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71.
James M Takacs Mohamad R Jaber Benjamin J Swanson Steven J Mehrman 《Tetrahedron: Asymmetry》1998,9(24):5768
Chiral N-acyloxazolidinones derived from conjugated dienoic acids undergo boron-mediated aldol condensation in good yield and with high regio- and diastereoselectivity to provide a convenient method for introducing a 1,3-diene subunit. The condensation of a homologous triene derivative is also described. 相似文献
72.
Mora JF Van Berkel GJ Enke CG Cole RB Martinez-Sanchez M Fenn JB 《Journal of mass spectrometry : JMS》2000,35(8):939-952
Editorial Comment Last month we presented, as a Special Feature, a set of five articles that constituted a Commentary on the fundamentals and mechanism of electrospray ionization (ESI). These articles produced some lively discussion among the authors on the role of electrochemistry in ESI. Six authors participated in a detailed exchange of views on this topic, the final results of which constitute this month's Special Feature. We particularly hope that younger scientists will find value in this month's Special Feature, not only for the science that it teaches but also what it reveals about the processes by which scientific conclusions are drawn. To a degree, the contributions part the curtains on these processes and show science in action. We sincerely thank the contributors to this discussion. The give and take of intellectual debate is not always easy, and to a remarkable extent this set of authors has maintained good humor and friendships, even when disagreeing strongly on substance. Graham Cooks and Richard Caprioli Copyright 2000 John Wiley & Sons, Ltd. 相似文献
73.
Van Berkel GJ Quirke JM Adams CL 《Rapid communications in mass spectrometry : RCM》2000,14(10):849-858
A survey of derivatization strategies and prospective derivatization reactions for conversion of simple alkenes and alkynes to 'electrospray-active' species is presented. General synthetic strategies are discussed and illustrative examples of prospective derivatives prepared from model compounds are presented along with their electrospray ionization (ES) mass spectra. The identified derivatives of these neutral, nonpolar analytes are either ionic or are ionizable in solution through Bronsted acid/base chemistry, by Lewis acid/base chemistry, or by chemical or electrochemical electron-transfer chemistry. Once ionized, the derivatives are expected to be amenable to detection by electrospray ionization-mass spectrometry. Derivatives are identified for positive and negative ion analysis of both alkenes and alkynes. Copyright 2000 John Wiley & Sons, Ltd. 相似文献
74.
Takacs JM Reddy DS Moteki SA Wu D Palencia H 《Journal of the American Chemical Society》2004,126(14):4494-4495
A strategy is described for modular catalyst development based upon metal-directed self-assembly of bifunctional subunits around a structural metal to form a heteroleptic complex in which a second set of ligating groups are now suitably disposed to bind a second metal to form a catalytic site. A library of chiral diphosphites was prepared via metal-directed self-assembly and used in a simple asymmetric allylic amination, giving enantiomeric excesses as high as 97%. 相似文献
75.
Christiane Takacs 《Journal of Theoretical Probability》2001,14(3):699-715
We consider a random walk on
in a stationary and ergodic random environment, whose states are called types of the vertices of
. We find conditions for which the speed of the random walk is positive. In the case of a Markov chain environment with finitely many states, we give an explicit formula for the speed and for the asymptotic proportion of time spent at vertices of a certain type. Using these results, we compare the speed of random walks on
in environments of varying randomness. 相似文献
76.
W. M. Reiff E. H. Witten J. Takacs J. H. Zhang C. C. Torardi 《Hyperfine Interactions》1990,56(1-4):1723-1728
The extremes of single ion slow paramagnetic relaxation and cooperative 3D-antiferromagnetic order are exemplified in a series
of structurally characterized complexes based on the anhydrous FeCl3-α-di-imine system. “Soft” Cl−Cl contacts, C−C (π-π) and hydrogen bonding interactions are found to lead to surprisingly strong
magnetic exchange among five and six coordinate high-spin iron III monomers. The latter form the building blocks of novel
“double chain” polymer magnets held together via the preceding “weak” interactions. 相似文献
77.
Christiane Takacs 《Probability Theory and Related Fields》1998,111(1):123-139
Summary. We define directed rooted labeled and unlabeled trees and find measures on the space of directed rooted unlabeled trees which
are invariant with respect to transition probabilities corresponding to a biased random walk on a directed rooted labeled
tree. We use these to calculate the speed of a biased random walk on directed rooted labeled trees. The results are mainly
applied to directed trees with recurrent subtrees, where the random walker cannot escape.
Received: 12 March 1997/ In revised form: 11 December 1997 相似文献
78.
79.
Subtle differences in the structure of the borane strongly influence the catalytic efficiency and level of enantioselectivity in the catalytic asymmetric hydroboration of β,γ-unsaturated Weinreb amides. 相似文献
80.
Dr. Bob C. Schroeder Dr. Zhe Li Michael A. Brady Dr. Gregório Couto Faria Dr. Raja Shahid Ashraf Dr. Christopher J. Takacs John S. Cowart Dr. Duc T. Duong Kar Ho Chiu Ching‐Hong Tan Dr. João T. Cabral Prof. Alberto Salleo Prof. Michael L. Chabinyc Prof. James R. Durrant Prof. Iain McCulloch 《Angewandte Chemie (International ed. in English)》2014,53(47):12870-12875
Cost‐effective, solution‐processable organic photovoltaics (OPV) present an interesting alternative to inorganic silicon‐based solar cells. However, one of the major remaining challenges of OPV devices is their lack of long‐term operational stability, especially at elevated temperatures. The synthesis of a fullerene dumbbell and its use as an additive in the active layer of a PCDTBT:PCBM‐based OPV device is reported. The addition of only 20 % of this novel fullerene not only leads to improved device efficiencies, but more importantly also to a dramatic increase in morphological stability under simulated operating conditions. Dynamic secondary ion mass spectrometry (DSIMS) and TEM are used, amongst other techniques, to elucidate the origins of the improved morphological stability. 相似文献