Thèses : « Magnetic molecule »

1

Beyene, Musie. « Magnetic field control of ultracold atom-molecule collision ». Thesis, Durham University, 2011. http://etheses.dur.ac.uk/3196/.

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In this work we investigate the potential of controlling cold (O(K)−mK) and ultracold (mK-μK) atom-molecule collisions by tuning scattering states across Feshbach resonances using magnetic fields. We are interested in particular in the prospect of suppressing the often undesirable inelastic collisions. The He-O_2 system provides the vehicle for our study. We calculate bound and quasi-bound states of several isotopic combinations, including their Zeeman structure, to reveal the underlaying pattern for easier characterization of quasi-bound states in terms of rigorous and approximately good quantum numbers. These calculations also help us locate the fields at which zero-energy resonances will occur. Scattering calculations are then performed for collisions of 3^He and 4^He with {16}^O_2 at fixed (1 μK) energy but varying magnetic field. The field is varied to sweep the scattering state across resonance. At low and ultralow energies we enter the Wigner threshold regime where the S-partial wave dominates the wavefunction. The cross sections, and the real and imaginary parts of the scattering length, vary dramatically across resonance. Their profiles are used to analyze the resonances. In a highlight of our results we show that dramatic suppression of inelastic cross sections occur for 4^He-{16}^O_2 . The resonances are relatively wide (of order 100 Gauss), with suppression of inelastic scattering over a similarly wide range of fields and for temperatures ranging from 10 mK down to 1 μK. We conclude that under certain conditions it is possible to almost completely eliminate inelastic collisions. This is potentially very important for cooling techniques, such as evaporative and sympathetic cooling, that require efficient elastic cross sections. Suppression of inelastic collisions can not only increase thermalization efficiency but it can also result in longer trap-lifetimes by reducing transitions to untrapable states.

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Pedersen, Anders Hjordt. « Molecule-based magnetic materials of the ReIV ion ». Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28885.

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The [ReCl6]2-, [ReBr6]2- and [ReCl4(ox)]2- anions are crystallised with the organic 4,4’- bipyridinium dication (4,4-H2bipy). Magnetometry reveals exotic behaviour of the [4,4’- H2bipy][ReCl6] and [4,4’-H2bipy][ReBr6] salts which demonstrate spin-canting, antiferromagnetic exchange interactions and metamagnetism. Single crystal X-ray structures at T = 3, 14 and 20 K of the [4,4’-H2bipy][ReBr6] salt reveal the behaviour to be purely of magnetic origin as no structural changes are observed. For the [4,4’-H2bipy][ReCl4(ox)] compound an antiferromagnetic exchange interaction of 10.2 cm-1 between the anions is observed (Chapter 2). The complexes (NBu4)2[(ReCl5)2(μ-pyrazine)], (NBu4)2[(ReBr5)2(μ-pyrazine)], (NBu4)2[(ReBr5)2(μ-pyrimidine)] and (NBu4)2[(ReBr5)2(μ-triazine)] are structurally and magnetically characterised in Chapter 3. Magnetic measurements reveal the ReIV ions bridged by a 1,4-heterocyclic amine to exhibit strong antiferromagnetic coupling induced by the linearity of the bridging ligand. The two dimers bridged by a 1,3-heterocyclic amine exhibit intramolecular ferromagnetic exchange and at low temperature an intermolecular antiferromagnetic coupling is observed for the (NBu4)2[(ReBr5)2(μ-triazine)] complex due to the presence of short intermolecular Br···Br distances. Six molecular ReIVCuII chains of formula {[Cu(L)4][ReCl6]}n (L = imidazole, 1- methylimidazole, 1-vinylimidazole, 1-butylimidazole, 1-vinyl-1,2,4-triazole or dimethylformamide) are characterised structurally and magnetically in Chapter 4. SQUID magnetometry and theoretical calculations reveal the chains to exhibit ferromagnetic exchange interactions, which increase as the Re–Cl–Cu bond angle decreases. The {[Cu(vinylimidazole)4][ReCl6]}n chain exhibit magnetic order at TC = 2.4 K, and the {[Cu(imidazole)4][ReCl6]}n network exhibits ferrimagnetic behaviour. Eight complexes of the [ReCl6]2- and [ReBr6]2- anions crystallised with the [MII(L•)2]2+ (M = Fe, Co or Cu) or [Ni(L•)(CH3CN)3]2+ cations (L• = 4-dimethyl-2,2-di(2-pyridyl)oxazolidine N-oxide) are characterised structurally and magnetically in Chapter 5. The [Co(L•)2]2+ cation shows evidence of a gradual, thermally induced spin-crossover transition in variable-temperature magnetic and structural experiments. The [Ni(L•)(CH3CN)3]2+ cation show exchange of the coordinated acetonitrile molecules for atmospheric water upon drying. The nickel-radical magnetic coupling is ferromagnetic in all cases, demonstrating spin-canting behaviour with an ordering temperature of T = 2.7 K for the [ReCl6]2- based compound, and intermolecular antiferromagnetic exchange interactions for the [ReBr6]2- based complex.

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3

Romero, Javier. « Electronic transport and correlations in single magnetic molecule devices ». Doctoral diss., University of Central Florida, 2014. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6348.

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In this dissertation, we study the most important microscopic aspects that grant molecules such as Single Molecule Magnets (SMMs) their preferential spin direction. We do so by proposing and solving a model that includes correlations between electrons occupying atomic orbitals. In addition, we study the relation between the non-equilibrium electronic transport signatures in a SMM model weakly coupled to a three-terminal single electron transistor device, and the interference features of the SMM model in the presence of a magnetic field. Finally, we investigate the equilibrium transport features in a giant-spin model of a SMM in the Kondo regime. We study how the magnetic field modulation of the energy in a highly anisotropic molecule can affect the conductance of the molecule in the Kondo regime.
Ph.D.
Doctorate
Physics
Sciences
Physics

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4

Luo, Guangpu. « Electron Transport via Single Molecule Magnets with Magnetic Anisotropy ». Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/87532.

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Single molecule magnets (SMMs) are molecules of mesoscopic scale which exhibit quantum properties such as quantum tunneling of magnetization, quantum interference, spin filtering effects, strong spin-phonon coupling and strong hyperfine Stark effects. These effects allow applications of SMMs to high-density information storage, molecular spintronics, and quantum information science. Therefore, SMMs are of interest to physicists, chemists, and engineers. Recently, experimental fabrication of individual SMMs within transistor set-ups have been achieved, offering a new method to examine magnetic properties of individual SMMs. In this thesis, two types of SMMs, specifically Eu2(C8H8)3 and Ni9Te6(PEt3)8, are theoretically investigated by simulating their electron transport properties within three-terminal transistor set-ups. An extended metal atom chain (EMAC) consists of a string of metallic atoms with organic ligands surrounding the string. EMACs are an important research field for nanoelectronics. Homometallic iron-based EMACs are especially attractive due to the high spin and large magnetic anisotropy of iron(II). We explore the exchange coupling of iron atoms in two EMACs: [Fe2(mes)2(dpa)2] and [Fe4(tpda)3Cl2]. Chapter 1 provides an introduction to SMMs, electron transport experiments via SMMs and an introduction to density functional theory (DFT). Chapter 2 presents a theoretical study of electron transport via Eu2(C8H8)3. This type of molecule is interesting since its magnetic anisotropy type changes with oxidation state. The unique magnetic properties lead to spin blockade effects at zero and low bias. In other words, the current through this molecule is completely suppressed until the bias voltage exceeds a certain value. Chapter 3 discusses a theoretical study of electron transport via Ni9Te6(PEt3)8. The magnetic anisotropy of this magnetic cluster has cubic symmetry, which is higher than most SMMs. With appropriate magnetic anisotropy parameters, in the presence of an external magnetic field, uncommon phenomena such as low-bias blockade effects, negative conductance and discontinuous conductance lines, are observed. In Chapter 2 and 3 DFT-calculated magnetic anisotropy parameters are used and electron transport properties are calculated by solving master equations at low temperature. Chapter 4 examines the exchange coupling between iron ions in EMACs [Fe2(mes)2(dpa)2] and [Fe4(tpda)3Cl2]. The exchange coupling constants are calculated by using the least-squares fitting method, based on the DFT-calculated energies from different spin configurations.
Ph. D.
Single molecule magnets (SMMs) are molecules of mesoscopic scale which exhibit quantum properties. Its quantum effects are used to describe the behavior of SMMs at the smallest scales. These quantum properties could also be used to reveal possible applications of SMMs to high-density information storage, molecular spintronics, and quantum information science. Thus SMMs are of interest to physicists, chemists, and engineers. Recently, electron transport via individual SMMs was achieved in experiments. Electron transport is obviously affected by the magnetic properties of the SMM, thus one can examine magnetic properties of an SMM indirectly by measuring electron transport via the SMM. In this thesis, two types of SMMs, Eu2(C8H8)3 and Ni9Te6(PEt3)8, are investigated theoretically by simulating their electron transport properties. An extended metal atom chain (EMAC) consists of a string of metallic atoms with organic ligands surrounding the string. EMACs are an important research field for nanoelectronics. Homometallic iron-based EMACs are especially attractive due to the high spin and large magnetic anisotropy of iron(II). If a molecule has magnetic anisotropy, its magnetic properties change with the direction of its magnetic moment. We explore how iron atoms interact with each other in the EMACs [Fe2(mes)2(dpa)2] and [Fe4(tpda)3Cl2]. Chapter 1 provides an introduction to SMMs, electron transport experiments via SMMs and an approximation method, density functional theory (DFT). DFT is a method to approximate electronic structure and magnetic properties of various many-body systems. Chapter 2 investigates theoretical electron transport via Eu2(C8H8)3. Eu2(C8H8)3 changes its type of magnetic anisotropy when it obtains an extra electron, which is different from most SMMs. If the Eu2(C8H8)3 is short of an extra electron, its magnetization direction is in-plane, that is, its magnetic energy is lowest when its magnetic moment is along any direction in a specific plane. If an extra electron is captured by Eu2(C8H8)3, its magnetization direction becomes out-of-plane, and its lowest energy is obtained when its magnetic moment is along the direction normal to the specific plane. The unique magnetic properties lead to blockade effects at low bias: the current through this molecule is completely suppressed until the bias voltage exceeds a certain value. The bias voltage on a molecule equals the electrical potential difference between two ends of the molecule. Chapter 3 investigates theoretical electron transport via Ni9Te6(PEt3)8. Magnetic anisotropy of Ni9Te6(PEt3)8 is cubic symmetric, and its symmetry is higher than most SMMs. With appropriate magnetic anisotropy parameters, in the presence of an external magnetic field, uncommon phenomena are observed. These phenomena include (1) current is completely suppressed when bias is low; (2) current via SMM decreases while bias on SMM increases; (3) there are discontinuous lines in the figures that describe electrical conductance of current. Chapter 4 examines the iron atoms’ interaction strength in both [Fe2(mes)2(dpa)2] and [Fe4(tpda)3Cl2]. Reasonable spin Hamiltonians are used to describe the energy of EMACs. Considering all possible directions of the spins of iron atoms in two EMACs, we calculate the energy of every possible spin configuration using DFT. The energy of each spin configuration can be expressed as an equation containing one or more coupling constants. We apply the least-squares fitting method to obtain the values of the coupling constants in the spin Hamiltonians.

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5

Pejaković, Dusan. « Optical control of magnetic order in molecule-based magnets ». The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343232538.

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6

Pejakovi?, Dušan. « Optical control of magnetic order in molecule-based magnets / ». The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486572165278271.

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7

Li, Jia Hui [Verfasser]. « Magnetic manipulation of membrane molecule motion / Jia Hui Li ». Berlin : Freie Universität Berlin, 2021. http://d-nb.info/1238074707/34.

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8

Bairagi, Kaushik. « Magnetic anisotropy and spin crossover at molecule-metal interfaces ». Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCC241/document.

