysophosphatidylcholine decreased during prolonged incubation times (6 to 21 hr) suggesting that the increased lysophosphatidylcholine
formed as a product of the LCAT reaction may be reused as substrate for the LCAT reaction or for hydrolysis by lysophosphatidylcholine
hydrolase.
Presented at the AOCS Meeting, New York, May 1977. 相似文献
106.
Robert K. Vander Meer Francisco Alvarez Clifford S. Lofgren 《Journal of chemical ecology》1988,14(3):825-838
TheSolenopsis invicta trail pheromone is synthesized by the Dufour's gland and is released through the sting apparatus. The recruitment subcategory of theS. invicta trail pheromone was shown to be composed of a mixture of the orientation pheromone, (Z,E)--farnesene and an unidentified homosesquiterpene consisting of three rings and one double bond (C-1). C-1 is present in worker Dufour's glands at only 75 pg per worker equivalent. This is the first report that demonstrates that different exocrine products from the same gland control different subcategories of behavior related to mass recruitment. 相似文献
107.
Barium Metaplumbate Ceramic Electrodes for Ceramic Capacitors 总被引:2,自引:0,他引:2
Frank P. Skeele Robert E. Newnham Leslie E. Cross 《Journal of the American Ceramic Society》1988,71(5):263-C
A novel approach to reduce electrode costs in ceramic capacitors is presented. Barium metaplumbate (BaPbO3 ) was fired onto sintered commercial (Ba, Sr)TiO3 disk capacitors as external electrodes. Samples were compared to disk capacitors of the same composition with electrodes made of sputtered gold and air-dried silver. The ceramic electrode led to substantial changes in the insulation resistance and dc breakdown strengths, but other properties remained the same. The feasibility of using BaPbO3 electrodes strongly depends on chemical reactions between the electrode and dielectric. 相似文献
108.
W.Wade Adams Robert M. Briber Edward S. Sherman Roger S. Porter Edwin L. Thomas 《Polymer》1985,26(1):17-26
The microstructure of a series of solid state extruded polyethylene fibres was examined by wide- and small-angle X-ray scattering. By measuring absolute intensities using a two dimensional position sensitive detector, accurate values of the small-angle invariant for anisotropic samples were obtained. This measurement coupled with wide-angle X-ray scattering and d.s.c. permitted determination of the density of the noncrystalline component. The use of a two phase model for solid state extruded polyethylene is justified if consideration is given to the effective densities of the crystalline and noncrystalline phases, which change with deformation. The effective density of the crystalline phase decreases by 1% (0.999–0.990 g cm?3) from the unextruded billet compared to a 36 draw ratio extrudate, while the noncrystalline phase density increases by 6% (0.84–0.89 g cm?3). These changes lead to an overall decrease in the mean squared electron density fluctuation of 63%. The average axial crystallite length measured by wide-angle X-ray scattering increases with extrusion draw ratio while the SAXS long period decreases and weakens considerably. These observations and the electron microscopy results from the previous paper, (Polymer, 1982, 23, 1069), are fully consistent with the key features of the Peterlin model of fibre microstructure. 相似文献
109.
The mechanisms and kinetics of radical entry in emulsion polymerizations utilizing redox initiation are investigated using polymerization rate data obtained by reaction calorimetry and electrospray mass spectroscopy analysis of initiator-derived aqueous-phase products. These data have been used to evaluate an initiation scheme for redox-initiated emulsion polymerizations of common monomers such as styrene and methyl methacrylate based around the oxidant, tert-butyl hydroperoxide. Redox initiators are broadly classed by the solubility of their radical products: Hydrophilic radicals enter by propagating to a critical degree of polymerization to become surface-active whilst more hydrophobic radicals may enter particles directly. When direct entry is applicable (the hydrophobic case), initiation efficiency will always be very high. 相似文献
110.
Robert S. Brookman 《乙烯基与添加剂工艺杂志》1988,10(1):33-36
The paper describes the development and properties of a new family of thermoplastic elastomers based on polyvinyl chloride. Comparisons of the new products with traditional flexible PVC's will be presented, pointing up differences in specific gravity, low temperature properties, heat resistance, melt viscosity, and general physical properties such as tensile modulus and elongation. The elastomeric properties of the new materials are explored and compared to some typical cured elastomers—chloroprene, chlorosulphonated polyethylene. The common thermoplastic elastomers based on block copolymers and polyurethanes are also considered in relation to the new compositions. Such properties as compression-set, flex and fatigue resistance, oil and chemical resistance, weatherability, and performance at elevated temperatures are detailed. The unique feature of this technology that allows one to tailor the surface characteristics from typically high PVC gloss to the fine dull satin finish of cured elastomers is discussed. 相似文献