Global ETD Search

1	Progress towards directly measuring the membrane dipole field in lipid bicelles using vibrational Stark effect spectroscopy Hu, Wenhui, M.A. 16 February 2012 (has links) The electrostatic field created by the inward pointing dipole moments of an oriented membrane leaflet has never been measured directly, but is thought to have an important influence on membrane function. Here we present the first direct measurement of the membrane dipole field in lipid bicelles using vibrational Stark effect spectroscopy which is based on the sensitivity of a nitrile oscillator’s vibrational frequency to its local electrostatic environment. The nitrile probe was introduced as the artificial amino acid p-cyanophenylalanine (CN-Phe) in four different locations of a α-helical peptide composed of alternating alanine and leucine residues. This peptide was intercalated into bicelles composed of mixtures of the long chain lipids 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and the short chain lipid 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) formed in two different sizes, 5 nm and 15 nm in radius. Formation of the bicelle above the phase transition temperature of the lipid mixture was confirmed by ³¹P NMR, and the structure of the [alpha]-helix within the bicelle was confirmed by circular dichroic spectroscopy. The absorption energy of the nitrile probe at 4 positions along the helical axis was measured by Fourier transform infrared spectroscopy, from which we estimate the magnitude of the membrane dipole electrostatic field to be -6 MV/cm. Then we successfully manipulated the dipole field in q = 0.5 DMPC/DHPC bicelles by incorporating the small molecule phloretin into the membrane and measured the corresponding ratiometric fluorescence signal of the co-intercalated voltage gated dye di-8-ANEPPS. We measured 0.7 ± 0.2 cm⁻¹ blue shift in absorption energy of the nitrile probe due to the decrease in dipole field caused by phloretin, corresponding to a dipole field of -4.2 MV/cm. This change was essentially identical to what has been estimated through ratiometric fluorescence methods, indicating that VSE spectroscopy will be useful tool for measurement of the biological effects of electrostatic fields in lipid membranes. / text Vibrational Stark effect Membrane dipole potential Membrane electrostatic field Bicelle DMPC DHPC p-cyanophenylalanine
2	Quantifying electrostatic fields at protein interfaces using classical electrostatics calculations Ritchie, Andrew William 17 September 2015 (has links) The functional aspects of proteins are largely dictated by highly selective protein- protein and protein-ligand interactions, even in situations of high structural homology, where electrostatic factors are the major contributors to selectivity. The vibrational Stark effect (VSE) allows us to measure electrostatic fields in complex environments, such as proteins, by the introduction of a vibrational chromophore whose vibrational absorption energy is linearly sensitive to changes in the local electrostatic field. The works presented here seek to computationally quantify electrostatic fields measured via VSE, with the eventual goal of being able to quantitatively predict electrostatic fields, and therefore Stark shifts, for any given protein-interaction. This is done using extensive molecular dynamics in the Amber03 and AMOEBA force fields to generate large ensembles the GTPase Rap1a docked to RalGDS and [superscript p]²¹Ras docked to RalGDS. We discuss how side chain orientations contribute to the differential binding of different mutations of Rap1a binding to RalGDS, where it was found that a hydrogen-bonding pocket is disrupted by the mutation of position 31 from lysine to glutamic acid. We then show that multi-dimensional umbrella sampling of the probe orientations yields a wider range of accessible structures, increasing the quality of the ensembles generated. A large variety of methods for calculating electrostatic fields are presented, with Poisson- Boltzmann electrostatics yielding the most consistent, reliable results. Finally, we explore using AMOEBA for both ensemble-generation as well as the electrostatic description of atoms for field calculations, where early results suggest that the electrostatic field due to the induce dipole moment of the probe is responsible for predicting qualitatively correct Stark shifts. Poisson-boltzmann Electrostatic field Continuum Implicit Vibrational Stark effect Protein-protein interactions
3	ECC-D4 Electostatic Oil Cleaner Design for Heavy-Duty Gas Turbine Applications Gorur, Murat January 2010 (has links) The turbine technology improvements from 1980 onwards have considerably increased mechanical and thermal stresses on turbine oils which, cause oil oxidation and thereby turbine oil degradation (Livingstone et al., 2007; Sasaki & Uchiyama, 2002). If the oil degradation problem is ignored, this might result in serious turbine system erratic trips and start-up operational problems (Overgaag et al., 2009). Oil oxidation by-products, in other words, sludge and varnish contaminants, lead stated turbine operation-tribological problems. Hence, sludge and varnish presence in turbine oil become a major reason for declining turbine reliability and availability. In the power generation industry, heavy-duty gas turbines as well as steam turbines have been lubricated with mineral based turbine oils for many decades (Okazaki & Badal, 2005). First, generally Group I oils (mineral base oils produced by solvent extraction, dewaxing) were used. Nevertheless, this group of oils has lower oxidation resistance. Therefore, modern gas turbines demand oils which have better oil oxidation