Magnetische Nanopartikel (MNP) wurden mit neuen Fettsäurederivaten modifiziert. Auf diese Art und Weise wurden wichtige biologische und organokatalytische Funktionen auf die Oberfläche von magnetischen Nanopartikeln aufgebracht. Das folgende Kapitel präsentiert eine Veränderung von mit Polydopamin (PDA) bedeckten magnetischen Nanopartikeln via CuAAC-Reaktion. Zum Beweis der Wirksamkeit dieser Methode wurden biologische Funktionen wie Biotin, Galaktose oder Dansyl an die magnetischen Nanopartikel über einen 1,2,3-Triazolring gebunden, ebenso Prolin als organokatalytische Einheit. Weiterhin wurde das unerwartete Verhalten von Polydopamin als Organokatalysator in Aldol- und Knoevenagel-Reaktionen gezeigt und untersucht. Für diese Reaktionen wurde ebenfalls das Recycling der mit PDA bedeckten Nanopartikel getestet. Desweiteren wurde gezeigt, daß PDA als reaktives Beschichtungsmaterial für oberflächeninitiierte Ringöffnungs-polymerisation von Lactid dienen kann. Somit kann Polymilchsäure (PLA) auf verschiedene Materialien, welche mit PDA beschichtet sind, aufgebracht werden – MNP, Kohlenstoff-beschichtete Eisennanopartikel, oder Aluminiumoxid. Das letzte Kapitel beschäftigt sich mit dem Einsatz von Polyacrylaten zur Funktionalisierung von MNP. Mit dieser Methode wurden Prolin-, Lysin- und Threoninderivate an die MNP gebunden. Die katalytische Aktivität dieser neuen Materialien wurde untersucht. / Magnetic nanoparticles (MNP) were modified with new fatty acid derivatives. In this way important biological and organocatalytic functions were introduced on the surface of magnetic nanoparticles. The following chapter is presenting a modification of polydopamine (PDA) coated magnetic nanoparticles via CuAAC reaction. As a proof of principle biological moieties like biotin, galactose, dansyl were bound to magnetic nanoparticles through a 1,2,3-triazole ring, as well as proline – an organocatalytic unit. Further unexpected behaviour of polydopamine as organocatalyst for aldol and Knoevenagel reaction was demonstrated. Recycling of MNP covered with PDA was tested for the aforementioned reactions. Furthermore, it has been proved that PDA may serve as reactive coating agent for surface initiated ring opening polymerization of lactide. As a result polylactic acid (PLA) can be introduced on different materials covered with PDA - MNP, carbon covered iron magnetic nanoparticles or aluminium oxide. The last chapter is describing the employment of polyacrylates for functionalization of MNP. Using this method proline, lysine and threonine derivatives are fixed to MNP. The catalytic activity of the newly prepared materials was investigated.

The idea of miniaturizing devices down to the nanoscale where quantum ffeffects become relevant demands a detailed understanding of the interplay between classical and quantum properties. Therefore, characterization of newly produced nanoscale materials is a very important part of the research in this fifield. Studying structural and magnetic properties of nano- and molecular magnets and the interplay between these properties reveals new interesting effects and suggests ways to control and optimize the respective material. The main task of this thesis is investigating the magnetic properties of molecular magnetic clusters and magnetic nanoparticles recently synthesized by several collaborating groups. This thesis contains two main parts focusing on each of these two topics. In the first part the fundamental studies on novel metal-organic molecular complexes is presented. Several newly synthesized magnetic complexes were investigated by means of different experimental techniques, in particular, by electron spin resonance spectroscopy. Chapter 1 in this part provides the theoretical background which is necessary for the interpretation of the effects observed in single molecular magnetic clusters. Chapter 2 introduces the experimental techniques applied in the studies. Chapter 3 contains the experimental results and their discussion. Firstly, the magnetic properties of two Ni-based complexes are presented. The complexes possess different ligand structures and arrangements of the Ni-ions in the metal cores. This difffference dramatically affffects the magnetic properties of the molecules such as the ground state and the magnetic anisotropy. Secondly, a detailed study of the Mn2Ni3 single molecular magnet is described. The complex has a bistable magnetic ground state with a high spin value of S = 7 and shows