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Experimental Example (experimental + example)

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Life Sciences33%

Selected Abstracts

High-precision measurement of internuclear distances using solid-state NMR

CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2008
Jae-Seung Lee
Abstract Today, nuclear magnetic resonance (NMR) is among the most efficient tools in structural studies. Measurement of interatomic distances is the most common way of determining high-resolution structures of molecules using NMR techniques. In this article, we describe NMR techniques for static powder samples, based on a two-dimensional single-echo scheme, enhanced with adiabatic cross-polarization. They can significantly increase the accuracy of measuring internuclear distances and turn NMR into a high-precision crystallographic technique, complementing the X-ray, and neutron-scattering methods. Experimental examples are presented for intramolecular CN and CC distances in ,-crystalline form of glycine. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 56,67, 2008. [source]

Cyclic Polymers by Kinetically Controlled Step-Growth Polymerization

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 5-6 2003
Hans R. Kricheldorf
Abstract The theory of step-growth polymerizations including the cascade theory is discussed in the light of new results focussing on the role of cyclization reactions. The identification of cyclic oligomers and polymers in reaction products of step-growth polymerizations has been eased considerably by means of MALDI-TOF mass spectrometry. Experimental examples concern syntheses of polyesters, polycarbonates, polyamides, polyimides, poly(ether sulfone)s, poly(ether ketone)s and polyurethanes. It was found in all cases that the percentage and molecular weight of the cycles increases when the reaction conditions favor high molecular weights. In the absence of side reactions all reaction products will be cycles when conversion approaches 100%. Cyclization may even take place in the nematic phase but even-numbered cycles are favored over odd-numbered ones due to electronic interactions between mesogens aligned in parallel. In contrast to Flory's cascade theory, cyclization also plays a decisive role in polycondensations of abn -type monomers, and at 100% conversion all hyperbranched polymers have a cyclic core. Furthermore, it is demonstrated that in a2+b3 polycondensations intensive cyclization in the early stages of the process has the consequence that either no gelation occurs or the resulting networks consist of cyclic and bicyclic oligomers as building blocks. Finally, a comparison between cyclization of synthetic polymers and biopolymers is discussed. Schematic representation of a network structure mainly consisting of cyclic oligomers and multicyclic building blocks as derived from "a2" + "b3" polycondensation. [source]

Simultaneous determination of specimen temperature and specimen displacement in high-temperature X-ray diffractometry applying Bragg,Brentano geometry

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2002
M. Beck
Temperature uncertainty and unknown specimen displacement are the most severe errors in high-temperature X-ray diffractometry, in particular when using a strip heater mounted on a Bragg,Brentano goniometer. A method is presented that enables the simultaneous determination of the specimen displacement and the temperature of the sample. The method splits the determination of the aberrations into two steps: at room temperature and at elevated temperature. It is based on the use of a reference material as an internal standard. An experimental example applying the method to a specific material is given, and shows that the method provides correct data. [source]

MicroCommentary: Subcellular localization of Escherichia coli osmosensory transporter ProP: focus on cardiolipin membrane domains

MOLECULAR MICROBIOLOGY, Issue 6 2007
Eugenia Mileykovskaya
Summary The role for specific lipids in the spatial distribution of the membrane proteins and formation of the lipid-protein membrane domains is an emerging theme in the studies of the supramolecular organization of the bacterial cell. A combination of the lipid and protein visualization techniques with manipulation of the cell lipid composition provides a useful tool for these studies. This MicroCommentary reviews the first experimental example demonstrating an involvement of the phospholipid cardiolipin in recruitment of a membrane protein (specifically H+ -osmoprotectant symporter ProP) to the Escherichia coli cell poles. The properties of cardiolipin domains employed in creating a specific environment for structural organization and function of membrane protein complexes are also discussed. [source]

Understanding heterologous protein overproduction under the T7 promoter: A practical exercise

BIOCHEMISTRY AND MOLECULAR BIOLOGY EDUCATION, Issue 3 2002
Evangelos Christodoulou
Abstract Because various genome projects have been advanced many genes are known, and large amounts of proteins are required to elucidate their function. Most biomolecular research laboratories have a need to overexpress a certain gene, or a part of it, in eukaryotic or prokaryotic expression systems. It is therefore important for young students to become familiar with the technology of heterologous gene expression systems. Gene expression in eukaryotic cells is rather complicated and costly and is therefore not ideally suited to exercises for students. The goal of this paper is to describe an experimental example of a well known and broadly used prokaryotic system, the pET system, that works under the strong T7 promoter. The clones described in this paper are suitable for the practical exercise and are available upon request. [source]

The Auxiliary Substrate Concept: From simple considerations to heuristically valuable knowledge

ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 4 2009
Wolfgang Babel
Abstract Microorganisms are used in biotechnology. They are either (i) aim and purpose of a process, e.g. with the production of single cell proteins, or (ii) mean to an end insofar as they serve as a catalyst or "factory" for syntheses (e.g. of products of primary and secondary metabolism, of enzymes and antibiotics) or for the degradation and detoxification of harmful organics and inorganics. In all cases, the efficiency and velocity, finally the productivity, are parameters which essentially determine the economy of the processes. Therefore, search for approaches to optimize these processes is a permanent task and challenge for scientists and engineers. It is shown that the auxiliary substrate concept is suitable to increase the yield coefficients. It is based on the energetic evaluation of organics, on the knowledge that organics as sources of carbon and energy for growth are deficient in ATP and/or reducing equivalents, and says that it is possible to improve the carbon conversion efficiency up to the carbon metabolism determined upper limit. The latter is determined by inevitable losses of carbon along the way of assimilation and anabolism and amounts to about 85% for so-called glycolytic substrates, e.g. glucose, methanol, and to about 75% for gluconeogenetic substrates, e.g. C2 -substrates (acetic acid, hexadecane). The approach is explained and some experimental examples are presented. By simultaneous utilization of an extra energy source (auxiliary substrate) the yield coefficient can be increased (i) in glucose from about 0.5 to 0.7,g/g (by means of formate), (ii) in acetate from 0.34,0.4 to 0.5,0.65,g/g (by means of formate and thiosulfate, respectively), and (iii) in hexadecane from about 0.94 to 1.26,g/g (by means of formate). The precalculated yield coefficients and mixing ratios agree well with the experimentally attained ones. The approach is easily feasible and economically valuable. [source]