Structure formation as studied by EPR spectroscopy: From simple solutions to nanoparticles

In this thesis, three nitroxide based ionic systems were used to investigate structure and dynamics of their respective solutions in mixed solvents by means of electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectroscopy at X- and W-band (9.5 and 94.5 GHz, respectively). rnFirst, the solvation of the inorganic radical Fremy’s salt (K2ON(SO3)2) in isotope substituted binary solvent mixtures (methanol/water) was investigated by means of high-field (W-band) pulse ENDOR spectroscopy and molecular dynamics (MD) simulations. From the analysis of orientation-selective 1H and 2H ENDOR spectra the principal components of the hyperfine coupling (hfc) tensor for chemically different protons (alcoholic methyl vs. exchangeable protons) were obtained. The methyl protons of the organic solvent approach with a mean distance of 3.5 Å perpendicular to the approximate plane spanned by ON(S)2 of the probe molecule. Exchangeable protons were found to be distributed isotropically, approaching closest to Fremy’s salt from the hydrogen-bonded network around the sulfonate groups. The distribution of exchangeable and methyl protons as found in MD simulations is in full agreement with the ENDOR results. The solvation was found to be similar for the studied solvent ratios between 1:2.3 and 2.3:1 and dominated by an interplay of H-bond (electrostatic) interactions and steric considerations with the NO group merely involved into H-bonds.rnFurther, the conformation of spin labeled poly(diallyldimethylammonium chloride) (PDADMAC) solutions in aqueous alcohol (methanol, ethanol, n-propanol, ethylene glycol, glycerol) mixtures in dependence of divalent sodium sulfate was investigated with double electron-electron resonance (DEER) spectroscopy. The DEER data was analyzed using the worm-like chain model which suggests that in organic-water solvent mixtures the polymer backbones are preferentially solvated by the organic solvent. We found a less serve impact on conformational changes due to salt than usually predicted in polyelectrolyte theory which stresses the importance of a delicate balance of hydrophobic and electrostatic interactions, in particular in the presence of organic solvents.rnFinally, the structure and dynamics of miniemulsions and polymerdispersions prepared with anionic surfactants, that were partially replaced by a spin labeled fatty acid in presence and absence of a lanthanide beta-diketonate complex was characterized by CW EPR spectroscopy. Such miniemulsions form multilayers with the surfactant head group bound to the lanthanide ion. Beta-diketonates were formerly used as NMR shift reagents and nowadays find application as luminescent materials in OLEDs and LCDs and as contrast agent in MRT. The embedding of the complex into a polymer matrix results in an easy processable material. It was found that the structure formation takes place in miniemulsion and is preserved during polymerization. For surfactants with carboxyl-head group a higher order of the alkyl chains and less lateral diffusion is found than for sulfat-head groups, suggesting a more uniform and stronger coordination to the metal ion. The stability of these bilayers depends on the temperature and the used surfactant which should be considered for the used polymerization temperature if a maximum output of the structured regions is wished.

Spektroskopische Untersuchungen an Technetium und Silizium - Ein Festkörperlasersystem für die Resonanzionisationsspektroskopie

Diese Arbeit beschreibt eine wesentliche Weiterentwicklung des Titan:Saphir-Lasersystems der Arbeitsgruppe LARISSA am Institut für Physik der Johannes Gutenberg-Universität Mainz und dessen Anwendung im Bereich der Resonanzionisationsspektroskopie. Die Entwicklungsarbeiten am Lasersystem umfassten drei Aspekte: die Erhöhung der Ausgangsleistung der vorhandenen Titan:Saphir-Laser um einen Faktor zwei, um damit für den vorgesehenen Einsatz an resonanten Laserionenquellen an ISOL-Einrichtungen optimale Voraussetzungen zu schaffen. Des Weiteren wurden zwei spezielle angepasste Titan:Saphir-Laser entwickelt: Das Lasersystem wurde damit um einen von 700 nm - 950 nm kontinuierlich abstimmbaren Titan:Saphir-Laser sowie einen geseedeten Titan:Saphir-Laser mit einer Linienbreite von nur 20 MHz (im Vergleich zu 3 GHz der konventionellen Laser) erweitert. Die Leistungsfähigkeit des neuen Lasersystems wurde durch Resonanzionisationsspektroskopie hochangeregter atomarer Zustände in Gold und Technetium demonstriert. Aus den gemessenen Energielagen konnte über die Rydberg-Ritz-Formel das Ionisationspotential von Gold bestätigt werden und das von Technetium erstmals mit hoher Präzision bestimmt werden. Mit dem geseedeten Titan:Saphir-Laser wurde dopplerfreie Zwei-Photonen-Spektroskopie innerhalb eines heißen Ofens demonstriert. Bei spektroskopischen Untersuchungen mit dieser Methode an Siliziumisotopen konnte sowohl die Hyperfeinstruktur als auch die Isotopieverschiebung bei einer Breite der Resonanzen von etwa 90 MHz klar aufgelöst werden.