X-ray crystallography is a technique for determining the structure (positions of atoms in space) of molecules. It is a well developed technique, and is applied routinely to both small inorganic and large organic molecules. However, the determination of the structures of large biological molecules by x-ray crystallography can still be an experimentally and computationally expensive task. The data in an x-ray experiment are the amplitudes of the Fourier transform of the electron density in the crystalline specimen. The structure determination problem in x-ray crystallography is therefore identical to a phase retrieval problem in image reconstruction, for which iterative transform algorithms are a common solution method. This thesis is concerned with iterative projection algorithms, a generalized and more powerful version of iterative transform algorithms, and their application to macromolecular x-ray crystallography. A detailed study is made of iterative projection algorithms, including their properties, convergence, and implementations. Two applications to macromolecular crystallography are then investigated. The first concerns reconstruction of binary image and the application of iterative projection algorithms to determining molecular envelopes from x-ray solvent contrast variation data. An effective method for determining molecular envelopes is developed. The second concerns the use of symmetry constraints and the application of iterative projection algorithms to ab initio determination of macromolecular structures from crystal diffraction data. The algorithm is tested on an icosahedral virus and a protein tetramer. The results indicate that ab initio phasing is feasible for structures containing 4-fold or 5-fold non-crystallographic symmetry using these algorithms if an estimate of the molecular envelope is available.

A une époque où les technologies nouvelles fleurissent chaque jour, un domaine particulier se détache : l’électronique organique. Par son utilité et sa facilité de mise en œuvre, l’électronique organique affiche de grandes promesses pour l’avenir. Dans le but d’améliorer le procédé de fabrication et la durée de vie de ces dispositifs, le travail de cette thèse s'est focalisé sur la synthèse de copolymères à architectures variées à base de poly(3-hexylthiophène) (P3HT). Après avoir exposé les problématiques et objectifs de la thèse dans une première partie, la synthèse de différents précurseurs P3HT est décrite. Ces matériaux représentent la base des travaux présentés dans cet ouvrage. Dans un premier temps, l'optimisation de la synthèse des copolymères à blocs rigide-flexible a été réalisée en suivant une stratégie adaptée pour une application en électronique organique. La conception de nouveaux matériaux semi-conducteurs à architectures ramifiées est traitée par la suite. Enfin, le dernier chapitre porte sur l'intégration d’un copolymère, le P3HT-b-Poly(4vinylpyridine), en cellule photovoltaïque organique en tant qu'additif de la couche active. Cette approche s’avère être particulièrement puissante, permettant notamment de diminuer le temps et le coût énergétique de la mise en œuvre de ces cellules en s’affranchissant d’une étape clé de la fabrication, le recuit. / At a time when new technologies emerge every day, a specific domain stands out: the organic electronic. Through its low cost processing or even its utility, the organic electronic constitutes a very promising future.In order to improve the fabrication process and the lifetime of the devices, the work of this thesis was focused on the synthesis of copolymers with various architectures based on poly(3-hexylthiophene) (P3HT). After a first part where main issues and objectives are presented, the synthesis of different P3HT-based precursors is described in a part which could be considered as the heart of these works. Starting with appropriated precursors, the optimization of rod-coil diblock copolymer synthesis was performed following a strategy designed specifically for organic electronic application. Moreover, the precursors were used for the conception of new semi-conducting materials with a variety of architectures, such as graft and star copolymers. Finally, the last part deals with the integration of the P3HT-b-Poly(4-vinylpyridine) copolymer into organic solar cell as an additive of the active layer. This approach turns out to be powerful, especially allowing decreasing the time and the energy cost by avoiding the key step of the fabrication process of those devices, the annealing step.

