Size exclusion chromatography is the method of choice for characterizing molecular weights and molecular weight distributions of polymers. An important advancement in SEC is multidetection SEC which includes multi-angle laser light scattering, viscometry, refractive index and UV spectroscopy to analyze block and graft copolymers as well as polymers with oligomeric molecular weights. Oligomeric molecular weights present special challenges since the light scattering and viscosity detectors are more sensitive to higher molecular weights and both detectors have low molecular weight threshold values. The molecular weights and distributions of poly(2-ethyl-2-oxazoline) oligomers and block copolymers as well as poly(2-ethyl-2-oxazoline) were investigated by SEC using multiple detectors. Both a universal calibration method and light scattering were used to determine molecular weights and molecular weight distributions. The solvent was N-methylpyrrolidone that contained 0.05M LiBr used to minimize interactions among the polymers and solvent. SEC was used to establish that the diblock copolymers had heterogeneous compositional distributions. The low molecular weights of the diblock and homopolymer made it necessary to use the universal calibration method with combined refractive index and viscometry detectors to determine absolute molecular weights. / Master of Science

Yes / The aim of this work was to investigate the feasibility of cross-linker free polyelectrolyte complex formation at the nanoscale between carrageenan (CAR) and protamine (PROT). The properties of CAR/PROT nanoparticles (NPs) were dependent on the carrageenan type: kappa (KC), iota (IC) and lambda (LC), concentration of components, addition of divalent cations, weight mixing ratio (WMR) of constituents and mode of component addition. In the case of 0.1% w/v solutions, IC-based NPs had the smallest particle sizes (100-150nm) and low polydispersity indices (0.1-0.4). A decrease in the solution concentration from 0.1% to 0.05% w/v enabled the formation of KC/PROT NPs. All carrageenans exhibited the ability to form NPs with surface charge ranging from -190 to 40mV. The inclusion of divalent cations caused an increase in the particle size and zeta potential. Infrared analysis confirmed the presence of a complex between CAR and PROT and showed that IC chains undergo structural changes when forming NPs. Colloidal stability of NPs was related to the initial surface charge of particles and was time- and pH-dependent. IC was found to be the most suitable type of CAR when forming nanoplexes with PROT.

Spin waves and their quanta, magnons, are the wave-like excitations of a magnetically ordered medium. The technological prospect of utilizing them as low-loss information carriers has driven various research efforts in the field of magnonics. Spin waves arise further interest due to their inherently strong nonlinear behavior which results from their interaction with the surrounding magnetic texture. Hence, magnons are subject to a variety of nonlinear effects and allow for extensive studies of such phenomena. In this work, the propagating spin-waves in micro structured Co25Fe75 conduits have been investigated by means of micro focused Brillouin light scattering spectroscopy. Due to the low intrinsic damping of this metallic compound, spin-wave decay lengths in the order of 20 μm can be observed which have not been reported elsewhere for other ferromagnet thin film materials. Furthermore, nonlinear four-magnon scattering processes can be observed when increasing the spin-wave amplitudes applying a sufficiently strong microwave excitation. This phenomenon introduces additional losses for propagating waves as it diverts energy into the parametric generation of secondary states. It is shown that the reduction of the spin-wave decay lengths reaches up to 50 %. In the second part, a novel approach for the utilization of four-magnon scattering is presented. It is shown that an additional driving signal at a secondary driving frequency can steer the nonlinear process in such a way, that a set of secondary parametric states with a well-defined frequency spacing is populated. This process is referred to as stimulated four-magnon scattering, as it enhances specific nonlinear scattering events. As a result, frequency combs with multiple equidistant modes are observed, which exhibit frequency spacings of 400 MHz up to 2 GHz. These complex spin-wave spectra can actively be tuned in various ways using external parameters such as the driving signals. These results advance the understanding of nonlinear spin waves in general and expands the range of possible technological applications of magnons.:List of Figures List of Tables List of Abbreviations and Acronyms List of Symbols 1 Introduction 2 Theoretical background 2.1 Interactions in microstructured thin film ferromagnets 2.1.1 Exchange interaction 2.1.2 Dipolar interaction and demagnetizing fields 2.2 Magnetization dynamics in ferromagnetic thin films 2.2.1 The Landau-Lifshitz and Gilbert equation 2.2.2 Spin waves 2.3 Nonlinear phenomena 2.3.1 Four-magnon scattering 3 Materials and Methods 3.1 Materials and sample fabrication 3.1.1 The low damping alloy Co25Fe75 3.1.2 Patterning: electron beam and optical lithography 3.1.3 Microwave antenna structures 3.2 Brillouin light scattering 3.2.1 Magnon-photon interaction 3.2.2 The Tandem Fabry Pérot interferometer 3.2.3 BLS microscopy (μBLS) 3.2.4 