TY  - THES
A1  - Faivre, Damien
T1  - Biological and biomimetic formation and organization of magnetic nanoparticles
T1  - Biologische und biomimetische Bildung und Anordnung von magnetischen Nanopartikel
N2  - Biological materials have ever been used by humans because of their remarkable properties. This is surprising since the materials are formed under physiological conditions and with commonplace constituents. Nature thus not only provides us with inspiration for designing new materials but also teaches us how to use soft molecules to tune interparticle and external forces to structure and assemble simple building blocks into functional entities. Magnetotactic bacteria and their chain of magnetosomes represent a striking example of such an accomplishment where a very simple living organism controls the properties of inorganics via organics at the nanometer-scale to form a single magnetic dipole that orients the cell in the Earth magnetic field lines. My group has developed a biological and a bio-inspired research based on these bacteria. My research, at the interface between chemistry, materials science, physics, and biology focuses on how biological systems synthesize, organize and use minerals. We apply the design principles to sustainably form hierarchical materials with controlled properties that can be used e.g. as magnetically directed nanodevices towards applications in sensing, actuating, and transport. In this thesis, I thus first present how magnetotactic bacteria intracellularly form magnetosomes and assemble them in chains. I developed an assay, where cells can be switched from magnetic to non-magnetic states. This enabled to study the dynamics of magnetosome and magnetosome chain formation. We found that the magnetosomes nucleate within minutes whereas chains assembles within hours. Magnetosome formation necessitates iron uptake as ferrous or ferric ions. The transport of the ions within the cell leads to the formation of a ferritin-like intermediate, which subsequently is transported and transformed within the magnetosome organelle in a ferrihydrite-like precursor. Finally, magnetite crystals nucleate and grow toward their mature dimension. In addition, I show that the magnetosome assembly displays hierarchically ordered nano- and microstructures over several levels, enabling the coordinated alignment and motility of entire populations of cells. The magnetosomes are indeed composed of structurally pure magnetite. The organelles are partly composed of proteins, which role is crucial for the properties of the magnetosomes. As an example, we showed how the protein MmsF is involved in the control of magnetosome size and morphology. We have further shown by 2D X-ray diffraction that the magnetosome particles are aligned along the same direction in the magnetosome chain. We then show how magnetic properties of the nascent magnetosome influence the alignment of the particles, and how the proteins MamJ and MamK coordinate this assembly. We propose a theoretical approach, which suggests that biological forces are more important than physical ones for the chain formation. All these studies thus show how magnetosome formation and organization are under strict biological control, which is associated with unprecedented material properties. Finally, we show that the magnetosome chain enables the cells to find their preferred oxygen conditions if the magnetic field is present. The synthetic part of this work shows how the understanding of the design principles of magnetosome formation enabled me to perform biomimetic synthesis of magnetite particles within the highly desired size range of 25 to 100 nm. Nucleation and growth of such particles are based on aggregation of iron colloids termed primary particles as imaged by cryo-high resolution TEM. I show how additives influence magnetite formation and properties. In particular, MamP, a so-called magnetochrome proteins involved in the magnetosome formation in vivo, enables the in vitro formation of magnetite nanoparticles exclusively from ferrous iron by controlling the redox state of the process. Negatively charged additives, such as MamJ, retard magnetite nucleation in vitro, probably by interacting with the iron ions. Other additives such as e.g. polyarginine can be used to control the colloidal stability of stable-single domain sized nanoparticles. Finally, I show how we can “glue” magnetic nanoparticles to form propellers that can be actuated and swim with the help of external magnetic fields. We propose a simple theory to explain the observed movement. We can use the theoretical framework to design experimental conditions to sort out the propellers depending on their size and effectively confirm this prediction experimentally. Thereby, we could image propellers with size down to 290 nm in their longer dimension, much smaller than what perform so far.