A existência de uma maior variedade de aminoácidos codificados pelo código genético tem estimado estudos sobre os mecanismos de síntese, reconhecimento e incorporação desses resíduos nas cadeias polipeptídicas nascentes. Um exemplo é a via de incorporação de selenocisteína evento cotraducional dirigido pelo códon UGA. Em bactérias, essa via conta com uma complexa maquinaria molecular composta por: Selenocisteína Sintase (SelA), Fator de Elongação Específico de Reconhecimento (SelB), Selenofosfato Sintetase (SelD), tRNA específico (SelC ou tRNAsec), sequência específica no mRNA (Sequência de Inserção de Selenocisteínas - SECIS) e Aminoacil tRNA Sintetase (aaRS). Pelo fato do selênio ter uma toxicidade elevada em ambientes celulares, é fundamental a compreensão do mecanismo catalítico e razão estequiométrica na formação dos complexos da via na etapa de incorporação junto ao tRNAsec, bem como sua caracterização estrutural foram os objetivos deste trabalho. A proteína SelA foi expressa e purificada para utilização em análises envolvendo microscopia de força atômica, microscopia eletrônica de transmissão com contraste negativo e em gelo vítreo foram realizadas nos complexos SelA e SelA-tRNAsec, visando obter um modelo estrutural e a razão estequiométrica dos complexos. A fim de compreender o mecanismo de passagem do selênio, ensaios de anisotropia de fluorescência e de microcalorimetria, corroborados pelas análises de troca de hidrogênio-deutério acoplado a espectrometria de massa e espectroscopia de infravermelho, elucidaram a formação e estequiometria do complexo ternário SelAtRNA sec-SelD. Tentativas de cristalização e análises cristalográficas também foram realizadas, no entanto, sem sucesso. Com os resultados obtidos foi possível propor que o reconhecimento de SelD e, consequentemente, a entrega do selenofosfato, seja uma etapa crucial da via de incorporação de selenocisteínas. / The existence of a greate variety of amino acids encoded by the genetic code has stimulated the study of the mechanisms of synthesis, recognition and incorporation of these residues in the nascent polypeptide chains. An example of genetic code expansion is the selenocysteine incorporation pathway an event cotraducional by the UGA codon. In bacteria, this pathway has a complex molecular machinery comprised: Selenocysteine Synthase (SelA), Specific Elongation Factor (SelB), Selenophosphate Synthetase (SelD), tRNA-specific (SelC or tRNAsec), Specific mRNA Sequence (SElenocysteine Insertion Sequence - SECIS) and Aminoacyl tRNA Synthetase (aaRS). Because selenium has high toxicity in cellular environments; it is essential for cell survival the association of this compound with proteins, in this case, selenoprotens and the associated proteins involved in the selenocysteine synthesis. Therfore the understanding of the catalytic mechanism, stoichiometric ratio, protein complex formation with the tRNAsec, and its structural characterization were the objectives of this work. The SelA protein was expressed and purified to used in analyzes involving atomic force microscopy, transmission electron microscopy with negative stain and in vitreous ice were performed in the complex SelA and SelA-tRNAsec in order to obtain a structural model of the complex and the stoichiometric ratio of its components. To study the selenium association with protein of the synthesis pathway, fluorescence anisotropy assays and isothermal titration calorimetry corroborated by the analysis hydrogen-deuterium exchange coupled to mass spectrometry and infrared spectroscopy were employed.Crystallization attempts were made and preliminary crystallographic analyzes were also performed, however, so far unsuccessfuly. The results obtained were possible to develop the hypothesis about the SelD recognition and, consenquently, the selenophosphate delivery, a crucial stage of the selenocysteine incorporation pathway.

A importância do estudo das celulases não se limita à aquisição de conhecimento científico, mas também ao grande potencial biotecnológico que elas representam. Isso se deve ao fato da celulose ser a molécula mais abundante presente na natureza e prover uma vasta gama de produtos e processos sustentáveis. Muitas famílias de celulases já foram bem caracterizadas, enquanto outras permanecem ainda desconhecidas. Dentre estas últimas, a família 45 das hidrolases de glicosídeos é a família de celulases fúngicas menos caracterizada tanto estruturalmente quanto funcionalmente. Recentemente foi proposta a divisão dessa família em três subfamílias e, até agora, apenas membros da subfamília A tiveram enzimas estruturalmente elucidadas. Nesse trabalho reportamos a estrutura cristalográfica da proteína recombinante endoglucanase de Phanerochaete chrysosporium (PcCel45A), a primeira das hidrolases de glicosídeos da subfamília C, e seu complexo com celobiose a 1,4 Å e 1,7 Å de resolução, respectivamente. A PcCel45A é uma enzima de domínio único, com uma estrutura em β-barril e seu empacotamento geral remete ao formato de âncora. O sítio ativo da enzima forma um longo sulco na superfície da estrutura, sendo que o seu centro catalítico é diferente das outras enzimas publicadas dessa família e o aspartato catalítico, que atua como aceptor de próton na reação de inversão, (Asp10) não é conservado. Adicionalmente, a estrutura cristalográfica dessa enzima apresenta mais similaridades com as β-expansinas (proteínas de plantas) e