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L'utilisation de matériaux organiques pour l'électronique de spin suscite actuellement un fort intérêt. En effet, le long temps de diffusion de spin, la possibilité de manipuler l'état de spin d'une molécule ainsi que son interaction avec une surface magnétique offrent a priori de nouvelles possibilités pour la réalisation de nouveaux dispositifs d'électronique de spin. L'incorporation dans des dispositifs de molécules possédant deux états de spin nécessite la compréhension du phénomène de transition de spin une fois que les molécules sont en contact direct avec des surfaces métalliques.L'objectif de ce travail de thèse est l'étude des interfaces molécule-métal. Dans une première partie, nous avons étudié le magnétisme d'interfaces ferromagnétique-organique en utilisant différentes molécules et différents métaux ferromagnétiques. Nous nous sommes particulièrement intéresses a l'anisotropie magnétique dans ces systèmes. Dans une deuxième partie, nous avons étudié le phénomène de transition de spin moléculaire en contact avec une surface métallique. La spectroscopie d'absorption et le dichroïsme magnétique des rayons x ont d'abord permis de mettre en évidence cette transition à l'échelle globale ensuite, nous avons utilise la microscopie a effet tunnel pour étudier ce phénomène à l'échelle moléculaire dans un cristal 2d de molécule. Nous avons notamment observe la dynamique de la transition sous irradiation laser pour la première fois à l'échelle moléculaire
The use of organic materials in spintronic devices has recently raised a lot of interest. Large spin diffusion time in organic materials along with the flexibility of manipulating the spin state of the molecule and their interaction with the ferromagnetic metal electrode offers new functionalities in molecular spintronics. Understanding the spin crossover (sco) phenomenon for spin active molecules attached to metallic substrate is also necessary for a primary step towards device application.The main goal of the thesis work was to study these molecule—metal interfaces. In one part, we have studied the magnetism of the organic—ferromagnetic interface with different molecules and different ferromagnetic metals. The study was mainly focused on the magnetic anisotropy at the molecule-metal interfaces. In other part, we focused on the spin crossover phenomena of sco molecules attached to metallic substrates. X—ray absorption spectroscopy and magnetic circular dichroism techniques enabled us to study globally the spin crossover phenomenon. Using scanning tunneling microscopy we were able to study the sco phenomena at the single molecular level in a 2d crystal of molecules on a metal substrate. We have then studied locally the dynamics of the spin transition phenomenon upon laser exposure on a single 2d layer molecular crystal

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9

Li, Lihong. « The design and synthesis of new molecule-based magnetic materials ». Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/45411/.

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Chapter One gives an overview of molecule-based magnetic materials, and a summary of topics of current interest in this field such as spin crossover (SCO), molecule-based magnets (particularly three room temperature metallo-organic magnets), Metallo-organic frameworks (MOFs), free radical magnets and single molecule magnets (SMMs). There is a brief introduction of key examples and developments in the specific topics, and a perspective at the end. Chapter Two introduces a family of optically pure Fe(II) polymeric chain complexes of formula {FeL2(μ-pz)}∞ and {FeL2(μ-bpy)}∞. [L = bidentate Schiff base ligands obtained from (R)-(+)-α-phenylethanamine and 4-substituted salicylaldehydes]. The structural and magnetic properties of the polymeric products are determined by single crystal X-ray diffraction and SQUID magnetometry. By fitting magnetic data of these complexes with the Bonner- Fisher 1-D chain model, the magnitudes of their magnetic exchanges are rationalised on the basis of substituent electronic properties and bridging ligand identity. Chapter Three describes two Fe(II) coordination polymers containing pyridineconjugated Schiff base isomer ligands. The isomerism of the two ligands leads to a change from trans to cis coordination in the [FeL2] SBU and thus from a tetrahedral diamond-like 3 D network exhibiting a gradual SCO to a 2 D hard magnet. Furthermore, we have also sythesised another four Cu(II) complexes based on these two ligands. Crystallographic studies reveal their structures ranging from 1 D zigzag chains and 2 D mat while their magnetic properties are transformed from ferro- to ferrimagnetic behavior. Chapter Four focuses on three pyrrole-2-ketone bidentate ligands. Three transition metal ions Mn2+, Fe2+ and Co2+ were studied, based on which twelve complexes have been made. The system is structurally diverse, with 1 D, 2 D, monometallic, trimetallic “sandwich” structures and a high nuclearity cluster being observed depending on the use of cations and solvents. Unusual magnetic phenomena are discovered, including a system in which SCO and ferromagnetic coupling are present. Chapter Five details the experimental procedures used to carry out the work in this thesis.

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10

Guo, Qing. « Single Molecule Optical Magnetic Tweezers Microscopy Studies of Protein Dynamics ». Bowling Green State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1435334948.

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11

Haque, Md Firoze. « CONTROLLED DEPOSITION OF MAGNETIC MOLECULES AND NANOPARTICLES ON ATOMICALLY FLAT GOLD SURFACES ». Master's thesis, University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2109.

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In this thesis I am presenting a detailed study to optimize the deposition of magnetic molecules and gold nanoparticles in atomically flat surfaces by self-assembling them from solution. Epitaxially grown and atomically flat gold surface on mica is used as substrate for this study. These surfaces have roughness of the order one tenth of a nanometer and are perfect to image molecules and nanoparticles in the 1-10 nanometers range. The purpose of these studies is to find the suitable parameters and conditions necessary to deposit a monolayer of nano-substance on chips containing gold nanowires which will eventually be used to form single electron transistors by electromigration breaking of the nanowire. Maximization of the covered surface area is crucial to optimize the yield of finding a molecule/nanoparticle near the gap formed in the nanowire after electromigration breaking. Coverage of the surface by molecules/nanoparticles mainly depends on the deposition time and concentration of the solution used for the self-assembly. Deposition of the samples under study was done for different solution concentrations and deposition times until a self-assembly monolayer covering most of the surface area is obtained. Imaging of the surfaces after deposition was done by tapping-mode AFM. Analysis of the AFM images was performed and deposition parameters (i.e. coverage or molecule/particle size distribution) were obtained. The subjects of this investigation were a molecular polyoxometalate, a single-molecule magnet and functionalized gold nanoparticles. The obtained results agree with the structure of each of the studied systems. Using the optimized deposition parameters found in this investigation, single-electron transport measurements have been carried out. Preliminary results indicate the right choice of the deposition parameters.
M.S.
Department of Physics
Sciences
Physics MS

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Schelter, Eric John. « Cyanide clusters of ReII with 3d metal ions and their magnetic properties : incorporating anisotropic ions into metal-cyanide clusters with high spin magnetic ground states ». Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/2205.

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Clusters of metal ions that possess large numbers of magnetically coupled unpaired electrons have attracted much interest in recent years due to their fascinating magnetic behavior. With an appreciable component of magnetic anisotropy, these large-spin paramagnetic molecules can exhibit an energy barrier to inversion of their magnetic dipole, leading to spontaneous magnetization and magnetic hysteresis below a critical temperature. Since this behavior is a property of an individual clusters rather than a collection of molecules, this phenomenon has been dubbed ??Single Molecule Magnetism??. Our approach to the study of new high-spin systems has been to exert a measure of synthetic control in the preparation of clusters. Specifically we are employing highly anisotropic metal ions with the anticipation that these ions would engender large overall magnetic anisotropy in the resulting clusters. The first step in this process was the development of the chemistry of two new d5 ReII (S = ??) complexes, namely [ReII(triphos)(CH3CN)3][PF6]2 and [Et4N][ReII(triphos)(CN)3]. The magnetic, optical and electrochemical properties were studied and theoretical models were developed to describe the origin of the large temperature independent paramagnetism that was observed. Next, we successfully employed transition metal cyanide chemistry using the ReII building blocks to prepare a family of isostructural, cubic clusters of the general formula {[MCl]4[Re(triphos)(CN)3]4} M = Mn, Fe, Co, Ni, Cu, Zn whose 3d ions adopt local tetrahedral geometries. Within the clusters, magnetic exchange is observed between the paramagnetic ions, which has been modeled using an Ising exchange model to account for the dominating anisotropy of the ReII ion. Despite the high pseudo-symmetry of the clusters (Td), this work has yielded a rare example of a metal-cyanide single molecule magnet, {[MCl]4[Re(triphos)(CN)3]4} with an S = 8 ground state, D = -0.39 cm-1 and an effective energy barrier for magnetization reversal of Ueff = 8.8 cm-1. The elucidation of this family of isostructural clusters has also allowed us to pursue fundamental work on the structure/property relationships of the exotic, paramagnetic ReII ion. As the clusters are soluble, stable compounds, the future of this chemistry lies in the development of a true building-block approach to ??super-clusters?? that exhibit very high ground state spin values.

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Selvanathan, Pramila. « Photochromic switches for luminescence, plasmonic resonance, single molecule magnetic properties, and molecular wires for nano junctions ». Thesis, Rennes 1, 2016. http://www.theses.fr/2016REN1S145.

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Ce travail est consacré à la synthèse et la caractérisation des commutateurs et des fils moléculaires incorporant l'unité et le ruthénium organométalliques fractions photochromiques. La première partie traite de lanthanides complexe Yb combiné avec l'unité et le ruthénium acétylure fractions photochromiques afin de moduler la luminescence avec l'aide de redox et de stimuli lumineux. Dans la deuxième partie explique la combinaison d'unités DTE photochromiques avec des fragments acétylures de ruthénium pour fixer sur la surface de nanoparticules métalliques afin d'affiner leur résonance plasmonique grâce à la modification de l'environnement de surface en utilisant la lumière et redox stimuli. La troisième partie décrit la préparation de complexes de lanthanides combinés avec une unité photochromique spiropyranne pour commuter les propriétés SMM des complexes via photoisomérisation de l'unité spiropyranne. Dans la dernière partie, nous présentons la synthèse de Oligo (phénylène éthylène) Les fils moléculaires avec différents noyaux centraux afin d'obtenir une variété de fil avec différents niveaux d'énergie HOMO-LUMO pour vérifier l'effet de l'épinglage
This work is devoted to the synthesis and characterization of novel molecular switches and wires incorporating photochromic unit and ruthenium organometallic moieties. The first part deals with lanthanide Yb complex combined with photochromic unit and ruthenium acetylide moieties in order to modulate the luminescence with the help of redox and light stimuli. In the second part explained the combination of photochromic DTE units with ruthenium acetylide moieties to attach on the surface of metal nanoparticles in order to tune their plasmonic resonance through the surface environment modification by using light and redox stimuli. The third part describes the preparation of lanthanide complexes combined with a spiropyran photochromic unit in order to switch the SMM properties of the complexes via photoisomerization of the spiropyran unit. In the last part, we report the synthesis of Oligo(phenylene ethylene) molecular wires with different central cores in order to obtain various wire with different HOMO-LUMO energy levels to check the effect of pinning

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Vongtragool, Suriyakan. « Frequency-domain magnetic resonance spectroscopy on the Mn12-acetate single-molecule magnet ». [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972905952.

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Erler, Philipp [Verfasser]. « Electronic and magnetic properties of single molecule magnets on surfaces / Philipp Erler ». Konstanz : Bibliothek der Universität Konstanz, 2016. http://d-nb.info/1114893889/34.

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Lendínez, Escudero Sergi. « Magnetization dynamics at the nanoscale in nanoparticles and thin films : single-molecule magnets, magnetic vortices, and magnetic droplet solutions ». Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/395194.

