Optische Mikroskopie an kolloidalen Suspensionen unter Nichtgleichgewichtsbedingungen

Kolloidale Suspensionen eignen sich aufgrund der für sierelevanten Längeskalen hervorragend zur Beobachtung mittelsoptischer Mikroskopie. Die Verwendung speziellerKontrastierverfahren kann bestimmte Aspekte kolloidalerStrukturen besonders hervorheben und eine verbesserteAnalyse von Nichtgleichgewichtszuständen in kolloidalenSystemen ermöglichen. Mittels Phasen- und Interferenzkontrast konnte die Ursachedes Kleinwinkelstreumaximums in der Lichtstreuung an einerSuspension aus Mikronetzteilchen auf die unterschiedlichenStrukturfaktoren von Kristall und Korngrenze zurückgeführtwerden.Der Zusammenhang von Struktur und Farbe eingetrockneterMultilagen wurde in hochauflösender Durchlichtmikroskopiedemonstriert und zur Analyse der inneren Struktur derKristalldomänen inklusive von Versetzungen und Stapelfehlernbenutzt.Mit der Polarisationsmikroskopie konnte die Veränderung derPartikelzahldichte um ein Ionentauscherbruchstück auf einenSalzkonzentrationsgradienten zurückgeführt werden. Die Untersuchung kolloidaler Suspensionen in einem Scherfeldmittels Fourier-Mikroskopie lieferte im Bereich fluiderGleichgewichtsstrukturen den Nachweis scherinduzierterhexagonaler Strukturen. Die Ultramikroskopie mit erweiterterSchärfentiefe ermöglichte die direkte Beobachtung desGleitmechanismus von verscherten hexagonalen Lagen und dieKlassifizierung durch die entwickelte2D-Partikelkorrelation. Die Scherung induziert in fluidenStrukturen hexagonale Ordnung und zerstört bei großenScherraten existierende Ordnung. Es wird eineWandstabilisierung der hexagonalen Strukturen beobachtet. Mittels Bragg-Mikroskopie konnte unter Scherung dieHomogenität der Struktur innerhalb der Scherzelledokumentiert werden sowie nach Scherung die Entstehung derGleichgewichts bcc Phase.

Tail bridging vs. patchiness

The subject of this thesis are the interactions between nucleosome core particles (NCPs). NCPs are the primary storage units of DNA in eucaryotic cells. Each NCP consists of a core of eight histone proteins and a strand of DNA, which is wrapped around about two times. Each histone protein has a terminal tail passing over and between the superhelix of the wrapped DNA. Special emphasis was placed on the role of the histone tails, since experimental ndings suggest that the tails have a great in uence on the mutual attraction of the NCPs. In those experiments Mangenot et al. observe a dramatic change in the con guration of the tails, which is accompanied by evidence of mutual attraction between NCPs, when a certain salt concentration is reached. Existing models used in the theoretical approaches and in simulations focus on the description of the histone core and the wrapped DNA, but neglect the histone tails. We introduce the multi chain complex as a new simulation model. Here the histone core and the wrapping DNA are modelled via a charged sphere, while the histone tails are represented by oppositely charged chains grafted on the sphere surface. We start by investigating the parameter space describing a single NCP. The Debye-Huckel potential is used to model the electrostatic interactions and to determine the e ective charge of the NCP core. This value is subsequently used for a study of the pairinteraction of two NCPs via an extensive Molecular Dynamics study. The monomer distribution of the full chain model is investigated. The existence of tail bridges between the cores is demonstrated. Finally, by discriminating between bridging and non-bridging con gurations, we can show that the effect of tail bridging between the spheres does indeed account for the observed attraction. The full chain model can serve as a model to study the acetylation of the histone tails of the nucleosome. The reduction of the charge fraction of the tails, that corresponds to the process of acetylation, leads to a reduction or even the disappearance of the attraction. A recent MC study links this e ect to the unfolding of the chromatin ber in the case of acetylated histone tails. In this case the acetylation of the histone tails leads to the formation of heterochromatin, and one could understand how larger regions of the genetic information could be inactivated through this mechanism.