transglicosilases líticas (proteínas que clivam o peptidoglicano de bactérias) do que com as outras representantes da família 45, o que a torna ainda mais singular. Para entendermos melhor seu funcionamento foram realizadas mutações sítio-dirigidas nos principais resíduos do sítio ativo. O Asp121, conhecido por participar da reação de inversão das outras enzimas da família como doador de próton, mostrou-se essencial para a atividade da enzima, enquanto que outros resíduos conservados como a Tyr25, o Trp161 e o Asp92 afetaram, mas não aniquilaram a atividade da enzima, apresentando aproximadamente 20%, 50% e 10% da atividade da enzima nativa, respectivamente. / The importance of the study of the cellulases is not limited to generating significant scientific knowledge, since these enzymes represents an enormous potential in biotechnology. This is partly because cellulose is the most abundant molecule in nature and provides a wide range of products and sustainable process. Many cellulases families have been well characterized, while others still remain unknown. Among them, the glycoside hydrolase family 45 is the least well characterized both structurally and functionally, between fungal cellulases. It was recently proposed the subdivision of this family into three subfamilies, with structural information available only for subfamily A. In this work, we report the chrystallographic structure of the recombinant endoglucanase from Phanerochaete chrysosporium (PcCel45A), the first GH45 subfamily C and its complex with cellobiose at 1.4 Å and 1.7 Å respectively. The PcCel45A is a single domain enzyme, which has a β-barrel structure with the overall shape resembling an anchor. The active site of the enzyme has a long cleft on the surface, being remarkably different from those members of subfamily A, and the catalytic aspartate responsible for acting as proton acceptor (Asp10) is not present. Additionally, the chrystallographic structure of this enzyme has shown more similarity with β -expansins (plant proteins) and lytic transglycosylase (proteins that cleave the peptidoglycan of bacteria) than others representants of family 45, which makes it more singular. For a better understanding of its function, we perform pontual mutations in the main residues from active site. The Asp121, known for acting as proton acceptor in the inversion reaction of others enzymes, proved to be essential for the enzyme activity, while others conserved residues as Tyr25, Trp161 and Asp92 affected but not annihilated the enzyme activity, leaving approximately 20%, 50% and 10% of the native enzyme activity.

A deformação plástica de polímeros semicristalinos na região situada entre suas Tg (temperatura de transição vítrea) e T m (temperatura de fusão cristalina), modifica suas propriedades termodinâmicas e morfológicas produzindo materiais com novas propriedades e aplicações. Neste trabalho polifluoreto de vinilideno (PVF2) e polietileno de alta densidade (PEAD) foram submetidos à deformação plana por compressão na região entre suas T 9 e T m, para a investigação de dois tipos de processos em nãoequilíbrio: a deformação plástica desses polímeros e o processo de relaxação do material deformado. As mudanças das propriedades termodinâmicas, coeficientes de expansão térmica linear (ai) e capacidades térmicas a pressão constante (Cp), ocorridas no primeiro processo foram registradas através de técnicas de Análise Termomecânica (TMA) e Calorimetria Diferencial de Varredura (DSC). Foi verificado aumento de ai e Cp nas amostras deformadas. As mudanças morfológicas ocorridas no primeiro processo foram registradas através das técnicas de Difração de Raios X e Densimetria. Observou-se aumento da fase amorfa bem como transição de fase na região cristalina em ambos materiais. Medidas de DSC mostraram maior grau de cristalinidade no PEAD que no PVF2. O segundo processo foi acompanhado submetendo-se o material deformado a ciclos consecutivos de aquecimento e resfriamento, com o auxílio das técnicas de TMA e DSC. As "memórias" de forma e termomecânica foram registradas através de transições relacionadas a mudanças irreversíveis no ai ao longo das coordenadas de deformação. Também foi observado que o PVF2 possui maior tendência à recuperação da forma que o PEAD. Relaxação da Cp não foi observada no intervalo de temperatura estudado. Os resultados obtidos neste trabalho levam a concluir que o processo de deformação plana por compressão permite a obtenção de materiais fisicamente modificados com novas propriedades mecânicas e termodinâmicas, os quais possuem a tendência a recuperar parcialmente seu estado original. Também foi verificada que a recuperação da forma e da Cp não estão diretamente relacionadas: enquanto a recuperação da forma do material semicristalino parece estar mais relacionada à mobilidade da fase amorfa, a recuperação da Cp está provavelmente mais relacionada à capacidade de recuperação da fase cristalina. / The plastic deformation of semi-crystalline polymers between Tg (glass transition temperature) and Tm (crystalline melting temperature), modifies their thermodynamics and morphological properties producing materiais with new properties and applications. In this work polyvinylidene fluoride (PVF2) and high density polyethylene (HOPE) were submitted to plane-strain compression in a deep channel die in a temperature range between their Tg and T m, in order to investigate two