Complete 1H and 13C NMR data assignment of new constituents from Severinia buxifolia

Phytochemical analysis of different organs of the rutaceaeous plant Severinia buxifolia led to the isolation of a new limonoid, a new acridone alkaloid, and a new flavone. Structure elucidation and signal assignment were achieved by the extensive use of 1D and 2D NMR experiments (selective 1D NOE, COSY, NOESY, HSQC, HMBC). Copyright © 2009 John Wiley & Sons, Ltd.     

Case studies of CSEARCH supported structure elucidation strategies: lupeol and a new germacrane derivative

The NMR based structure elucidation of secondary natural products can be supported by the CSEARCH database system. In the case of the triterpene lupeol the correct identification was performed without further experiments. The structure proposal for the new germacrane derivate hydroxygermacrene-D was proven by isomer generation and subsequent ranking of the eight isomers obtained by weighted spectrum estimation.     

Electronic excitations of 1,4-disilyl-substituted 1,4-disilabicycloalkanes: a MS-CASPT2 study of the influence of cage size

We present a multistate complete active space second-order perturbation theory computational study aimed to predict the low-lying electronic excitations of four compounds that can be viewed as two disilane units connected through alkane bridges in a bicyclic cage. The analysis has focused on 1,4-disilyl-1,4-disilabicyclo[2.2.1]heptane (1a), 1,4-bis(trimethylsilyl)-1,4-disilabicyclo[2.2.1]heptane (1b), 1,4-disilyl-1,4-disilabicyclo[2.1.1]hexane (2a), and 1,4-bis(trimethylsilyl)-1,4-disilabicyclo[2.1.1]hexane (2b). The aim has been to find out the nature of the lowest excitations with significant oscillator strengths and to investigate how the cage size affects the excitation energies and the strengths of the transitions. Two different substituents on the terminal silicon atoms (H and CH3) were used in order to investigate the end group effects. The calculations show that the lowest allowed excitations are of the same character as that found in disilanes but now red-shifted. As the cage size is reduced from a 1,4-disilabicyclo[2.2.1]heptane to a 1,4-disilabicyclo[2.1.1]hexane, the Si...Si through-space distance decreases from approximately 2.70 to 2.50 A and the lowest allowed transitions are red-shifted by up to 0.9 eV, indicating increased interaction between the two Si-Si bonds. The first ionization potential, which corresponds to ionization from the Si-Si sigma orbitals, is lower in 1b and 2b than in Si2Me6 by approximately 0.9 and 1.2 eV, respectively. Moreover, 1b and 2b, which have methyl substituents at the terminal Si atoms, have slightly lower excitation energies than the analogous species 1a and 2a.     

Naturally occurring sesquiterpene-coumarin ethers,VI. New sesquiterpene-isofraxidin ethers fromAchillea depressa

The roots ofAchillea depressa afforded in addition to known sesquiterpene-isofraxidine ethers three new derivatives: the bicyclic drimenol derived albartol and the monocyclic derivatives deparnol and acetyldeparnol. The compounds were characterized by¹H-NMR, MS, UV, IR, and CD data.Herrn Prof. Dr.U. Schmidt mit den besten Wünschen zum 60. Geburtstag gewidmet.     

Quantum and Classical Radiation Reaction from Lightfront QED

We examine dynamical radiation reaction in lightfront QED. We take the classical limit and compare with predictions from various classical equations of motion.     

Logic-based Benders decomposition

 Benders decomposition uses a strategy of ``learning from one's mistakes.' The aim of this paper is to extend this strategy to a much larger class of problems. The key is to generalize the linear programming dual used in the classical method to an ``inference dual.' Solution of the inference dual takes the form of a logical deduction that yields Benders cuts. The dual is therefore very different from other generalized duals that have been proposed. The approach is illustrated by working out the details for propositional satisfiability and 0-1 programming problems. Computational tests are carried out for the latter, but the most promising contribution of logic-based Benders may be to provide a framework for combining optimization and constraint programming methods. Received: November 2000 / Accepted: January 2003 Published online: March 21, 2003 RID="⋆" ID="⋆" This research was partially supported by U.S. Office of Naval Research Grant N00014-95-1-0517 and by the Engineering Design Research Center at Carnegie Mellon University, an Engineering Research Center of the National Science Foundation, under grant EEC-8943164.