Cellulose based Lithium ion polymer electrolytes for Lithium batteries

The separator membrane in batteries and fuel cells is of crucial importance for the function of these devices. In lithium ion batteries the separator membrane as well as the polymer matrix of the electrodes consists of polymer electrolytes which are lithium ion conductors. To overcome the disadvantage of currently used polymer electrolytes which are highly swollen with liquids and thus mechanically and electrochemically unstable, the goal of this work is a new generation of solid polymer electrolytes with a rigid backbone and a soft side chain structure. Moreover the novel material should be based on cheap substrates and its synthesis should not be complicated aiming at low overall costs. The new materials are based on hydroxypropylcellulose and oligoethyleneoxide derivatives as starting materials. The grafting of the oligoethyleneoxide side chains onto the cellulose was carried out following two synthetic methods. One is based on a bromide derivative and another based on p-toluolsulfonyl as a leaving group. The side chain reagents were prepared form tri(ethylene glycol) monoethyl ether. In order to improve the mechanical properties the materials were crosslinked. Two different conceptions have been engaged based on either urethane chemistry or photosensitive dimethyl-maleinimide derivatives. PEO - graft - cellulose derivatives with a high degree of substitution between 2,9 and 3,0 were blended with lithium trifluoromethane-sulfonate, lithium bis(trifluorosulfone)imide and lithium tetrafluoroborate. The molar ratios were in the range from 0,02 to 0,2 [Li]/[O]. The products have been characterized with nuclear magnetic resonance (NMR), gel permeation chromatography (GPC) and laserlight scattering (LS) with respect to their degree of substitution and molecular weight. The effect of salt concentration on ionic conductivity, thermal behaviour and morphology has been investiga-ted with impedance spectroscopy, differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The crosslinking reactions were controlled with dynamic mechanical analysis (DMS). The degree of substitution of our products is varying between 2,8 and 3,0 as determined by NMR. PEO - graft - cellulose derivatives are highly viscous liquids at room temperature with glass transition temperatures around 215 K. The glass transition temperature for the Lithium salt complexes of PEO - graft - cellulose deri-vatives increase with increasing salt content. The maximum conductivity at room temperature is about 10-4 and at 100°C around 10-3 Scm-1. The presence of lithium salt decreases the thermal stability of the complexes in comparison to pure PEO - graft - cellulose derivatives. Complexes heated over 140 – 150°C completely lose their ionic conductivity. The temperature dependence of the conductivity presented as Arrhenius-type plots for all samples is similar in shape and follows a VTF behaviour. This proofs that the ionic transport is closely related to the segmental motions of the polymer chains. Novel cellulose derivatives with grafted oligoethylen-oxide side chains with well-defined chemical structure and high side chain grafting density have been synthesized. Cellulose was chosen as stiff, rod like macromolecule for the backbone while oligoethylen-oxides are chosen as flexible side chains. A maximum grafting density of 3.0 have been obtained. The best conductivity reaches 10-3 Scm-1 at 100°C for a Li-triflate salt complex with a [Li]/[O] ratio of 0.8. The cross-linked complexes containing the lithium salts form elastomeric films with convenient mechanical stability. Our method of cellulose modification is based on relatively cheap and commercially available substrates and as such appears to be a promising alternative for industrial applications.

The collapse of linear polyelectrolyte chains in a poor solvent: When does a collapsing polyelectrolyte collect its counter ions?

The collapse of linear polyelectrolyte chains in a poor solvent: When does a collapsing polyelectrolyte collect its counter ions? The collapse of polyions in a poor solvent is a complex system and is an active research subject in the theoretical polyelectrolyte community. The complexity is due to the subtle interplay between hydrophobic effects, electrostatic interactions, entropy elasticity, intrinsic excluded volume as well as specific counter-ion and co-ion properties. Long range Coulomb forces can obscure single molecule properties. The here presented approach is to use just a small amount of screening salt in combination with a very high sample dilution in order to screen intermolecular interaction whereas keeping intramolecular interaction as much as possible (polyelectrolyte concentration cp ≤ 12 mg/L, salt concentration; Cs = 10^-5 mol/L). This is so far not described in literature. During collapse, the polyion is subject to a drastic change in size along with strong reduction of free counterions in solution. Therefore light scattering was utilized to obtain the size of the polyion whereas a conductivity setup was developed to monitor the proceeding of counterion collection by the polyion. Partially quaternized PVP’s below and above the Manning limit were investigated and compared to the collapse of their uncharged precursor. The collapses were induced by an isorefractive solvent/non-solvent mixture consisting of 1-propanol and 2-pentanone, with nearly constant dielectric constant. The solvent quality for the uncharged polyion could be quantified which, for the first time, allowed the experimental investigation of the effect of electrostatic interaction prior and during polyion collapse. Given that the Manning parameter M for QPVP4.3 is as low as lB / c = 0.6 (lB the Bjerrum length and c the mean contour distance between two charges), no counterion binding should occur. However the Walden product reduces with first addition of non solvent and accelerates when the structural collapse sets in. Since the dielectric constant of the solvent remains virtually constant during the chain collapse, the counterion binding is entirely caused by the reduction in the polyion chain dimension. The collapse is shifted to lower wns with higher degrees of quaternization as the samples QPVP20 and QPVP35 show (M = 2.8 respectively 4.9). The combination of light scattering and conductivity measurement revealed for the first time that polyion chains already collect their counter ions well above the theta-dimension when the dimensions start to shrink. Due to only small amounts of screening salt, strong electrostatic interactions bias dynamic as well as static light scattering measurements. An extended Zimm formula was derived to account for this interaction and to obtain the real chain dimensions. The effective degree of dissociation g could be obtained semi quantitatively using this extrapolated static in combination with conductivity measurements. One can conclude the expansion factor a and the effective degree of ionization of the polyion to be mutually dependent. In the good solvent regime g of QPVP4.3, QPVP20 and QPVP35 exhibited a decreasing value in the order 1 > g4.3 > g20 > g35. The low values of g for QPVP20 and QPVP35 are assumed to be responsible for the prior collapse of the higher quaternized samples. Collapse theory predicts dipole-dipole attraction to increase accordingly and even predicts a collapse in the good solvent regime. This could be exactly observed for the QPVP35 sample. The experimental results were compared to a newly developed theory of uniform spherical collapse induced by concomitant counterion binding developed by M. Muthukumar and A. Kundagrami. The theory agrees qualitatively with the location of the phase boundary as well as the trend of an increasing expansion with an increase of the degree of quaternization. However experimental determined g for the samples QPVP4.3, QPVP20 and QPVP35 decreases linearly with the degree of quaternization whereas this theory predicts an almost constant value.