kind of nonequilibrium processes: the plastic deformation of these polymers and the relaxation process of the deformed material. The changes of thermodynamical properties, linear thermal expansion coefficients (ai) and constant pressure heat capacities (Cp), occurred in the first process were registered by Thermomechanical Analysis (TMA) and Oifferential Scanning Calorimetry COSC) techniques. An increase in ai and Cp in deformed samples has been observed. The morphological changes occurred in the first process were registered by X-Ray Diffraction and Densimetry techniques. It was observed an amorphous phase increase as well as a phase transition in the crystalline region in both materiais. The DSC measurements have shown a better cristalinity degree in PEAO than in PVF2. The second process was followed by submitting the samples to consecutive cycles of heating and cooling using TMA and DSC techniques. The shape and thermomechanical "memory" were registered by means of transitions related to irreversible changes in the linear thermal expansion coefficient, along the deformation coordinates. It was also observed that PVF2 has a better tendency to shape recovery than PEAD. Relaxation in the heat capacity has not been observed in temperature range studied. The results obtained in this work lead to the conclusion that the plane-strain compression allows physically modified materiais with new thermodynamical and mechanical properties, which have the tendency to recover its original state, to be obtained. It was also verified that shape and Cp recovery are not directly related: while the shape recovery of semi-crystalline materiais seems to be more related to the amorphous phase mobility, the Cp recovery is most probably related to the ability of crystalline phase recovery.

This thesis reports work in three areas of X-ray crystallography. An initial chapter describes the structure of a protein, the methods based on the use of X-rays and computer analysis of diffraction patterns to determine crystal structure, and the subsequent derivation of the structure of part or all of a protein molecule. Work to determine the structure of the protein cytokine receptor-like factor 3 (CRLF3) leading to the successful generation of a structural model of a significant part of this molecule is then described in Chapter 2. A variety of techniques had to be deployed to complete this work, and the steps undertaken are described. Analysis was performed principally using phaser, using maximum likelihood methods. Areas for improvement in generating non-crystallographic symmetry (NCS) operators in existing programmes were identified and new and modified algorithms implemented and tested. Searches based on improved single sphere algorithms, and a new two-sphere approach, are reported. These methods showed improvements in many cases and are available for future use. In Chapter 4, work on determining the relative importance of low resolution and high intensity data in molecular replacement solutions is described. This work has shown that high intensity data are more important than the low resolution data, dispelling a common perception and helping in experimental design.

<p>There are still technique hurdles that needed to be overcome in the commercialization of electrochromic devices (ECDs) for energy-saving smart windows. Among them, the long-term stability of ECDs and the high fabrication cost are <a>the critical issues</a>. The pricey ECDs can only be paid off through saving the energy for years, and their price will be dramatically lower if they can be solution-processed. Here, we studied the ions behaviors in the open-circuit state of electrochromic conjugated polymers (ECPs) which is important to the stability of ECDs during the operation. Moreover, we investigated the solution-processable ion storage layers and paired them with p-type ECPs and demonstrated the possibility of using them in the highly efficient roll-to-roll fabrication of ECD.</p> <p>The crosslinkable non-color changing nitroxy radical-based polymer was investigated as the ion storage layer. With the applied of crosslinking strategy, the dissolution problems of radical polymers-based counter electrode in the electrolyte was suppressed, resulting in the enhancement of both performance and cycling stability of ECDs. Although p-type ion storage materials are widely studied as the ion storage layers for ECPs, they need to go through complicated pretreatment processes, including pre-oxidation, washing, and drying, before they can be paired with ECPs in an ECD. This complicated process greatly increases the fabrication cost. </p> <p>In our last work, we applied the UV ozone (UVO) pretreatment to the solution-processed n-type niobium oxide and evaluated its potentials to be used as the ion storage layer for p-type ECPs. The UVO pretreatment generates strong oxidants like ozone or atomic oxygen which induce the photolysis of organic residues of ligands and organic solvent trapped in the solution-processed metal oxide layer led to the formation of free radical species. These highly reactive species promoted the formation of the amorphous metal−oxygen network. Following by low-temperature annealing (< 150 ^oC), the ion-storage properties of niobium oxide is comparable with the high temperature annealed (300 ^oC) niobium oxide. The method is successfully applied to fabricate niobium oxide on a flexible conductive substrate and demonstrate the capability to pair with p-type ECPs and fabricate high-performance ECDs without the need of any pretreatments. The low-temperature solution processing of both layers will significantly reduce the fabrication cost of ECDs. </p>