Phase-resolved BLS (PR-μBLS) 3.2.5 Temporal resolution (TR-μBLS) 3.3 Micromagnetic simulations in MuMax3 3.3.1 Mesh and material parameters 3.3.2 Simulation of magnetization dynamics 4 Results 4.1 Magnon transport in Co25Fe75 micro-conduits 4.1.1 Low external fields and magnetic groundstate 4.1.2 Magnon transport at low driving powers 4.1.3 Impact of nonlinear four-magnon scattering on magnon transport 4.2 Magnon frequency combs 4.2.1 Introduction on stimulated four-magnon scattering 4.2.2 Experimental realization 4.2.3 Amplitude-dependent observations 4.2.4 Tunability of spin-wave frequency combs 4.2.5 Variations of the excitation geometry 5 Summary and outlook Own publications Bibliography 109 Acknowledgement A Appendix A.1 Fabrication of Co25Fe75 microstructures A.2 Atomic Force Microscopy measurement on a 5 μm wide conduit A.3 BLS measurement of spin-wave decay lengths in a 5 μm wide conduit A.4 Calculations: Temporal profile of stimulated four-magnon scattering A.5 Power dependent frequency comb formation measured at positions II & III A.6 Averaged frequency comb mode numbers at reversed magnetic field polarity

Noble metal nanoparticles such as gold and silver are of interest because of the unique electro-optical properties (e.g., localized surface plasmon resonance [LSPR]) that originate from the collective behavior of their surface electrons. These nanoparticles are commonly developed and used for biomedical and industrial application. A recent report has predicted that the global market for gold nanoparticles will be over 12.7 tons by year 2020. However, these surface-functionalized nanoparticles can be potential environmental persistent contaminants post-use due to their high colloidal stability in the aquatic systems. Despite, the environmental risks associated with these nanoparticles, just a few studies have investigated the effect of nanofeature factors such as size and shape on the overall fate/transport and organismal uptake of these nanomaterials in the aquatic matrices. This study presents a comprehensive approach to evaluate the colloidal stability, fate/transport, and organismal uptake of these nanoparticles while factoring in the size and shape related properties. We demonstrate the importance and effect of anisotropicity of a gold nanoparticle on the colloidal behavior and interaction with ecologically susceptible aquatic biota. We also show how readily available characterization techniques can be utilized to monitor and assess the fate/transport of this class of nanoparticles. We further describe and investigate the relationship between the aspect ratio (AR) of these elongated gold nanoparticles with clearance mechanisms and rates from the aquatic suspension columns including aggregation, deposition, and biopurification. We illustrate how a fresh water filter-feeder bivalve, Corbicula fluminea, can be used as a model organism to study the size and shape-selective biofiltration and nanotoxicity of elongated gold nanoparticles. The results suggest that biofiltration by C. fluminea increases with an increase in the size and AR of gold nanoparticle. We develop a simple nanotoxicity assay to investigate the short-term exposure nanotoxicity of gold nanoparticles to C. fluminea. The toxicity results indicate that for the tested concentration and exposure period that gold nanoparticles were not acutely toxic (i.e., not lethal). However, gold nanoparticles significantly inhibited the activities of some antioxidant enzymes in gill and digestive gland tissues. These inhibitions could directly affect the resistance of these organisms to a secondary stressor (temperature, pathogens, hypoxia etc.) and threaten organismal health. / Ph. D. / Nanoparticles are fine particles that cannot be seen with naked eye and possess unique chemical and physical properties. Gold and silver nanoparticles are specifically of interest due to tunable optical properties and are commonly developed and used for biomedical and industrial applications. Unfortunately, these metallic nanoparticles can be potential environmental persistent contaminants post-use in the soil and aquatic systems. Despite, the environmental risks associated with these metallic nanoparticles, just a few studies have investigated the effect of size and shape of these nanoparticles on their interaction and transportation in the surrounding environment and with existing organisms. This study presents a comprehensive approach to evaluate the stability, transportation, and organismal uptake of these nanoparticles while factoring in the size and shape related properties. We also show how readily available detection techniques can be utilized to monitor and assess the presence and transport of this class of nanoparticles. We illustrate how a fresh water bivalve, Corbicula fluminea, can be used as a model organism to study the size and shape-selective uptake and toxicity of gold nanoparticles. The results suggest that nanoparticles uptake by C. fluminea increases with an increase in the size of gold nanoparticle. We develop a simple toxicity assay to investigate the short-term exposure toxicity of gold nanoparticles to C. fluminea. The toxicity results suggest that for the tested concentration and exposure period that gold nanoparticles were not acutely toxic (i.e., not lethal) but affect the resistance of these organisms to an environmental change (temperature, pathogens, hypoxia etc.) and threaten organismal health.

