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991.
Ir-catalyzed (20 °C) or thermal (70 °C) dehydrocoupling of the linear diborazane MeNH(2)-BH(2)-NHMe-BH(3) led to the formation of poly- or oligoaminoboranes [MeNH-BH(2)](x) (x = 3 to >1000) via an initial redistribution process that forms MeNH(2)·BH(3) and also transient MeNH═BH(2), which exists in the predominantly metal-bound and free forms, respectively. Studies of analogous chemistry led to the discovery of metal-free hydrogenation of the B═N bond in the "model" aminoborane iPr(2)N═BH(2) to give iPr(2)NH·BH(3) upon treatment with the diborazane Me(3)N-BH(2)-NHMe-BH(3) or amine-boranes RR'NH·BH(3) (R, R' = H or Me). 相似文献
992.
An efficient synthesis of NP25302 is presented that relies on 5-endo-dig N-cyclization to establish the bicyclic core and Curtius rearrangement to install the N-acyl vinylogous urea functionality. 相似文献
993.
Kennedy AR Mulvey RE O'Hara CT Robertson GM Robertson SD 《Angewandte Chemie (International ed. in English)》2011,50(36):8375-8378
Molecular salt cellars: The addition of substoichiometric quantities of lithium halides to the lithium hexamethyldisilazide was studied. Surprisingly, a novel class of mixed amido-halide macrocyclic complexes, namely metal anionic crowns (MACs) was revealed (see picture: Li?pink, N?yellow, Cl?green, Si?orange, C?black). 相似文献
994.
995.
M. E. Coleman M. D. Glascock J. D. Robertson 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(3):935-941
A new instrumental epithermal neutron activation analysis procedure to quantitatively determine titanium, barium, and bromine
in obsidian with improved sensitivity has been developed. The advantage of epithermal activation for Ti, Ba, and Br is demonstrated
with multiple geological standards and the ability to determine arsenic in obsidian is demonstrated. The results for titanium
are compared to previous electron-microprobe results for Kenyan obsidian. 相似文献
996.
Sarah L. Masters Iain D. Mackie Derek A. Wann Heather E. Robertson David W. H. Rankin Simon Parsons 《Structural chemistry》2011,22(2):279-285
The molecular structures of 1-Br-4-F-C6H4 and 1-Cl-4-F-C6H4 have been studied in the gas phase using gas electron diffraction (GED) and ab initio methods. The structure of 1-Cl,4-F-C6H4 in the crystalline phase has also been studied, but whilst the gaseous structures were found to possess C
2v symmetry, the solid-state structure was found to be quite distorted, with three molecules in the asymmetric unit. These fragments
only possess C
s symmetry in the plane of the molecules, as opposed to the C
2v symmetry observed in the gas phase. The bonding motifs within the solid-state structure are very unusual and unexpected,
with quite different C–F bond lengths for the three moieties, and are a result of weak hydrogen-halogen interactions within
the structure. 相似文献
997.
Current phase-shift cavity ring-down spectroscopy (PS-CRDS) experiments make use of equations originally developed for fluorescence studies. As these equations fail to take the length of the optical cavity and the superposition of reflecting beams into account, they lose validity as the length of the cavity increases. A new set of equations, based solely on the principles of PS-CRDS, is developed for determining the ring-down time from either the phase shift or the intensity of the waveform exiting the cavity. It is shown that the PS-CRDS equations reduce to those developed for fluorescence study for short cavities. The new equations provide a more accurate method in determining the characteristic ring-down time and phase shift for long cavities, especially fiber optic cavities, which is promising in on-site chemical sensing. 相似文献
998.
Structural vibrational analyses of four 5-hydroxyisoflavones: genistein, biochanin A, prunetin and 4′,7-dimethoxygenistein have been performed using a combination of computational and experimental investigations of Raman and infrared spectra. Normal vibrational modes in the Raman and infrared spectra were assigned and correlated with the aid of calculations using density functional theory (DFT), adopting the B3LYP functional with the 6-31+G(d) basis set. As the four isoflavones differ by methoxy substitutions of the hydroxyl groups, shifts between phenol and anisole were also used to assist in the assignments. This work offers insight into some of the variations observed in the vibrational spectra of genistein and other isoflavones and lays the foundation for analysis of related compounds as well as further spectral analysis of the present isoflavones. 相似文献
999.
Karen E. LambDavid Greenhalgh Chris Robertson 《Journal of Computational and Applied Mathematics》2011,235(7):1812-1818
Streptococcus pneumoniae (S. pneumoniae) is a bacterium commonly found in the throat of young children. Pneumococcal serotypes can cause a variety of invasive and non-invasive diseases such as meningitis and pneumonia. In 2000 a vaccine was introduced in the USA that not only prevents vaccine type disease but has also been shown to eliminate carriage of the vaccine serotypes. One key problem with the vaccine is that it has been observed that the same sequence types (genetic material found in the serotypes) are able to manifest in more than one serotype. This is a potential problem if sequence types associated with invasive disease may express themselves in multiple serotypes.We present a basic differential equation mathematical model for exploring the relationship between sequence types and serotypes where a sequence type is able to manifest itself in one vaccine serotype and one non-vaccine serotype. An expression for the effective reproduction number is found and an equilibrium and then a global stability analysis carried out. We illustrate our analytical results by using simulations with realistic parameter values. 相似文献
1000.
Robertson CM Leitch AA Cvrkalj K Myles DJ Reed RW Dube PA Oakley RT 《Journal of the American Chemical Society》2008,130(44):14791-14801
A series of five isostructural bisthiaselenazolyl radicals 2 have been prepared and characterized by X-ray crystallography. The crystal structures, all belonging to the tetragonal space group P42(1)m, consist of slipped pi-stack arrays of undimerized radicals packed about 4 centers running along the z-direction, an arrangement which gives rise to a complex lattice-wide network of close intermolecular Se---Se' contacts. Variations in R1 (Et, Pr, CH2CF3) with R2 = Cl lead to significant changes in the degree of slippage of the pi-stacks and hence the proximity of the Se---Se' interactions. By contrast, variations in R2 (Cl, Br, Me) with R1 = Et induce very little change in either the degree of slippage or the intermolecular contacts. Variable-temperature conductivity (sigma) measurements show relatively constant values for the conductivity sigma(300 K) (10(-5)-10(-4) S cm(-1)) and thermal activation energy E(act) (0.27-0.31 eV). Variable-temperature magnetic susceptibility measurements indicate that radicals 2b and 2c (R1 = Pr, CH2CF3; R2 = Cl) behave as weakly antiferromagnetically coupled Curie-Weiss paramagnets, but in 2a, 2d and 2e (R1 = Et; R2 = Cl, Me, Br) ferromagnetic ordering is observed, with T(c) values of 12.8 (R2 = Cl), 13.6 (R2 = Me), and 14.1 K (R2 = Br). The origin of the dramatically different magnetic behavior across the series has been explored in terms of a direct through-space mechanism by means of DFT calculations on individual pairwise exchange energies. These indicate that antiferromagnetic exchange between radicals along the pi-stacks increases with pi-stack slippage. 相似文献