N2  - Biologische Materialien wie Knochen, Muscheln und Holz wurden von den Menschen seit den ältesten Zeiten verwendet. Diese biologisch gebildeten Materialien haben bemerkenswerte Eigenschaften. Dies ist besonders überraschend, da sie unter physiologischen Bedingungen und mit alltäglichen Bestandteilen gebildet sind. Die Natur liefert uns also nicht nur mit Inspiration für die Entwicklung neuer Materialien, sondern lehrt uns auch, wie biologische Additiven benutzen werden können, um einfache synthetische Bausteine in funktionale Einheiten zu strukturieren. Magnetotaktischen Bakterien und ihre Kette von Magnetosomen sind ein Beispiel, wo einfache Lebewesen die Eigenschaften von anorganischen Materialien steuern, um sich entlang den magnetischen Feldlinien der Erde zu orientieren. Die von den Bakterien gebildeten Magnetosomen sind von besonderem Interesse, da mit magnetischen Eisenoxid-Nanopartikeln in den letzten zehn Jahren einer Vielzahl von Bio-und nanotechnologischen Anwendungen entwickelt worden sind. In dieser Arbeit stelle ich eine biologische und eine bio-inspirierte Forschung auf der Grundlage der magnetotaktischen Bakterien vor. Diese Forschung verbindet die neuesten Entwicklungen von Nanotechnik in der chemischen Wissenschaft, die neuesten Fortschritte der Molekularbiologie zusammen mit modernen Messverfahren. Mein Forschungsschwerpunkt liegt somit an der Schnittstelle zwischen Chemie, Materialwissenschaften, Physik und Biologie. Ich will verstehen, wie biologische Systeme Materialien synthetisieren und organisieren, um Design-Prinzipien zu extrahieren, damit hierarchischen Materialien mit kontrollierten Eigenschaften nachhaltig gebildet werden.
KW  - magnetotaktische Bakterien
KW  - Magnetit Nanopartikel
KW  - Biomineralisation
KW  - magnetite
KW  - nanoparticle
KW  - biomineralization
KW  - magnetosome
KW  - magnetotactic bacteria
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-72022
ER  - 
TY  - THES
A1  - Giordano, Cristina
T1  - A neglected world: transition metal nitride and metal carbide based nanostructures
T1  - Eine vernachlässigte Welt: Übergangsmetallnitrid- und Metallcarbid-basierte Nanostrukturen
BT  - novel synthesis and future perspectives
BT  - neuartige Synthese und Zukunftsperspektiven
N2  - Potentiality of nanosized materials has been largely proved but a closer look shows that a significant percentage of this research is related to oxides and metals, while the number drastically drops for metallic ceramics, namely transition metal nitrides and metal carbides. The lack of related publications do not reflect their potential but rather the difficulties related to their synthesis as dense and defect-free structures, fundamental prerequisites for advanced mechanical applications. 
The present habilitation work aims to close the gap between preparation and processing, indicating novel synthetic pathways for a simpler and sustainable synthesis of transition metal nitride (MN) and carbide (MC) based nanostructures and easier processing thereafter. In spite of simplicity and reliability, the designed synthetic processes allow the production of functional materials, with the demanded size and morphology. 
The goal was achieved exploiting classical and less-classical precursors, ranging from common metal salts and molecules (e.g. urea, gelatin, agar, etc), to more exotic materials, such as leafs, filter paper and even wood. It was found that the choice of precursors and reaction conditions makes it possible to control chemical composition (going for instance from metal oxides to metal oxy-nitrides to metal nitrides, or from metal nitrides to metal carbides, up to quaternary systems), size (from 5 to 50 nm) and morphology (going from mere spherical nanoparticles to rod-like shapes, fibers, layers, meso-porous and hierarchical structures, etc). The nature of the mixed precursors also allows the preparation of metal nitrides/carbides based nanocomposites, thus leading to multifunctional materials (e.g. MN/MC@C, MN/MC@PILs, etc) but also allowing dispersion in liquid media. Control over composition, size and morphology is obtained with simple adjustment of the main route, but also coupling it with processes such as electrospin, aerosol spray, bio-templating, etc. Last but not least, the nature of the precursor materials also allows easy processing, including printing, coating, casting, film and thin layers preparation, etc). 
The designed routes are, concept-wise, similar and they all start by building up a secondary metal ion-N/C precursor network, which converts, upon heat treatment, into an intermediate “glass”. This glass stabilizes the nascent nanoparticles during their nucleation and impairs their uncontrolled growth during the heat treatment (scheme 1). This way, one of the main problems related to the synthesis of MN/MC, i.e. the need of very high temperature, could also be overcome (from up to 2000°C, for classical synthesis, down to 700°C in the present cases). The designed synthetic pathways are also conceived to allow usage of non-toxic compounds and to minimize (or even avoid) post-synthesis purification, still bringing to phase pure and well-defined (crystalline) nanoparticles.
