The aims of this thesis are concerned with the synthesis of layered double hydroxide nanoparticles with controlled morphology and particle size distribution and an investigation of their physical properties. An introduction of layer double hydroxide chemistry, especially existing synthetic approaches, is reviewed in Chapter 1. Structural investigations, characterisation techniques, the properties and the applications of LDHs are discussed consecutively. The first successful synthesis of lithium aluminium nanorods using the hydrothermal treatment of a gibbsite precursor with a rod-like morphology is described in Chapter 2. The rod morphology is depicted using electron microscopy and confirmed by comparing refined X-ray diffraction patterns to a standard sample. Chapter 3 describes the application of reverse microemulsion method to prepare Co-Al and Ni-Al LDH nanoplatelets. The LDH particle sizes can be effectively controlled, and the structures of the nanoplatelets are investigated. The magnetic properties of the LDH nanoplatelets are dependent on the size of the nanoplatelets. A novel single component microemulsion system for the synthesis of LDHs is developed in Chapter 4. Mg-Al LDH nanoplatelets were successfully synthesised with precise particle size control. The factors affecting the formation of the microemulsions and the mechanism of the synthesis are discussed. Chapter 5 focuses on the applications of the novel single component microemulsion methods to prepare a range of LDHs with different metal combinations including Co-Al, Ni-Al, Zn-Al, Li-Al, Ca-Al, and Ni-Fe. This method proves very effective at controlling the particle sizes. The magnetic properties of the LDHs containing paramagnetic transition metal centres have been studied in detail. In Chapter 6, the DIFFaX program has been used to simulate the XRD patterns of layered structures. The factors influencing the XRD patterns in these materials have been systematically investigated including the effects of particle size, stacking faults, and disorder. The XRD patterns of materials described in previous chapters are simulated using the latest DIFFaX+ code in order to estimate the particle sizes and stacking sequences. The characterising techniques and the experimental details are listed in Chapter 7.

Knowledge of how intermolecular interactions of amyloidogenic proteins cause protein aggregation and how those interactions are affected by sequence and solution conditions is essential to our understanding of the onset of many degenerative diseases. Of particular interest is the aggregation of the amyloid-β (Aβ) peptide, linked to Alzheimer's disease, and the aggregation of the Sup35 yeast prion peptide, which resembles the mammalian prion protein (PrP) linked to spongiform encephalothopies. To facilitate the study of these important peptides, experimentalists have identified small peptide congeners of the full-length proteins that exhibit amyloidogenic behavior, including the KLVFFAE sequence of the Aβ protein, and the GNNQQNY sequence of Sup35. Reverse micelles provide an important environment for the study of protein folding and aggregation. In a reverse micelle, it is possible to observe the effects that confinement and water activity, believed to play a critical role in an in vivo cellular environment, have on protein folding, misfolding, and aggregation. We employed molecular dynamics simulations of reverse micelles as well as peptides encapsulated in reverse micelles in order to characterize the reverse micelle environment and identify fundamental principles that inform how sequence and solution environment influence protein aggregation. The peptides studied include the alanine-rich peptide AKA2 as well as the amyloidogenic KLVFFAE and GNNQQNY peptide fragments. The results of these studies suggest that substantial fluctuations in reverse micelle shape away from an idealized spherical geometry enables significant interaction between peptides and the surfactant interface. Analysis these results, including evaluation of water dynamics and calculated IR spectra of the amide I vibration of the peptides, indicate that our model of the reverse micelle is a robust one which captures essential features of this complex system. Moreover, our studies provide critical insight into the complex role played by a heterogeneous cellular environment in the earliest stages of protein aggregation and amyloid formation.

No description available.