Synthese und Charakterisierung von multivalenten kationischen Tensiden und Polymeren

Der Einsatz von den Polyelektrolytkomplexen von DNA / RNA mit Polykationen oder Lipiden in der Gen-Therapie ist für Wissenschaftler von besonderem Interesse, da sie als Träger für den Transport von genetischem Material in lebende Zellen fungieren können. Interessant ist auch die Komplexbildung aus Gadolinium und Polykation, hier können die stabil gebildeten Aggregate als Kontrastmittel zur Anwendung in der Magnetresonanztomographie eingeführt werden. Ziel der vorliegenden Arbeit war es, strukturdefinierte, positiv geladene, polyvalente sperminanaloge Polymere zu synthetisieren. Durch die polyelektrolytische Natur erlauben solche Polymere die Komplexierung von mehr Gadolinium-Polyoxometalaten und wären deshalb sehr gut als Kontrastmittel geeignet. Aufbauend auf den Vorarbeiten, wurde insbesondere die Komplexbildung von kationischem Polymer mit der Green Fluorescent Protein DNA in physiologischem Salzgehalt untersucht. Die Beschreibung der Synthese im Rahmen dieser Arbeit zeigt, dass es mit dem entwickelten Syntheseprinzip, also unter Einsatz von orthogonaler Schutzgruppenchemie und funktionaler Transformation gelungen ist, durch einfache nukleophile Substitution die Kopplung der Elementareinheiten zu komplexeren, auch ionischen Tensiden durchzuführen. Die Komplexierung von Gadolinium-Polyoxometalat mit kationisch geladenem Polymer in reinem Wasser und in physiologischem Salzgehalt hat gezeigt, dass bei einem Ladungsverhältnis von ungefähr 2:1 stabile sphärische Komplexe gebildet werden. HeLa-Zellen zeigen keine hohe Empfindlichkeit gegenüber Polykation-POM-Komplexen, da deren toxische Wirkung nur einen Anteil toter Zellen von maximal 24 % zur Folge hatte. Die Bildqualität einer MRT-Aufnahme der gebildeten Polykation-POM-Komplexe wurde im Vergleich zu den reinen Gadolinium-Polyoxometalat-Lösungen erheblich verbessert. Die Komplexierung von DNA mit dem im Überschuss vorliegenden kationisch geladenen Polymer wurde mittels Rasterkraftmikroskopie, statischer sowie dynamischer Lichtstreuung untersucht. Die Molmasse und Größe der Polykation-DNA-Komplexe geben eindeutige Hinweise darauf, dass sich in physiologischer Salzlösung Multi-Ketten-Komplexe bilden. Neben der Untersuchung der Polymer-Komplexe wurde eine Reihe neuartiger multivalenter kationischer Tenside hergestellt, wobei ihre Eigenschaften beispielsweise mit Tensid B (C12N4), Tensid C (EG8N4) und Tensid F (EG8C12N4) in wässriger Lösung bei verschiedener Salzkonzentration im Vordergrund stehen.