<p dir="ltr">Imaging and sensing through opaque scattering media is a topic of broad interest with a wide range of applications. Methods are impacted by speckle, which refers to grainy patterns of bright and dark spots resulting from coherent interference as light propagates through a randomly scattering medium. This phenomenon is most often considered undesirable in applications. However, it is possible to leverage the information contained in speckle patterns to image hidden objects. In practice, most methods are limited to situations in which the scattering medium is either thin or weakly scattering. This thesis explores a motion-based coherent imaging and sensing method originally developed by prior researchers. This technique takes advantage of heavy scatter and object motion, with no theoretical limit on the amount of scatter. In this method, intensity correlations are performed on speckle images taken with the object at different spatial locations. Prior research led to the development of a theory that describes the relationship between speckle intensity correlations and the object's geometry. This thesis presents substantial new understanding pertaining to the theory that allows for the imaging of general objects in heavily scattering media. Additionally, it is shown that two nominally identical objects can be distinguished through speckle intensity correlations over far-subwavelength translation distances, implying access to the microstructure of objects. Finally, the combining of this method with diffusion-based localization is demonstrated, providing a way to apply this imaging and sensing method without prior knowledge of the object's relative spatial locations.</p>

This thesis is devoted to improve our knowledge on the theory of polarized line formation in a magneto-turbulent medium, and in a scattering dominated magnetized medium, where partial redistribution (PRD) effects become important. Thus the thesis consists of two parts. In the first part we carry out a detailed investigation on the effect of random magnetic fields on Zeeman line radiative transfer. In the second part we develop the theory of polarized line formation in the presence of arbitrary magnetic fields and with PRD. We present numerical methods of solution of the relevant transfer equation in both part-I and II. In Chapter I we give a general introduction, that describes the basic physical concepts required in both parts of the thesis. Chapters 2-6 deal with the part-I, namely stochastic polarized Zeeman line formation. Chapters 7-10 deal with part –II, namely the theory and numerics of polarized line formation in scattering media. Chapter II is devoted to the future outlook on the problems described in part-I and II of the thesis. Appendices are devoted to additional mathematical details. Part-I of the Thesis: Stochastic polarized line formation in magneto-turbulent media Magneto-convection on the Sun has a size spectrum that spans several orders of magnitudes and hence develops turbulent elements or eddies the sizes of which are much smaller than the spatial resolution of current spectro-polarimeters (about 0.2 arcsec or 150km at the photospheric level). We were thus strongly motivated to consider the Zeeman effect in a medium where the magnetic field is random with characteristic scales of variation comparable to the radiative transfer characteristic scales. In Chapter 2, we consider the micro-turbulent limit and study the mean zeeman absorption matrix in detail. The micro-turbulent limit refers to the case when the scales of fluctuations of the random field are much smaller than the photon mean free paths associated to the line formation. The ‘mean’ absorption and anomalous dispersion coefficients are calculated for random fields with a non-Zero mean value - isotropic or anisotropic Gaussian distributions that are azimuthally invariant about the direction of the mean field. The averaging method is described in detail, and fairly explicit expressions for the mean coefficients are established. A detailed numerical investigation of the mean coefficients illustrates two simple effects of the magnetic field fluctuations: (i) broadening of the components by fluctuations of the field strength, leaving the π-components unchanged, and (ii) averaging over the angular dependence of the π and components. Angular averaging can modify the frequency profiles of the mean coefficients quite drastically, namely, the appearance of an unpolarized central component in the diagonal absorption coefficient, even when the mean field is in the direction of the line-of-sight. For isotropic fluctuations, the mean coefficients can be expressed in terms of generalized Voigt and Faraday-Voigt functions, which are related to the derivatives of the Voigt and Faraday-Voigt functions. In chapter 3, we study these functions in detail. Simple recurrence relations are established and used for the calculation of the functions themselves and of their partial derivatives. Asymptotic expansions are also derived. In Chapter 4, we consider the Zeeman effect from a magnetic field which has a finite correlation length(meso-turbulence) that can be varied from zero to infinity and thus made comparable to the photon mean free-path. The random vector magnetic field B is modeled by a Kubo-Anderson process – a piecewise constant Markov process characterized by a correlation length and a probability distribution function(PDF) for the random values of the magnetic field. The micro- and macro-turbulent limits are recovered when the correlation length goes to zero or infinity respectively. Mean values and rms fluctuations around the mean values are calculated numerically for a random magnetic field with isotropic Gaussian fluctuations. The effects of a finite correlation length are discussed in detail. The rms fluctuations of the Stokes parameters are shown to be very sensitive to the correlation length of the magnetic field. It is suggested to use them as a diagnostic tools to determine the scale of unresolved features in the solar atmosphere. In Chapter 5, using statistical approach, we analyze the effects of random magnetic fields on Stokes line profiles. We consider the micro and macro-turbulent regimes, which provide bounds for more general random fields with finite scales of variations. The mean Stokes parameters are obtained