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61.
The transformation of a simple disubstituted pyridine into a pyridinium ion bearing an exocyclic hydroxyl group, protected as a silane, enabled an intramolecular hydride transfer reaction to take place when fluoride was used as a nucleophile. The addition was both regio- and stereoselective and enabled the formation of enantiopure dihydropyridones when enantiopure pyridine derivatives were used in this sequence. The heterocyclic products contain ample functionality for further elaboration reactions and subsequent derivatization. 相似文献
62.
Stoyanov AV Rohlfing CL Connolly S Roberts ML Nauser CL Little RR 《Journal of chromatography. A》2011,1218(51):9244-9249
An application of ion exchange chromatography for C-peptide analysis is described here. At the stage of C-peptide isolation, a strong cation exchanger (SP HP or MonoS) was used to purify the analyte from ballast proteins and peptides. The conditions of ion-exchange chromatographic separations were optimized using theoretical modeling of the net surface electric charge of the peptide as a function of pH. The purified and concentrated sample was further subjected to LC-MS/MS. In order to improve the reliability of analysis, two fragment ions were monitored simultaneously both for native C-peptide and internal standard, isotopically labeled C-peptides analogues (fragments with m/z of 927.7 and 147.2). Using ion-exchange chromatography, it became possible to process larger sample volumes, important for testing patients with very low C peptide levels, compared to currently used solid phase extraction methods. 相似文献
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Hoover S Nam J Gorham PW Grashorn E Allison P Barwick SW Beatty JJ Belov K Besson DZ Binns WR Chen C Chen P Clem JM Connolly A Dowkontt PF DuVernois MA Field RC Goldstein D Vieregg AG Hast C Israel MH Javaid A Kowalski J Learned JG Liewer KM Link JT Lusczek E Matsuno S Mercurio BC Miki C Miočinović P Naudet CJ Ng J Nichol RJ Palladino K Reil K Romero-Wolf A Rosen M Ruckman L Saltzberg D Seckel D Varner GS Walz D Wu F 《Physical review letters》2010,105(15):151101
We report the observation of 16 cosmic ray events with a mean energy of 1.5 × 101? eV via radio pulses originating from the interaction of the cosmic ray air shower with the Antarctic geomagnetic field, a process known as geosynchrotron emission. We present measurements in the 300-900 MHz range, which are the first self-triggered, first ultrawide band, first far-field, and the highest energy sample of cosmic ray events collected with the radio technique. Their properties are inconsistent with current ground-based geosynchrotron models. The emission is 100% polarized in the plane perpendicular to the projected geomagnetic field. Fourteen events are seen to have a phase inversion due to reflection of the radio beam off the ice surface, and two additional events are seen directly from above the horizon. Based on a likelihood analysis, we estimate angular pointing precision of order 2° for the event arrival directions. 相似文献
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Valence-electron ionization and optical excitation energies of NiO have been calculated by the SCF?Xα cluster method and transition-state procedure. Ni 3d-like spin orbitals are localized above the O 2p band, leading to well defined peaks in the photoemission spectra. Ligand-to-metal charge-transfer excitations are responsible for strong optical absorption between 4 and 7eV. 相似文献
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The NilK-theory groups or a ring,N
r
K
i
(R), are never finitely generated Abelian groups unless they are zero. But we show here thatN
r
K
i
(R) is a commutative ring,Z[N
r
], whereN is the monoid of positive integers. We then further show that, for any finite group , the Nil group,N
r
K
0(Z[]), is a finitely generatedZ[N
r
] module. It is annihilated by a power of the order of Partially supported by NSF Grant no. DMS 90-01729. 相似文献