Synthesis of copper nanoparticles by a colloidal recipe in a two-phase liquid-liquid mixture (toluene/water) was investigated. The synthesis recipe used in this work was originally applied for the fabrication of alkylamine-capped gold nanoparticles. This method involves transferring metal cations from the aqueous layer to the organic one by the phase transfer reagent, tetraoctylammonium bromide, followed by reduction with sodium borohydride in the presence of oleylamine, which was used as the stabilising ligand. Several modifications were made to the original recipe to produce copper nanoparticles with high degrees of purity and stability. These particles are potentially applicable in various industries and are considered as an alternative for expensive metal nanoparticles, such as gold, silver, and platinum. Due to the high tendency of copper for oxidation, all of the synthesis experiments were carried out in a glove box under the flow of an inert gas (N2 or Ar). The concentration of Cl− was initially increased to form anionic complexes of copper that could later react with the cationic phase transfer reagent. This modification was followed to enhance the efficiency of the transferring step; however, the presence of anion, Cl−, at the surface of the synthesized particles was reported to change their properties; thus, increasing chloride concentration was eventually ignored. The decanting of two phases prior to the reduction step was also investigated to examine whether the site of the reduction reaction could be limited to cores of reverse micelles. The aggregated nanoparticles, which were fabricated by reducing the decanted organic phase, were heated after the synthesis at 150°C for 30 minutes to obtain a light green solution of nanoparticles. However, further characterization was not possible due to the hydrocarbon impurities. Dodecane, which was employed as the solvent for post-synthesis heating procedure, is believed to result in these impurities. Further investigation is required to explain the mechanism by which post-synthesis heating facilitates nanoparticle stabilization. Duplication of the original recipe for copper in an inert atmosphere resulted in a mixture of assembled layers of separated copper nanocrystals with an average size of ~ 5 nm and aggregated clusters of cubic copper (I) oxide nanoparticles. The possible mechanism for this division is believed to be the presence of the phase transfer reagent capped to the surface of a portion of synthesized particles leading to their metastability.

Synthesis of copper nanoparticles by a colloidal recipe in a two-phase liquid-liquid mixture (toluene/water) was investigated. The synthesis recipe used in this work was originally applied for the fabrication of alkylamine-capped gold nanoparticles. This method involves transferring metal cations from the aqueous layer to the organic one by the phase transfer reagent, tetraoctylammonium bromide, followed by reduction with sodium borohydride in the presence of oleylamine, which was used as the stabilising ligand. Several modifications were made to the original recipe to produce copper nanoparticles with high degrees of purity and stability. These particles are potentially applicable in various industries and are considered as an alternative for expensive metal nanoparticles, such as gold, silver, and platinum. Due to the high tendency of copper for oxidation, all of the synthesis experiments were carried out in a glove box under the flow of an inert gas (N2 or Ar). The concentration of Cl− was initially increased to form anionic complexes of copper that could later react with the cationic phase transfer reagent. This modification was followed to enhance the efficiency of the transferring step; however, the presence of anion, Cl−, at the surface of the synthesized particles was reported to change their properties; thus, increasing chloride concentration was eventually ignored. The decanting of two phases prior to the reduction step was also investigated to examine whether the site of the reduction reaction could be limited to cores of reverse micelles. The aggregated nanoparticles, which were fabricated by reducing the decanted organic phase, were heated after the synthesis at 150°C for 30 minutes to obtain a light green solution of nanoparticles. However, further characterization was not possible due to the hydrocarbon impurities. Dodecane, which was employed as the solvent for post-synthesis heating procedure, is believed to result in these impurities. Further investigation is required to explain the mechanism by which post-synthesis heating facilitates nanoparticle stabilization. Duplication of the original recipe for copper in an inert atmosphere resulted in a mixture of assembled layers of separated copper nanocrystals with an average size of ~ 5 nm and aggregated clusters of cubic copper (I) oxide nanoparticles. The possible mechanism for this division is believed to be the presence of the phase transfer reagent capped to the surface of a portion of synthesized particles leading to their metastability.