slow relaxation and quantum tunnelling of the magnetization. The third section concentrates on a Mn(III)-based single chain magnet showing ferromagnetic ordering of the Mn-spins and a strong magnetic anisotropy which leads to a hysteretic behavior of the magnetization. The last section describes a detailed study of the static and dynamic magnetic properties of three Mn-dimer molecular complexes by means of static magnetization, continuous wave and pulse electron spin resonance measurements. The results indicate a systematic dependence of the magnetic properties on the nearest ligands surrounding of the Mn ions. The second part of the thesis addresses magnetic properties of nano-scaled magnets such as carbon nanotubes fifilled with magnetic materials and carbon-coated magnetic nanoparticles. These studies are eventually aiming at the possible application of these particles as agents for magnetic hyperthermia. In this respect, their behavior in static and alternating magnetic fifields is investigated and discussed. Moreover, two possible hyperthermia applications of the studied magnetic nanoparticles are presented, which are the combination of a hyperthermia agents with an anticancer drug and the possibility to spatially localize the hyperthermia effffect by applying specially designed static magnetic fifields.

The idea of miniaturizing devices down to the nanoscale where quantum ffeffects become relevant demands a detailed understanding of the interplay between classical and quantum properties. Therefore, characterization of newly produced nanoscale materials is a very important part of the research in this fifield. Studying structural and magnetic properties of nano- and molecular magnets and the interplay between these properties reveals new interesting effects and suggests ways to control and optimize the respective material. The main task of this thesis is investigating the magnetic properties of molecular magnetic clusters and magnetic nanoparticles recently synthesized by several collaborating groups. This thesis contains two main parts focusing on each of these two topics. In the first part the fundamental studies on novel metal-organic molecular complexes is presented. Several newly synthesized magnetic complexes were investigated by means of different experimental techniques, in particular, by electron spin resonance spectroscopy. Chapter 1 in this part provides the theoretical background which is necessary for the interpretation of the effects observed in single molecular magnetic clusters. Chapter 2 introduces the experimental techniques applied in the studies. Chapter 3 contains the experimental results and their discussion. Firstly, the magnetic properties of two Ni-based complexes are presented. The complexes possess different ligand structures and arrangements of the Ni-ions in the metal cores. This difffference dramatically affffects the magnetic properties of the molecules such as the ground state and the magnetic anisotropy. Secondly, a detailed study of the Mn2Ni3 single molecular magnet is described. The complex has a bistable magnetic ground state with a high spin value of S = 7 and shows slow relaxation and quantum tunnelling of the magnetization. The third section concentrates on a Mn(III)-based single chain magnet showing ferromagnetic ordering of the Mn-spins and a strong magnetic anisotropy which leads to a hysteretic behavior of the magnetization. The last section describes a detailed study of the static and dynamic magnetic properties of three Mn-dimer molecular complexes by means of static magnetization, continuous wave and pulse electron spin resonance measurements. The results indicate a systematic dependence of the magnetic properties on the nearest ligands surrounding of the Mn ions. The second part of the thesis addresses magnetic properties of nano-scaled magnets such as carbon nanotubes fifilled with magnetic materials and carbon-coated magnetic nanoparticles. These studies are eventually aiming at the possible application of these particles as agents for magnetic hyperthermia. In this respect, their behavior in static and alternating magnetic fifields is investigated and discussed. Moreover, two possible hyperthermia applications of the studied magnetic nanoparticles are presented, which are the combination of a hyperthermia agents with an anticancer drug and the possibility to spatially localize the hyperthermia effffect by applying specially designed static magnetic fifields.

