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Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

In this work, transparent and rigid organogels suitable for intravitreal drug delivery applications were produced with pharmaceutical/food grade polar and amphiphilic solvents with HLB values ranging from 0-19. Maximum sterol solubility was obtained with solvents with approximately HLB=6. Solvents with high sterol solubility also required higher sterol concentrations to produce a gel. However, the strength of all the organogels increased with increasing sterol concentration. Furthermore, DSC and SAXS data suggest that the structure of all the organogels was similar. An in vitro release of dexamethasone was performed over a 5.5 month period using novel organogel- dexamethasone implants. The release of dexamethasone varied from 2 to 5.5 months (or more) depending on the organogel used for the implant. These multiple-month release in vitro profiles are comparable and/or exceed the release of commercially available and FDA approved dexamethasone delivery system Ozurdex (~2 month dexamethasone release).

In this work, transparent and rigid organogels suitable for intravitreal drug delivery applications were produced with pharmaceutical/food grade polar and amphiphilic solvents with HLB values ranging from 0-19. Maximum sterol solubility was obtained with solvents with approximately HLB=6. Solvents with high sterol solubility also required higher sterol concentrations to produce a gel. However, the strength of all the organogels increased with increasing sterol concentration. Furthermore, DSC and SAXS data suggest that the structure of all the organogels was similar. An in vitro release of dexamethasone was performed over a 5.5 month period using novel organogel- dexamethasone implants. The release of dexamethasone varied from 2 to 5.5 months (or more) depending on the organogel used for the implant. These multiple-month release in vitro profiles are comparable and/or exceed the release of commercially available and FDA approved dexamethasone delivery system Ozurdex (~2 month dexamethasone release).

<p>Hybrid polymeric networks constructed using both covalent and reversible cross-links have been shown to be effective in preventing fracture and ultimately failure in polymeric materials. The prevention of failure has been largely attributed to the ability of the reversible cross-links to dissipate energy without breaking the covalent cross-links. The ability to rationally design materials that optimize this strategy would benefit from quantitative and systematic studies of the relationship between the number and strength of reversible interactions and the failure behavior of hybrid networks. This dissertation describe studies of fracture under compression in a family of hybrid networks, in which the timescale of reversible cross-linker dissociation is varied over several orders of magnitude, whereas the covalent components are kept constant. </p><p>Polymeric networks were constructed with 4-vinylpyridine. Bimetallic pincer Pd and Pt complexes were inserted into the network, forming reversible metal-ligand bonds that cross-link pyridine residues. The additional reversible cross-links prolong the lifetime of the hybrid networks under compressive strain when compared to their covalent counterparts. The observed failure behavior is dependent on the rate at which the networks are compressed as well as the strength of reversible interaction. Most interestingly, the addition of very dynamic and weak reversible interactions, so weak as to make no measurable contribution to bulk modulus, still leads to enhanced fracture strains. The failure of the covalent component within these hybrid networks was probed directly by incorporating a mechanophore that emits light upon chain scission. It was confirmed that the addition of these dynamic and weak reversible cross-links delays the catastrophic bond scission events associated with failure in the materials.</p> / Dissertation

Orientador: Daniel Barrera Arellano / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-20T11:35:24Z (GMT). No. of bitstreams: 1 Rocha_JulioCesarBarbosa_M.pdf: 24598807 bytes, checksum: 90f87fe1c3e7c9e31d7d85e39bf82613 (MD5) Previous issue date: 2012 / Resumo: Os óleos e gorduras representam um papel nutricional chave na alimentação humana e apresentam importância como estrutura de muitos produtos alimentícios que consumimos, como margarinas, por exemplo. Gorduras sólidas, ricas em ácidos graxos saturados foram, durante muito tempo, utilizadas para obter produtos com as características tecnológicas desejáveis de textura e dureza, sendo substituídas por gorduras ricas em ácidos graxos trans. Com a descoberta dos efeitos negativos dos ácidos graxos trans para a saúde esses materiais foram substituídos por