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Research in magnetic materials leads to new devices and technologies. As the technology progresses, the devices become smaller and this miniaturization allows more storage capacity and lower costs in the production of new technologies. As new and smaller materials are fabricated, new phenomena appear and thus new physics is needed to describe them. Nanomaterials meet characteristics of both the microscopic quantum world and the macroscopic classic world. This intermediate length scale is known as mesoscale. Nanomaterials can be obtained in a variety of forms, being nanoparticles and magnetic ultra-thin films some of the most used. These magnetic systems are very different in their composition: nanoparticles are grown with chemical reactions, and thin films are grown on a substrate by nanofabrication techniques such as sputtering or electron-beam evaporation. The magnetization might not be uniform in a magnetic thin film or in a large magnetic nanoparticle leading to the formation of magnetic domains. Magnetic domains are static structures that appear due to competition of the different magnetic energies and can be used to store and transport information. In all these systems, the magnetization dynamics gives rise to new behavior not visible in static measurements: quantum steps of the magnetization in molecular magnets; characteristic resonant frequencies that can be used to control the magnetic state of vortices; and formation of magnetic droplet solitons in thin films with perpendicular magnetic anisotropy. Understanding the dynamics of nanomaterials and the evolution of the magnetization is a key process to develop faster devices and technologies. The early studies of molecular magnets showed quantum effects at the macroscopic scale, which have allowed a better understanding of spin. Magnetic vortices have been proposed for multiple applications, from magnetic storage of information to cancer cell destruction. The recently discovered magnetic droplet soliton is also a very good candidate for technological applications due to the low current and magnetic field needed for its generation, and it is now a system with a growing interest in spintronics. In this dissertation we show some new dynamic phenomena. In the first part of the thesis we study systems that allow a macroscopic-spin model where spatial variations of magnetization are neglected. We develop a theory that sets the requirements for the observation of the rotational Doppler effect in a ferromagnetic system and we measure quantum effects in randomly oriented nanoparticles of a single-molecule magnet, which might be a good candidate for the observation of the Doppler effect. In the second part of the thesis, we study the magnetization dynamics in macroscopic systems that require a spatial dependence of the magnetic moment. We generate and control the dynamic states of the magnetic domains with oscillating fields, in the case of magnetic vortices, and with electrical currents, in the case of droplet solitons.
La investigación en materiales magnéticos ha dado lugar a nuevos dispositivos y tecnologías. A medida que la tecnología progresa, los dispositivos se hacen más pequeños. Esto permite una mayor capacidad de almacenamiento y reducir los costes de producción. A medida que se fabrican materiales más pequeños, surgen nuevos comportamientos. Los nanomateriales reúnen características tanto del mundo cuántico microscópico como del mundo clásico macroscópico. Esta escala de longitud se conoce como mesoescala. Existen variedad de forms de nanomateriales, entre las cuales nanopartículas y capas magnéticas ultrafinas. La composición de estos sistemas es diversa: las nanopartículas se obtienen a partir de reacciones químicas y las capas finas se crecen en un sustrato mediante técnicas de nanofabricación. La magnetización en las capas finas o en nanopartículas magnéticas grandes puede no ser uniforme, lo que lleva a la formación de dominios magnéticos. En todos estos sistemas, la dinámica de la magnetización da lugar a un nuevo comportamiento que no es visible en las mediciones estáticas: fenómenos cuánticas de la magnetización en imanes moleculares; frecuencias de resonancia características que se pueden utilizar para controlar el estado magnético de los vórtices; y la formación de solitones “droplet” magnéticos en capas finas con anisotropía magnética perpendicular. La comprensión de la dinámica de los nanomateriales y la evolución de la magnetización es un proceso clave para el desarrollo de dispositivos y tecnologías más rápidas. Los primeros estudios de imanes moleculares mostraron efectos cuánticos a escala macroscópica, que han permitido una mejor comprensión del espín. Los vórtices magnéticos se han propuesto para múltiples aplicaciones, desde el almacenamiento magnético de la información a la destrucción de células de cáncer. El solitón “droplet” magnético, descubierto recientemente, es también muy buen candidato para aplicaciones tecnológicas debido al bajo campo magnético y baja corriente necesarios para su generación. En esta tesis se muestran algunos nuevos fenómenos dinámicos. En la primera parte de la tesis, estudiamos sistemas que permite un modelo de macroespín, en el que no hay variaciones espaciales de la magnetización. En la segunda parte estudiamos la dinámica en sistemas con dominios magnéticos, lo cual requiere una dependencia espacial de la magnetización.

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Golze, Christian. « Tunable High-Field/ High-Frequency ESR and High-Field Magnetization on Single-Molecule Clusters ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1199739868406-44757.

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In this work, low dimensional iron group clusters have been studied by application of high magnetic fields. The magnetization has been probed with an MPMS as function of temperature and field. The combination with pulse field measurements up to 52\,T allowed determination of the magnetic exchange coupling parameters, and to probing the effective spin of the ground state. The main focus was on tunable high-field/high-frequency (tHF) ESR in static fields < 17 T and pulse field ESR up to 36 T. This magnetic resonance method has been used for the characterization of the local magnetic properties: The detailed analysis of the field dependence of dedicated spin states allowed to determine the magnetic anisotropy and g-factors. The results were analyzed in the framework of the appropriate effective spin Hamiltonians in terms of magnetization fits and ESR spectrum simulations.

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Lim, Ren Chong. « Application of magnetic torque on the bacterial flagellar motor ». Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:2f18fdff-e876-4be6-8ac2-c8281a4a905a.

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There is a strong need to develop a mechanical method to apply external torque to the bacterial flagellar motor. Such a method will allow us to probe the behaviour of the motor at a range of different speeds under different external conditions. In this thesis, I explored various methods to deliver torque at the single-molecule level, in particular the use of angular optical trapping and magnetic tweezers. I have identified rutile particles as suitable handles for use in angular optical trapping due to their high birefringence. Further progress was not achieved using angular optical trapping due to the lack of a suitable method to attach birefringent particles to the bacterial flagellar motor. On the other hand, I was able to make further progress using magnetic tweezers. A highly-reproducible and high-yielding magnetic bead assay was developed along with electromagnets capable of generating fast-rotating magnetic fields at magnitudes on the order of tens of mT. Using the system of delivering magnetic torque developed, I was able to stall and rotate the motor forward at speeds up to 220 Hz and in the reverse direction. Stalling experiments carried out on the motor revealed the stator mechanosensing depends on torque and not rotation. Signatures of stators dropping out at low load experiments further confirm the load dependence of stators.

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Golze, Christian. « Tunable High-Field/ High-Frequency ESR and High-Field Magnetization on Single-Molecule Clusters ». Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A24034.

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In this work, low dimensional iron group clusters have been studied by application of high magnetic fields. The magnetization has been probed with an MPMS as function of temperature and field. The combination with pulse field measurements up to 52\,T allowed determination of the magnetic exchange coupling parameters, and to probing the effective spin of the ground state. The main focus was on tunable high-field/high-frequency (tHF) ESR in static fields < 17 T and pulse field ESR up to 36 T. This magnetic resonance method has been used for the characterization of the local magnetic properties: The detailed analysis of the field dependence of dedicated spin states allowed to determine the magnetic anisotropy and g-factors. The results were analyzed in the framework of the appropriate effective spin Hamiltonians in terms of magnetization fits and ESR spectrum simulations.

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DaSilva, Jack Guy. « Pressure dependent magnetic investigation of tetracyanoethylene-based molecule-based magnets and their analogues ». Thesis, The University of Utah, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3593070.

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Several metal-tetracyanoethylene (TCNE) compounds, including the [bis(pentamethylcyclopentadienyl)iron(III)][tetracyanoethylene], [FeCp*²][TCNE], family of molecule-based magnets and two cyanide based MBMs were investigated by pressure dependent DC magnetic measurements. The 0-D electron transfer salts: [FeCp*²][TCNE], ferromagnetic [FeCp*²][TCNQ] (TCNQ = 7,7,8,8-tetracyanoquinodimethane), metamagnetic [FeCp*²][TCNQ], [FeCp*²][HCBD] (HCBD = hexacyanobutadiene), and [FeCp*²][DDQ] (DDQ = 2,3-dichloro-5,6-dicyano-p-benzoquinone) exhibited an array of magnetic behavior both at ambient and applied pressure. [FeCp*²][TCNE] and [FeCp*²][HCBD] exhibited weak ferromagnetism above 4.2 and 3.1 kbar, respectively. The ferromagnetic polymorph of [FeCp*²][TCNQ] displayed linear increase to the critical temperature, T_c, and the bifurcation temperature, T_b, reaching 5.01 and 5.46 K, respectively at 10.3 kbar. The coercive field, H_cr, displayed exponential-like increase, reaching 550 Oe at 10.3 kbar. The metamagnetic polymorph of [FeCp*²][TCNQ] displayed linear increase of the Tc at low applied pressure, reaching 2.90 at 2.9 kbar, then transitioned to a paramagnetic state at further applied pressure. [FeCp*²][HCBD] transitioned from a paramagnetic state at ambient pressure to a weak ferromagnetic state at 3.1 kbar with a T_c, H_cr, and H_c of 2.46 K, 25 Oe, and 2,200 Oe, respectively. The T_c and H_c then increased linearly with further applied pressure to 4.80 K and 10,000 Oe, while the H_cr increased exponentially to 795 Oe, at 11.4 kbar. [FeCp*²][DDQ] exhibited paramagnetic behavior at ambient and applied pressures up to 9.2 kbar. The structurally related 2-D Mn^II(TCNE)I(H₂O) and 3-D MnII(TCNE)_3/2(I₃)_1/2, showed significant increases to the T_c, T_b, and H_cr with applied pressure. A high- and low-pressure regions were observed for Mn^II(TCNE)I(H₂O). 2-D [Ru₂(O₂CBu^t)₄][M(CN)₆] · H2O (M = Fe, Cr) displayed suppression of hysteretic properties at high applied pressure and irreversibility of the suppression. A Mean Field (MF) analysis of three structurally related non-cubic Prussian blue analogues (PBA) was performed to assess the intensity of their coupling modes. These values were framed by the reinvestigation of several known cubic PBAs and comparing the coupling intensities, as well as evaluating the MF theory in the context of these structures as several had been evaluated by other means.

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Waters, Michael. « Synthesis, characterisation and magnetic studies of substituted lanthanide (Bis) phthalocyanine single molecule magnets ». Thesis, University of Nottingham, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602425.

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Single molecule magnets (SMMs) are an area of significant research due to their potential applications for data storage, magnetic refrigeration and quantum computing. SMMs are molecules that have the properties of bulk magnets but also show quantum effects such as quantum tunnelling of the magnetisation. One class of molecules that have been found to be SMMs are lanthanide (bis) phthalocyanines, also known as double deckers. These complexes contain a single lanthanide ion which is 'sandwiched' between two phthalocyanine rings. This class of SMMs have been found to have large energy barriers to magnetic relaxation making them suitable for magnetic data storage applications. In this Thesis four new substituted lanthanide double deckers have been successfully synthesised and characterised. The substituents added to the phthalocyanine rings include cyano groups, esters, carboxylic acids and imides. The double deckers magnetic properties were investigated using a superconducting quantum interference device (SQUID) magnetometer and some complexes were found to have their magnetic properties changed by the addition of the substituents, in some cases the magnetic properties are improved. All complexes have been found to show magnetic hysteresis and slow relaxation of the magnetisation in an oscillating field, indicating that the complexes are SMMs. A range of other measurements were carried out to determine their magnetic and electronic properties, including far infrared (FIR) spectroscopy and magnetic circular dichroism (MeD) spectroscopy. The internal structure of the double deckers was probed with extended X-ray absorption fine structure (EXAFS) spectroscopy to investigate the effect that the substituents have on the structure

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Caulfield, Jason M. « Magnetic quantum oscillations in organic metals based on the molecule bis(ethylenedithio)tetrathiafulvalene ». Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:5fbf2599-96d8-4eac-b882-ac74213ac3a5.