The combination of water and surface active compounds found naturally in commercially refined vegetable oils have been postulated to form physical structures known as association colloids. This research studied the ability of 1,2-dioleoyl-sn-glycerol-3-phosphocholine (DOPC) and water to form physical structures in stripped soybean oil. Interfacial tension and fluorescence spectrometry results showed the critical micelle concentration (CMC) of DOPC in stripped soybean oil was 650 and 950 microM, respectively. Light scattering attenuation results indicated that the structure formed by DOPC was reverse micelles. The physical properties of DOPC reverse micelles were determined using small-angle X-ray scattering (SAXS) and fluorescence probes. These studies showed that increasing the water concentration altered the size and shape of the reverse micelles formed by DOPC. The impact of DOPC reverse micelles on the lipid oxidation of stripped soybean oil was investigated by following the formation of primary and secondary lipid oxidation products. DOPC reverse micelles had a prooxidant effect, shortening the oxidation lag phase of SSO at 55 °C. It also was not able to change the lipid oxidation of stripped soybean oil compared with DOPC reverse micelles at same concemtration ( i.e., 950 microM). 1,2-dibutyl-sn-glycerol-3-phosphocholine (DC4PC) which has the shorter fatty acid than DOPC was not able to form association colloids and did not impact lipid oxidation rates. This indicated that the choline group of the phospholipid was not responsible for the increased oxidation rates and suggested that the physical structure formed by DOPC was responsible for the prooxidant effect. The impact of the DOPC reverse micelles on the effectiveness and physical location of the antioxidants, alpha-tocopherol and Trolox was also studied. Both non-polar (alpha-tocopherol) and polar (Trolox) were able to inhibit lipid oxidation in stripped soybean oil in the presence of DOPC reverse micelles. Trolox was a more effective antioxidant than alpha-tocopherol. Fluorescence steady state and lifetime decay studies suggested that both alpha-tocopherol and Trolox were associated with DOPC reverse micelle in bulk oil. Trolox primarily concentrated in the water pool of reverse micelle since it quenched NBD-PE fluorescence intensity with increasing concentrations. A portion of alpha-tocopherol was also associated with the aqueous phase of the DOPC reverse micelles but this was likely at the oil-water interface since alpha-tocopherol is not water soluble. The addition of ferric chelator, deferoxamine (DFO) to stripped soybean oil significantly prevented the lipid oxidation caused by DOPC reverse micelles as the lag phase was extended from 2 to 7 days. DFO was also found to increase the antioxidant activity of both Trolox and alpha-tocopherol. Trolox and alpha-tocopherol were found to be rapidly decomposed by high-valence Fe(III) while low-valence-state (Fe (II) was much less reactive. Fe(III) was also consumed by both hydrophilic Trolox and lipophilic alpha-tocopherol presumably though reduction to Fe (II). DOPC reverse micelles were able to decrease antioxidants-iron interactions as evidence by a decrease in antioxidant depletion by iron and a decrease in iron reduction by the antioxidants. These results suggested that the ability of DFO to increase the antioxidant activity of alpha-tocopherol and Trolox was due to its ability to decrease free radical production and not its ability to decrease direct iron-antioxidant interactions. Overall, the results presented in this dissertation show phospholipids and water can form reverse micelles in edible oils. These reverse micelles increase lipid oxidation rates by increasing the prooxidant activity of iron. Free radical scavenging antioxidants can inhibit oxidation promoted by the reverse micelles with polar Trolox being more effective than non-polar alpha-tocopherol presumably because Trolox is more highly associated with the reverse micelle. The reverse micelles produced by DOPC protected alpha-tocopherol and Trolox from direct degradation by iron. The knowledge gained from this study will improve our understanding of the mechanism of lipid oxidation in bulk oils which will hopefully provide new technologies to improve the oxidation stability of edible oils. For example, it may be able to use oil refining technologies to remove prooxidative minor components that for physical structure in bulk oils.