in the micro-turbulent regime, by first averaging the Zeeman absorption matrix Φ over the PDF P(B) of the magnetic field and then solving the concerned radiative transfer equation. In the macro-turbulent regime, the mean solution is obtained by averaging the emergent solution over P(B). In this chapter, we consider the same Gaussian PDFs that are used to construct (Φ) in chapter 2. Numerical simulations of magneto-convection and analysis of solar magnetograms provide the empirical PDF for the magnetic field line-of-sight component on the solar atmosphere. In Chapter 6, we explore the effects of different kinds of PDFs on Zeeman line formation. We again consider the limits of micro and macro-turbulence. The types of PDFs considered are: (a) Voigt function and stretched exponential type PDFs for fields with fixed direction but fluctuating strength. (b) Cylindrically symmetrical power law for the angular distribution of magnetic fields with given field strength. (c) Composite PDFs accounting for randomness in both strength and direction obtained by combining a Voigt function or a stretched exponential with an angular power law. The composite PDF proposed has an angular distribution peaked about the vertical direction for strong fields and is nearly isotropically distributed for weak fields, which could mimic solar surface random fields. We also describe how the averaging technique for a normal Zeeman triplet may be generalized to the more common case of anomalous Zeeman splitting patterns. Part-II of the Thesis: Polarized line formation in scattering media-Theory and numerical methods Many of the strongest and most conspicuous lines in the Second Solar Spectrum are strong lines that are formed rather high, often in the chromosphere above the temperature minimum. From the standard, unpolarized and non-magnetic line-formation theory such lines are known to be formed under the conditions that are very far from local thermodynamic equilibrium. They are characterized by broad damping wings surrounding the line core. Doppler shifts in combination with collisions cause photons that are absorbed at a given frequency to be redistributed in frequency across the line profile in a complex way during the scattering process. Two idealized, limiting cases to describe this redistribution are “frequency coherence” and “complete redistribution” (CRD), but the general theory that properly combines these two limiting cases goes under the name “partial frequency redistribution” (PRD). Resonance lines which are usually strong can be properly modeled only when PRD is taken into account. To use these strong lines for magnetic field diagnostics we need a line scattering theory of PRD in the presence of magnetic fields of arbitrary strength. In the second part of the thesis we develop such a theory and derive the polarized PRD matrices. These matrices are then used in the polarized line transfer equation to compute the emergent Stokes parameters. Polarized scattering in spectral lines is governed by a 4 x 4 matrix that describes how the Stokes vector is scattered in all directions and redistributed in frequency within the line. In Chapter 7, using a classical approach we develop the theory for this redistribution matrix in the presence of magnetic fields of arbitrary strength and direction, and for a J = 0 → 1 → 0 transition. This case of arbitrary magnetic fields is called the Hanle-Zeeman regime, since it covers both the partially overlapping weak and strong-field regimes, in which the Hanle and Zeeman effects respectively dominate the scattering polarization. In this general regime the angle-frequency correlations that describe the so-called PRD are intimately coupled to the polarization properties. We also show how the classical theory can be extended to treat atomic and molecular scattering transitions for any combinations of J quantum numbers. In chapter 8 , we show explicitly that for a J = 0 → 1 → 0 scattering transition there exists an equivalence between the Hanle-Zeeman redistribution matrix that is derived through quantum electrodynamics(Bommier 1997b) and the one derived in Chapter 7 starting from the classical, time-dependent oscillator theory of Bommier & Stenflo (1999). This equivalence holds for all strengths and directions of the magnetic field. Several aspects of the Hanle-Zeeman redistribution matrix are illustrated, and explicit algebraic expressions are given, which are of practical use for the polarized line transfer computations. In chapter 9, we solve the polarized radiative transfer equation numerically, taking into account both the Zeeman absorption matrix and the Hanle-Zeeman redistribution matrix. We compute the line profiles for arbitrary field strengths, and scattering dominated line transitions. We use a perturbation method (see eg. Nagendra et al. 2002) to solve the Hanle-Zeeman line transfer problem. The limiting cases of weak field Hanle scattering and strong field Zeeman true absorption are retrieved. The ilntermediate regime, where both Zeeman absorption and scattering effects are important, is studied in some detail. Numerical method used to solve the Hanle-Zeeman line transfer problem in Chapter 9 is computationally expensive. Hence it is necessary to develop fast iterative methods like PALI (Polarized Approximate Lambda Iteration). As a first step in this direction we develop such a method in Chapter 10 to solve the transfer problem with weak field Hanle scattering. We use a ‘redistribution matrix’ with coupling between frequency redistribution and polarization and no domain decomposition. Such a matrix is constructed by angle-averaging the frequency dependent terms in the exact weak field Hanle redistribution matrix for a two-level atom with unpolarized ground level (that can be obtained by taking the weak field limit of the Hanle-Zeeman redistribution matrix). In the past, the PALI technique has been applied to redistribution matrices in which frequency redistribution is ‘decoupled’ from scattering polarization, the decoupling being achieved by an adequate decomposition of the frequency space into several domains. In this chapter, we examine the consequences of frequency space decomposition, and the resulting decoupling between the frequency redistribution and polarization, on the solution of the polarized transfer equation for the Stokes parameters.

