Bielefeld University

About: Bielefeld University is a education organization based out in Bielefeld, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Population & Quantum chromodynamics. The organization has 10123 authors who have published 26576 publications receiving 728250 citations. The organization is also known as: University of Bielefeld & UNIVERSITAET BIELEFELD.

π Bonding to Main-Group Elements

Abstract: Publisher Summary This chapter discusses the π complexes of all main-group elements, including their synthesis, structure, and bonding and the literature up to 1985. Compounds described have been characterized by X-ray or electron diffraction or at least by conclusive infrared (IR) or nuclear magnetic resonance (NMR) data. The term “π complex” is connected with compounds in which π ligands are polyhapto bonded to a transition metal. Many examples of the interaction between lithium and diverse π systems are documented in the literature. There are many examples known of π bonding between the heavier alkali metals and carbanionic fragments. There is no example in the literature of a stable alkene (or alkyne) complex with magnesium as central atom. Many compounds of the heavier alkaline–earth metals with organic ligands are described in the literature, for which from spectroscopic data π-interactions can be anticipated. π complexation is believed to be involved in the first step of the hydroboration of alkenes and alkynes; rearrangement reactions of organoboranes most likely involve the intermediates of a π-complex type. Alkene or alkyne complexes are mechanistically important intermediates in hydroalumination and carboalumination reactions. Using the isolobal relationship between CH or CH 2 units and corresponding transition metal or main-group element fragments, the majority of the nonclassical carbocations can be theoretically treated as π complexes.

Pure Multiple RNA Secondary Structure Alignments: A Progressive Profile Approach

Abstract: In functional, noncoding RNA, structure is often essential to function. While the full 3D structure is very difficult to determine, the 2D structure of an RNA molecule gives good clues to its 3D structure, and for molecules of moderate length, it can be predicted with good reliability. Structure comparison is, in analogy to sequence comparison, the essential technique to infer related function. We provide a method for computing multiple alignments of RNA secondary structures under the tree alignment model, which is suitable to cluster RNA molecules purely on the structural level, i.e., sequence similarity is not required. We give a systematic generalization of the profile alignment method from strings to trees and forests. We introduce a tree profile representation of RNA secondary structure alignments which allows reasonable scoring in structure comparison. Besides the technical aspects, an RNA profile is a useful data structure to represent multiple structures of RNA sequences. Moreover, we propose a visualization of RNA consensus structures that is enriched by the full sequence information.

High sensitivity and versatility of the DEER experiment on nitroxide radical pairs at Q-band frequencies

Abstract: Measurement of distances with the Double Electron-Electron Resonance (DEER) experiment at X-band frequencies using a pair of nitroxides as spin labels is a popular biophysical tool for studying function-related conformational dynamics of proteins. The technique is intrinsically highly precise and can potentially access the range from 1.5 to 6-10 nm. However, DEER performance drops strongly when relaxation rates of the nitroxide spin labels are high and available material quantities are low, which is usually the case for membrane proteins reconstituted into liposomes. This leads to elevated noise levels, very long measurement times, reduced precision, and a decrease of the longest accessible distances. Here we quantify the performance improvement that can be achieved at Q-band frequencies (34.5 GHz) using a high-power spectrometer. More than an order of magnitude gain in sensitivity is obtained with a homebuilt setup equipped with a 150 W TWT amplifier by using oversized samples. The broadband excitation enabled by the high power ensures that orientation selection can be suppressed in most cases, which facilitates extraction of distance distributions. By varying pulse lengths, Q-band DEER can be switched between orientationally non-selective and selective regimes. Because of suppression of nuclear modulations from matrix protons and deuterons, analysis of the Q-band data is greatly simplified, particularly in cases of very small DEER modulation depth due to low binding affinity between proteins forming a complex or low labelling efficiency. Finally, we demonstrate that a commercial Q-band spectrometer can be readily adjusted to the high-power operation.