Cell transplantation and stem cell therapy are promising approaches for regenerative medicine and are of interest to researchers and clinicians worldwide. However, currently, no imaging technique that allows three-dimensional in vivo inspection of therapeutically administered cells in host tissues is available. Therefore, we investigate magnetomotive optical coherence tomography (MM-OCT) of cells labeled with magnetic particles as a potential noninvasive cell tracking method. We develop magnetomotive imaging of mesenchymal stem cells for future cell therapy monitoring. Cells were labeled with fluorescent iron oxide nanoparticles, embedded in tissue-mimicking agar scaffolds, and imaged using a microscope setup with an integrated MM-OCT probe. Magnetic particle-induced motion in response to a pulsed magnetic field of 0.2 T was successfully detected by OCT speckle variance analysis, and cross-sectional and volumetric OCT scans with highlighted labeled cells were obtained. In parallel, fluorescence microscopy and laser speckle reflectometry were applied as two-dimensional reference modalities to image particle distribution and magnetically induced motion inside the sample, respectively. All three optical imaging modalities were in good agreement with each other. Thus, magnetomotive imaging using iron oxide nanoparticles as cellular contrast agents is a potential technique for enhanced visualization of selected cells in OCT.

Ziel der vorliegenden Arbeit ist es, das Preisach-Modell bezüglich stochastischer äußerer Felder und temperaturbezogener Aspekte zu untersuchen. Das phänomenologische Preisach-Modell wird oft erfolgreich angewendet, um Systeme mit Hysterese zu beschreiben. Im ersten Teil der Arbeit wird die Antwort des Preisach-Modells auf stochastische äußere Felder untersucht. Hier liegt das Augenmerk hauptsächlich auf der Autokorrelation; sie dient dazu den Einfluss des hysteretischen Gedächtnisses zu quantifizieren. Mit analytischen Methoden wird gezeigt, dass sich ein Langzeitgedächtnis, sichtbar in der Autokorrelation der Systemantwort, entwickeln kann, selbst wenn das treibende Feld unkorreliert ist. Im Anschluss werden diese Resultate, m.H. von Simulationen, auf äußere Felder ausgeweitet, die selbst Korrelationen aufweisen können. Der zweite Teil der Arbeit befasst sich mit dem Einfluss einer endlichen Temperatur auf das Preisach-Modell. Es werden unterschiedliche Methoden besprochen, wie das Nichtgleichgewichtsmodell in seiner mikromagnetischen Interpretation mit Temperatur als Gleichgewichtseigenschaft verknüpft werden kann. Eine Formulierung wird genutzt, um die Magnetisierung von Nickelnanopartikeln in einer Fullerenmatrix zu simulieren und mit Experimenten zu vergleichen. Des Weiteren wird die Relaxationsdynamik des Gedächtnisses des Preisach-Modells bei endlichen Temperaturen untersucht. / The aim of this thesis is to investigate the Preisach model in regard to stochastically driving and temperature-related aspects. The Preisach model is a phenomenological model for systems with hysteresis which is often successfully applied. Hysteresis is a widespread phenomenon which is observed in nature and the key feature of certain technological applications. Further, it contributes to phenomena of interest in social science and economics as well. Prominent examples are the magnetization of ferromagnetic materials in an external magnetic field or the adsorption-desorption hysteresis observed in porous media. Hysteresis involves the development of a hysteresis memory, and multistability in the interrelations between external driving fields and system response. In the first part, we mainly investigate the response of Preisach hysteresis models driven by stochastic input processes with regard to autocorrelation functions to quantify the influence of the system’s memory. Using rigorous methods, it is shown that the development of a hysteresis memory is reflected in the possibility of long-time tails in the autocorrelation functions, even for uncorrelated driving fields. In the case of uncorrelated driving, these long-time tails in the autocorrelations of the system’s response are determined only by the tails of the involved densities. They will be observed if there are broad Preisach densities assigning a high weight to elementary loops of large width and narrow input densities such that rare extreme events of the input time series contribute significantly to the output for a long period of time. Afterwards, these results are extended by simulations to driving fields which themselves show correlations. It is shown that the autocorrelation of the output does not decay faster than the autocorrelation of the input process. Further, there is a possibility that long-term memory in the hysteretic response is more pronounced in the case of uncorrelated driving than in the case of correlated driving. The behavior of the output probability distribution at the saturation values is quite universal. It is not affected by the presence of correlations and allows conclusions whether the input density is much more narrow than the Preisach density or not. Moreover, the existence of effective