This thesis describes the synthesis of yttrium oxide nanoparticles in an AOT/isooctane reverse micelle solution. Two synthetic methods are compared. First is the precipitation reaction between yttrium nitrate and ammonia, second is the hydrolysis of yttrium isopropoxide. The effects of annealing of the resulting the yttrium oxide nanoparticles are also described. The nitrate method produced network-like aggregates of yttrium oxide nanoparticles ranging from 10 nm to 40 nm in diameter. Reaction conditions, including the water/AOT ratio (1 to 15), the nitrate concentration (0.02 M to 1.0 M), the ammonia concentration (2 M to 14.8 M), the AOT concentration (0.1 M and 0.5 M), the aging time (1 h to 5 d), and the washing method, were varied to investigate their influence on nanoparticle formation. The optimized synthetic conditions were: a water/AOT ratio of 7.5, [NO₃⁻] = 0.5 M, [NH₃] = 2 M, and [AOT] = 0.1 M. The as-prepared yttrium oxide nanoparticles had highly distorted structures related to the cubic Y2O3 phase. Annealing improved the crystallinity of the as-prepared nanoparticle products and led to larger particles. As annealing temperatures increased, the yttrium oxide nanoparticles gradually evolved into the cubic Y₂O₃ phase. However, an unknown intermediate phase was also observed during the annealing process, which disappeared when the annealing temperature was sufficiently high and the annealing time was long enough (>1000 °C and 4 h). As-prepared products from the isopropoxide hydrolysis also contained network-like nanoparticle aggregates. Particle sizes ranged from 10 nm to 20 nm. Some experimental conditions were varied; they were the water/AOT ratio (10 to 40), the isopropoxide concentration (0.0001 M to 0.003 M), the aqueous phase pH (7.0 and 12.0), the aging temperature (room temperature, approximately 25 °C, and refluxing temperature, approximately, 100 °C), and the aging time (1 h to 5 d). Transmission Electronic Micrographs showed that products of desirable morphology could be produced in a much wider range of experimental conditions by this method compared to those produced by nitrate hydrolysis. / Master of Science

Cette thèse a pour objectif l’élaboration de nanoparticules hybrides à base de silice par microémulsion inverse. Les nanoparticules de silice constituent une matrice de base permettant de confiner et de protéger des molécules organiques et/ou des nanoparticules métalliques. L’incorporation combinée de différentes entités dans la silice ouvre ainsi de larges perspectives de par l'introduction de nouvelles propriétés liées à la structure hybride. Afin d’élaborer de tels objets, nous avons utilisé des micelles inverses à base d'eau, de Triton X-100, d'hexanol et de cyclohexane comme milieu réactionnel. L’influence des conditions opératoires sur le contrôle de la taille des micelles inverses a d'abord été étudiée. Ces micelles inverses ont ensuite été mises à profit comme nanoréacteurs pour la synthèse de nanoparticules de silice par procédé sol-gel en utilisant les précurseurs alkoxysilanes adéquats. Nous avons regardé dans quelle mesure il était possible de contrôler la taille des nanoparticules de silice en fonction du pourcentage d’eau par rapport au tensioactif. Il a ainsi été possible d’accéder de façon reproductible à des nanoparticules avec de tailles variables, de 30 nm à 200 nm. Nous avons ensuite regardé qu'il était possible d'encapsuler au sein de cette matrice nanométrique des fluorophores et des nanoparticules d’or et d’argent de façon contrôlée. En vue d’assurer une bonne stabilisation colloïdale en solution, ces nanoparticules hybrides ont été fonctionnalisées d'une part par ajout d'un silane fonctionnel et d'autre part par click chemistry. Nous avons ainsi pu montrer qu’il est possible d’effectuer dans un même milieu micellaire l’ensemble des processus de fabrication de la nanoparticule hybride, de la matrice de silice à sa fonctionnalisation en passant par l’incorporation d’entités fonctionnelles. Cette méthode de synthèse séquentielle nous a ainsi permis de supprimer les étapes de purification et de redispersion qui peuvent s’avérer problématiques dans les procédés classiques. L’ensemble de ce travail a été mis à profit pour la conception d’un agent antibactérien à base de nanoparticules argent/silice capables d’empêcher la prolifération bactérienne grâce au relargage progressif des ions argent. Les tests effectués en solution comme sur le coton et le polyéthylène téréphtalate imprégnés montrent effectivement un caractère antibactérien certain de ces systèmes. / This thesis aims at developing hybrid nanoparticles based on silica by reverse microemulsion. The silica nanoparticles are the basic matrix containing and protecting organic molecules and/or metallic nanoparticles. The combined incorporation of different entities within the silica opens wide prospects for the introduction of new properties related to the hybrid structure. To develop such objects, we used reverse micelles based on water, Triton X-100, hexanol and cyclohexan as reaction medium. The influence of operating conditions on the control of the size of reverse micelles was first studied. These micelles were then set to be used as nanoreactors for the synthesis of silica nanoparticles by sol-gel using suitable alkoxysilanes precursors. We monitored how it was possible to control the size of silica nanoparticles based on the water to surfactant ratio. It was thus possible to prepare in a reproducible way nanoparticles with sizes varying from 30 nm to 200 nm. We then investigated the possibility to encapsulate, in this nanoscaled matrix, fluorophores and nanoparticles of gold and silver in a controlled manner. To ensure a good colloidal stability in solution, these hybrid nanoparticles were, on the one hand, modified by adding a functional silane and, on the other hand, by click chemistry. We have thus shown that it is possible to perform, in a same micellar media, all of manufacturing process of the hybrid nanoparticle, from the silica matrix to its functionalization passing by the incorporation of functional entities. This method of sequential synthesis allowed us to bypass the purification and redispersion steps that can be problematic in the conventional methods. All this work has been extended to the design of an antibacterial agent based of silver/silica nanoparticles, capable of preventing bacterial growth through the gradual release of silver ions. Tests conducted in solution on the impregnated cotton and polyethylene terephtalate indeed show an interesting antibacterial character of these systems.

