Universiẗat, Diss., 2007--Frankfurt (Main). / Zsfassung in dt. und engl. Sprache.

Univ., Diss., 2006--Frankfurt (Main) / Enth. Sonderabdr. aus versch. Zeitschr. - Zsfassung in dt. und engl. Sprache

Understanding the interaction of polyelectrolytes with oppositely charged lipid membranes is an important issue of soft matter physics, which provides an insight into mechanisms of interactions between biological macromolecules and cell membranes. Despite the fact that many (bio)macromolecules and filamentous supramolecular assemblies show semiflexible behavior, prior to this work very little was known about the conformational dynamics and Brownian motion of semiflexible particles attached to freestanding lipid membranes. In order to address these issues, diffusion and conformational dynamics of semiflexible DNA molecules and filamentous fd-virus particles electrostatically adsorbed to cationic freestanding lipid membranes were studied on the single particle level by means of optical wide-field fluorescence microscopy. Supergiant unilamellar vesicles (SGUVs) with diameters larger than 100 m represent a perfect model of a freestanding membrane. In this work, a method was developed that enabled the reliable and efficient electroformation of cationic SGUVs on ITO-coated coverslips. The utilization of SGUVs as model freestanding lipid bilayers allowed for determination of the previously unknown surface viscosity of DOPC/DOTAP membranes. In particular, the analysis of the translational diffusion coefficients of small (10, 20, 50 nm) membrane-attached anionic polystyrene beads has shown that the surface viscosity of DOPC/DOTAP membranes with CDOTAP = 1–7 mol% is independent of the DOTAP concentration and equals η = (5.9 ± 0.2) × 10−10 Pa s m. The fluorescence video-microscopy investigation of single DNA molecules attached to cationic SGUVs revealed a previously unreported conformational transition of a membrane-bound DNA molecule from a 2D random coil, the original conformation in which DNA attaches to the membrane, to a compact globule. This membrane-mediated DNA condensation is favored at high cationic lipid concentrations in the membrane and long DNA contour lengths. The DNA compaction rate in the coil–globule transition is 124 ± 46 kbp/s, and the resulting DNA globule sizes were found to be 250–350 nm at DOPC membranes containing 1 mol% DOTAP and 130–200 nm for 7 mol% DOTAP, indicating a stronger compaction for higher charge densities in the membrane. Additional experiments with freestanding cationic membranes in the gel state and supported cationic lipid membranes with gel–fluid coexistence suggest that the DNA collapse on a freestanding fluid cationic membrane may be initiated by a local lipid segregation in the membrane and is accompanied by local membrane deformations, which eventually stabilize the compact DNA globule. Furthermore, in this work single molecule studies of random-coil DNA molecules and filamentous fd-virus particles on a freestanding cationic lipid bilayer with a low charge density were carried out. The experiments revealed that these particles can be described as semiflexible chains in 2D. Taken together, DNA molecules and fd-virus particles cover a broad range of the ratio of contour length and persistence length from 0.4 to 82. The results of this work demonstrate that the mobility of such membrane-attached semiflexible particles is strongly affected by hydrodynamics in the lipid membrane and the surrounding bulk fluid, and can in essence be described using a hydrodynamics-based theory for a disk-shaped solid membrane inclusion with a characteristic size approximately equal to the radii of gyration of the particles.

Understanding the interaction of polyelectrolytes with oppositely charged lipid membranes is an important issue of soft matter physics, which provides an insight into mechanisms of interactions between biological macromolecules and cell membranes. Despite the fact that many (bio)macromolecules and filamentous supramolecular assemblies show semiflexible behavior, prior to this work very little was known about the conformational dynamics and Brownian motion of semiflexible particles attached to freestanding lipid membranes. In order to address these issues, diffusion and conformational dynamics of semiflexible DNA molecules and filamentous fd-virus particles electrostatically adsorbed to cationic freestanding lipid membranes were studied on the single particle level by means of optical wide-field fluorescence microscopy. Supergiant unilamellar vesicles (SGUVs) with diameters larger than 100 m represent a perfect model of a freestanding membrane. In this work, a method was developed that enabled the reliable and efficient electroformation of cationic SGUVs on ITO-coated coverslips. The utilization of SGUVs as model freestanding lipid bilayers allowed for determination of the previously unknown surface viscosity of DOPC/DOTAP membranes. In particular, the analysis of the translational diffusion coefficients of small (10, 20, 50 nm) membrane-attached anionic polystyrene beads has shown that the surface viscosity of DOPC/DOTAP membranes with CDOTAP = 1–7 mol% is independent of the DOTAP concentration and equals η = (5.9 ± 0.2) × 10−10 Pa s m. The fluorescence video-microscopy investigation of single DNA molecules attached to cationic SGUVs revealed a previously unreported conformational transition of a membrane-bound DNA molecule from a 2D random coil, the original conformation in which DNA attaches to the membrane, to a compact globule. This membrane-mediated DNA condensation is favored at high cationic lipid concentrations in the membrane and long DNA contour lengths. The DNA compaction rate in the coil–globule transition is 124 ± 46 kbp/s, and the resulting DNA globule sizes were found to be 250–350 nm at DOPC membranes containing 1 mol% DOTAP and 130–200 nm for 7 mol% DOTAP, indicating a stronger compaction for higher charge densities in the membrane. Additional experiments with freestanding cationic membranes in the gel state and supported cationic lipid membranes with gel–fluid coexistence suggest that the DNA collapse on a freestanding fluid cationic membrane may be initiated by a local lipid segregation in the membrane and is accompanied by local membrane deformations, which eventually stabilize the compact DNA globule. Furthermore, in this work single molecule studies of random-coil DNA molecules and filamentous fd-virus particles on a freestanding cationic lipid bilayer with a low charge density were carried out. The experiments revealed that these particles can be described as semiflexible chains in 2D. Taken together, DNA molecules and fd-virus particles cover a broad range of the ratio of contour length and persistence length from 0.4 to 82. The results of this work demonstrate that the mobility of such membrane-attached semiflexible particles is strongly affected by hydrodynamics in the lipid membrane and the surrounding bulk fluid, and can in essence be described using a hydrodynamics-based theory for a disk-shaped solid membrane inclusion with a characteristic size approximately equal to the radii of gyration of the particles.