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ET charge transfer salts (where ET is bis(ethylenedithio)- tetrathiafulvalene) have relatively simple quasi two-dimensional Fermi surface topologies, making them ideal for the study of the relationship between bandstructure and properties such as superconductivity. Experimental studies of the Fermi surface areas and associated effective masses have been carried out using the Shubnikov-de Haas (SdH) and de Haas-van Alphen (dHvA) effects. By comparing the experimental results to theoretical bandstructure calculations the strength of many body interactions has been estimated. High pressure magnetotransport experiments have been carried out on the superconductor κ-ET₂Cu(NCS)₂. The observation of SdH and magnetic breakdown oscillations has allowed the pressure dependences of the Fermi surface topology and effective masses to be deduced and compared with simultaneous measurements of the superconducting critical temperature. The data strongly suggest that the enhancement of the effective mass and the superconducting behaviour are directly connected. The results are compared with several current theories of superconductivity. The dHvA effect has been used to probe the superconducting mixed state of κ-ET₂Cu(NCS)₂. A recent model of the superconducting mixed state is applied to the experimental data in an attempt to determine the value and symmetry of the superconducting energy gap. SdH measurements up to 30 T have been used to study spin densitywave formation in α-ET₂KHg(SCN)₄, and the reasons why a very slight increase of the unit cell volume (i.e. replacing the K in α-ET₂KHg(SCN)₄ by NH₄) stabilises a superconducting state. Galvanomagnetic techniques have been used to measure the quasi onedimensional Fermi surface orientation below the spin-density-wave transition, and to accurately determine the shape of the quasi twodimensional Fermi surface above it. The application of pressure has been used to gradually reduce the onset temperature of a metal-insulator transition and to eventually stabilise a superconducting state in ET₃Cl₂2H₂O. The bandstructure of ET₃C1₂2H₂O has been investigated using the SdH effect whilst hydrostatic pressure has been used to pass through the superconducting part of the phase diagram.

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Manoli, Maria. « Single-molecule magnets and magnetic refrigerants from polynuclear manganese complexes and tripodal ligands ». Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/12560.

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We have investigated the coordination chemistry of the tripodal alcohols H₃thme, H₃tmp, Br-mpH₃, H₄peol and their analogues aepH₂and ampH₂, with a particular focus on Mn. In combination with other bridging/chelating ligands such as carboxylates or β-diketonates a plethora of polymetallic clusters whose topologies are based on shared triangular Mn₃ units have been synthesised. 25 New complexes are reported. These are: a family of seven “rod-like” structures; a family of three “wheel-like” structures; two supertedrahedra; a family of deca- and tetradecametallic “planar discs”; edge-sharing bioctahedra and a bioctahedral polymer.

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Kmety-Stevenson, Carmen R. « Phase transitions in molecule-based magnets : neutron diffraction, magnetic and specific heat studies / ». The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343146984.

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Sharp, Laura E. « Synthesis of cobalt complexes towards single-molecule magnets : a structural and magnetic investigation ». Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/5259/.

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The syntheses and characterisation of eighteen cobalt containing complexes are reported. These complexes range from simple monomers to complexes containing up to fourteen metal centres. Magnetic susceptibility measurements were carried out on ten complexes, to investigate the possibility of SMM properties. Cobalt monomers were synthesised using the ligand, 2-Bis(2-hydroxyethyl)amino-2-(hydroxymethyl)-1,3-propanediol, “bis-tris” (H5L) and subsequently utilised as starting materials to form polynuclear complexes, a homometallic mixed valence Co10 complex (4) and a heterometallic {MnII5CoIII4} complex (5). Magnetic susceptibility measurements on both these complexes were complicated due to the presence of MII ions in multiple geometries. A collection of complexes containing two to four metal centres was synthesised using the ligands diethanolamine and triethanolamine. Magnetic susceptibility measurements were carried out on a bromide bridged dimer (7), the CoII ions were found to be weakly ferromagnetically coupled and the complex has an effective spin ground state S′ = 1 with g > 4. A mixed valent tetramer (10) with two tetrahedral CoII ions was found to have antiferromagnetic interactions. Five new seven-membered mixed valence disc complexes were synthesised; three homometallic and using the ligands diethanolamine, N-methyldiethanolamine and bis-tris propane; and two heterometallic discs that incorporated MnII ions, using the ligands 2-amino-2-(hydroxymethyl)-propane-1,3-diol, “tris” and diethanolamine (dea). Magnetic susceptibility measurements carried out on two homometallic Co7 discs, (11) and (12), found them to have an effective spin ground state S′ = 2 with g > 4. The magnetic properties of one heterometallic disc were measured [Co6Mn(dea)6(NO3)3][NO3]2 (15); it was not possible to clarify whether all MII-MII interactions occurring in this complex were ferromagnetic or whether other effects such as zero-field splitting were operative. Of the larger complexes synthesised a homometallic Co10 (17 and 17a) complex was found to display predominantly ferromagnetic interactions. A novel heterometallic mixed valence ‘double disc’ complex with chloride bridges [Co12Mn2(NO3)4(dea)12Cl2][Cl]2[NO3]2 (18) was also synthesised.

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Vongtragool, Suriyakan. « Frequency domain magnetic resonance spectroscopy on the Mn 12 -acetate single molecule magnet ». [S.l. : s.n.], 2004. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11513999.

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Brunet, Gabriel. « Molecular Engineering of Metal-Organic Assemblies : Advances Toward Next Generation Porous and Magnetic Materials ». Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40385.

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The controlled assembly of molecular building blocks is an emerging strategy that allows for the preparation of materials with tailor-made properties. This involves the precise combination of molecular subunits that interact with one another via specifically designed reactive sites. Such a strategy has produced materials exhibiting remarkable properties, including those based on metal-organic frameworks and single-molecule magnets. The present Thesis aims to highlight how such metal-organic assemblies can be engineered at the molecular level to promote certain desired functionalities. Specifically, Chapter 2 will focus on the confinement effects of a crystalline sponge on a ferrocene-based guest molecule that is nanostructured within the porous cavities of a host material. In doing so, we evaluate how one can exert some level of control over the binding sites of the guest molecule, through the addition of electron-withdrawing groups, as well as tuning the physical properties of the guest itself through molecular encapsulation. Notably, we demonstrate a distinct change in the dynamic rotational motion of the ferrocene molecules once confined within the crystalline sponge. In Chapter 3, we investigate the generation of slow relaxation of the magnetization from a Co(II)-based metal-organic framework. We compare this to a closely related 2D Co(II) sheet network, and how slight changes in the crystal field, probed through computational methods, can impact the magnetic behaviour. This type of study may be particularly beneficial in the optimization of single-ion magnets, by sequestering metal centres in select chemical environments, and minimizing molecular vibrations that may offer alternative magnetic relaxation pathways. We extend these principles in Chapter 4, through the use of a nitrogen-rich ligand that acts as a scaffold for Ln(III) ions, thereby yielding 0D and 1D architectures. The coordination chemistry of Ln(III) ions with N-donor ligands remains scarce, especially when evaluated from a magnetic perspective, and therefore, we sought to determine the magnetic behaviour of such compounds. The monomeric unit displays clear single-molecule magnet behaviour with an energetic barrier for the reversal of the magnetization, while the 1D chain displays weaker magnetic characteristics. Nevertheless, such compounds incorporating nitrogen-rich ligands offer much promise in the design of environmentally-friendly energetic materials. In Chapter 5, we take a look at different two different systems that involve the formation of radical species. On one hand, we can promote enhanced magnetic communication between Ln(III) ions, which is typically quite challenging to achieve given the buried nature of the 4f orbitals, and on the other hand, we rely on a redox-active ligand to design stimuli-responsive metal-organic assemblies. The latter case provides access to “smart” molecular materials that can respond to changes in their environment. Here, a multi-stimuli responsive nanobarrel was studied, which displayed sensitivity to ultraviolet radiation, heat and chemical reduction. Lastly, Chapter 6 provides a new method for the systematic generation of cationic frameworks, termed Asymmetric Ligand Exchange (ALE). This strategy focuses on the replacement of linear dicarboxylates with asymmetric linkers that features one less negative charge, in order to tune the ionicity of porous frameworks. This allows for the retention of the structural topology and chemical reactivity of the original framework, representing distinct advantages over other similar strategies. Methods to retain permanent porosity in such cationic frameworks are also proposed. Altogether, these studies highlight how the directed assembly of ordered networks can generate varied properties of high scientific interest.

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Feng, Patrick Lulick. « Quantum magnetic phenomena in 0-D through 3-D MnIII₃-based single-molecule magnets ». Diss., [La Jolla] : University of California, San Diego, 2010. http://wwwlib.umi.com/cr/ucsd/fullcit?p3389021.

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Thesis (Ph. D.)--University of California, San Diego, 2010.
Title from first page of PDF file (viewed February 12, 2010). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

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Cross, Stephen John. « Combining magnetic tweezers and single-molecule fluorescence microscopy to probe transcription-coupled DNA supercoiling ». Thesis, University of York, 2013. http://etheses.whiterose.ac.uk/4998/.

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Previous studies have shown that translocation of an actively transcribing RNA polymerase leads to local increases or decreases in DNA torsion (twin-supercoiled domain), which cannot be resolved in vivo due to interactions of the template DNA, nascent RNA and polymerase with the crowded cellular environment. Local changes in DNA supercoiling are biologically relevant as they have been shown to regulate transcription initiation at promoters located downstream. Current in vitro single-molecule approaches are not able to directly probe transcription-coupled DNA supercoiling due to an inability to simultaneously monitor changes in torsional stress and localise individual transcribing RNA polymerase(s) on the DNA. Described here is a novel optical microscope, which utilises a combination of magnetic tweezers, bright-field illumination and wide-field epifluorescence imaging to permit the visualisation of fluorescently tagged polymerases transcribing in real-time on a torsionally constrained DNA template. With this unique geometry, transcription as a function of applied torsion can be probed directly in vitro. Unlike standard magnetic tweezers configurations this system extends tethers horizontally relative to the microscope slide surface, which allows individual enzymes to be directly viewed via attached fluorophores. The magnetic tweezers allow both the relative extension and linking number of the DNA tether to be manipulated, thus enabling transcription to be studied under conditions of constant DNA extension and defined torsional stress.

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Wu, Meiling. « Single-molecule magnetic tweezers development and application in studies of enzyme dynamics and cell manipulation ». Bowling Green State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1581433776367167.

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Bircher, Roland. « Studies of single-molecule magnets and spin clusters by inelastic neutron scattering and magnetic measurements / ». Bern : [s.l.], 2005. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.

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Russell, Camilla. « Development of Electrical Readouts for Amplified Single Molecule Detection ». Doctoral thesis, Uppsala universitet, Institutionen för immunologi, genetik och patologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-247945.

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Molecular diagnostics is a fast growing field with new technologies being developed constantly. There is a demand for more sophisticated molecular tools able to detect a multitude of molecules on a single molecule level with high specificity, able to distinguish them from other similar molecules. This becomes very important for infectious diagnostics with the increasing antibiotic resistant viruses and bacteria, in gene based diagnostics and for early detection and more targeted treatments of cancer. For increased sensitivity, simplicity, speed and user friendliness, novel readouts are emerging, taking advantage of new technologies being discovered in the field of nanotechnology. This thesis, based upon four papers, examines two novel electrical readouts for amplified single molecule detection. Target probing is based upon the highly specific amplification technique rolling circle amplification (RCA). RCA enables localized amplification resulting in a long single stranded DNA molecule containing tandem repeats of the probing sequence as product. Paper I demonstrates sensitive detection of bacterial genomic DNA using a magnetic nanoparticles-based substrate-free method where as few as 50 bacteria can be detected. Paper II illustrates a new sensor concept based on the formation of conducting molecular nanowires forming a low resistance circuit. The rolling circle products are stretched to bridge an electrode gap and upon metallization the resistance drops by several orders of magnitude, resulting in an extremely high signal to noise ratio. Paper III explores a novel metallization technique, demonstrating the efficient incorporation of boranephosphonate modified nucleotides during RCA. In the presence of a silver ion solution, defined metal nanoparticles are formed along the DNA molecule with high spatial specificity. Paper IV demonstrates the ability to manipulate rolling circle products by dielectrophoresis. In the presence of a high AC electric field the rolling circle products stretch to bridge a 10 µm electrode gap.

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Feuersenger, Jürgen. « Synthesis and characterisation of 3d-4f-complexes and their magnetic properties ». Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14195/document.