Este trabajo se ubica en una perspectiva marcada por dos fuentes de inspiración y exigencia, que se complementan mutuamente: La primera está relacionada con el campo tecnológico y la segunda viene del ambiente científico. Por un lado, es sabido que los productos plásticos y compuestos de matriz polimérica se usan cada vez más en ingeniería y, como la mayoría de los materiales utilizados en este ámbito, muchos están sometidos a cargas dinámicas; de tal manera que en este momento resulte tan necesario el estudio de sus propiedades como el desarrollo de métodos de ensayo fiables para poder caracterizarlos bajo diferentes condiciones de aplicación de carga, siendo de especial interés conocer la respuesta de los mismos a altas velocidades de solicitación. Por otro lado, desde la óptica de la ciencia de los materiales, la relación entre la estructura y el comportamiento de fractura de los polímeros es una de sus más importantes ramas, en la que los ensayos de impacto juegan un rol principal. Cada vez más un conocimiento cuantitativo del comportamiento a impacto, en términos de la ciencia de los materiales, requiere de un conjunto de técnicas adicionales para suplir -teórica y experimentalmente- los métodos de ensayo de impacto básicos especificados por las entidades de normalización. En este sentido, el objetivo central de la presente Tesis es el diseño y puesta a punto de técnicas de ensayo para el estudio de la fractura de los materiales poliméricos, a altas velocidades de solicitación y en el dominio de baja energía.Como resultado y según la orientación del objetivo de la Tesis, se proponen dos metodologías de ensayo de impacto de baja energía: flexión por impacto de baja energía e indentación por impacto. Asimismo, cada metodología incluye el diseño de un "modelo" que permite una aproximación al fenómeno de impacto de baja energía en las geometrías de flexión e indentación respectivamente.Se ha verificado la validez de los mencionados modelos en el estudio del comportamiento mecánico del polimetilmetacrilato, poliestireno y compuestos de poliestireno y microesferas de vidrio. Las técnicas de impacto de baja energía aplicadas según las metodologías de ensayo propuestas fueron apropiadas y permitieron evaluar la respuesta de estos materiales en el campo elástico, determinar sus características elásticas a elevadas velocidades, así como estimar el inicio del daño en los mismos. Los resultados de estos ensayos, tanto el módulo elástico como las tensiones a las cuales comienzan los fenómenos de emblanquecimiento, crazing y rotura, fueron interpretados según los modelos propuestos. Finalmente, por extensión, las metodologías y modelos propuestos son válidos y apropiados para el estudio de los plásticos, cuando menos similares a los estudiados.Este trabajo se ha estructurado en concordancia con la metodología utilizada en la investigación correspondiente. Así, en el primer capítulo se ha hecho una revisión sobre los temas afines a la tesis, desde sus aspectos conceptuales hasta los más avanzados; para examinar la evolución y el estado actual del tema en cuestión y precisar los conocimientos que sirvan de base a esta investigación. En el segundo capítulo se describen las características generales y particulares de los materiales sometidos a estudio experimental. En el tercer capítulo se exponen los métodos de ensayo utilizados y las herramientas experimentales necesarias para su realización. Finalmente, antes de exponer las conclusiones, fue de rigor abordar un cuarto capítulo referido a la flexión por impacto de baja energía y otro quinto capítulo similar que versa sobre la indentación por impacto, para la presentación, interpretación y análisis de resultados, así como la correspondiente discusión. / This work is situated in a perspective highlighted by two inputs of inspiration and exigency, that complement each other: the first input is related with the technology field, and the second comes from a scientific field. On one hand, it is known that plastic products and composites of polymeric matrix are used increasingly in the engineering industry, and as many of the materials used in this field, they are usually exposed to dynamic charges. Therefore, it is necessary the study of their properties like the development of methods and tests to be able to characterize them under different conditions of charge applications, being of special interest to know the results at high speeds. On the other hand, from the material science point of view, the relation between the structure and the behavior of fracture of the polymers is one of the most important subjects, in which the impact tests play a fundamental role. The knowledge of fracture behavior, in terms of science of the materials, requires a group of additional techniques in order to supply (theoretically and experimentally) the basic impact test methods specified by the normalization entities. In this sense, the principal objective of this thesis is the design and development of test techniques for the study of the fracture of polymers at high speeds of solicitation and in the domain of low energy.As a result and based in the objective of this thesis, it is