gorduras de alta tecnologia obtidas por processos químicos de interesterificação que novamente se utilizam da presença de ácidos graxos saturados. Alternativas tecnológicas visando à redução dos teores de ácidos graxos saturados se fazem necessárias. Sendo o óleo de soja de baixo custo, elevada disponibilidade e baixo teor de ácidos graxos saturados, ele se mostra adequado ao desenvolvimento de novas gorduras tecnológicas utilizando ceras vegetais como agentes estruturantes, para a obtenção de organogéis. Organogéis são misturas com capacidade de se auto-sustentarem, formadas por uma fase contínua líquida e um agente estruturante, neste caso a cera. A cera de cana- de-açúcar tem seu interesse elevado devido ao alto potencial produtivo brasileiro, aliado à suas características físicas. O objetivo deste trabalho foi avaliar o potencial de formação de organogéis com a cera de cana-de-açúcar e suas frações solúvel e insolúvel em etanol a quente e avaliar o comportamento físico desses organogéis. Os três estruturantes estudados apresentaram capacidade de formar organogéis na condição de cristalização estática a 5°C nas concentrações estudadas (1, 2, 3 e 4% m/m), e apenas a fração insolúvel em etanol a quente incapaz de formar organogéis estáveis sob a condição de cristalização estática a 25°C. As propriedades térmicas dos géis foram as esperadas para o material, sendo diferentes para cada um dos estruturantes as temperaturas de início de cristalização variaram entre 42 e 47°C e de fusão entre 49 e 59°C. Os géis apresentaram resistência mecânica, sendo que os géis mais resistentes foram os de 4% (m/m) da cera clarificada e purificada e da fração solúvel em etanol. O comportamento reológico foi típico para géis termorreversíveis com aumento de viscosidade nas temperaturas entre 40 e 44°C, coincidindo com a temperatura encontrada por DSC. A microestrutura observada para os organogéis foi característica de uma rede tridimensional organizada para as amostras contendo cera cristalizada e purificada e a fração solúvel em etanol e desorganizada para o organogel obtido pela fração insolúvel em etanol. Os organogéis apresentaram estabilidade por 7 dias em diferentes condições de temperatura (5, 25 e 35°C) com exceção do organogel obtido com a fração insolúvel em etanol cristalizada em 25°C. Os organogéis formados apresentaram baixa resistência mecânica e térmica, sendo de fácil fusão, porém podem ser adequados para aplicações industriais como substitutos de gorduras moles / Abstract: Fats and oils present a key role in our diet, as nutrients and as structure for many food products that we consume such as margarines. Solid fats rich in saturated fatty acids were used during a long time to obtain food products with desirable technological characteristics of hardness and texture, being replaced by rich in trans fatty acids fats. With the discovery of the negative health effects of trans fatty acids, these materials were replaced by high technology fats such as chemically modified interesterified fats that again used saturated fatty acids to get the desirable texture. Technological alternatives to reduce the intake of saturated fatty acids are needed. Soybean oil is a low cost, highly available and low in saturated fatty acids source of lipid, being adequate for the development of new technological fats using vegetable waxes as structuring agents, forming organogels. Organogels are mixtures that are capable of self-support, formed by a liquid continuous phase and a structuring agent, in this case wax. Sugarcane wax is interesting because of its high productive potential presented in Brazil and because of its physical characteristics. The goal of this study was to evaluate the potential of sugarcane wax and its hot ethanol soluble and insoluble fractions to form organogels and evaluate the physical behavior of these organogels. The three structurants presented the ability to form organogels at static crystallization at 5°C at the studied concentration (1, 2, 3 and 4%, w/w), but the hot ethanol insoluble fraction wasn¿t capable of forming stable organogels at static crystallization at 25°C. The thermal properties of the studied organogels were as expected for the kind of material, being different for each structurant in a range of 42 to 47°C for crystallization and 49 to 59°C for melting. The organogels presented mechanical hardness, being the most resistant the 4% (w/w) of clarified and purified wax and hot ethanol soluble fraction. The organogels also presented a typical rheological behavior presenting thermoreversibility and an increase of viscosity at the temperature range of 40 to 44°C, similar to measure on DSC. The observed microstructure was a tridimensional organized network for the samples clarified and purified sugarcane wax and hot ethanol soluble fraction and more disorga nized for the hot ethanol insoluble fraction. The organogels presented stability for 7 days at different temperature conditions (5, 25 and 35°C) with the exception being the hot ethanol insoluble fraction crystallized at 25°C. The developed organogels presented low mechanical and thermal resistance, being easily melted, however they can be adequate for technological application as replacement for soft fats / Mestrado / Tecnologia de Alimentos / Mestre em Tecnologia de Alimentos