Generating, miniaturizing and controlling spin waves on the nanometer scale is of great interest for magnonics. For instance, this holds the prospect of exploring wave-based logic concepts and reduced Joule heating, by avoiding charge transport, in spin-wave circuitry. In this work, a novel approach is for the first time confirmed experimentally, which allows confining spin-wave transport to nanometre-wide channels defined by magnetic domain walls. This is investigated for different domain wall types( 90deg and180deg Néel walls) in two material systems of polycrystalline Ni81Fe19 and epitaxial Fe. The study covers the thermal, linear and non-linear regime utilizing micro- focused Brillouin light scattering microscopy complemented by micromagnetic simulations. An initially linear dispersion dominated by dipolar interactions is found for the guided spin waves. These are transversally confined to sub-wavelength wide beams with a well-defined wave vector along the domain wall channel. In the non-linear regime, higher harmonic generation of additional spin-wave beams at the sides of the domain wall channel is observed. Furthermore, the possibility to shift the position of the domain wall over several microns by small magnetic fields is demonstrated, while maintaining its spin-wave channeling functionality. Additionally, spin-wave transmittance along domain walls, which change direction at the edges of the structure as well as between interconnected walls of identical and different type is studied. Characterization of spin-wave transmission through interconnected domain walls is an important step towards the development of magnonic circuitry based on domain wall(-networks). With respect to developing flexible and scalable spin-wave sources, the second part of this thesis addresses auto-oscillations in spin Hall oscillators (based on a Pt / Ni81Fe19 bilayer) of tapered nanowire geometry. In these systems, a simultaneous formation of two separate spin-wave bullets of distinct localization and frequency has been indicated. This spin-wave bullet formation is con- firmed experimentally and investigated for different driving currents. Subsequently, control over these bullets by injecting external microwave signals of varying frequency and power is demon- strated, switching the oscillator into single-mode operation. Three synchronized auto-oscillatory states are observed, which can be selected by the frequency of the externally imprinted signal. This synchronization results in linewidth reduction and frequency-locking of the individual bullet modes. Simultaneously the bullet-amplitude is amplified and is found to scale as P2/3 with the injected microwave power P. This amplification and control over position and frequency of the spin-wave bullets is promising for the development of microwave amplifiers/detectors and spin- wave sources on the nanoscale based on spin Hall oscillators.:1 Introduction 1 2 Theoretical background 4 2.1 Energy density of thin film ferromagnets and domain(wall) formation 2.2 Magnetizationdynamicsinthinfilmferromagnets 11 2.2.1 Spin-wavedispersioninthelinearregime 13 2.2.2 Magnetizationdynamicsinthenon-linearregime 17 2.3 SpinHallOscillators 21 2.3.1 Spin Hall effect and spin transfer torque in a ferromagnet/heavy-metal bi- layersystem 21 2.3.2 Characteristics of magnetization auto-oscillations 25 2.3.3 Improvement of monochromaticity, coherence and output power by injec- tionlocking 28 3 Materials and Methods 31 3.1 ElectronBeamLithography,EBL 31 3.2 Ni81Fe19 microstructures 32 3.3 Femicrostructures 34 3.4 TaperedspinHalloscillators 35 3.5 Micro-focused Brillouin Light Scattering Spectroscopy, μBLS 36 3.5.1 μBLSspatialresolution 40 4 Experimental results 43 4.1 Spin-wave dynamics in multi-domain magnetic configurations 43 4.1.1 Spin-wave dynamics of 180◦ Néel walls in rectangular elements 44 4.1.2 Spin-wave dynamics of 90◦ Néel walls in square elements 63 4.1.3 Spin-wave dynamics of interconnected Néel walls in Fe wires 76 4.2 Auto-oscillationintaperedwiregeometries 88 4.2.1 Initial static magnetic configuration and effective field 89 4.2.2 Thermally excited dynamics and spectral properties 91 4.2.3 Direct microwave excitation of spin-wave dynamics 93 4.2.4 Auto-oscillatoryresponse 96 4.2.5 Microwaveamplificationandinjectionlocking 104 5 Summary and outlook 114 Own publications 118 Bibliography 120 Acknowledgement 141 A Appendix 143 A.1 Splitting process in magnetic domains confined by domain walls 143 A.2 reconfigurable remanent states in square structures stabilized by local ion irradiation 144 A.3 Domain wall displacements induced by a scanning laser beam 145 A.4 Magnetic Force Microscopy investigation of the domain wall type and width 147 A.5 Micromagnetic simulations: problem definition and analysis 149 A.6 Current dependence of auto-oscillations in the tapered SHO 152 A.7 Fabrication of Ni81Fe19 microstructures for spin waves in domain walls 153