resistance, and lower sludge and varnish contaminants tendency (Hannon, 2009). Today, there are many turbine lubricants available on the market. Besides Group I oils, more and more Group II oils (mineral base oils produced by hydro cracking and hydro treating) are selected in service, and having increased oil oxidation resistance. However field inspections demonstrate that Group II oils also experience sludge and varnish problems as well as Group I oils. Primary reason for these phenomena is the antioxidant additive packages that are used in Group II oils (Overgaag et al., 2009). In any case with recent oil formulations, oil degradation products still exist in current turbine oils, and will continue to do so in natural process. These sludge and varnish contaminants are less than 1 micron in size. Thus, they can pass turbine oil system standard mechanical filters without obstruction. With regard to keep the turbine systems in best operational conditions, external turbine oil cleaning practices became crucial to remove these less than 1 micron size oil degradation products from turbine oils. Current effective method for removing the sludge and varnish is to use electrostatic oil cleaners (Moehle & Gatto et al., 2007). Since the majority of turbine user and operator population have been shifted to use Group II based oils to counter the increased sludge and varnish problems, traditional oil cleaners became insufficient to remove sludge and varnish from Group II. (Due to Group II oils have different oil characteristics such as oil oxidation stability and solvency capability). With this awareness, thesis project is looking for ways to introduce and develop an Advanced Electrostatic Oil Cleaner to increase the availability and reliability figures of heavy-duty gas turbines against the rising amount of oil degradation products in modern formulated turbine oils. ECC (Electrostatic Cooled Cleaner) is an electrostatic oil cleaner device to clean and cool mineral based turbine oils for heavy-duty gas turbine applications by removing the sludge and varnish - oil contaminants from turbine oils. The basic principle of the ECC is based on the electrostatic force produced by parallel positioned electrodes which are charged with a high D.C. voltage. Oil contaminants- sludge and varnish have polar nature. Therefore, they are attracted by electrostatic forces whose intensity is proportional to the voltage applied. With the oil flowing in parallel to these electrodes, the polar particles in the oil (which is only neutral /no polar) are caught by filter media positioned between these electrodes. Small investments on advanced oil cleaner result in big savings on turbine system performance. Increased turbine availability and reliability predominantly reduce maintenance costs and risks besides, and thus maximizing revenue by extending heavy-duty gas turbine operational life. An introduced prototype of the ECC-D4 model was tested using two Group II and one Group I oils. The amounts of 200 liter (each) test oils were circulated approximately 300 times through the ECC-D4. In each 3 oil cleaning test sessions, it is proved that the oil insolubles content decreased approximately 40% in tested turbine oils within about 240 ECC-D4 operating hours. With taken base of heavy-duty gas turbine characteristics such as 400 MW power production capacity, annually 8000 operating hours, and 15000 liter oil reservoir volume; it is estimated that the ECC-D4 can extend the oil service-life from 24000 to 48000 operating hours (which is approximately the oil service end-life). In addition to that, assuming the ECC-D4 investment cost as 30k€, about 15k€ savings per year through the new turbine oil and component replacement costs, besides turbine operation profit losses. Moreover, the ECC-D4 returns on investment with a rate of 39 % for defined heavy-duty gas turbine. In general perspective of ECC-D4, it makes heavy-duty gas turbine infrastructure innovative, fully integrated and committed to fulfilling the need for clean, efficient, reliable power production practices in an environmental manner. Energy System Electrostatic Cleaner Gas Turbines Electrostatic Field Turbine Oil Oil Clenaer Mechanical energy engineering Mekanisk energiteknik
4	Photodissoziation von Halogenwasserstoff- und orientierten Wasserstoff-Edelgas-Halogen-Molekülen in Clusterumgebungen / Photodissociation of hydrogen halide and oriented hydrogen-rare gas-halogen molecules in cluster environments Nahler, Nils Hendrik 28 October 2002 (has links) No description available. 530 Physik Mathematics and Computer Science Photodissoziation Cluster Halogenwasserstoff Edelgas UV Photodissoziation HBr HI HCl große Ar/sub n/ Cluster adsorbiertes Molekül eingebettes Molekül mittlere Größe Größenverteilung Energieverteilung Käfigeffekt Adsorptionsort orientierte Moleküle Gasphase Xe/sub n/ asymmetrische Verteilung gepulste Laserstrahlung elektrostatisches Feld Ausrichtung Orientierung Polarisierbarkeit Dipolmoment HXeI HXeCl Anisotropieparameter Verzweigungsverhältnis polarisierte Laserstrahlung Flugzeitmassenspektrometer Spin-Bahn Aufspaltung 243 nm 193 nm photodissociation cluster hydrogen halide rare gas UV photodissociation HBr HI HCl large Ar/sub n/ clusters adsorbed molecule embedded molecule mean size size distribution kinetic energy distribution cage effect adsorption sites oriented molecules gas phase Xe/sub n/ asymmetric distribution pulsed laser electrostatic field alignment orientation polarizability dipole moment HXeI HXeCl anisotropy parameter branching ratio polarized laser light time-of-flight mass spectrometer spin-orbit state 243 nm 193 nm 33.30 SD

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