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921.
Andreas J. Illies Linda S. Nichols Mary A. James 《Journal of the American Society for Mass Spectrometry》1997,8(6):605-609
An experimental study of the metastable and collision-induced dissociation (CID) spectra of [Me2S∵SMe2]+ and [Et2S∵SEt2]+ has been carried out. These ions are examples of species that contain two-center-three-electron (2c–3e) sulfur-sulfur bonds. The metastable and CID spectra provide experimental evidence of the atomic connectivity and of the 2c–3e bonds. The metastable cleavage of the S∵S 2c–3e bonds appears to occur with no reverse activation barriers and to result in small average kinetic energy releases. Fragmentation of the same bonds by CID results in the most intense product for both ions. Comparisons with the metastable and CID spectra of [MeSSMe]+, an ion with a two-center-two-electron (2c–2e) sulfur-sulfur bond, are made and strongly support the difference in the sulfur-sulfur bonding. 相似文献
922.
Marianne Riklin Alexander vonZelewsky Alan Bashall Mary McPartlin Akin Baysal JosephA. Connor JohnD. Wallis 《Helvetica chimica acta》1999,82(10):1666-1680
The elusive chiral twisted alkene, 5,5′-bi-5H-cyclopenta[2,1-b : 3,4-b′]dipyridinylidene, known also as 9,9′-bi-4,5-diazafluorenylidene (BDAF), has been prepared in racemic form from 9-bromo-4,5-diazafluorene and from 9,9′-bi-4,5-diazafluorenyl and fully characterised. X-Ray measurements show that there is a twist of 37.8° about the double bond between the 4,5-diazafluorenylidene units. A 1 : 1 charge-transfer compound with 7,7,8,8-tetracyanoquinodimethane (TCNQ) contains an unusual packing arrangement which is centred around the formation of spiral stacks. Each BDAF molecule contributes one 4,5-diazofluorenylidene unit to the backbone of the stack, while the second half is involved in hydrogen-bonding interactions and additional stacking with TCNQ. Examples of complexes containing the axially symmetric tetradentate ligand binding to one and to two metal ions, [M(bdaf)Cl2] and [(MCl2)2(bdaf)] (M=Co, Ni, Zn), are reported. 相似文献
923.
Mary Pat McCurdie Laurence A. Belfiore 《Journal of Polymer Science.Polymer Physics》1999,37(4):301-309
Solid‐state characterization of poly(L ‐histidine) was obtained via differential scanning calorimetry, thermogravimetric analysis, optical microscopy, and infrared spectroscopy. The glass transition temperature of poly(L ‐histidine) is 169°C. This thermal transition has not been reported previously. Poly(L ‐histidine)'s Tg increases when complexes are produced with the following divalent transition metal chlorides: cobalt chloride hexahydrate, nickel chloride hexahydrate, copper chloride dihydrate, and anhydrous zinc chloride. At 10 mol % salt, nickel chloride increases Tg by 69°C. The enhancement in poly(L ‐histidine)'s Tg correlates well with ligand field stabilization energies for pseudo‐octahedral dn complexes (n = 7, 8, and 10) from the first row of the d‐block. However, d9 copper(II) complexes do not conform to this empirical correlation. Infrared spectroscopic evidence indicates that these metal chlorides form complexes with the imidazole ring in the histidine side group and the amide group in the main chain of the polymer. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 301–309, 1999 相似文献
924.
L. J. Francisca Mary P. Kannan 《Journal of polymer science. Part A, Polymer chemistry》1999,37(12):1755-1761
Three series of poly(pyromellitimide‐ester)s were synthesized from various N,N′‐bis(ω‐hydroxyalkyl)pyromellitimides (HAPMIs) by melt condensation with dicarboxylic acids, including terephthalic acid (TPA), 4,4′‐biphenyldicarboxylic acid (BPDA), and 4,4′‐azobenzenedicarboxylic acid (ABDA). Polymers were characterized by elemental analysis, solubility, inherent viscosity, spectra (IR, 1H‐NMR, 13C‐NMR), and X‐ray diffraction (XRD). Thermal stability and phase transition behaviour were evaluated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and hot‐stage optical polarized microscopy (HOPM). The d‐spacings, calculated from XRD data, showed an odd‐even effect with varying numbers of methylene spacers. Crystallinity of polymers decreased in the following order: azobenzene > biphenyl > phenyl polymers. Similarly, DSC‐obtained melting temperatures (Tm's) showed an odd‐even effect, and glass transition temperatures (Tg's) decreased with increasing numbers of methylene spacers. Thermal stability decreased as methylene chain length increased. Thermal stability of polymers occurred in the following order: phenyl > biphenyl > azobenzene polymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1755–1761, 1999 相似文献
925.