Neuf maladies neurodégénératives sont le produit de l’expression de gènes mutés, dans lesquels le codon CAG est répété au-delà d’un seuil pathologique. Ceci produit des protéines mutantes dans lesquelles sont insérés des segments de polyglutamines (polyGln), qui perdent leur activité et acquièrent une nouvelle fonction, ce qui est toxique pour le neurone. Ces altérations sont attribuables aux propriétés particulières de la polyGln. En effet, ces dernières possèdent la capacité de s’assembler pour former des corps d’inclusion intracellulaires. Cette propension à l’agrégation de la polyGln rend difficile l’étude de ces pathologies. C’est ainsi que l’utilisation de peptides peut s’avérer une approche avantageuse. Toutefois, la synthèse de polyGln est associée à de nombreuses délétions et nécessite l’ajout de groupements chargés afin de permettre leur purification. Cependant, ce prérequis donne lieu à des interactions électrostatiques qui biaisent la structure et la cinétique d’agrégation de ces peptides, en plus d’interférer avec l’évaluation d’éventuels agents thérapeutiques. L’objectif du projet est de développer un système permettant l’étude de la polyGln en s’affranchissant des effets de charges. Pour ce faire, deux approches ont été explorées, la première utilise la polyGln non chargée et la seconde utilise une structure polyGln-morpholine ayant des charges labiles en fonction du pH. Ces peptides ont été produits en utilisant une approche linéaire de synthèse peptidique sur support solide avec protection maximale des chaînes latérales. La purification a été effectuée par chromatographie de haute performance en phase inverse en milieu acide. Ces stratégies ont permis de produire des peptides de polyGln de grande pureté avec des rendements acceptables. Une procédure de solubilisation des peptides alliant sonication et lyophilisation a été développée afin d’étudier chacun de ces peptides à l’aide de diverses techniques physicochimiques, telles que la diffusion de la lumière, la spectroscopie de résonance magnétique nucléaire, Raman et UV-visible, le dichroïsme circulaire et la microscopie optique polarisée. La polyGln non chargée solubilisée dans le trifluoroéthanol-eau a montré que la taille des particules et la vitesse d’agrégation sont proportionnelles à la fraction volumique en eau. De plus, la structure secondaire en solution est à prédominance alpha et semble être peu sensible à la fraction d’eau jusqu’à un certain seuil (25%) après lequel la structure aléatoire prédomine. L’analyse des agrégats à l’état solide montre des structures hélicoïdales > aléatoires et ont les caractéristiques des fibrilles amyloïdes. Le peptide de polyGln-morpholines a un pKa de 7,3 en milieu aqueux. Il demeure en solution lorsque le pH < pKa et à faible force ionique, alors qu’il s’autoassemble lorsque ces conditions ne sont pas respectées. Ceci suggère que la répulsion électrostatique est responsable de la stabilisation du peptide en solution. La dimension fractale nous indique que le peptide forme des agrégats compacts dont les constituants ont une taille de 2,5 nm, compatibles avec une conformation aléatoire compacte, en coude bêta ou hélicoïdale. Ceci est en accord avec l’étude structurale des peptides en solution qui a montré des espèces aléatoires > bêta > alpha. De plus, en RMN, l’élargissement des signaux du 1Hγ en cours d’agrégation suggère une interaction via les chaînes latérales. Les analyses en phase solide ont plutôt montré une prédominance de structures bêta et alpha. L’inhibition de l’agrégation à pH 8 varie selon rouge de Congo > tréhalose, alors que le peptide liant la polyGln 1 et la thioflavine T ne semble pas avoir d’effet. Ces approches ont donc permis pour la première fois de s’affranchir des effets de charges auparavant inhérents à l’étude de la polyGln en solution et par conséquent d’obtenir des informations inédites quant à la solubilité, la structure et la cinétique d’agrégation. Enfin, le dispositif à charges labiles permet d’évaluer l’efficacité d’éventuels agents thérapeutiques à pH quasi physiologique. / Nine neurodegenerative diseases come from mutated genes expression in which the CAG codon is repeated above a pathological threshold. This is producing mutant proteins, in which are inserted polyglutamine (polyGln) segments, which lose their activity and acquire a new function that is toxic for the neuron. These alterations are related to the peculiar properties of the polyGln. Indeed, these polypeptides have the capacity of autoassemble to form intracellular inclusion bodies. This aggregation tendency of polyGln makes difficult the study of these pathologies. Thus, the use of peptides could constitute an advantageous approach. However, the synthesis of polyGln is associated with numerous deletions and necessitates the addition of charged moieties to achieve purification. Unfortunately, this requirement creates electrostatic interactions that modify the structure and aggregation kinetics of these peptides, in addition to interfering