proposed two methods of test for impact of low energy: flexion by impact of low energy and indentation by impact. In the same way, every methodology includes the design of a "model" that allows an approximation for the phenomenon of impact of low energy in the geometric of flexion and indentation, respectively. The validity of the models mentioned above in the study of the mechanic behavior of the polymethylmetacrilate, polystyrene and polystyrene filled with different percentages of glass beads has been verified. The techniques for impact of low energy applied according to the methodology of proposed test were appropriate and allowed to evaluate the response of these materials in the elastic field, to determine its elastic characteristics at high speeds, and to estimate the initial damage of components. The results of these tests, likewise the elastic module and the tensions at which begin the whitening phenomena, crazing and rupture, where interpreted according to the proposed models. Finally, per extension, the methodology and proposed methods are valid and appropriate for the study of plastics, at least similar to the ones studied. This work has been structured in accordance with the methodology utilized in the correspondent investigation. Thus, in the first chapter, a revision of the subjects corresponding to the thesis were made, from its conceptual aspects to the more advanced, in order to examine the evolution and estate of the actual subject in question and precise the knowledge that can be use as a base for this investigation. In the second chapter, the general and particular characteristics of the materials submitted to the experimental studies are described. In the third chapter the methods of test utilized and the necessary experimental tools for its realization are exposed. Finally, before the conclusions are presented, it was consistent to add a fourth chapter that refers to the flexion by impact, and another fifth chapter similar that contains the indentation by impact for the presentation, interpretation and analysis of results, and the related discussion.

Dicho trabajo de investigación se basa en la preparación, caracterización y evaluación de propiedades de poliamidas derivadas de la L-lisina y de los ácidos L y D tartáricos, con posibilidades de utilización como polímeros biomédicos.La síntesis de estos monómeros seguirá las técnicas modernas de la Química Orgánica y su caracterización se completará con todos los medios analíticos disponibles.La regularidad estructural de los polímeros que se sintetizarán será un punto importante, por todo ello, buena parte de este trabajo tiene por objetivo la preparación de los monómeros adecuados en cada caso. Las poliamidas se obtendrán por policondensación de los diversos monómeros derivados de la lisina y del ácido tartárico. Se compararán las propiedades de los polímeros dependiendo de su regicidad y de su estereorregularidad. Esta última propiedad sólo se modificará según los dos enantiómeros del ácido tartárico (L y D) con sus hidroxilos protegidos como éteres metílicos. La lisina participará como diamina en forma de éster metílico o como dicetopiperacina.Por último se realizará un estudio del poder de degradación hidrolítica en medios fisiológicos de la poliamida ar-PLLT y de la asociación de dicha poliamida con tensioactivos, aniónicos y catiónicos.Se sintetizarán, en primer lugar, poliamidas derivadas del ácido di-O-metil tartárico (L o D) y de la metil L-lisina.Serán los siguientes:- ar-PLLT y ar-PLDT, poliamidas arrégicas (y por ello no regulares) obtenidas por condensación directa de la metil L-lisina y de los ésteres activos de los ácidos L y D tartáricos - sr-PLLT y sr-PLDT, poliamidas sindiorrégicas (y por ello estructuralmente regulares) obtenidas por condensación de un sesquímero derivado de la metil L-lisina y de los ésteres activos de los ácidos L y D tartáricos - ir-PLLT y ir-PLDT, polioamidas isorrégicas (y por ello estructuralmente regulares y direccionales) obtenidas por condensación de un monómero direccional derivado de la metil L-lisina y de los ácidos L y D tartáricosEn segundo lugar se preparan poliamidas derivadas de la dicetopiperacina de la L-lisina y de los ácidos di-O-metil L y D tartáricos- Estas poliamidas se nombrarán como PDK-LL y PDK-LD La caracterización de los polímeros se hizo por análisis elemental, por espectrocopía de infrarrojo y por resonancia magnética nuclear, siendo la esperada.Todas las poliamidas obtenidas son ópticamente activas, siendo el signo del poder rotatorio dependiente de la configuración del ácido tartárico de partida.En los ensayos de calorimetría diferencial de barrido de las poliamidas ar-PLLT, ar-PLDT, sr-PLLT, sr-PLDT, ir-PLLT y ir-PLDT, se detecta una temperatura de transición vítrea alrededor de los 100ºC y en ningún caso se ha obtenido fases cristalinas. Todas las poliamidas se detectan dos etapas de descomposición térmica.El estudio de degradación hidrolítica de la poliamida ar-PLLT muestra un aumento aparente del peso molecular con el tiempo, para luego disminuir. Ello es explicable por una degradación en dos partes. La primera, la hidrólisis del grupo éster lateral, lo que lleva a un polielectrolito, de propiedades en disolución particulares. La segunda es la rotura de la cadena del polímero. Esta conclusión se basa en los datos de cromatografía de permeabilidad en gel y espectroscopía de resonancia magnética nuclear.

