University of Paderborn

About: University of Paderborn is a education organization based out in Paderborn, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Computer science & Context (language use). The organization has 6684 authors who have published 16929 publications receiving 323154 citations.

A Rigorous Numerical Method for the Global Analysis of Infinite-Dimensional Discrete Dynamical Systems

Abstract: We present a numerical method to prove certain statements about the global dynamics of infinite-dimensional maps. The method combines set-oriented numerical tools for the computation of invariant sets and isolating neighborhoods, the Conley index theory, and analytic considerations. It not only allows for the detection of a certain dynamical behavior, but also for a precise computation of the corresponding invariant sets in phase space. As an example computation we show the existence of period points, connecting orbits, and chaotic dynamics in the Kot--Schaffer growth-dispersal model for plants.

Hybrid SCC-DFTB/molecular mechanical studies of H-bonded systems and ofN-acetyl-(L-Ala)nN?-methylamide helices in water solution

Abstract: A hybrid quantum mechanical (QM) and molecular mechanical (MM) approach has been developed and used to study the aqueous solvation effect on biological systems. The self-consistent charge density functional tight-binding (SCC-DFTB) method is employed to perform the quantum mechanical calculations in the QM part, while the AMBER 4.1 force field is used to perform the molecular mechanical calculations in the MM part. The coupling terms between these two parts include electrostatic and van der Waal's interactions. As a test of feasibility, this approach has been first applied to some small systems H-bonded with water molecule(s), and very good agreement with the ab initio results has been achieved. The hybrid potential was then used to investigate the solvation effect on the capped (L-Ala)n helices with n=4, 5, 8 and 11. (L-Ala)n was treated with the SCC-DFTB method and the water molecules with the TIP3P water model. It has been shown that, in gas phase, the α helices of (L-Ala)n are less stable than the corresponding 310 helices. In water solution, however, the α helices are stabilized and, compared with 310 helices, the α helices have stronger charge–charge interactions with the surrounding water molecules. This may be explained by the larger dipole moment of α helices in aqueous solution, which will influence and organize the orientations of the surrounding water molecules. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 459–479, 2000

The Connection between NHC Ligand Count and Photophysical Properties in Fe(II) Photosensitizers: An Experimental Study

Abstract: Four homo- and heteroleptic complexes bearing both polypyridyl units and N-heterocyclic carbene (NHC) donor functions are studied as potential noble metal-free photosensitizers. The complexes [FeII(L1)(terpy)][PF6]2, [FeII(L2)2][PF6]2, [FeII(L1)(L3)][PF6]2, and [FeII(L3)2][PF6]2 (terpy = 2,2':6',2″ terpyridine, L1 = 2,6-bis[3-(2,6-diisopropylphenyl)imidazol-2-ylidene]pyridine, L2 = 2,6-bis[3-isopropylimidazol-2-ylidene]pyridine, L3 = 1-(2,2'-bipyridyl)-3-methylimidazol-2-ylidene) contain tridentate ligands of the C^N^C and N^N^C type, respectively, resulting in a Fe-NHC number between two and four. Thorough ground state characterization by single crystal diffraction, electrochemistry, valence-to-core X-ray emission spectroscopy (VtC-XES), and high energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) in combination with ab initio calculations show a correlation between the geometric and electronic structure of these new compounds and the number of the NHC donor functions. These results serve as a basis for the investigation of the excited states by ultrafast transient absorption spectroscopy, where the lifetime of the 3MLCT states is found to increase with the NHC donor count. The results demonstrate for the first time the close interplay between the number of NHC functionalities in Fe(II) complexes and their photochemical properties, as revealed in a comparison of the activity as photosensitizers in photocatalytic proton reduction.

A new class of phenazines with activity against a chloroquine resistant Plasmodium falciparum strain and antimicrobial activity.

Abstract: New phenazines were synthesized by oxygenation of 1- and 2-naphthol with transition metal peroxo complexes and in situ reaction with 1,2-diamines. The title compounds were evaluated for in vitro antimalarial activity against Plasmodium falciparum and chloroquine-resistant strains. Phenazines 12, 27, and 28 were most prominent in growth inhibition. In vivo protection against cerebral malaria was observed with the phenazines 11, 12, 20, and 27, whereas partial protection was provided by 19.