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La première partie de cette thèse concerne la synthèse et les études structurales de 2:1-[α/aza]-oligomères linéaires et cycliques possédant des acides aminés hydrophobes et/ou basiques. Les études RMN et IRTF ont démontré que les oligomères adopteraient des conformations de type coude β en solution. Les calculs de dynamiques moléculaires des oligomères à base de résidus lysine ont révèlé l’importance du motif aza dans le repliement de ces oligomères indépendamment de l’impact de la chaîne latérale. Les études par DRX, IRTF et RMN ont révélé que les deux hexamère cycliques (L- ou D-Phe-azaPhe-Ala)2 homo- et hétérochiraux adoptent des conformations de type coude ß en solution et à l’état solide. Ils s’organisent en structures 3D très ordonnées, stabilisées par des ponts hydrogènes et des empilements π. La deuxième partie démontre l'auto-assemblage de quelques 2:1-[α/aza]-oligomères dans certains solvants pour former des gels supramoléculaires. Le cyclooligomère hétérochiral (D-Phe-azaPhe-Ala)2 peut former des organogels. La spectroscopie et rhéologie des organogels ont révélé de bonnes stabilités thermique et mécanique avec un comportement de type solide. La MEB/MET de l'aérogel a montré une structure fibreuse 3D. De plus, deux hydrogels Fmoc-D- ou L-Phe-azaPhe-Ala-OH ont été obtenus aux pH 7.0 et 10.0. Les spectres UV et de fluorescence ont révélé une stabilisation des hydrogels par interaction π entre les groupes aromatiques. Leur analyse par CD montre que les trimères s'auto-assemblent sous forme de feuillet β en accord avec les résultats ATR/IRTF. Ainsi, leurs études rhéologiques ont révélé un comportement de type solide. La MEB des xérogels a montré une structure fibreuse. La troisième partie propose deux applications; (i) les oligomères à base de résidus lysine ont révélé de bonnes performances pour la séparation CO2/N2 dans des membranes polymères Pebax®, et (ii) le cyclohexamère hétérochiral (D-Phe-azaPhe-Ala)2 convient pour la gélification sélective avec un bon pourcentage de récupération / The first part of this thesis reported the synthesis and structural studies of linear and cyclic 2:1-[α/aza]-oligomers possessing hydrophobic and/or basic amino acids (lysine). NMR and FTIR results demonstrated that the oligomers could adopt β-turn conformations in solution. Molecular dynamic calculations for oligomers based lysine residues reflected the important role of the aza-motif(s) in structuring the backbones regardless the chirality and nature of the amino acids. In the other hand, X-ray, FTIR, and NMR studies showed that homo- and heterochiral cyclo-(L- or D-Phe-azaPhe-Ala)2-hexamers adopt β-turn conformations in solution and solid states. Both molecules could organize into 3D highly ordered structures stabilized by hydrogen bonds and π-stacking. The second part reflected the propensity of some 2:1-[α/aza]-oligomers to self-assemble in some solvents to form supramolecular gels. Interestingly, the heterochiral cyclo-(D-Phe-azaPhe-Ala)2-hexamer could form organogels. The spectroscopic and rheological studies of the organogels revealed good thermal and mechanical stability with solid-like behavior. SEM and TEM images of the aerogel showed fibrous structure. Furthermore, two hydrogelators, Fmoc-D- or L-Phe-azaPhe-Ala-OH, have been developed and they could achieve hydrogels at pHs 7.0 and 10.0. UV and Flu studies demonstrated that the hydrogels are supported by π-stacking between the aromatic groups. CD analysis reflected that the two hydrogelators self-assemble into β-sheet like structure in consistent with ATR-FTIR results. Both hydrogels exhibited solid-like behavior through rheological studies and the SEM analysis of the xerogels revealed fibrous structure. The third part offered two applications; (i) oligomers based lysine residues reflected good performances in CO2/N2 separation when used as additives in polymeric Pebax® membrane, and (ii) the heterochiral cyclo-(D-Phe-azaPhe-Ala)2-hexamer is suitable for phase selective gelation with good recovery percentages

