Comparison of two force fields in MD-simulations of α-helical structures in keratins

Molecular dynamic (MD) simulations based on two different force fields, CVFF and CFF91, were carried out in order to check their feasibility for the structural investigation of the wool intermediate filament (IF) monomeric unit. Selecting an ideal α-helix as start conformation, all MD-simulations with CVFF in vaccum show the α-helix to be unstable. Independently of the amino acid sequence of the α-helix, a new helical structure with a larger diameter arises during the MD-simulation, due to a shift of the intrahelical hydrogen bonds. However in simulations with surrounding water the α-helix remains stable throughout the simulations with the CVFF force field. In contrast to this, MD-simulations in vaccume based on the CFF91 force field are able to determine different stabilities for the α-helical start conformation of various IF-segments, that agree well with secondary structure predictions. The simulation results obtained with CFF91 in vacuum can like wise be verified using an explicit water environment. We found that higher partial charges attributed to the atoms of the amide groups that form the intrahelical hydrogen bonds are the reason for the superiority of the CFF91 force field.     

State reconstruction of the kicked rotor

We propose two experimentally feasible methods based on atom interferometry to measure the quantum state of the kicked rotor.     

Calculation of the photon-anticorrelation effect in a degenerate optical parametric amplifier

If two initially coherent light fields with the frequencies ω and 2ω, which have been produced by a second harmonic generator, pass a degenerate parametric amplifier photon-anticorrelation effects can develop. We calculate the time-development of the photon distribution for the signal wave by treating both fields quantum mechanically.     

Herstellung und Umsetzungen von β-Lactamen

The cycloaddition of N-chlorosulfonyl-isocyanate with isoprene, butadiene and a polyolefin as well as the reaction of ketenes with some bis-azomethines were investigated. Suitably substituted bis-azomethines could be separated in the rac. and the meso-form. The reactivity of the azetidinones towards hydrolysis and hydrogenation was tested. Attempts to polymerise 4-vinyl-azetidin-2-one, polyazetidinone and N-substituted bis-azetidinones to give cross-linked poly-β-amides were not successful.     

Observation of an interedge magnetoplasmon mode in a degenerate two-dimensional electron gas

We study the propagation of edge magnetoplasmons by time-resolved current measurements in a sample which allows for selective detection of edge states in the quantum Hall regime. At filling factors close to nu=3 we observe two decoupled modes of edge excitations, one of which is related to the innermost compressible strip and is identified as an interedge magnetoplasmon mode. From the analysis of the propagation velocities of each mode the internal spatial parameters of the edge structure are derived.