182 research outputs found
Conformational Flexibility of Glycosylated Peptides
No full textBollmann S, Burgert A, Plattner C, et al. Conformational Flexibility of Glycosylated Peptides. ChemPhysChem. 2011;12(16):2907-2911.With a twist: The conformational dynamics of glycosylated glycine–serine peptides is studied using contact- induced fluorescence quenching analysed by fluorescence correlation spectroscopy. End-to-end contact rates on ns–μs timescales reveal enthalpic and entropic contributions to the reduction of contact formation rates in glycopeptides (see picture)
The Earth's energy balance and its changes: implications for past and future temperature change
No full textDistributed multipole moments in atomistic force fields. implementation and applications
No full textThe accuracy of atomistic force fields depends on the complexity of the interatomic potential function as well as on the parametrization of the potential. In conventional
force fields, the electrostatic potential is represented by atom-centered point charges. Point charges can be understood as the first term of multipole expansions, which converge with increasing number of terms towards the accurate representation of the molecular potential given by the electron density distribution.
Here, the distributed multipole analysis (DMA) is used to obtain atomic multipole moments. The accuracy of distributed multipole potentials is tested for several molecules and compared to point charge potentials. The investigation is focused on convergence of the multipole expansion and conformational dependence. Energies and forces required for molecular dynamics (MD) simulations with atomic multipole
potentials are implemented into the CHARMM program. Important points to consider for the implementation are the orientation of the multipole moments and the conformational dependence of multipole parameters.
The implementation is applied to different systems: The splitting of the infrared (IR) absorption band for photodissociated CO in Myoglobin is analyzed comparing different multipole models for CO. A relationship is established between the IR frequency and the CO orientation in the binding pocket. The experimental IR spectrum of CO
in amorphous ice is reproduced using multipole potentials for CO and water. The relationship between infrared frequencies and ice structures is analyzed. Furthermore,
atomic multipole moments are applied to methane and CO clathrate hydrates. Lattice modes are calculated and compared to experiment. The influence of different guest
molecules on lattice modes and structure is characterized
Laser-basierte Messsysteme für Weltraumanwendungen
No full textIn the frame of this thesis, fiber-based laser systems for measurement applications have been further developed to cope with the requirements for space-borne systems. The necessary theoretical background of linear and nonlinear optics as well as of the technologies of optical frequency combs and fiber-optic sensing and the engineering techniques to achieve compatibility with space environment (radiation, vacuum, microgravity, …) have been worked out. The description of effects of mode-locked fiber lasers during thermal-vacuum and radiation tests and particular Peak-Tracking and Time-of-Flight algorithms have been developed and verified by evaluation of test results. The new knowledge gained within this work contributes to current national and European space projects.Im Rahmen dieser Dissertation wurden faser-basierte Lasersysteme für messtechnische Anwendungen weiterentwickelt um den Anforderungen während des späteren Betriebs im Weltraum gerecht zu werden. Die notwendigen theoretischen Grundlagen der linearen und nichtlinearen Optik und der Technologien von optischen Frequenzkämmen und faseroptischer Sensorik sowie die erforderlichen Ingenieurmaßnahmen um Kompatibilität zu den Bedingungen im Weltraum (Strahlungsbelastung, Vakuum, Schwerelosigkeit, …) zu Erreichen wurden dazu erarbeitet. Die Beschreibung von Effekten modengekoppelter Faserlaser während Thermal-Vakuum und Bestrahlungstests sowie spezielle Peak-Tracking und Time-of-Flight Algorithmen zur Effizienzsteigerung von faseroptischer Sensorik wurden entwickelt und deren Richtigkeit und Funktionalität durch Auswertung von Testergebnissen nachgewiesen. Die neuen Erkenntnisse aus dieser Arbeit tragen zu aktuellen nationalen und europäischen Raumfahrtprojekten bei
Aspects of third stream works : an analytical study of compositions by Gunther Schuller, Don Banks and Bozidar Kos
No full textTriazole-linked reduced amide isosteres: An approach for the fragment-based drug discovery of anti-Alzheimer's BACE1 inhibitors and NH-assisted Fürst-Plattner opening of cyclohexene oxides
No full textIn the scope of our BACE1 inhibitor project we used an originally designed microtiter plate-based screening to discover 4 triazole-linked reduced amide isosteres that showed modest (single digit micromolar) BACE1 inhibition. Our ligands were designed based on a very potent (single digit nanomolar) isopththalamide ligand from Merck. We supplanted one of the amide linkages in order to incorporate our triazole and saw a 1000-fold decrease in potency. We then enlisted Molsoft, L.L.C. to compare our ligand to Merck's in silico to account for this discrepancy. They found that the triazole linkage gives rise to a significantly different docking pose in the active site of the BACE1 enzyme, therefore diminishing its potency relative to the Merck ligand.
The ability to control the regio- and stereochemical outcome of organic reactions is an ongoing interest and challenge to synthetic chemists. The pre-association of reacting partners through hydrogen bonding (H-bonding) can often to yield products with extremely high stereoselectivity. We were able to show that anilines, due to their enhanced acidity relative to amines, can serve as substrate directing moieties in the opening of cyclohexene oxides. We observed that by judicious choice of conditions we could control the regiochemical outcome of the reaction. These studies demonstrate that an intramolecular anilino-NH hydrogen bond donor can direct Fürst-Plattner epoxide opening. A unified mechanism for this phenomenon has been proposed in this work which consists of a novel mechanistic route we call "NH-directed Fürst-Plattner." We further studied the opening of cyclohexene oxides by incorporating amide and amide derivative substituents in both the allylic and homoallylic position relative to the epoxide moiety. Our attempts to control regioselectivity in the allylic systems were unsuccessful; however when the directing substituent was in the homoallylic position, we could demonstrate some degree of regioselectivity.