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Ce travail de thèse décrit (i) la synthèse de complexes hétérométalliques d’ions 3d et 4f à partir de précuseurs de Mn, Fe et Co, de sels de lanthanides et de ligands organiques et (ii) l'étude de leurs structures et propriétés. 41 complexes polynucléaires ont été synthétisés dans le cadre de ce travail. Les structures moléculaires de tous les composés ont été déterminées par diffraction des rayons X. Les propriétés magnétiques de 22 complexes ont été étudiées, dont quatre montrent une relaxation lente de leur aimantation considérée comme la signature d’un comportement de molécule-aimant. L'activité catalytique du complexe {Mn4Dy6Li2} calciné a aussi été étudiée et s'est avérée efficace pour l'oxydation du monoxyde de carbone. L'étude systématique de complexes isostructuraux de lanthanides a montré que l'incorporation d’ions 4f peut introduire de l’anisotropie magnétique et que l’ion DyIII est généralement le meilleur candidat pour le ciblage de molécules-aimants hétérométalliques 3d- 4f
This dissertation describes the syntheses of 3d-4f-metal complexes starting from preformed compounds of Mn, Fe and Co, lanthanide salts and organic ligands and also the investigation of their structures and properties. 41 new polynuclear heterometallic metal complexes were synthesised in the course of this work with different interesting properties. The structures of all obtained compounds have been confirmed using X-ray diffraction. The magnetic properties of 22 complexes were studied, of which four show frequency dependent out-of-phase signals as expected for SMMs. The catalytic activity of calcinated {Mn4Dy6Li2} was investigated and proved effective for the oxidation of CO. It was established, that the use of precursors leads to new families of compounds. Moreover the study of isostructural compounds across the lanthanide series showed 1) that the incorporation of 4f ions introduces magnetic anisotropy and 2) DyIII is usually the best candidate for targeting 3d-4f-SMMs

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Huang, Gang. « Synthesis, crystallographic and magnetic studies of lanthanide-based molecular edifices ». Thesis, Rennes, INSA, 2017. http://www.theses.fr/2017ISAR0008/document.

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Les molécules-aimants ou Single–Molécule Magnets (SMM) ont attiré une attention croissante au cours des dernières années en raison de leur potentiel attrayant en tant que dispositifs de stockage magnétique à haute densité. Beaucoup d'efforts ont été faits pour améliorer la performance magnétique de ces molécules à l’aide des techniques de chimie de coordination.Dans cette thèse, le travail est organisé en deux parties principales. La première partie est constituée des chapitres 2 et 3 qui se concentrent principalement sur les familles Lanthanide-radicaux zéro- et mono-dimensionnelles. La deuxième partie contient les chapitres 4 et 5, ou des ligands diamagnétiques sont utilisés afin concevoir des matériaux multifonctionnels.Dans la première partie, neuf radicaux TEMPO-R (R représente le substituant) sont utilisés. Leur structure cristalline, ainsi que leurs propriétés magnétiques ont été caractérisées. Dans le chapitre 2, quatre radicaux (TEMPO-OCH3, TEMPO-NH2 TEMPO-Acetamido et TEMPO-OCH2CCH) sont utilisés pour synthétiser des complexes zéro-dimensionnels, dont trois présentent des propriétés de SMM. Dans le cas particulier de TEMPO-OCH3, un très rare comportement de SMM avec lanthanides légers est observé (CeIII, PrIII et NdIII). La première SMM à base de PrIII est ainsi reportée. Dans le chapitre 3, l'objectif est de concevoir des SMM organisés mono-dimensionnellement dans l’empilement cristallin. Cinq autres radicaux sont utilisés: TEMPO-Méthacrylate, TEMPO-OCOPh, TEMPO-oxo, TEMPO-OH et TEMPO-CN. Parmi toutes les chaînes obtenues, [Pr(hfac)3(H2O)(TEMPO-OH)]n (17), [Dy(hfac)3-TEMPO-OH)]n (18) et [Tb(hfac)TEMPO-CN)]n (22) sont identifiés comme SMM. 22 présente la relaxation magnétique la plus lente parmi tous les SMM 4f-2p obtenues dans cette thèse, avec une d'hystérèse magnétique à basse température. Son analogue à base GdIII (23) présente une des plus grandes valeurs d'échange dans les composés de Gd-2p. Enfin un très rare exemple de réseau bidimensionnel 4f-2p de formule [(Ce(hfac)3)3(Oxo-TEMPO)4]n (15) est obtenu. Dans la deuxième partie, une chaine de dimère est obtenue par réaction d'un ligand carboxylique photo-commutable avec des sels d’ions LnIII. La photo-sensibilité du ligand sous irradiation UV a été testée et des mesures magnétiques en solution ont été entreprises. En outre, un composé de type Metal-Organic-Framework (MOF) présentant un comportement de SMM de {[Dy2(o-PDA)3(H2O)2]2H2O}n (28) a été conçu et caractérisé. Une interaction ferromagnétique Ln-Ln a été observée dans ce MOF-SMM et le dopage diamagnétique démontre que, contrairement à ce qui est observé sur [Ln(AZO)3(DMSO)(H2O)]2•4DMSO, cette interaction favorise le comportement de SMM
Single-molecule-magnet (SMM) has attracted increasing attention in recent years due to their appealing potential for high-density storage devices. Much effort has been made to improve the magnetic performance through flexible coordination chemistry strategy.In this thesis, the work is organized in two main parts. The first part is constituted of chapter 2 and chapter 3, primarily focus on the Ln-Radical families aiming at designing zero-dimensional and one-dimensional single-molecule-magnet (SMM). The second part contains chapter 4 and chapter 5, in which the ligands are replaced by diamagnetic ones for the purpose of designing the multifunctional materials.In the first part, nine TEMPO-R (R represents the substituent) radicals are employed to construct zero-dimensional and one-dimensional complexes. These kinds of compounds were prepared by reactions in the dichloromethane/n-heptane co-solvents between the precursor [Ln(hfac)3(H2O)2] and TEMPO radicals. Subsequently their molecular structure as well as magnetic properties have been characterized and described. In chapter 2, four radicals (TEMPO-OCH3, TEMPO-NH2 TEMPO-Acetamido and TEMPO-OCH2CCH) are used to synthesize monometallic or dimetallic complexes, among which three are successful to construct the SMM. For the special case of TEMPO-OCH3 a rare light lanthanide ions (CeIII, PrIII and NdIII) SMM behavior is reported. The PrIII derivative is the first PrIII-based SMM ever reported. In chapter 3, the target is to design SMM in one dimension by using another five radicals: TEMPO-Methacrylate, TEMPO-OCOPh, TEMPO-oxo, TEMPO-OH and TEMPO-CN. Among all the chains, [Pr(hfac)3(H2O)(TEMPO-OH)]n (17), [Dy(hfac)3-TEMPO-OH)]n (18) and [Tb(hfac)3(TEMPO-CN)]n (22) are identified as chains of SMM. 22 exhibits the slowest magnetic relaxation among all the 4f-2p SMMs obtained in this thesis, with a small opening of magnetic hysteresis. Its analogue of [Gd(hfac)3(TEMPO-CN)]n (23) even exhibits one of the largest exchange values in Gd-2p compounds. Last a very rare example of bidimensional 4f-2p network of formula [(Ce(hfac)3)3(Oxo-TEMPO)4]n (15) is obtained.In chapter 4, the salt of a photo-switchable carboxylic ligand was reacted with LnIII ions to afford a chain-like arrangement of dinuclear complexes of formula [Ln(AZO)3(DMSO)(H2O)]2•4DMSO. Photo-sensitivity of the ligand under the irradiation of UV has been tested together with magnetic measurements in solution. In chapter 5, a Metal-Organic-Framework (MOF) (28) has been designed and characterized. Ln-Ln ferromagnetic interaction has been observed and diamagnetic doping highlight that, contrary to what observed on [Ln(AZO)3(DMSO)(H2O)]2•4DMSO, this interaction promote SMM behavior in a so-called MOF-SMM

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Kettles, Fraser J. « Synthesis, structure and magnetic properties of heterometallic complexes towards single-molecule magnets using flexible aminopolyol ligands ». Thesis, University of Glasgow, 2016. http://theses.gla.ac.uk/7488/.

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Inglis, Ross. « Oxime based manganese molecular magnets ». Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4755.

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The synthesis and characterisation of a large family of hexametallic [MnIII 6] Single-Molecule Magnets with general formula [MnIII 6O2(R-sao)6(X)2(L)4-6] (where sao2- = dianion of salicylaldoxime; R = H, Me, Et, Ph; X = O2CR' (R' = H, Me, Ph etc), Hal , O2PHPh or O2P(Ph)2; L = solvent) are presented. Deliberate structural distortions of the [Mn3O] trinuclear moieties within the complexes are used to tune the observed magnetic properties. These findings highlight a qualitative magnetostructural correlation whereby the type (anti- or ferromagentic) of each Mn2 pairwise magnetic exchange is dominated by the magnitude of each individual Mn-N-O-Mn torsion angle. To shed further light on this intriguing family of nanomagnets, a large family of the analogous “half” molecules has been synthesised and fully characterised. These trimetallic [MnIII 3] complexes can be divided into three categories with general formulae (type 1) [MnIII 3O(R-sao)3(X)(sol)3-4] (where R = H, Me, tBu; X = O2CR (R = H, Me, Ph etc); sol = py and / or H2O), (type 2) [MnIII 3O(R-sao)3(X)(sol)3-5] (where R = Me, Et, Ph, tBu; X = O2CR (R = H, Me, Ph etc); sol = MeOH, EtOH and / or H2O), and (type 3) [MnIII 3O(R-sao)3(sol)3](XO4) (where R = H, Et, Ph, Naphth; sol = py, MeOH, -pic, Et-py, tBu-py; X = Cl, Re). In the crystals the ferromagnetic triangles are involved in extensive inter-molecular H-bonding which is clearly manifested in the magnetic behaviour, producing exchange-biased SMMs. These interactions can be removed by ligand replacement to give “simpler” SMMs. The [MnIII 6] and [MnIII 3] molecular nanomagnets are then exploited as building blocks to construct supramolecular architectures by means of host-guest interactions and coordination driven self-assembly. A number of discrete and infinite architectures based on the molecular triangle [Mn3] and various pyridyl-type ligands were obtained and structurally and magnetically characterised.

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Flores, Gonzalez Jessica. « Isotopic Enrichments of lanthanide based single molecule magnets ». Thesis, Rennes 1, 2019. http://www.theses.fr/2019REN1S064.

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Les matériaux moléculaires, et plus précisément ceux à base d’ions lanthanides, ont été largement étudiés pour leur utilisation dans différentes applications, dont le stockage de l’information ou l’ordinateur quantique. Cet intérêt s’explique du fait que des systèmes contenant des ions lanthanides donnent lieu à une large anisotropie et une bistabilité magnétiques d‘origine purement moléculaire. Durant les vingt-cinq dernières années, beaucoup d’articles ont été publiés dans lesquels les composés à base de ces ions montraient une relaxation lente de leur aimantation et une hystérèse magnétique à basse température. Récemment, des recherches ont menées à l’obtention de systèmes moléculaires présentant des températures de blocage (température maximale à laquelle le système se comporte comme à superparamagnétique) proche de l’azote liquide ce qui facilite le transfert dans des dispositifs basés sur ces systèmes.Cependant, cette relaxation lente de l’aimantation est souvent accompagnée des phénomènes quantiques, donnant lieu à d’autres relaxations beaucoup plus rapides. Les phénomènes quantiques peuvent donner lieu à de nouvelles applications mais à condition de bien comprendre leurs mécanismes d’action. Les interactions dipolaires et les hyperfines, les premiers provenant des molécules voisines et la deuxième de l’interaction spin-noyau dans le métal, sont connus pour participer à l’origine de ces phénomènes. Quelques systèmes ont été choisis durant ce travail de thèse dans le but de mieux comprendre les évènements quantiques et la contribution des différentes interactions. Ceci a mené à la synthèse et aux caractérisations magnétiques de différents systèmes magnétiquement dilués (étude des interactions dipolaires) et isotopiquement enrichis (étude des interactions hyperfines), afin de mettre en évidence une tendance générale pour l’optimisation des processus de relaxation lente
Molecular materials, and in particular those based on Lanthanides, have been extensively studied for their use in data storage, spintronics and quantum computing, as they promise high anisotropic systems and magnetic bistability of the discrete entity. Actually, in Athe last twenty-five years a plethora of compounds have been reported, thus showing slow of their magnetic relaxation and the characteristic magnetic hysteresis at low temperature. Moreover, some of the last investigations have reach blocking temperatures (temperature for which the system shows superparamagnetic behavior) at the liquid nitrogen level, hence facilitating the applicability of devices based on these molecules. However, the slow relaxation is commonly accompanied by quantum phenomena, favoring a fasten relaxation. The quantum effects open the possibility to different magnetic objects, but only if the operating mechanisms are well known. Dipolar interactions, with the neighboring molecules, and hyperfine interactions, with the metal ion, are known to be some of the reasons why this fast relaxations occurs. With the aim of acquiring a better understanding of the quantum events, and the contribution of the different interactions, different systems have been chosen to be studied in this work. Thus, the synthesis and magnetic characterization of magnetically diluted (suppression of dipolar interactions) and isotopic enrichment (tuning of the hyperfine interactions) of the different systems have been performed in order to find a general direction for the optimization of the slow relaxation process

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Jiang, Yu Ting. « The Synthesis, Structure and Magnetic Properties of O-Vanillin-Derived Schiff Base Polynuclear Lanthanide Single-Molecule Magnets ». Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32122.

