Identity formation at the beginning of the twenty-first century: Intersubjectivity, art, and medicine in Siri Hustvedt’s works

„Ich bin, weil du bist“ – so lautet eines der Schlüsselzitate in What I Loved, dem 2003 erschienenen dritten Roman der zeitgenössischen amerikanischen Autorin Siri Hustvedt. Die Bedeutung von Beziehung und Interaktion für die Identitätsbildung spielt eine zentrale Rolle nicht nur in diesem Roman, sondern auch in ihrem Gesamtwerk, das vier Romane, ein memoir, drei Essay-Sammlungen und einen Lyrikband umfasst. Hustvedt erforscht die Identität als ein vielschichtiges Produkt bewusster und unbewusster Verknüpfungen innerhalb der sozialen und biologischen Umwelt. Das Bewusstsein wird als eine dialogisch geprägte Entität gezeigt, dessen Identität erst durch die Beziehung auf ein Anderes geformt werden kann. Um dem Mysterium der menschlichen Identitätsfindung nachzuspüren, bedient sich Hustvedt sowohl philosophischer, psychoanalytischer, biologischer als auch kunsttheoretischer Diskurse. In ihren Romanen stellt sich die Frage nach der Erklärung von Identität als komplexe Problematik dar: Ist die Beziehung zu anderen Menschen vor allem durch unsere Entwicklung als Kind und die Nähe zu Bezugspersonen geprägt? In welchem Ausmaß ist das Empfinden von Subjektivität beeinflusst von körperlichen und unbewussten Mechanismen? Inwiefern ist die Wahrnehmung visueller Kunst eine Kooperation zwischen Betrachter und Künstler? rnDiesen und anderen Fragen geht diese Dissertation nach, indem sie Hustvedts Werk als Anlass für eine Analyse intersubjektiver Strukturen der Identität nimmt. Die Intersubjektivitätsphiloso¬phien von Hegel, Buber, Bakhtin, Husserl, und Merleau-Ponty dienen hierbei als Ausgangspunkt für die Interpretation von relationaler Identität in Hustvedts Werken. Die Dissertation konzentriert sich auf Hustvedts Darstellung der Beziehung zwischen Selbst und Anderem in der Photographie und in der Malerei, der Überschreitung von Körpergrenzen in Hysterie und Anorexie sowie der Auswirkung des Verlustes von Bezugspersonen auf die persönliche Identität. Entscheidend für den Hustvedtschen Kunstbegriff ist das Zusammenspiel von Kunstobjekt, Künstler und Betrachter. Die Grenzen zwischen Innerem und Äußeren werden aufgelöst: mal wird der Rezipient Teil des Kunstwerks, mal verschmilzt der Künstler förmlich mit seinem Objekt. Auch hier wird wiederum deutlich, dass Identität nur in Wechselbeziehung und als zwischenmenschliche Kooperation entsteht. Hustvedt betritt durch ihre einzigartige Auseinandersetzung mit den Wechselbeziehungen und fragilen Grenzen zwischen Ich und Umwelt Neuland auf dem Gebiet der literarischen Identitätsforschung, da sie ihr Prinzip des „mixing,“ des unausweichlichen Eindringens fremder Substanz in die eigene Identität, aus dem Blickwinkel dieser verschiedenen Erklärungsansätze beleuchtet. rn

NMR spectroscopy and imaging of hyperpolarized gases

Since the discovery of the nuclear magnetic resonance (NMR) phenomenon, countless NMR techniques have been developed that are today indispensable tools in physics, chemistry, biology, and medicine. As one of the main obstacles in NMR is its notorious lack of sensitivity, different hyperpolarization (HP) methods have been established to increase signals up to several orders of magnitude. In this work, different aspects of magnetic resonance, using HP noble gases, are studied, hereby combining different disciplines of research. The first part examines new fundamental effects in NMR of HP gases, in theory and experiment. The spin echo phenomenon, which provides the basis of numerous modern experiments, is studied in detail in the gas phase. The changes of the echo signal in terms of amplitude, shape, and position, due to the fast translational motion, are described by an extension of the existing theory and computer simulations. With this knowledge as a prerequisite, the detection of intermolecular double-quantum coherences was accomplished for the first time in the gas phase. The second part of this thesis focuses on the development of a practical method to enhance the dissolution process of HP 129Xe, without loss of polarization or shortening of T1. Two different setups for application in NMR spectroscopy and magnetic resonance imaging (MRI) are presented. The continuous operation allows biological and multidimensional spectroscopy in solutions. Also, first in vitro MRI images with dissolved HP 129Xe as contrast agent were obtained at a clinical scanner.