Preisach densities is shown which define equivalence classes of systems of input and Preisach densities which lead to realizations of the same output variable. The asymptotic behavior of an effective Preisach density determines the asymptotic correlation decay of the system’s response in the case of uncorrelated driving. In the second part, temperature-related effects are considered. It is reviewed how the non-equilibrium Preisach model in its micromagnetic picture can be related to temperature within the framework of extended irreversible thermodynamics. The irreversible response of a ferromagnetic material, namely, Nickel nanoparticles in a fullerene matrix, is simulated. The model includes superparamagnetism where ferromagnetism breaks down at temperatures lower than the Curie temperature and the results are compared to experimental data. Furthermore, we adapt known results for the thermal relaxation of the system’s memory in the form of a front propagation in the Preisach plane derived basically from solving a master equation and by the use of a contradictory assumption. A closer look is taken at short time scales which dissolves the contradiction and shows that the known results apply, taking into account the fact that the dividing line propagation starts with an additional delay time depending on the front coordinates in the Preisach plane. Additionally, it is outlined how thermal relaxation behavior in the Preisach model of hysteresis can be studied using a Fokker-Planck equation. The latter is solved analytically in the non-hysteretic limit using eigenfunction methods. The results indicate a change in the relaxation behavior, especially on short time scales.

Ziel der vorliegenden Arbeit ist es, das Preisach-Modell bezüglich stochastischer äußerer Felder und temperaturbezogener Aspekte zu untersuchen. Das phänomenologische Preisach-Modell wird oft erfolgreich angewendet, um Systeme mit Hysterese zu beschreiben. Im ersten Teil der Arbeit wird die Antwort des Preisach-Modells auf stochastische äußere Felder untersucht. Hier liegt das Augenmerk hauptsächlich auf der Autokorrelation; sie dient dazu den Einfluss des hysteretischen Gedächtnisses zu quantifizieren. Mit analytischen Methoden wird gezeigt, dass sich ein Langzeitgedächtnis, sichtbar in der Autokorrelation der Systemantwort, entwickeln kann, selbst wenn das treibende Feld unkorreliert ist. Im Anschluss werden diese Resultate, m.H. von Simulationen, auf äußere Felder ausgeweitet, die selbst Korrelationen aufweisen können. Der zweite Teil der Arbeit befasst sich mit dem Einfluss einer endlichen Temperatur auf das Preisach-Modell. Es werden unterschiedliche Methoden besprochen, wie das Nichtgleichgewichtsmodell in seiner mikromagnetischen Interpretation mit Temperatur als Gleichgewichtseigenschaft verknüpft werden kann. Eine Formulierung wird genutzt, um die Magnetisierung von Nickelnanopartikeln in einer Fullerenmatrix zu simulieren und mit Experimenten zu vergleichen. Des Weiteren wird die Relaxationsdynamik des Gedächtnisses des Preisach-Modells bei endlichen Temperaturen untersucht. / The aim of this thesis is to investigate the Preisach model in regard to stochastically driving and temperature-related aspects. The Preisach model is a phenomenological model for systems with hysteresis which is often successfully applied. Hysteresis is a widespread phenomenon which is observed in nature and the key feature of certain technological applications. Further, it contributes to phenomena of interest in social science and economics as well. Prominent examples are the magnetization of ferromagnetic materials in an external magnetic field or the adsorption-desorption hysteresis observed in porous media. Hysteresis involves the development of a hysteresis memory, and multistability in the interrelations between external driving fields and system response. In the first part, we mainly investigate the response of Preisach hysteresis models driven by stochastic input processes with regard to autocorrelation functions to quantify the influence of the system’s memory. Using rigorous methods, it is shown that the development of a hysteresis memory is reflected in the possibility of long-time tails in the autocorrelation functions, even for uncorrelated driving fields. In the case of uncorrelated driving, these long-time tails in the autocorrelations of the system’s response are determined only by the tails of the involved densities. They will be observed if there are broad Preisach densities assigning a high weight to elementary loops of large width and narrow input densities such that rare extreme events of the input time series contribute significantly to the output for a long period of time. Afterwards, these results are extended by simulations to driving fields which themselves show correlations. It is shown that the autocorrelation of the output does not decay faster than the autocorrelation of the input process. Further, there is a possibility that long-term memory in the hysteretic response is more pronounced in the case of uncorrelated driving than in the case of correlated driving. The behavior of the output probability