An additional project that the author worked on for approximately one year during his graduate student tenure is not described within this work. In February of 2009 AstraZeneca, Mayo Clinic, and Virginia Tech Intellectual Properties Inc. concomitantly announced that AstraZeneca licensed a portfolio of preclinical Triple Reuptake Inhibitor (TRI) compounds for depression. The lead compound, PRC200, was discovered by a collaborative effort between the Carlier and Richelson (Mayo Clinic Jacksonville) research groups in 1998. The author was tasked to develop backup candidates of PRC200 in order to improve the pharmacokinetics of the lead compound. Due to confidentiality agreements, this work is not reported herein.Ph. D
Higher order multipole moments for molecular dynamics simulations
No full textIn conventional force fields, the electrostatic potential is represented by atom-centred point charges. This choice is in principle arbitrary, but technically convenient. Point charges can be understood as the first term of multipole expansions, which converge with an increasing number of terms towards the accurate representation of the molecular potential given by the electron density distribution. The use of multipole expansions can therefore improve the force field accuracy. Technically, the implementation of atomic multipoles is more involved than the use of point charges. Important points to consider are the orientation of the multipole moments during the trajectory, conformational dependence of the atomic moments and stability of the simulations which are discussed her
Exploring the Unesco world heritage property in the shallow waters at Rose Island using unmanned surface vehicles (USV)
No full textRose Island (Germany) is part of the UNESCO World Heritage site “Prehistoric Pile Dwellings around the Alps” and a pilot site of the EU funded project TRIQUETRA, which targets the risks of climate change on cultural heritage. With the lack of a detailed bathymetric map of the waters around Rose Island and in search for an efficient approach for documenting the wooden relics from Iron Age at the lake bottom, both a sonar and a photogrammetric campaign were conducted by the German Aerospace Center (DLR). From the sonar measurements, the first reliable bathymetric map of the area was generated and provided to TRIQUETRA’s decision support system and WebGIS. During the photogrammetric survey, ~15.000 high resolution images of the lake floor were taken by an unmanned surface vehicle (USV) and processed to high-resolution 3D models by using the structure-from-motion method (SfM). The models provide an unprecedented level of detail for the documentation and examination of the archaeologic remains at Rose Island and a fascinating insight to the prehistoric settlement remains for the general public
Exploring the UNESCO world heritage property in the shallow waters at Rose Island using unmanned surface vehicles (USV)
No full textRose Island (Germany) is part of the UNESCO World Heritage
site "Prehistoric Pile Dwellings around the Alps" and a pilot site
of the EU funded project TRIQUETRA, which targets the risks
of climate change on cultural heritage. With the lack of a detailed
bathymetric map of the waters around Rose Island and in search
for an efficient approach for documenting the wooden relics from
Iron Age at the lake bottom, both a sonar and a photogrammetric
campaign were conducted by the German Aerospace Center (DLR).
From the sonar measurements, the first reliable bathymetric map
of the area was generated and provided to TRIQUETRA's decision
support system and WebGIS. During the photogrammetric
survey, ~15.000 high resolution images of the lake floor were
taken by an unmanned surface vehicle (USV) and processed to
high-resolution 3D models by using the structure-from-motion
method (SfM). The models provide an unprecedented level of
detail for the documentation and examination of the archaeologic
remains at Rose Island and a fascinating insight to the prehistoric
settlement remains for the general publi
The Wide Field Imager instrument for Athena
No full textESA's next large X-ray mission ATHENA is designed to address the Cosmic Vision science theme 'The Hot and Energetic Universe'. It will provide answers to the two key astrophysical questions how does ordinary matter assemble into the large-scale structures we see today and how do black holes grow and shape the Universe. The ATHENA spacecraft will be equipped with two focal plane cameras, a Wide Field Imager (WFI) and an X-ray Integral Field Unit (X-IFU). The WFI instrument is optimized for state-of-The-Art resolution spectroscopy over a large field of view of 40 amin x 40 amin and high count rates up to and beyond 1 Crab source intensity. The cryogenic X-IFU camera is designed for high-spectral resolution imaging. Both cameras share alternately a mirror system based on silicon pore optics with a focal length of 12 m and large effective area of about 2 m2at an energy of 1 keV. Although the mission is still in phase A, i.e. studying the feasibility and developing the necessary technology, the definition and development of the instrumentation made already significant progress. The herein described WFI focal plane camera covers the energy band from 0.2 keV to 15 keV with 450 Î1⁄4m thick fully depleted back-illuminated silicon active pixel sensors of DEPFET type. The spatial resolution will be provided by one million pixels, each with a size of 130 Î1⁄4m x 130 Î1⁄4m. The time resolution requirement for the WFI large detector array is 5 ms and for the WFI fast detector 80 Î1⁄4s. The large effective area of the mirror system will be completed by a high quantum efficiency above 90% for medium and higher energies. The status of the various WFI subsystems to achieve this performance will be described and recent changes will be explained here
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