Dirk Pfeiffer Mary Jane Heeg Charles H. Winter 《Angewandte Chemie (International ed. in English)》1998,37(18):2517-2519
Despite the small size of the magnesium ion , η2-bound pyrazolato ligands are found in complexes 1 – 3 . These complexes provide new insight into the design of volatile Group 2 metal complexes for use in chemical vapor deposition processes. 相似文献
926.
Nayan K. Solanki Eric J. L. McInnes Frank E. Mabbs Sanja Radojevic Mary McPartlin Neil Feeder John E. Davies Malcolm A. Halcrow 《Angewandte Chemie (International ed. in English)》1998,37(16):2221-2223
Replacing the 3- and 3′′-protons of the ligand 2,6-di(pyrazol-1-yl)pyridine L by mesityl groups changes the electronic ground state of [Cu(L)2]2+ complexes from {d}1 to {d}1. This is the best example so far for a “homoleptic” Jahn–Teller-compressed six-coordinate CuII complex. 相似文献
927.
928.
Pradyut Ghosh Mary Lee Amirpour William M. Lackowski Michael V. Pishko Richard M. Crooks 《Angewandte Chemie (International ed. in English)》1999,38(11):1592-1595
Hydrophobic n -alkanethiolate bottoms and walls consisting of hydrophilic three-layer poly(acrylic acid)/poly(ethylene glycol) nanocomposite polymers are used for making patterned corrals having lateral dimensions of 63 μm. Macrophage cells are confined within these corrals and are unable to grow over the corral walls (see picture). 相似文献
929.
General mechanical considerations provide an upper bound for the take-off velocity of any jumper, animate or inanimate, rigid or soft body, animal or vegetal. The take-off velocity is driven by the ratio of released energy to body mass. Further, the mean reaction force on a rigid platform during push-off is inversely proportional to the characteristic size of the jumper. These general considerations are illustrated in the context of Alexander's jumper model, which can be solved exactly and which shows an excellent agreement with the mechanical results. 相似文献
930.
Mary E. Rampey Carrie E. Halkyard Angela R. Williams April J. Angel Douglas R. Hurst Jessica D. Townsend Anne E. Finefrock Charles F. Beam Shannon L. Studer-Martinez 《Photochemistry and photobiology》1999,70(2):176-183
Abstract. The carbomethoxyhydrazone of 2'-hydroxyacetophenone was trilithiated with excess lithium diisopropylamide and C-acylated with a variety of benzoate esters followed by acid cyclization of the intermediates to 2-(5-aryl-l-car-bomethoxy-lHpyrazol-3-yl)phenols [3-(2-hydroxyphen-yl)-lH-pyrazoles]. The products were characterized by Fourier transform-IR, l H NMR, 13 C NMR, UV-visible absorption and fluorescence. All the derivatives in n -heptane have an absorption maximum at ˜304 nm and an extremely weak (φr = 10 4 ) fluorescence with maxima in the range of 335–460 nm. The broad range of fluorescence maxima and fluorescence quantum yields is attributed to varying contributions of charge transfer that are dependent on both the identity of the substituent and solvent polarity. A phenomenally large Stokes-shifted fluorescence maximum at 620 nm was observed for 2-(l-car-bomethoxy-5-[4-dimethylaminophenyl]-lff-pyrazol-3-y1)phenol in n-heptane and attributed to excited-state intramolecular proton transfer. As a result, competitive excited-state proton/charge transfer properties have been observed in the pyrazoles studied, of which the spectral properties can be fine tuned by substituent as well as solvent effects. 相似文献