This research aids to simplify the preparation of MN/MC, making these systems now readily available in suitable amounts both for fundamental and applied science. The prepared systems have been tested (in some cases for the first time) in many different fields, e.g. battery (MnN0.43@C shown a capacity stabilized at a value of 230 mAh/g, with coulombic efficiencies close to 100%), as alternative magnetic materials (Fe3C nanoparticles were prepared with different size and therefore different magnetic behavior, superparamagnetic or ferromagnetic, showing a saturation magnetization value up to 130 emu/g, i.e. similar to the value expected for the bulk material), as filters and for the degradation of organic dyes (outmatching the performance of carbon), as catalysts (both as active phase but also as active support, leading to high turnover rate and, more interesting, to tunable selectivity). Furthermore, with this route, it was possible to prepare for the first time, to the best of our knowledge, well-defined and crystalline MnN0.43, Fe3C and Zn1.7GeN1.8O nanoparticles via bottom-up approaches. 
Once the synthesis of these materials can be made straightforward, any further modification, combination, manipulation, is in principle possible and new systems can be purposely conceived (e.g. hybrids, nanocomposites, ferrofluids, etc).
N2  - Materialien sind wichtige Hilfsmittel, die wir täglich benutzen, um unser Leben einfacher zu machen. Materialien werden durch ihre Eigenschaften charakterisiert. Manche sind stark, manche sind elektrisch, manche magnetisch, usw. Wenn ein Stoff auf die Dimension eines Virus verkleinert wird, zeigen sich besondere Veränderungen. War das Material groß z.B. elektrisch, hat es klein diese Eigenschaft nicht mehr. Groß war es glanzlos, aber klein ist es transparent... Das heißt, dass jedes bekannte Material prinzipiell ein neues Material werden kann, nur durch die Veränderung seiner Größe. Wegen dieser besonderen Entdeckung, ist seit vielen Jahren ein Großteil der Forschung Nanopartikeln gewidmet. Dennoch werden in diesem Gebiet meistens besondere Materialien untersucht, weil ihre Anwendungsfelder weithin bekannt und wichtig sind. Meine Forschung basiert auf der Untersuchung neuer oder weniger bekannter Materialien, nämlich Übergangsmetallnitride und Übergangsmetallcarbide als Nanostrukturen. Sie sind nicht so bekannt, weil sie nicht so einfach herzustellen waren (die klassische Synthese braucht eine hohe Temperatur bis 2000°C, und oft toxische Reaktionsmittel). Trotzdem sind sie sehr interessante Materialien, weil sie auf der Grenze zwischen reinen Metallen und reinen keramischen Materialien hinsichtlich der Eigenschaften liegen. Das heißt, sie sind z.B. sehr fest, aber auch leitend, sie haben einen hohen Schmelzpunkt und sind magnetisch, etc. Durch die hier vorgestellte Forschung wird die Synthese dieser Materialien einfacher gemacht, bei niedrigen Temperaturen, mit natürlichen Produkten (z.B. Harnstoff, Gelatine, Agar, Zellulose, etc). Die Eigenschaften und Anwendungsmöglichkeiten dieser Systeme wurden auch studiert, ebenso wie die Kontrolle der Größe und Form. So konnten wir sphärische, rohrförmige, und fiber-basierte Nanostrukturen synthetisieren, aber sogar Blätter und Holz konnten als Reaktionsmittel benutzt werden und in Nitrid und Carbid umgewandelt werden, ohne die Form zu ändern. Weil die Synthese dieser Materialien direkt gemacht werden konnte, ist prinzipiell jede weitere Modifikation, Kombination und Manipulation möglich. So können jetzt neue Systeme entworfen werden.
KW  - metal carbides
KW  - metal nitrides
KW  - nanostructures
KW  - sol-gel
KW  - Metallnitride
KW  - Metallcarbide
KW  - Nanostrukturen
KW  - Sol-Gel
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-75375
ER  -