Effect of drug physicochemical properties on the release from liposomal systems in vitro and in vivo

Liposomes were discovered about 40 years ago by A. Bangham and since then they became very versatile tools in biology, biochemistry and medicine. Liposomes are the smallest artificial vesicles of spherical shape that can be produced from natural untoxic phospholipids and cholesterol. Liposome vesicles can be used as drug carriers and become loaded with a great variety of molecules, such as small drug molecules, proteins, nucleotides and even plasmids. Due to the variability of liposomal compositions they can be used for a large number of applications. In this thesis the β-adrenoceptor antagonists propranolol, metoprolol, atenolol and pindolol, glucose, 18F-Fluorodeoxyglucose (FDG) and Er-DTPA were used for encapsulation in liposomes, characterization and in vitro release studies. Multilamellar vesicles (MLV), large unilamellar vesicles (LUV) and smaller unilamellar vesicles (SUV) were prepared using one of the following lipids: 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC), 1,2-Distearoyl-sn-Glycero-3-Phosphocholine (DSPC), Phospholipone 90H (Ph90H) or a mixture of DSPC and DMPC (1:1). The freeze thawing method was used for preparation of liposomes because it has three advantages (1) avoiding the use of chloroform, which is used in other methods and causes toxicity (2) it is a simple method and (3) it gives high entrapping efficiency. The percentage of entrapping efficiencies (EE) was different depending on the type and phase transition temperature (Tc) of the lipid used. The average particle size and particle size distribution of the prepared liposomes were determined using both dynamic light scattering (DLS) and laser diffraction analyzer (LDA). The average particle size of the prepared liposomes differs according to both liposomal type and lipid type. Dispersion and dialysis techniques were used for the study of the in vitro release of β-adrenoceptor antagonists. The in vitro release rate of β-adrenoceptor antagonists was increased from MLV to LUV to SUV. Regarding the lipid type, β-adrenoceptor antagonists exhibited different in vitro release pattern from one lipid to another. Two different concentrations (50 and 100mg/ml) of Ph90H were used for studying the effect of lipid concentration on the in vitro release of β-adrenoceptor antagonists. It was found that liposomes made from 50 mg/ml Ph90H exhibited higher release rates than liposomes made at 100 mg/ml Ph90H. Also glucose was encapsulated in MLV, LUV and SUV using 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC), 1,2-Distearoyl-sn-Glycero-3-Phosphocholine (DSPC), Phospholipone 90H (Ph90H), soybean lipid (Syb) or a mixture of DSPC and DMPC (1:1). The average particle size and size distribution were determined using laser diffraction analysis. It was found that both EE and average particle size differ depending on both lipid and liposomal types. The in vitro release of glucose from different types of liposomes was performed using a dispersion method. It was found that the in vitro release of glucose from different liposomes is dependent on the lipid type. 18F-FDG was encapsulated in MLV 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC), 1,2-Distearoyl-sn-Glycero-3-Phosphocholine (DSPC), Phospholipone 90H (Ph90H), soybean lipid (Syb) or a mixture of DSPC and DMPC (1:1). FDG-containing LUV and SUV were prepared using Ph90H lipid. The in vitro release of FDG from the different types of lipids was accomplished using a dispersion method. Results similar to that of glucose release were obtained. In vivo imaging of FDG in both uncapsulated FDG and FDG-containing MLV was performed in the brain and the whole body of rats using PET scanner. It was found that the release of FDG from FDG-containing MLV was sustained. In vitro-In vivo correlation was studied using the in vitro release data of FDG from liposomes and in vivo absorption data of FDG from injected liposomes using microPET. Erbium, which is a lanthanide metal, was used as a chelate with DTPA for encapsulation in SUV liposomes for the indirect radiation therapy of cancer. The liposomes were prepared using three different concentrations of soybean lipid (30, 50 and 70 mg/ml). The stability of Er-DTPA SUV liposomes was carried out by storage of the prepared liposomes at three different temperatures (4, 25 and 37 °C). It was found that the release of Er-DTPA complex is temperature dependent, the higher the temperature, the higher the release. There was an inverse relationship between the release of the Er-DTPA complex and the concentration of lipid.

Advances in hardware and molecular design of polarizing agents for dynamic nuclear polarization

