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881.
Ion mobility and calorimetry measurements have been used to probe the nature of the phase transitions in gallium clusters with 29-55 atoms. While most clusters appear to undergo a first-order transition between solidlike and liquidlike phases, a few show the signature of melting without a significant latent heat. These transitions appear to be the finite size analogue of a second-order phase transition, and they presumably occur for some cluster sizes because their solidlike phase is amorphous. 相似文献
882.
Steven R. Caldwell James C. Turley Gary E. Martin 《Journal of heterocyclic chemistry》1980,17(6):1153-1162
The synthesis of the first diazaphenoxathiins, 1,9-diazaphenoxathiin and 1,7-diazaphenoxathiin, are described. Complete assignments are made for the 13C-nmr spectra of these compounds based on additivity correlation and 1H-13C spin-coupling constants. The isolation and confirmation of the structure of 2-[2′(-3′-nitropyridylthio)]-3-[2″-(3″-nitropyridyloxy)] pyridine using 13C-nmr and appropriate model compounds is also discussed. A preliminary evaluation of spontaneous motor depression in mice showed a substantial difference between the observed activities of the two diazaphenoxathiins reported. The possibility of the observed difference being associated with the relative positions of the annular aza-substitutions is discussed. 相似文献
883.
Three phenolic derivatives of 2-aminoanthracene have been prepared as their diacetyl derivatives by Bucherer-type amination of appropriately substituted anthracenes. 相似文献
884.
Gary M. Singerman 《Journal of heterocyclic chemistry》1975,12(5):877-882
A novel synthesis of 2,1-benzisothiazoles is described. When an o-toluidine or N-sulfinyl-o-toluidine is allowed to react with an N-sulfinylsulfonamide, a 2,1-benzisothiazole is formed. 相似文献
885.
M. N. Afsar Kenneth J. Button Gary L. McCoy 《International Journal of Infrared and Millimeter Waves》1980,1(3):513-524
High intensity magnetic fields are needed for the far infrared photoconductivity method to be used reliably in the identification of unitentional contaminants in ultra high purity epitaxial GaAs. We show experimental evidence that the inhomogeneous Stark broadening of the 1s2p (m=–1) transition of the hydrogen-like donor almost disappears as the magnetic field is increased to 20 Tesla. Since the spectral lines also become narrower and the central cell correction (chemical shift) becomes larger, the signature curve method of identification permits positive identification of donor species. In particular, the donors Ge and Se have been identified in specimens that were reported to contain carbon and Sn respectively.Work supported by the U.S. Air Force Office of Scientific Research under Grant #AFOR-78-3708.Supported by the National Science Foundation. 相似文献
886.
The photoinduced polymerization of acrylic monomers using dyes in a protein-restricted medium is reported. We studied dyes of different families as potential polymerization catalysts, exploiting the observation that the photophysical properties of some dyes are altered when bound to biopolymers. The light induced polymerization of acrylic monomers in the presence of bovine serum albumin or gelatin using triphenylmethane and azo dyes proceeded smoothly. Using GE Miser 120 W spotlights as a convenient illumination source, we found polymerization could be achieved in some cases within 60 min of irradiation. The polymerization rates were found to be dependent on the concentrations of the dye and the protein. In the absence of protein or dye polymerization was virtually non-existent. When the reaction mixture was blanketed with nitrogen, polymerization was observed to be faster than that that in air equilibrated samples. We believe these photopolymerizations may proceed via a free-radical pathway. Our results suggest the possible role of some of these dyes as polymerization catalysts, though they had previously seemed inert in fluid solutions. 相似文献
887.
Richard C. Titmas Thelma S. Angeles Renee Sugasawara Nurredin Aman Michael J. Darsley Gary Blackburn Mark T. Martin 《Applied biochemistry and biotechnology》1994,47(2-3):277-292
Because there are many known C-terminally amidated peptides of biological importance, there is great potential in medicine
and organic synthesis for antibodies that catalyze primary amide bond hydrolysis or formation. We characterized a catalytic
antibody, 13D11, raised to a phosphinate hapten, that hydrolyzed the primary amide of a dansyl-alkylated derivative of (R)-phenylalaninamide
(DNS-(R)F-NH2). At pH 9.0, 13D11 hydrolyzed DNS-(R)F-NH2 with a kcat of 1.65 × 10-7 s-1 (kcat/kuncat = 132) and a Km of 432 μM, and was stereospecifically hapten-inhibited (Ki = 14.0 μM). Control experiments indicated that the catalytic activity was not the result of a contaminating protease. In
accordance with the hapten being a transition-state analog of base hydrolysis, the rate of DNS-(R)F-NH2 hydrolysis increased with hydroxide concentration to an optimum pH of 9.5. Above pH 9.5, activity declined rapidly suggesting
the antibody was inactivated during the long incubation period. This work demonstrates the feasibility of generating catalytic
antibodies to hydrolyze unactivated amide bonds without cofactor assistance. 相似文献
888.
889.
A field expedient analytical method for detecting the chemical warfare agent (CWA) sulfur mustard as a soil contaminant was developed using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). Five commercially available SPME fibers were investigated to determine the optimal fiber, and extraction conditions. Polyacrylate and carbowax-divinylbenzene fiber coatings gave a statistically indistinguishable and best response compared to the other three types examined in a simple system studied without soil. The polyacrylate fiber coating was selected for study of a system in which sulfur mustard was spiked to an agricultural soil (Standard Reference Material 2709, San Joaquin type). With soil samples, the greatest sensitivity occurred by the addition of deionized water to spiked soil and extraction at ambient temperature for 20 min or longer. SPME sampling with GC-MS analyses afforded good reproducibility (relative standard deviation between 2 and 10%), and analyte concentrations as low as 237 ng/g were detected in soil (total ion chromatograms). As completed here, total time for sampling and analysis was just under 1 h, and use of organic solvents or special sample introduction equipment was avoided. 相似文献
890.
Xavier Fr. D. Chillier Gary J. Van Berkel Fazil O. Gülaar Armand Buchs 《Journal of mass spectrometry : JMS》1994,29(11):672-678
Chlorins in a sedimentary mixture were characterized, without prior isolation of individual components, using electrospray ionization combined with ion trap mass spectrometry. Collision-induced dissociation in the atmospheric sampling interface and multi-step mass spectrometry (i.e. MSn where n ? 2) were used in order to obtain structural information about the macrocycle. Fragmentation pathways are proposed for different macrocycle types based on data from model chlorins. Three unknown chlorins (RMM = 888, 844 and 790) are assigned as having bacteriochlorophyll macrocycle types esterifled to unusual side-chains (i.e. dihydrophytol for the unknown with a bacteriopheophorbide a structure, phytol and an alcohol with a molecular mass of 242 u for the two unknowns with a proposed bacteriopyropheophorbide d structure). 相似文献