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This thesis describes the synthesis, characterization and magnetic investigation of homometallic lanthanide complexes based on two different o-vanillin-derived Schiff base ligands: H2ovph and H2ovgrd. The studies were performed using single crystal X-ray diffractometry, Powder XRD and SQUID magnetometry. Chapter 2 focuses on dinuclear systems 1-8 coordinated to the ligand H2ovph and presents their structural and magnetic properties, mainly with respect to their intramolecular interactions. Chapter 3 describes two hexanuclear systems, 9 (DyIII) and 10 (GdIII), with trigonal prism-assembled core structures. A structural comparison to other similar complexes in the literature is performed. A series of dinuclear complexes, 11-15, based on the ligand H2ovgrd are described in Chapter 4, focusing on the synthetic strategy, crystal structures and magnetism. The presence of the lanthanide contraction is evident in this system of complexes and is consistent with the intrinsic lanthanide contraction property.

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Frauhammer, Timo [Verfasser], et W. [Akademischer Betreuer] Wulfhekel. « Single-Molecule Magnets and their Electronic and Magnetic Interactions with Metallic Surfaces / Timo Frauhammer ; Betreuer : W. Wulfhekel ». Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/1223027848/34.

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Wang, Jinglong. « Insights into the mechanism of DNA double-strand breaks and classic NHEJ by single-molecule magnetic tweezers ». Thesis, Université de Paris (2019-....), 2019. http://www.theses.fr/2019UNIP7063.

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La réparation des coupures de double brin (DSB) de l'ADN par une jonction d'extrémité non homologue (NHEJ) nécessite de multiples protéines pour reconnaître et lier les extrémités de l'ADN, les traiter pour des raisons de compatibilité et les lier ensemble. Nous avons construit de nouveaux substrats d'ADN pour la nano-manipulation à une seule molécule nous permettant de détecter, de sonder et de rompre mécaniquement la synapsis du DSB en temps réel par des composants spécifiques du NHEJ humain. DNA-PKcs et Ku permettent la synapsis des extrémités de l'ADN à une échelle de temps inférieure à la seconde, et l'ajout de PAXX étend cette durée de vie à ~ 2 secondes. Une addition supplémentaire de XRCC4, XLF et Ligase IV a entraîné une synapsis à l'échelle minute et conduit à une réparation robuste des deux brins de l'ADN nanomanipulé. Contrairement à PAXX, un long ARN non codant LINP1 peut également aider la DNA-PK à attacher ensemble les extrémités de l'ADN, ce qui pourrait être plus nécessaire lorsque les extrémités de l'ADN se séparent. De plus, nous interrogeons également le système bactérien Bacillus subtilis NHEJ, qui vient de composer Ku et la ligase D, la bactérie Ku peut également lier l’ADN et introduire la Ligase D renforcer la synapsis et conduire à la ligature. La contribution énergétique des différents composants à la stabilité synaptique est généralement faible, à l’échelle de quelques kCal / mol. Nos résultats combinés définissent les règles d’assemblage des machines NHEJ et révèlent l’importance des interactions faibles, rapidement rompues même sous des forces sous-picoNewton, dans la régulation de ce système chimico-mécanique à plusieurs composants pour l’intégrité du génome. De plus, nous identifions également un nouveau modèle de clivage à double brin d’ADN régulé par Cas9 PAM. En résumé, ce travail de thèse porte sur la génération DSB et le processus détaillé allant de la connexion de l’ADN à la ligature
Repairing DNA double-strand breaks (DSBs) by non-homologous end-joining (NHEJ) requires multiple proteins to recognize and bind DNA ends, process them for compatibility, and ligate them together. We constructed novel DNA substrates for single-molecule nano-manipulation allowing us to mechanically detect, probe, and rupture in real-time DSB synapsis by specific human NHEJ components. DNA-PKcs and Ku allow DNA end synapsis on the sub second timescale, and addition of PAXX extends this lifetime to ~2s. Further addition of XRCC4, XLF and Ligase IV resulted in minute-scale synapsis and led to robust repair of both strands of the nanomanipulated DNA. In contrast with PAXX, a long non-coding RNA LINP1 can also help DNA-PK to tether DNA ends together, which could be more required when DNA ends falling apart in distance. Moreover, we also interrogate the bacteria Bacillus subtilis NHEJ system, which just composed Ku and Ligase D, bacteria Ku also can tether DNA together and introducing the Ligase D strengthen the synapsis and lead to ligation. The energetic contribution of the different components to synaptic stability is typically small, on the scale of a few kCal/mol. Our combined results define assembly rules for NHEJ machinery and unveil the importance of weak interactions, rapidly ruptured even at sub-picoNewton forces, in regulating this multicomponent chemomechanical system for genome integrity. Moreover, we also identify a novel the DNA double strand cleavage pattern regulated by Cas9 PAM. In sum, this PhD work investigates the DSB generation and the detailed process from DNA end tethering to ligation

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Prescimone, Alessandro. « Effect of high-pressure on molecular magnetism ». Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4619.

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The effect of pressure on a number of magnetically interesting compounds such as single-molecule magnets and dimeric copper and manganese molecules has been investigated to probe the validity of ambient magneto-structural correlations. The first chapter is an introduction to the equipment and methodologies that have been adopted to carry out the experimental high-pressure work. The second chapter reports the first combined high-pressure single crystal X-ray diffraction and high pressure magnetism study of four single-molecule magnets (SMMs). At 1.5 GPa the structures [Mn6O2(Et-sao)6(O2CPh(Me)2)2(EtOH)6] (1) – an SMM with a record effective anisotropy barrier of ~86 K – and [Mn6O2(Etsao) 6(O2C-naphth)2(EtOH)4(H2O)2] (2) both undergo significant structural distortions of their metallic skeletons which has a direct effect upon the observed magnetic response. Up to 1.5 GPa pressure the effect is to flatten the Mn-N-O-Mn torsion angles weakening the magnetic exchange between the metal centres. In both compounds one pairwise interaction switches from ferro- to antiferromagnetic, with the Jahn-Teller (JT) axes compressing (on average) and re-aligning differently with respect to the plane of the three metal centres. High pressure dc χMT plots display a gradual decrease in the low temperature peak value and slope, simulations showing a decrease in |J| with increasing pressure with a second antiferromagnetic J value required to simulate the data. The “ground states” change from S = 12 to S = 11 for 1 and to S = 10 for 2. Magnetisation data for both 1 and 2 suggest a small decrease in |D|, while out-of-phase (χM //) ac data show a large decrease in the effective energy barrier for magnetisation reversal. The third SMM is the complex [Mn3(Hcht)2(bpy)4](ClO4)3·Et2O·2MeCN (3·Et2O·2MeCN) that at 0.16 GPa loses all associated solvent in the crystal lattice, becoming 3. At higher pressures structural distortions occur changing the distances between the metal centres and the bridging oxygen atoms making |J| between the manganese ions weaker. No significant variations are observed in the JT axis of the only MnIII present in the structure. Highpressure dc χMT plots display a gradual decrease in the low temperature peak value and slope. Simulations show a decrease in J with increasing pressure although the ground state is preserved. Magnetisation data do not show any change in |D|. The fourth SMM, [(tacn)6Fe8O2(OH)12](ClO4)3.9Br4.1⋅6H2O, (4) is the largest inorganic compound ever studied at high-pressure. Up to 2.0 GPa the conformation of the complex remains largely unaffected, with the counter ions and water molecules moving around to accommodate a compression of the unit cell volume. High pressure magnetic susceptibility data collected up to 0.93 GPa confirm minimal changes in the intra-molecular exchange interactions. The third chapter focuses on three hydroxo-bridged CuII dimers: [Cu2(OH)2(H2O)2(tmen)2](ClO4)2 (5), [Cu2(OH)2(tben)2](ClO4)2 (6) and [Cu2(OH)2(bpy)2](BF4)2 (7) have been structurally determined up to 2.5, 0.9 and 4.7 GPa, respectively. 6 and 7 have never been reported before. Pressure imposes important distortions in the structures of all three complexes, particularly on the bond distances and angles between the metal centres and the bridging hydroxo groups. 5 undergoes a phase transition between 1.2 and 2.5 GPa caused by the loss of a coordinated water molecule. This leads to a loss of symmetry and dramatic changes in the molecular structure of the complex. The structural changes are manifested in different magnetic behaviours of the complexes as seen in dc susceptibility measurements up to ~0.9 GPa: J becomes less antiferromagnetic in 5 and 6 and more ferromagnetic in 7. The fourth chapter shows the compression of two oxo-bridged MnII/MnIII mixed valence dimers: [Mn2O2(bpy)4](ClO4)3⋅3CH3CN, (8) has been squeezed up to 2.0 GPa whilst [Mn2O2(bpy)4](PF6)3⋅2CH3CN⋅1H2O, (9) could be measured crystallographically up to 4.55 GPa. 9 has never been reported before, while 8 has been reported in a different crystallographic space group. The application of pressure imposes significant alterations in the structures of both complexes. In particular, in 8 the Mn-Mn separation is reduced by the contraction of some of the Mn-O bond distances, 9 shows essentially analogous behaviour: the Mn-Mn distance and nearly all the Mn-N bonds shrink significantly. The magnetic behaviour of the complexes has been measured up to 0.87 GPa for 8 and 0.84 GPa for 9, but neither display any significant differences with respect to their ambient data.

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Tang, Minao. « SYNTHESES, STRUCTURES AND MAGNETIC CHARACTERIZATION OF DI- AND TRIVALENT HYDRIDOTRIS(3,5-DIMETHYLPYRAZOL-1-YL)BORATE CYANOMANGANATES ». UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_theses/546.

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The syntheses, structures, and magnetic properties of a series of di/trivalent hydridotris(3,5-dimethylpyrazol-1-yl)borate (Tp*) cyanomanganates were investigated. Treatment of manganese(III)acetylacetonate with KTp* followed by tetra(ethyl)- ammonium cyanide affords [NEt4][(Tp*)MnII(acac)(CN)] (1). Attempts to oxidize 1 with iodine affords {(Tp*)MnII(κ2O-acac-CN)}n (7); a minor complex {[NEt4][(Tp*)MnII(κ2O-acac-3-CN)]2(µ-CN) (8) was also isolated. The manganese(II) complex [NEt4][(Tp*)MnII(κ2O-acac-3-CN)(κ1N -3-NC-acac)] (2) was obtained via treatment of Mn(3-acacCN)3 with KTp* and [NEt4]CN. [NEt4]2[MnII(CN)4] (3) was prepared via treatment of Mn(OTf)2 with excess [NEt4]CN. [NEt4][(Tp*)MnIII(CN)3] (4), is prepared via treatment of 4 with Mn(3-acacCN)3, KTp* and excess [NEt4]CN. [PPN][(Tp*)MnIII(CN)3] (5) is obtained via treatment of [PPN]3[MnII(CN)6] with (Tp*)SnBu2Cl. Combination of 4 with [MnII(bipy)2(OH2)2][OTf]2 afforded a tetranuclear rectangular cluster {MnIII 2MnII 2} (9). At low temperature, {MnIII2NiII2} (10) was prepared via treatment of 4 and [Ni(II)(bipy)2(H2O)2][OTf]2. Treatment of 4 with [CoII(bipy)2(OH2)2][OTf]2 at low temperature failed to give the desired {MnIII2CoII2} complex. Magnetic measurements indicate that 1, 2, and 7 contain high-spin isotropic MnII with no long-range magnetic order observed for 7 (T > 2 K); 4 contains low-spin MnIII that likely adopt an isotropic 3A2 spin ground state. Surprisingly 9 and 10 do not exhibit slow relaxation of the magnetization (for T > 1.8 K) despite the presence of significant molecular anisotropy.