Die Kernmagnetresonanz (NMR) ist eine vielseitige Technik, die auf spin-tragende Kerne angewiesen ist. Seit ihrer Entdeckung ist die Kernmagnetresonanz zu einem unverzichtbaren Werkzeug in unzähligen Anwendungen der Physik, Chemie, Biologie und Medizin geworden. Das größte Problem der NMR ist ihre geringe Sensitivtät auf Grund der sehr kleinen Energieaufspaltung bei Raumtemperatur. Für Protonenspins, die das größte magnetogyrische Verhältnis besitzen, ist der Polarisationsgrad selbst in den größten verfügbaren Magnetfeldern (24 T) nur ~7*10^(-5).rnDurch die geringe inhärente Polarisation ist folglich eine theoretische Sensitivitätssteigerung von mehr als 10^4 möglich. rnIn dieser Arbeit wurden verschiedene technische Aspekte und unterschiedliche Polarisationsagenzien für Dynamic Nuclear Polarization (DNP) untersucht.rnDie technische Entwicklung des mobilen Aufbaus umfasst die Verwendung eines neuen Halbach Magneten, die Konstruktion neuer Probenköpfe und den automatisierten Ablauf der Experimente mittels eines LabVIEW basierten Programms. Desweiteren wurden zwei neue Polarisationsagenzien mit besonderen Merkmalen für den Overhauser und den Tieftemperatur DNP getestet. Zusätzlich konnte die Durchführbarkeit von NMR Experimenten an Heterokernen (19F und 13C) im mobilen Aufbau bei 0,35 T gezeigt werden. Diese Ergebnisse zeigen die Möglichkeiten der Polarisationstechnik DNP auf, wenn Heterokerne mit einem kleinen magnetogyrischen Verhältnis polarisiert werden müssen.rnDie Sensitivitätssteigerung sollte viele neue Anwendungen, speziell in der Medizin, ermöglichen.

Expanding the scope of poly(ethylene glycol)s for bioconjugation to squaric acid-mediated PEGylation and pH-sensitivity

Poly(ethylene glycol) (PEG) is used in a broad range of applications due to its unique combination of properties and is approved use in formulations for body-care products, edibles and medicine. This thesis aims at the synthesis and characterization of novel heterofunctional PEG structures and the establishment of diethyl squarate as a suitable linker for the covalent attachment to proteins. Chapter 1 is an introduction on the properties and applications of PEG as well as the fascinating chemistry of squaric acid derivatives. In Chapter 1.1, the synthesis and properties of PEG are described, and the versatile applications of PEG derivatives in everyday products are emphasized with a focus on PEG-based pharmaceuticals and nonionic surfactants. This chapter is written in German, as it was published in the German Journal Chemie in unserer Zeit. Chapter 1.2 deals with PEGs major drawbacks, its non-biodegradability, which impedes parenteral administration of PEG conjugates with polyethers exceeding the renal excretion limit, although these would improve blood circulation times and passive tumor targeting. This section gives a comprehensive overview of the cleavable groups that have been implemented in the polyether backbone to tackle this issue as well as the synthetic strategies employed to accomplish this task. Chapter 1.3 briefly summarizes the chemical properties of alkyl squarates and the advantages in protein conjugation chemistry that can be taken from its use as a coupling agent. In Chapter 2, the application of diethyl squarate as a coupling agent in the PEGylation of proteins is illustrated. Chapter 2.1 describes the straightforward synthesis and characterization of squaric acid ethyl ester amido PEGs with terminal hydroxyl functions or methoxy groups. The reactivity and selectivity of theses activated PEGs are explored in kinetic studies on the reactions with different lysine and other amino acid derivatives, followed by 1H NMR spectroscopy. Further, the efficient attachment of the novel PEGs to a model protein, i.e., bovine serum albumin (BSA), demonstrates the usefulness of the new linker for the PEGylation with heterofunctional PEGs. In Chapter 2.3 initial studies on the biocompatibility of polyether/BSA conjugates synthesized by the squaric acid mediated PEGylation are presented. No cytotoxic effects on human umbilical vein endothelial cells exposed to various concentrations of the conjugates were observed in a WST-1 assay. A cell adhesion molecule - enzyme immunosorbent assay did not reveal the expression of E-selectin or ICAM-1, cell adhesion molecules involved in inflammation processes. The focus of Chapter 3 lies on the syntheses of novel heterofunctional PEG structures which are suitable candidates for the squaric acid mediated PEGylation and exhibit superior features compared to established PEGs applied in bioconjugation. Chapter 3.1 describes the synthetic route to well-defined, linear heterobifunctional PEGs carrying a single acid-sensitive moiety either at the initiation site or at a tunable position in the polyether backbone. A universal concept for the implementation of acetal moieties into initiators for the anionic ring-opening polymerization (AROP) of epoxides is presented and proven to grant access to the degradable PEG structures aimed at. The hydrolysis of the heterofunctional PEG with the acetal moiety at the initiating site is followed by 1H NMR spectroscopy in deuterium oxide at different pH. In an exploratory study, the same polymer is attached to BSA via the squarate acid coupling and subsequently cleaved from the conjugate under acidic conditions. Furthermore, the concept for the generation of acetal-modified AROP initiators is demonstrated to be suitable for cholesterol, and the respective amphiphilic cholesteryl-PEG is cleaved at lowered pH. In Chapter 3.2, the straightforward synthesis of α-amino ω2-dihydroxyl star-shaped three-arm PEGs is described. To assure a symmetric length of the hydroxyl-terminated PEG arms, a novel AROP initiator is presented, who’s primary and secondary hydroxyl groups are separated by an acetal moiety. Upon polymerization of ethylene oxide for these functionalities and subsequent cleavage of the acid-labile unit no difference in the degree of polymerization is seen for both polyether fragments.