Chapter 1. A Brief Overview of Low Molecular Mass Gels and their Applications This chapter deals with molecular gels derived from the self-assembly of small organic molecules (typical molecular weight < 2000 daltons), endowed with appropriate functions to promote anisotropic growth of supramolecular aggregates, by means of various non-covalent interactions like van der Waals, π-πstacking, H-bonding etc., leading to a self-assembled fibrillar network (SAFIN). Several representative examples from the literature (Chart 1) are discussed to demonstrate the structural diversity of the gelator molecules which form self-assembled organogels or hydrogels. Chart 1 Besides emphasizing on the diverse molecular structures of the gelators, applications of gel phase materials as functional nanostructures are also discussed (Scheme 1). Some of the aspects that have been elaborated in this context include the use of gels as reaction media, as sensors, in light harvesting, as biomaterials and in optoelectronic applications. Scheme 1 Chapter 2. Supramolecular Chirality in Organogels: Spectroscopic, Morphological and Rheological Investigations of Gels/Xerogels derived from Alkyl Pyrenyl Urethanes This chapter addresses the formation of chiral supramolecular structures in the organogels derived from chiral 1R (or 2R), and its mixture with its enantiomer (1S) and a series of achiral analogues (3-9) by extensive circular dichroism (CD) spectroscopic measurements (Chart 2). Morphological studies by atomic force microscopy (AFM) and scanning electron microscopy (SEM) were complemented by the measurements of their bulk properties by thermal stability and rheological studies. Specific molecular recognition events (1/3 vs 2/3) and solvent effects (isooctane vs dodecane) were found to be critical in the formation of the chiral aggregates. Computational studies were carried out to understand the interactions responsible for the formation of chiral superstructures. Chapter 3. Self-assembled Composite Organogels based on a Thermo-reversible Photoactive n-Acene Fibrillar Scaffold and Organic Ligand stabilized ZnO Nanoparticles Organic/inorganic composite organogels were obtained in n-BuOH by the self-assembly of 2,3-di-n-decyloxyanthracene (DDOA, Chart 3) in this solvent in the presence of ZnO nanoparticles (NPs) capped with different organic ligands (Chart 4). When ligands (oleic acid or 2,3-substituted anthracenic acid/oleic acid mixed shell) having structural similarity with the gelator molecule were used to cap the NPs, a homogeneous dispersion of the NPs in the gel matrix was obtained, as confirmed by microscopy (TEM and confocal fluorescence microscopy) experiments. The efficient integration of these NPs into the gel fibers resulted in a significant quenching (20-25%) of DDOA emission, even with extremely small loading of these NPs (~ 10-4mol% compared to DDOA) into the gel fibers. The mechanical properties (rheology were unaffected relative to the pristine DDOA organogel. However, the presence of the NPs lowered the critical gelation concentration and accelerated the gelation kinetics. Attempts to disperse these NPs (the ones without fluoro capping) on the aerogel fibers of DDOA by dissolving both DDOA and the NPs in supercritical (sc) CO2 were not successful (Fig. 1), since the NPs could not be dissolved in scCO2. Figure 1. (a) TEM images of DDOA aerogels obtained from scCO2, containing A23-NPs, scale bar 200 nm; (b) SEM image of DDOA aerogel obtained in the presence of OL-NPs, scale bar 10 µm. Chapter 4. Donor-Acdeptor Interaction Promoted Gelation Of Organic Fluids by Anthracene Carboxamides/2,4,7-Trinitrofluorenone Tris Carboxamides of anthracene were found to form charge-transfer driven organogels in a range of aliphatic alcohols in the presence of an equivalent of (electron-deficient) 2,4,7-trinitrofluorenone (TNF) (Chart 5). Intense color developed in the gel state during the sol to gel phase transition process (Fig 2) Besides, none of these carboxamides were able to form gel in the absence of TNF, suggesting the importance of charge-transfer interaction in the gel formation. Importantly, most of these gels formed only through rapid cooling of the hot solution, otherwise, leading to the precipitation of the CT complex from the solvent. This result indicated that the kinetics is very important for the formation of these gels. Optimum stoichiometry of the donor and acceptor was found to be 1:1. At this molar ratio of the donor and the acceptor, the gels not only showed the highest thermal stability (thermal gel melting experiments), they also displayed the highest values of the mechanical strength and the yield stress (rheology experiments). All the gels showed extensive quenching of the emission of the monomeric anthracenic donor. For the gels derived from the 2-substituted donor, a low energy emission at high wavelength indicated the formation of an emissive CT exciplex. X-ray powder diffraction studies of these xerogels revealed the presence of layered, fibrillar structures in the xerogel phase. (For structural formula pl see the abstract file)