Se han obtenido y caracterizado una serie de poli(a-n-alquil g-glutamato)s (PAAG-n) con n³12 y de poli(a-n-alquil b,L-aspartato)s (PAALA-n), mediante transesterificación con n-alcoholes y se ha estudiado la influencia que ejerce el grupo lateral sobre la estructura y propiedades de estos polímeros. Los polímeros se han caracterizado mediante FTIR, RMN de 1H y 13C y análisis elemental. La composición enantiomérica se ha determinado midiendo rotaciones específicas de los polímeros hidrolizados y/o mediante HPLC. Los pesos moleculares se han evaluado por viscosimetría y/o SEC/LS. La caracterización térmica se ha llevado a cabo mediante DSC, TGA y DMTA. El análisis estructural se ha realizado mediante las técnicas de DIR, 13C-CP/MAS-RMN, difracción de rayos X y de electrones. Los PAAG-n se han obtenido a partir del ácido poli(g-glutámico) (PGGA) de biosíntesis, de dos composiciones enantioméricas diferentes, uno enriquecido en el isómero D y otro de composición cercana a la racémica. El procedimiento general está basado en dos reacciones sucesivas (esterificación y transesterificación) y ha resultado especialmente útil para la preparación de ésteres de cadena larga difíciles de obtener por otros métodos. Las conversiones han sido completas no observándose racemización significativa. Los PAAG-n con n³14 forman una estructura bifásica supramolecular en láminas. Las cadenas principales adoptan una conformación helicoidal tipo hélice a y se alinean en láminas con las cadenas laterales interdigitadas formando una microfase entre las láminas. La distancia interlaminar es proporcional a n. Para estos polímeros se han encontrado las transiciones de fase A®B y B®C, a temperaturas T1 y T2. La transición A®B es reversible y tiene lugar a temperaturas entre 20 y 80 ºC. La transición B®C se ha observado para los PAAG-n con n³18 a temperaturas superiores a los 100 ºC. En la fase A las cadenas laterales están cristalizadas en una red hexagonal y dispuestas perpendicularmente a la cadena principal. En la fase B las cadenas laterales están desordenadas pero más o menos estiradas. La fase C presenta las cadenas laterales totalmente desordenadas. No se han observado efectos termocrómicos al calentar las muestras desde temperatura ambiente hasta temperaturas superiores a T2 cuando se observan bajo luz polarizada.Los PAALA-n y el PIBLA (poli(a-isobutil b,L-aspartato)) se han obtenido por transesterificación del PABLA (poli(a-bencil b,L-aspartato)). Resultó difícil conseguir conversiones completas debido a la existencia de reacciones de imidación. Los PAALA-n obtenidos mediante transesterificación mostraron temperaturas de descomposición similares a las de los PAALA-n obtenidos mediante polimerización. Las transiciones a y b (DMTA) se observan en los PAALA-n de cadenas cortas e intermedias a temperaturas más elevadas que las descritas para los PAAG-n con el mismo valor de n. La Ta disminuye a medida que aumenta n. La Tb aumentó ligeramente con n para los PAALA-n con n£ 8. La relajación g se observa para los PAALA-n con n³6.