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Santiesteban, Oscar. « Assessment of molecular interactions via magnetic relaxation : a quest for inhibitors of the anthrax toxin ». Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5481.

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Anthrax is severe disease caused by the gram-positive Bacillus anthracis that can affect humans with deadly consequences. The disease propagates via the release of bacterial spores that can be naturally found in animals or can be weaponized and intentionally released into the atmosphere in a terrorist attack. Once inhaled, the spores become activated and the anthrax bacterium starts to reproduce and damage healthy macrophages by the release of the anthrax toxin. The anthrax toxin is composed of three virulent factors: (i) anthrax protective antigen (APA), (ii) anthrax lethal factor (ALF), and (iii) anthrax edema factor (AEF) that work in harmony to effectuate the lethality associated with the disease. Out of the two internalized factors, ALF has been identified to play a critical role in cell death. Studies in animals have shown that mice infected with an anthrax strain lacking ALF survive the infection whereas when ALF is present the survivability of the mice is eliminated. Although the current therapy for anthrax is antibiotic treatment, modern medicine faces some critical limitations when combating infections. Antibiotics have proven very efficient in eliminating the bacterial infection but they lack the ability to destroy or inhibit the toxins released by the bacteria. This is a significant problem since ALF can remain active in the body for days after the infection is eliminated with no way of inhibiting its destructive effects. The use of inhibitors of ALF is an attractive method to treat the pathogenesis of anthrax infections. Over the last decade several inhibitors of the enzymatic activity of ALF have been identified. In order to identify inhibitors of ALF a variety of screening approaches such as library screenings, Mass Spectroscopy- based screenings and scaffold-based NMR screening have been used. Results from these screening have yielded mainly small molecules that can inhibit ALF in low micromolar to nanomolar concentrations. Yet, although valuable, these results have very little significance with regards to treating ALF in a real-life scenario since pharmaceutical companies are not willing to invest in further developing these inhibitors. Furthermore, the low incidence of inhalation anthrax, the lack of a market for an ALF inhibitor, and the expenses associated with the approval process of the FDA, have hindered the motivation of pharmaceutical companies to pursuit these kind of drugs. Therefore we have screened a small-molecule library of FDA approved drugs and common molecules in order to identify currently approved FDA drugs that can also inhibit ALF (Chapter III). The screening revealed that five molecules: sulindac, fusaric acid, naproxen, ketoprofen and ibuprofen bound to either ALF or APA with sulindac binding both. Additionally, we have developed a nanoparticle-based screening method that assesses molecular interactions by magnetic relaxation changes (Chapter II). Using this assay, we were able to accurately measure the dissociation constants of different interactions between several ligands and macromolecules. Moreover, we have used computational docking studies to predict the binding site of the identified molecules on the ALF or APA (Chapter IV). These studies predicted that two molecules sulindac and fusaric acid could be potential inhibitors of ALF since they bind at the enzymatic pocket. As a result, we tested the inhibitory potential of these molecules as well as that of the metabolic derivatives of sulindac (Chapter V). Results from these studies provided conclusive evidence that fusaric acid and sulindac were both strong inhibitors of ALF. Furthermore, the metabolic derivatives of sulindac, sulindac sulfide and sulindac sulfone also inhibited ALF. Overall, taking together these results we have discovered the alternate use of a currently used drug for the treatment of ALF pathogenesis.
Ph.D.
Doctorate
Chemistry
Sciences
Chemistry

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Farghal, Ahmed M. S. « Co(II) Based Magnetic Systems. Part I Spin Crossover Systems and Dendritic Frameworks. Part II Co(II) Single Molecule Magnets ». Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/20689.

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This work comprises two main parts. The first part outlines our efforts to expand on the recent work of Gütlich et.al. by synthesizing Co(II) based spin crossover systems within a dendritic framework. We wanted to investigate the possibility of synthesizing different first generation, triazole containing dendrimers using “click” type reactions and their coordination ability with Co(II) ions. To this end we have had limited success mainly due to the numerous challenges in synthesizing a pure dendrimer product. The second part details our efforts in the synthesis of a mononuclear Co(II) based single molecule magnet. This comes as an extension to recent reports by Chang and Long where they have successfully obtained mononuclear Fe(II) single molecule magnets by inducing structural distortions within the complexes to amplify the spin-orbit coupling. We postulated that the use of Co(II) in conjunction with a bulky ligand framework would lead to desirable magnetic properties. We chose the known bis(imino)pyridine ligand scaffold due to its rich chemistry and its interesting and unexpected coordination behaviour, as we have seen in previous research efforts by our lab. To this end we were successful in isolating and characterizing 4 compounds, and we have carried out detailed magnetic measurements on the two most magnetically interesting species.

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Ma, Xiaozhou. « Synthesis and study of redox-active molecular nanomagnets ». Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0128.

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Ce travail de thèse portait sur la synthèse et l'étude de complexes magnétiques redox-actifs comme prototypes pour la conception d'aimants moléculaires à haute température. L'activité redox est assurée par le ligand pontant, qui peut moduler et parfois améliorer significativement les propriétés magnétiques. Après un chapitre d'introduction présentant les derniers développements dans le domaine des matériaux magnétiques moléculaires, un accent particulier est mis sur l'importance d'avoir un fort couplage d'échange magnétique J entre les porteurs de spin. Une étude bibliographique présentant deux approches émergentes pour augmenter J dans les composés polynucléaires est également présentée et discutée. Le chapitre 2 présente les synthèses et caractérisations de complexes dinucléaires [M2(tphz)(tpy)2](PF6)n (M = Co(II) ou Ni(II); n = 4, 3, 2, tphz = tétrapyridophénazine, tpy = terpyridine) construits à partir de ligands pontant (tphz) et bloquant (tpy) fortement coordinants et redox-actifs. Les études approfondies de ces composés montrent que le ligand pontant redox-actif peut être utilisé comme un outil de choix pour promouvoir une délocalisation des spins, de forts couplages magnétiques, ainsi que de la commutabilité. L’analyse des résultats obtenus permet également de mieux comprendre les paramètres clés pour l’élaboration de systèmes fortement couplés magnétiquement. Dans le prolongement de ce travail visant à sélectionner les meilleurs composants pour la conception rationnelle d'aimants moléculaires à haute température, le chapitre 3 décrit une nouvelle série de complexes mononucléaires [Cr(III)(tphz)(tpy)](CF3SO3)n (n = 3, 2, 1). Les complexes mono- et doublement réduits présentent des interactions magnétiques remarquablement fortes entre les ions métalliques et les ligands radicalaires, et pourraient servir d'unités magnétiques intéressantes pour la conception d'aimants de plus hautes nucléarités
The thesis work aims at the synthesis and study of redox-active magnetic molecules as prototypes towards the design of molecule-based magnets with high operating temperature, a prerequisite for technological applications. The redox activity is provided by the bridging ligand, which could tune and sometimes enhance significantly the magnetic properties of the resulting molecular architectures. After an introduction chapter presenting the latest developments in the field of molecule-based magnetic materials, special emphasis is given on the importance of having large magnetic exchange coupling J between the spin carriers to reach high operating temperature. This is supported by a bibliographic study concerning two emerging approach to enhance J values in polynuclear compounds. Chapter 2 presents the syntheses and characterizations of dinuclear M(II) complexes [M2(tphz)(tpy)2](PF6)n (M = Co or Ni; n = 4, 3, 2, tphz = tetrapyridophenazine) built by using strongly complexing, redox-active bridging ligand (tphz), and terpyridine (tpy) as capping ligands. The extensive studies on these compounds show that the redox-active bridging ligand can be used as a tool to promote spin delocalization, high spin complexes and magnetic multi-switchability. Importantly the work reveals the key parameters towards building strongly magnetically coupled systems. As a continuation research of finding the best magnetic components for the rational design of high temperature molecule-based magnets, Chapter 3 describes a new series of [Cr(III)(tphz)(tpy)](CF3SO3)n (n = 3, 2, 1) mononuclear complexes. Both the mono and doubly-reduced complexes show remarkable magnetic interactions between metal center and radical ligands, which could further act as interesting magnetic units for the design of higher nuclearities magnets

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Mitcov, Dmitri. « Rational functionalization of molecular magnetic materials : towards liquid crystalline phases, improved solubility and modulation of physical properties ». Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0029/document.

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Ce travail de thèse a été dédié à l’élaboration et l’étude de nouveaux matériaux hybrides obtenus par la fonctionnalisation de molécule-aimants (en anglais single-molecule magnets, SMMs) et de complexes à transfert d’électron. Le premier chapitre fait un état de l’art des deux classes de composés magnétiques utilisées dans ce travail : les molécule-aimants et les systèmes à transfert d’électrons. Une brève description des systèmes magnétiques hybrides présents dans la littérature est ensuite présentée dans le but d’illustrer les motivations qui ont conduit à ce travail. Le chapitre II décrit la fonctionnalisation des molécule-aimants de type [Mn12] dans le but d’obtenir des systèmes cristaux liquides hybrides. Deux approches ont été étudiées : (a) la fonctionnalisation des ligands périphériques avec des groupements fortement lipophiles (longues chaines alkyle) ou (b) le greffage de promoteurs mésogènes par l’intermédiaire d’espaceurs aliphatiques flexibles. Les chapitres III à V présentent les études sur des carrés moléculaires à ponts cyanure {Fe2Co2} qui montrent un transfert d’électron thermo- et photo-induit. Le chapitre III discute de la possibilité de moduler le processus de transfert d’électron de ces carrés moléculaires via le changement du contre anion. La fonctionnalisation du carré moléculaire {Fe2Co2} avec de chaines aliphatiques et son impact induit sur les propriétés physiques à l’état solide et en solutions sont décrits dans le chapitre IV. Le chapitre V discute de l’effet de la fonctionnalisation avec des groupements fortement électrodonneurs, tels que les groupements méthoxy, sur le processus de transfert d’électron des carrés moléculaires {Fe2Co2}
The work presented in this thesis was focused on the design and investigation of novel hybrid materials via ligand functionalization of the single-molecule magnets (SMMs) and electron transfer complexes. Chapter I contains general information about these two classes of the magnetic systems. In order to illustrate the motivation behind our work, a brief review on previously reported soft hybrid magnetic systems, is presented. Chapter II is dedicated to the functionalization of [Mn12]-based SMMs towards hybrid liquid crystalline systems via two different approaches: (a) the functionalization of peripheral ligands with strongly lipophilic groups (long alkyl chains), or (b) the grafting of mesogenic promoters through flexible aliphatic spacers. Chapters III – V are focused on cyanido-bridged molecular {Fe2Co2} squares that exhibit thermally or photo-induced electron transfer. Thus, in Chapter III, the possibility to modulate the electron transfer properties in {Fe2Co2} molecular squares via the use of different counter-anion is discussed. The functionalization with long aliphatic chains and its influence over the properties of {Fe2Co2} molecular squares in solid state and solutions are discussed in Chapter IV. Finally, the effect of the ligand functionalization with strongly electron density donating groups (methoxy) over the electron transfer properties of {Fe2Co2} molecular squares is investigated in Chapter V

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Tombers, Matthias [Verfasser], et Gereon [Akademischer Betreuer] Niedner-Schatteburg. « Spin and orbital magnetic moments of isolated single molecule magnets and transition metal clusters / Matthias Tombers. Betreuer : Gereon Niedner-Schatteburg ». Kaiserslautern : Technische Universität Kaiserslautern, 2015. http://d-nb.info/1075492750/34.