distribution at the saturation values is quite universal. It is not affected by the presence of correlations and allows conclusions whether the input density is much more narrow than the Preisach density or not. Moreover, the existence of effective Preisach densities is shown which define equivalence classes of systems of input and Preisach densities which lead to realizations of the same output variable. The asymptotic behavior of an effective Preisach density determines the asymptotic correlation decay of the system’s response in the case of uncorrelated driving. In the second part, temperature-related effects are considered. It is reviewed how the non-equilibrium Preisach model in its micromagnetic picture can be related to temperature within the framework of extended irreversible thermodynamics. The irreversible response of a ferromagnetic material, namely, Nickel nanoparticles in a fullerene matrix, is simulated. The model includes superparamagnetism where ferromagnetism breaks down at temperatures lower than the Curie temperature and the results are compared to experimental data. Furthermore, we adapt known results for the thermal relaxation of the system’s memory in the form of a front propagation in the Preisach plane derived basically from solving a master equation and by the use of a contradictory assumption. A closer look is taken at short time scales which dissolves the contradiction and shows that the known results apply, taking into account the fact that the dividing line propagation starts with an additional delay time depending on the front coordinates in the Preisach plane. Additionally, it is outlined how thermal relaxation behavior in the Preisach model of hysteresis can be studied using a Fokker-Planck equation. The latter is solved analytically in the non-hysteretic limit using eigenfunction methods. The results indicate a change in the relaxation behavior, especially on short time scales.

Im Rahmen der vorliegenden Dissertationsschrift „Semi-quantitative röntgentomographische Untersuchungen zur Biodistribution von magnetischen Nanopartikeln in biologischem Gewebe“ wurden tomographische Untersuchungen an biologischen Objekten durchgeführt. Bei diesen Objekten handelt es sich um Gewebeproben nach minimal-invasiven Krebstherapien wie zum Beispiel magnetischem Drug Targeting und magnetischer Wärmebehandlung. Der Erfolg dieser Therapien ist sowohl abhängig von der korrekten Verteilung der magnetischen Nanopartikel als auch von der Tatsache, dass diese in der Zielregion in einer ausreichenden Menge vorhanden sind. Das Vorliegen dieser beiden Voraussetzungen ist in der vorliegenden Arbeit untersucht worden. Dabei lag der Schwerpunkt der Arbeit auf der Quantifizierung von magnetischem Material in unterschiedlichen biologischen Gewebeproben mittels Röntgenmikrocomputertomographie (XµCT). Für diesen Zweck wurde ein Kalibrationssystem mit speziellen Phantomen entwickelt, mit dessen Hilfe eine Nanopartikelkonzentration einem Grauwert voxelweise zugewiesen werden kann. Mit Hilfe der Kalibration kann der Nanopartikelgehalt sowohl in monochromatischen als auch in polychromatischen tomographischen Daten im Vergleich zu magnetorelaxometrischen Ergebnissen mit wenigen Prozent Abweichung ermittelt werden. Trotz Polychromasie und damit einhergehenden Artefakten können 3-dimensionale röntgentomographische Datensätze mit einer geringfügigen Konzentrationsabweichung im Vergleich zur quantitativen Messmethode Magnetorelaxometrie semi-quantitativ ausgewertet werden. / The success of the minimal invasive cancer therapies, called magnetic drug targeting and magnetic heating treatment, depends strongly on the correct distribution of the magnetic nanoparticles on one side. On the other side it depends on the fact that a sufficient amount of magnetic nanoparticles carrying drugs is accumulated in the target region. To study whether these two requirements are fulfilled motivates this PhD thesis „Semi-quantitative X-ray-tomography examinations of biodistribution of magnetic nanoparticles in biological tissues“. The analysis of the distribution of the magnetic nanoparticles in tumours and other tissue examples is realized by means of X-ray-micro computer tomography (XμCT). The work focuses on the quantification of the magnetic nanoparticles in different biological tissue samples by means of XµCT. A calibration of the tomographic devices with adequate phantoms, developed in the frame of this work, opens now the possibility to analyze tomographic data in a semi-quantitative manner. Thus, the nanoparticle concentration can be allocated voxel-wise to the grey values of the three-dimensional tomographic data. With the help of calibration of the tomography equipments used, polychromatic as well as monochromatic three-dimensional representations of objects can be analyzed with regard to the biodistribution of magnetic nanoparticles as well as with regard to their quantity. The semi-quantitative results have been compared with results obtained with a quantitative measurement method magnetorelaxometry (MRX). Thereby a good agreement of the semi-quantitative and quantitative data has been figured out.