with the evaluation of potential therapeutical agents. The aim of this project is to develop a system to study polyGln without the charge effects. To do so, two approaches were explored, the first used uncharged polyGln and the second used a polyGln-morpholine structure bearing pH-dependent labile charges. These peptides were produced by solid-support synthesis using a linear and maximal protection approach. Purification was performed by reverse phase high-performance liquid chromatography. These strategies allowed the production of peptides of high purity in good yields. A solubilization procedure combining sonication and lyophilization was developed to study each of these peptides by physicochemical techniques such as light scattering, magnetic resonance, Raman and UV-visible spectroscopies, circular dichroism and polarized optical microscopy. The uncharged polyGln solubilized in trifluoroethanol-water showed that particle size and aggregation kinetics are proportional to volumetric water fraction. Furthermore, the secondary structure in solution is alpha-predominant and seems rather insensitive to water fraction up to a threshold (25%) above which random coil structure predominates. The analysis of solid-state aggregates showed that helicoidal structures are more abundant than random structures and have the characteristics of amyloid fibrils. The polyGln-morpholines peptide has a pKa of 7.3 in aqueous media. It is soluble when pH < pKa and at low ionic strength, but it autoassociates when these conditions are not respected. This suggests that electrostatic repulsion is responsible for the stabilization of the peptide in solution. The fractal dimension indicates that the peptide forms compact aggregates whose constituents are 2.5 nm in size, in agreement with compact random coil, beta-hairpin or helicoidal structures. This is in agreement with the results of solution peptide structure studies showing that random coil > beta > alpha. Furthermore, the broadening of 1Hγ NMR signals while the peptide is aggregating suggests an interaction between side-chains. Solid-phase studies showed predominant beta and alpha structures. The aggregation inhibition at pH 8.0 was higher for Congo red than for trehalose, while polyglutamine binding peptide 1 and thioflavine T did not seem to be effective. These approaches permitted for the first time to overcome the charge effects that were previously inherent to polyGln solution studies and to obtain new information about solubility, structure and aggregation kinetics. Finally, the labile charge groups allow the evaluation of the efficiency of potential therapeutic agents at near physiological pH.

La sédimentation des suspensions aqueuses de particules minérales microniques, polydisperses et concentrées a été analysée à l’aide du Turbiscan MA 2000 fondé sur la diffusion multiple de la lumière, en vue d’établir la procédure qui permet de déceler la présence d’une morphologie fractale, puis de déduire les règles de comportements des suspensions fractales par la modélisation avec les réseaux de neurones. Le domaine des interactions interparticulaires physicochimiques (0 à 10% volumique en solide) a été privilégié.La méthodologie de détermination de la structure multifractale des agglomérats et de la suspension a été proposée. La modification structurale des agglomérats qui est à l’origine de comportements non linéaires des suspensions et qui dépend des propriétés cohésives des particules primaires, est interprétée par la variation de la mobilité électrophorétique des particules en suspension. Une approche d’estimation de ces modifications structurales par les réseaux de neurones, à travers la dimension fractale, a été présentée. Les limites du modèle à assimiler ces comportements particuliers ont été expliquées comme résultant du faible nombre d’exemples et de la grande variabilité des mesures aux faibles fractions volumiques en solide. / The sedimentation of aqueous suspensions of micron-sized mineral particles, polydisperses and concentrated, was analyzed using the Turbiscan MA 2000 based on the multiple light scattering in order to establish the procedure to detect the presence of a fractal morphology, and then to deduce the set of laws of fractal behavior of suspensions by modeling with neural networks. The methodology for determining the multifractal structure of agglomerates and the suspension was proposed. The structural modifications of the agglomerates at the origin of the nonlinear behavior of suspensions and which depends on cohesive properties of primary particles, is interpreted by the change of the electrophoretic mobility of suspended particles. The estimation by neural networks of these structural changes, through the fractal dimension has been presented. The limits of the model to learn these specific behaviors have been explained as resulting from the low number of examples and the great variability in the measurements at low volume fractions of solid.