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Helmstedt, Andreas [Verfasser]. « Probing the magnetic properties of [MnIII6CrIII]3+ single-molecule magnets by XAS, XMCD and spin-resolved electron spectroscopy / Andreas Helmstedt ». Bielefeld : Universitätsbibliothek Bielefeld, 2014. http://d-nb.info/1068621702/34.

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Barelier, Sarah. « Probing protein-small molecule interactions by Nuclear Magnetic Resonance : towards a better understanding of the Fragment-Based Drug Design methodology ». Thesis, Lyon 1, 2010. http://www.theses.fr/2010LYO10222.

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La méthode de conception de médicaments à partir de molécules « fragments » (connue sous le nom de « Fragment-Based Drug Design ») a été proposée au milieu des années 90, et a depuis été reconnue comme une alternative tangible aux techniques plus classiques de recherche de médicaments telles que le criblage à haut débit par exemple. La méthode des fragments consiste à cribler un petit nombre (< 10000) de composés organiques de faible poids moléculaire (< 300 Da) afin de détecter ceux qui se lient à la cible (protéine ou acides nucléiques). Du fait de leur faible complexité, les fragments présentent une affinité faible pour la cible, et la détection s'effectue généralement grâce à une technique biophysique (en particulier, résonance magnétique nucléaire (RMN), cristallographie aux rayons X, résonance plasmonique de surface). Les fragments « hits » sont ensuite modifiés par addition de nouvelles fonctions chimiques, ou par liaison de deux fragments, afin d'élaborer, étape par étape, une molécule capable d'établir des interactions plus nombreuses avec la cible, et d'améliorer ainsi l'affinité. Comparée aux méthodes classiques de criblage haut débit, la méthode des fragments offre divers avantages, notamment une meilleure exploration de l'espace chimique, une meilleure efficacité de liaison des molécules « hits », et une plus grande facilité d'optimisation des hits en molécules plus affines. Dans le cadre de ce projet de thèse, plusieurs aspects de la méthode des fragments ont été abordés : dans une première partie, nous étudions un cas concret d'application de la méthode des fragments à la recherche d'un inhibiteur de la peroxiredoxine 5 humaine, en utilisant la RMN comme outil de criblage des fragments ainsi que comme outil d'étude des interactions protéine-fragment. La découverte d'un inhibiteur de cette enzyme représente une avancée importante, qui devrait permettre de mieux comprendre son fonctionnement. Les autres parties de ce projet de thèse abordent des aspects plus méthodologiques de la méthode des fragments : les fragments conservent-ils leur site de liaison, leur efficacité de liaison et leur mode d'interaction au cours de leur élaboration en inhibiteur ? Les fragments peuvent-ils être spécifiques d'une protéine ? D'un site de liaison particulier ? Ces questions, rarement traitées, sont pourtant essentielles à la compréhension du comportement des molécules fragments, et sont abordées d'une part en défragmentant plusieurs inhibiteurs de la protéine Bcl-xL et en étudiant par RMN le comportement de ces fragments vis-à-vis de la protéine en termes d'affinité et de site de liaison, d'autre part en réalisant le criblage par RMN d'une série de fragments sur cinq protéines différentes (peroxiredoxine 5 humaine, sérum albumine humaine et trois protéines homologues de la famille Bcl-2). De manière générale, ce projet de thèse vise à étudier des aspects peu abordés de la méthode des fragments et à proposer des pistes permettant de mieux comprendre le comportement des fragments vis-à-vis de leur cible, au cours du criblage initial comme lors de leur optimisation
Fragment-Based Drug Design (FBDD) has been proposed in 1996 and has since been recognized as a tangible alternative to the more classical drug discovery methods such as High-Throuput Screening. FBDD consists of screening a small number (< 10 000) of low-molecular weight (< 300 Da) compounds and detect those that bind to the target (protein or nucleic acids). Because of their low complexity, fragment molecules usually display low affinities for their target, hence detecting fragment-protein interactions is mostly achieved using a biophysical technique (mostly Nuclear Magnetic Resonance (NMR), X-ray crystallography or Surface Plasmon Resonance). “Hit” fragments are then modified by addition of chemical substituents, or linked together, so as to elaborate a more complex molecule, forming more interactions with the target and hence displaying an improved affinity. As compared to the more classical High Throughput Screening method, fragment screening provides several advantages, including a better exploration of chemical space, highly ligand-efficient hits and easier optimization of the hits into more affine molecules. In this PhD project, several aspects of FDBB have been addressed : first, FBDD approaches were applied to the research of an inhibitor of the human peroxiredoxin 5 protein, using NMR not only as a screening method but also for the characterization of the protein-fragment interactions. The discovery of an inhibitor against this enzyme would allow to better understand its function. Next, methodological aspects of the FBDD method were addressed : Do fragments conserve their binding site, binding efficiency and mode of interaction upon optimization? Can the fragments display specificity towards a given target? Towards a given binding site? These issues, rarely studied, are yet essential to the understanding of the behavior of fragment molecules, and will be addressed firstly by defragmentating several Bcl-xL inhibitors into fragments and studying their behavior towards the protein in terms of a_nity and binding mode, secondly by screening a set of fragments against five different proteins (human peroxiredoxin 5, human serum albumin and three homologous proteins of the Bcl-2 family of proteins). More generally, this PhD project aims at studying less characterized aspects of the fragment methodology and proposing answers to better understand the behavior of fragment molecules towards their targets, both in the initial screening step and then during their optimization

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Klaue, Daniel. « DNA Unwinding by Helicases Investigated on the Single Molecule Level ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-97596.

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Each organism has to maintain the integrity of its genetic code, which is stored in its DNA. This is achieved by strongly controlled and regulated cellular processes such as DNA replication, -repair and -recombination. An essential element of these processes is the unwinding of the duplex strands of the DNA helix. This biochemical reaction is catalyzed by helicases that use the energy of nucleoside triphophate (NTP) hydrolysis. Although all helicases comprise highly conserved domains in their amino acid sequence, they exhibit large variations regarding for example their structure, their function and their target nucleic acid structures. The main objective of this thesis is to obtain insight into the DNA unwinding mechanisms of three helicases from two different organisms. These helicase vary in their structures and are involved in different pathways of DNA metabolism. In particular the replicative, hexameric helicase Large Tumor-Antigen (T-Antigen) from Simian virus 40 and the DNA repair helicases RecQ2 and RecQ3 from Arabidopsis thaliana are studied. To observe DNA unwinding by these helicases in real-time on the single molecule level, a biophysical technique, called magnetic tweezers, was applied. This technique allows to stretch single DNA molecules attached to magnetic particles. Simultaneously one can measure the DNA end-to-end distance. Special DNA hairpin templates allowed to characterize different parameters of the DNA unwinding reaction such as the unwinding velocity, the length of unwound DNA (processivity) or the influence of forces. From this mechanistic models about the functions of the helicases could be obtained. T-Antigen is found to be one of the slowest and most processive helicases known so far. In contrast to prokaryotic helicases, the unwinding velocity of T-Antigen shows a weak dependence on the applied force. Since current physical models for the unwinding velocity fail to describe the data an alternative model is developed. The investigated RecQ helicases are found to unwind and close short stretches of DNA in a repetitive fashion. This activity is shown for the first time under external forces. The experiments revealed that the repetitive DNA unwinding is based on the ability of both enzymes to switch from one single DNA strand to the other. Although RecQ2 and RecQ3 perform repetitive DNA unwinding, both enzymes differ largely in the measured DNA unwinding properties. Most importantly, while RecQ2 is a classical helicase that unwinds DNA, RecQ3 mostly rewinds DNA duplexes. These different properties may reflect different specific tasks of the helicases during DNA repair processes. To obtain high spatial resolution in DNA unwinding experiments, the experimental methods were optimized. An improved and more stable magnetic tweezers setup with sub-nanometer resolution was built. Additionally, different methods to prepare various DNA templates for helicase experiments were developed. Furthermore, the torsional stability of magnetic particles within an external field was investigated. The results led to selection rules for DNA-microsphere constructs that allow high resolution measurements
Jeder Organismus ist bestrebt, die genetischen Informationen intakt zu halten, die in seiner DNA gespeichert sind. Dies wird durch präzise gesteuerte zelluläre Prozesse wie DNA-Replikation, -Reparatur und -Rekombination verwirklicht. Ein wesentlicher Schritt ist dabei das Entwinden von DNA-Doppelsträngen zu Einzelsträngen. Diese chemische Reaktion wird von Helikasen durch die Hydrolyse von Nukleosidtriphosphaten katalysiert. Obwohl bei allen Helikasen bestimmte Aminosäuresequenzen hoch konserviert sind, können sie sich in Eigenschaften wie Struktur, Funktion oder DNA Substratspezifität stark unterscheiden. Gegenstand der vorliegenden Arbeit ist es, die Entwindungsmechanismen von drei verschieden Helikasen aus zwei unterschiedlichen Organismen zu untersuchen, die sich in ihrer Struktur sowie ihrer Funktion unterscheiden. Es handelt sich dabei um die replikative, hexamerische Helikase Large Tumor-Antigen (T-Antigen) vom Simian-Virus 40 und die DNA-Reparatur-Helikasen RecQ2 und RecQ3 der Pflanze Arabidopsis thaliana. Um DNA-Entwindung in Echtzeit zu untersuchen, wird eine biophysikalische Einzelmolekültechnik, die \"Magnetische Pinzette\", verwendet. Mit dieser Technik kann man ein DNA-Molekül, das an ein magnetisches Partikel gebunden ist, strecken und gleichzeitig dessen Gesamtlänge messen. Mit speziellen DNA-Konstrukten kann man so bestimmte Eigenschaften der Helikasen bei der DNA-Entwindung, wie z.B. Geschwindigkeit, Länge der entwundenen DNA (Prozessivität) oder den Einfluß von Kraft, ermitteln. Es wird gezeigt, dass T-Antigen eine der langsamsten und prozessivsten Helikasen ist. Im Gegensatz zu prokaryotischen Helikasen ist die Entwindungsgeschwindigkeit von T-Antigen kaum kraftabhängig. Aktuelle Modelle sagen dieses Verhalten nicht vorraus, weshalb ein alternatives Modell entwickelt wird. Die untersuchten RecQ-Helikasen zeigen ein Entwindungsverhalten bei dem permanent kurze Abschnitte von DNA entwunden und wieder zusammengeführt werden. Dieses Verhalten wird hier zum ersten Mal unter dem Einfluß externer Kräfte gemessen. Es wird gezeigt, dass die permanente Entwindung auf die Fähigkeit beider Helikasen, von einem einzelen DNA-Strang auf den anderen zu wechseln, zurückzuführen ist. Obwohl RecQ2 und RecQ3 beide das Verhalten des permanenten Entwindens aufzeigen, unterscheiden sie sich stark in anderen Eigenschaften. Der gravierendste Unterschied ist, dass RecQ2 wie eine klassische Helikase die DNA entwindet, während RecQ3 eher bestrebt ist, die DNA-Einzelstränge wieder zusammenzuführen. Die unterschiedlichen Eigenschaften könnten die verschieden Aufgaben beider Helikasen während DNA-Reparaturprozessen widerspiegeln. Weiterhin werden die experimentellen Methoden optimiert, um möglichst hohe Auflösungen der Daten zu erreichen. Dazu zählen der Aufbau einer verbesserten und stabileren \"Magnetischen Pinzette\" mit sub-nanometer Auflösung und die Entwicklung neuer Methoden, um DNA Konstrukte herzustellen. Außerdem wird die Torsions\\-steifigkeit von magnetischen Partikeln in externen magnetischen Feldern untersucht. Dabei finden sich Auswahlkriterien für DNA-gebundene magnetische Partikel, durch die eine hohe Auflösung erreicht wird

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