Im Rahmen der vorliegenden Dissertationsschrift „Semi-quantitative röntgentomographische Untersuchungen zur Biodistribution von magnetischen Nanopartikeln in biologischem Gewebe“ wurden tomographische Untersuchungen an biologischen Objekten durchgeführt. Bei diesen Objekten handelt es sich um Gewebeproben nach minimal-invasiven Krebstherapien wie zum Beispiel magnetischem Drug Targeting und magnetischer Wärmebehandlung. Der Erfolg dieser Therapien ist sowohl abhängig von der korrekten Verteilung der magnetischen Nanopartikel als auch von der Tatsache, dass diese in der Zielregion in einer ausreichenden Menge vorhanden sind. Das Vorliegen dieser beiden Voraussetzungen ist in der vorliegenden Arbeit untersucht worden. Dabei lag der Schwerpunkt der Arbeit auf der Quantifizierung von magnetischem Material in unterschiedlichen biologischen Gewebeproben mittels Röntgenmikrocomputertomographie (XµCT). Für diesen Zweck wurde ein Kalibrationssystem mit speziellen Phantomen entwickelt, mit dessen Hilfe eine Nanopartikelkonzentration einem Grauwert voxelweise zugewiesen werden kann. Mit Hilfe der Kalibration kann der Nanopartikelgehalt sowohl in monochromatischen als auch in polychromatischen tomographischen Daten im Vergleich zu magnetorelaxometrischen Ergebnissen mit wenigen Prozent Abweichung ermittelt werden. Trotz Polychromasie und damit einhergehenden Artefakten können 3-dimensionale röntgentomographische Datensätze mit einer geringfügigen Konzentrationsabweichung im Vergleich zur quantitativen Messmethode Magnetorelaxometrie semi-quantitativ ausgewertet werden. / The success of the minimal invasive cancer therapies, called magnetic drug targeting and magnetic heating treatment, depends strongly on the correct distribution of the magnetic nanoparticles on one side. On the other side it depends on the fact that a sufficient amount of magnetic nanoparticles carrying drugs is accumulated in the target region. To study whether these two requirements are fulfilled motivates this PhD thesis „Semi-quantitative X-ray-tomography examinations of biodistribution of magnetic nanoparticles in biological tissues“. The analysis of the distribution of the magnetic nanoparticles in tumours and other tissue examples is realized by means of X-ray-micro computer tomography (XμCT). The work focuses on the quantification of the magnetic nanoparticles in different biological tissue samples by means of XµCT. A calibration of the tomographic devices with adequate phantoms, developed in the frame of this work, opens now the possibility to analyze tomographic data in a semi-quantitative manner. Thus, the nanoparticle concentration can be allocated voxel-wise to the grey values of the three-dimensional tomographic data. With the help of calibration of the tomography equipments used, polychromatic as well as monochromatic three-dimensional representations of objects can be analyzed with regard to the biodistribution of magnetic nanoparticles as well as with regard to their quantity. The semi-quantitative results have been compared with results obtained with a quantitative measurement method magnetorelaxometry (MRX). Thereby a good agreement of the semi-quantitative and quantitative data has been figured out.