L’utilisation accrue des nanomatériaux manufacturés (NM) fait en sorte que les différents acteurs de réglementation se questionnent de plus en plus par rapport à leur destin et leurs impacts sur les écosystèmes et la santé humaine suite à leur rejet dans l’environnement. Le développement de techniques analytiques permettant de détecter et de caractériser les NM en matrice environnementale est impératif étant donné la nécessité d’évaluer le risque relié à ces polluants émergents. Une des approches de plus en plus favorisée est d’utiliser une technique chromatographique et un ou plusieurs détecteurs sensibles dans les buts de réduire les effets de matrice, d’identifier des nanoparticules (NP) selon leurs temps de rétention et de les quantifier à des concentrations représentatives de la réalité environnementale. Une technique analytique utilisant la chromatographie hydrodynamique (HDC) et des détecteurs en ligne ou hors ligne (détecteurs de diffusion statique ou dynamique de la lumière, spectromètre de masse par torche à plasma en mode particule unique (SP-ICPMS), l’ultracentrifugation analytique) a donc été développée. Le couplage de la colonne HDC avec ces détecteurs a permis de caractériser des NP standards et l’optimisation des conditions de séparation de ces nanoparticules de polystyrène, d’or et d’argent a permis de confirmer que les NP y sont bel et bien séparées seulement selon leur taille, tel que la théorie le prédit. De plus, l’utilisation de la colonne HDC couplée au SP-ICPMS a permis de séparer un mélange de nanoparticules d’argent (nAg) et de les détecter à des concentrations représentatives de celles rencontrées dans l’environnement, soit de l’ordre du μg L-1 au ng L-1. Par exemple, dans un échantillon d’eau usée (effluent), un mélange de nAg de 80 et de 40 nm a été séparé et les nAg ont été détectées à l’aide du SP-ICPMS connecté à la colonne HDC (temps de rétention de 25.2 et 25.6 minutes et diamètres déterminés de 71.4 nm et 52.0 nm). Finalement, pour plusieurs échantillons environnementaux auxquels aucun ajout de nanoparticules n’a été fait, les analyses HDC-SP-ICPMS effectuées ont permis de déterminer qu’ils ne contenaient initialement pas de nAg. / Due to the widespread use of engineered nanoparticles (ENP), regulatory agencies are very concerned about their fate and their impacts on the environment and on human health. The development of analytical techniques, which will allow the detection, characterization and quantification of ENP in environmental matrices, is therefore critical in order to properly evaluate the exposure associated with these emerging pollutants. One promising approach to detect and quantify the nanoparticles is to couple a chromatographic technique to a sensitive detector in order to: (i) reduce matrix effects; (ii) identify nanoparticles from their retention times and (iii) quantify the ENP at environmentally relevant concentrations. Consequently, the coupling of hydrodynamic chromatography (HDC) was performed with both on-line and off-line detectors (light scattering detectors, inductively coupled plasma mass spectrometer in its single particle mode (SP-ICPMS) and an analytical ultracentrifuge). HDC was first used for the characterization of ENP standards. Separation conditions were optimized for standard nanoparticle suspensions of polystyrene, gold and silver, which allowed us to confirm that the separation was occurring, based on hydrodynamic size, as predicted by theory. By coupling the HDC column to the ICPMS detector in its ‘‘single particle’’ mode, it was possible to separate an ENP mixture and to detect the nanoparticles at environmental concentrations, i.e., in the μg L-1 to ng L-1 range. For example, in a wastewater sample (effluent wastewater), a mixture of two silver nanoparticles (nAg) of 40 and 80 nm were separated and the nAg were detected by SP-ICPMS at retention times of 25.2 and 25.6 minutes. Diameters of 71.4 nm and 52.0 nm were found. HDC-SP-ICPMS analysis carried out on different non-spiked wastewater samples allowed us to conclude that nAg was below the detection limit of 0.1 µg L-1.