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No description available.

Heterogeneous line broadening and spectral diffusion of the fluorescence emission spectra of perylene diimide molecules have been investigated by means of time dependent single molecule spectroscopy. The influence of temperature and environment has been studied and reveals strong correlation to spectral diffusion processes. We followed the freezing of the molecular mobility of quasi free molecules on the surface upon temperature lowering and by embedding into a poly(methyl methacrylate) (PMMA) polymer. Thereby changes of optical transition energies as a result of both intramolecular changes of conformation and external induced dynamics by the surrounding polymer matrix could be observed. Simulations of spectral fluctuations within a two-level system (TLS) model showed good agreement with the experimental findings.

In the title monohydrate compound, 1a, and the methanol solvate compound, 1b, the tri­ethyl­benzene derivative, C35H51N5O, has three functionalized side arms and three ethyl groups, the former being located on one side of the central benzene ring, while the latter are directed to the opposite side. Both the crystals are constructed of structurally similar dimers of 1:1 host–guest complexes held together by N—H...O and O—H...N hydrogen bonds, and in 1a additionally by O—H...O hydrogen bonds. The structure of 1b contains additional highly disordered solvent mol­ecules. Thus, the SQUEEZE routine [Spek (2015). Acta Cryst. C71, 9–18] in PLATON was used to generate a modified data set, in which the contribution of the disordered mol­ecules to the structure amplitudes is eliminated. These solvent mol­ecules are not considered in the reported chemical formula.

Funktionalisierte organische Perylenbisimidfarbstoffe (PBI) und aus Cadmiumselenid bestehende Halbleiternanokristalle werden hinsichtlich physikalischer sowie chemischer Wechselwirkungsprozesse miteinander und mit ihrer Umgebung mittels zeitaufgelöster optischer Spektroskopie untersucht. Im Mittelpunkt der Studien an diesem organisch/anorganischen Modellsystem nanoskopischer Größe steht die Aggregatbildungskinetik und die Identifikation und Quantifizierung von Transferpozessen. Die Anbindung der gut löslichen PBI-Farbstoffe an die Oberfläche solcher Halbleiternanokristalle mittels spezieller Ankergruppen wird durch Selbstorganisation in Lösung realisiert. Die Kombination von Absorptions- und zeitaufgelöster Fluoreszenzspektroskopie zeigt einen unterschiedlich starken Einfluss von Liganden und Farbstoffen auf die Fluoreszenzlöschung der Nanokristalle und belegt, dass Resonanzenergietransfer zum Farbstoff nur in sehr geringem Maße die physikalische Ursache der Fluoreszenzlöschung ist. Die Anzahl adsorbierter Farbstoffe und die Stärke der Fluoreszenzlöschung eines einzelnen Farbstoffmoleküls werden aus zeitaufgelösten Einzelmolekülexperimenten an immobilisierten Emittern gewonnen, welche den direkten spektroskopischen Zugang zur Verteilung gebundener und freier Farbstoffe/Nanokristalle erlaubt. Darüber hinaus werden ankergruppen- und umgebungsspezifische Einflüsse auf die Konformations- und Orientierungsdynamik von Perylenbisimidmolekülen dargestellt. Abschließend werden photo-physikalische Gemeinsamkeiten chemisch unterschiedlich hervorgerufener Fluoreszenzlöschungsprozesse herausgearbeitet und im Kontext von Einzelkristall-Blinkprozessen diskutiert.

<p>This study addresses the issue of how to convert peptides into drug-like non- peptides with retained biological activities at peptide receptors. Angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe, Ang II) was used as a model peptide. </p><p>Knowledge of the bioactive conformations of endogenous peptides is invaluable for the conversion of peptides into less peptidic analogues. Effectively constrained cyclic analogues, with retained pharmacological activities, may provide valuable information about the bioactive conformations of the peptide in question. </p><p>This thesis describes the development of synthesis for a number of protected, aldehyde-functionalized building blocks for standard solid phase peptide synthesis, and their use for the preparation of cyclic peptide analogues. The effect of variations in the side-chain lengths of the building blocks, on the outcome of the cyclizations was studied. Incorporation of a building block derived from L-aspartic acid afforded bicyclization towards the C-terininal end of the peptide, while for the corresponding L-glutamic acid derived building block, N-terminal directed bicyclization was achieved. A building block derived from L-2-aminoadipic acid was exploited for monocyclization furnishing <i>cis-</i> and <i>trans-</i> vinyl sulfide bridged peptide analogues. </p><p>The described cyclization methods have been applied to the synthesis of a number of conformationally constrained Ang II analogues, for which the pharmacological properties have been evaluated. Two of the Ang II analogues synthesized displayed high affinities and full agonist activities at the AT₁ angiotensin receptor, and have proven to be useful tools in the search for the bioactive conformation of Ang II.</p>