Geladene Phosphatgruppen sind von wesentlicher Bedeutung für die Hydratisierung von Phospholipiden und DNS. Hydratisierungshüllen spielen eine wichtige Rolle für die Ausbildung und Stabilisierung von Zellmembranen und der DNS-Doppelhelixstruktur. In dieser Arbeit werden elementare Phosphat-Wasser-Wechselwirkungen in einem Phospholidmodellsystem – sogenannten inversen Mizellen - mit variablen Wassergehalt zwischen einem und 16 Wassermolekülen pro Phospholipid untersucht. Die schnellsten Prozesse an den Grenzflächen wie z.B. Phosphat-Wasser-Wasserstoffbrückendynamik und Schwingungsenergieumverteilung finden auf einer Femto- bis Pikosekundenzeitskala statt. Molekulare Schwingungen sind sensitive lokale Sonden für die Struktur und Dynamik. Deshalb ermöglicht Femtosekunden-Schwingungsspektroskope, insbesondere zweidimensionale Infrarotspektroskopie (2D IR) und Pump-Probe-Spektroskopie in einem breiten Spektralbereich, die Dynamik mikroskopischer Phosphat-Wasser-Wechselwirkungen in Echtzeit zu beobachten. Wir zeigen die ersten zweidimensionalen Infrarotspektren von Phosphat-Streckschwingungen, die unabhängig vom Wassergehalt grenzflächensensitive Sonden darstellen. Solche Spektren belegen, dass die schnellsten strukturellen Fluktuationen der Phospholipid-Kopfgruppen auf einer 300-fs Zeitskala ablaufen, wohingegen die Phosphat-Wasser-Wasserstoffbrücken länger als 10 ps bestehen bleiben. Die Schwingungsdynamik intramolekularer Wasserschwingungen, d.h. der OH-Streck- und Biegeschwingung, zeigen, dass sich kleine Wasserpools um die Phosphatgruppen bilden, sobald drei oder mehr Wassermoleküle pro Phospholipid vorliegen. Solche Wasserpools dienen als effiziente Wärmesenken für intramolekulare Schwingungen des Wassers und der Phosphatgruppen. / Charged phosphate groups are the major hydration sites of biomolecules such as phospholipids and DNA. Hydration shells play a key role in the formation and stabilization of cell membranes and the DNA double helix structure. Here, we introduce phospholipid reverse micelles with variable water content (between one and sixteen water molecules per phospholipid) as a model system to study elementary phosphate-water interactions. The fastest processes at phosphate-water interfaces , e.g. hydrogen-bond dynamics and vibrational energy transfer occur on a femto- to picosecond time scale. Since molecular vibrations are sensitive local probes of the structure and dynamics, the use of femtosecond vibrational spectroscopy, in particular two-dimensional infrared spectroscopy (2D IR) and pump-probe spectroscopy in a broad spectral range, allow for the observation of microscopic phosphate-water interactions in real time. We present the first two-dimensional infrared spectra of phosphate stretching vibrations that represent true interfacial probes independent of the hydration level. Such spectra reveal that the fastest structural fluctuations of phospholipid headgroups occur on a 300-fs timescale whereas phosphate-water hydrogen bonds are preserved for >10 ps. Vibrational dynamics of intramolecular water vibrations, i.e., the OH stretching and bending modes show that small water pools around the phosphate groups form when three or more water molecules per phospholipid are present. Such water pools act as efficient heat sinks of excess energy deposited in intramolecular vibrations of water or the phosphate groups.