The inevitable aging process can be partially attributed to the accumulation of oxidative damage that results from the action of free radicals. Methionine sulfoxide reductases (Msr) are a class of enzymes that repair oxidized methionine residues. The two known forms of Msr are MsrA and MsrB which reduce the R- and S- enantiomers of methionine sulfoxide, respectively. Our lab has created the first genetic animal model that is fully deficient for any Msr activity. Previously our lab showed that these animals exhibit a 20 hour delay in development of the third instar larvae (unpublished data). My studies have further shown that the prolonged third-instar stage is due to a reduced growth rate associated with slower food intake and a markedly slower motility. These Msr-deficient animals also exhibit decreased egg-laying that can be attributed to a lack of female receptivity to mating. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

La connaissance des interactions interfaciales et l'énergie de surface est nécessaire pour étudier et modéliser les processus qui se déroulent dans le mouillage, l'adhésion ou la diffusion. Tels phénomènes sont rencontrés dans la préparation des suspensions, des émulsions et les peintures. Dans ce contexte, l'énergie de surface représente un paramètre important dans l'étude des propriétés interfaciales solide/liquide où plusieurs applications sont impliquées. Nous avons étudié l'effet de la modification chimique sur l'énergie de surface de deux silices choisies selon deux différentes échelles: l'OX qui présente un substrat nanométrique et les wafers de silicium qui est un substrat millimétrique. Pour la silice OX 50, La modification chimique de la surface a été réalisée avec l'hexadecyltrichlosilane (HTS) à caractère hydrophobe. L'infrarouge en transmission et la quantification de carbone organique ont été efficaces pour estimer les quantités croissantes d'HTS greffées à la surface de la silice. Deux isothermes d'adsorption ont été tracées. Ensuite, la volumétrie d'adsorption continue d'argon et d'azote a été utilisée pour étudier l'évolution de l'hétérogénéité énergétique. Ceci a été achevé en faisant recours à une stratégie d'analyse de volume adsorbée à la monocouche (Vm) d'azote et d'argon. Les résultats obtenus ont servi pour tracer une troisième isotherme d'adsorption. La quantification de l'énergie de surface a été réalisée avec la montée capillaire (technique macroscopique) et la chromatographie gazeuse en phase inverse (CGI) (technique moléculaire). Pour les wafers de silicium, deux types de surfaces ont été élaborées durant cette étude. Le premier hydrophile (traitement Piranha, formations des groupements OH). Cette surface a été obtenue par oxydation de ces wafers (traitement Piranha). La deuxième a été obtenue par le greffage d'HTS (greffons CH3). La quantification de l'énergie de surface a été réalisée avec la mouillabilité (technique macroscopique) et la microscopie à force atomique (AFM) (technique nanoscopique). Enfin, les différentes valeurs d?énergie de surface de la silice vierge OX 50 ont été comparées avec celles de la surface plane hydrophile (OH). Pour les surfaces hydrophobes, on a comparé les valeurs d?énergie de surface de la silice OX 50 modifiée d'une quantité maximale d?HTS avec le wafer de silicium à greffons CH3 / The knowledge about interfacial free energy interactions and surface energy is necessary for understanding and modeling many surface and interface processes. The investigation of the surface properties of solids is very important in several applications such as wetting, spreading and adhesion processes. Such processes occur during the preparation of suspensions, emulsions, painting, printing and corrosion protection. Knowledge about surface free energy of solids appears as a very important parameter determining the interfacial properties in solid/liquid and solid/gas interfaces where many implementations are involved. We have studied the effect of the chemical modification on surface energy for two types of silica: Aerosil OX 50 is chosen as a nanometric substrate and the wafers of silicium chosen as micrometric substrate. For silica OX 50, the chemical modification was carried out using the hydrophobic hexadecyltrichlorosilane (HTS). Transmission infrared and the quantification of organic carbon were helpful in the estimation of increasing quantities of HTS grafted to the surface. Two adsorption isotherms were drawn. Then, continuous adsorption isotherm of argon and nitrogen was used to study the evolution of energetic heterogeneity in the course of the chemical reaction. This was achieved by applying an analysis strategy of the monolayer volume (Vm) of adsorbed argon and nitrogen. Results enabled the drawing of a third adsorption isotherm. The quantification of surface energy for various samples was realize using capillary rise (macroscopic technique) and inverse gas chromatography (IGC) (molecular technique). For silicon wafers, two types of surfaces were elaborated in this study. The first hydrophilic (OH grafting), was obtained by oxidation of silicon wafers (Piranha treatment), the second hydrophobic (CH3 grafting), was obtained by grafting HTS molecules to the surface. The quantification of the surface free energy was achieved using the wettability (macroscopic technique) and the atomic force microscopy (AFM) (nanoscopic technique). Finally the different values of surface free energy obtained for native silica are compared to those of hydrophilic (OH) flat surfaces. As for hydrophobic surfaces, the silica OX 50 modified with maximum quantity of HTS is compared to Hydrophobic (CH3) flat surfaces

<p>The glutathione transferases (GSTs) represent a superfamily of dimeric proteins involved in cellular detoxication by catalyzing the nucleophilic addition of the reduced glutathione (GSH) to the hydrophobic electrophiles. The present work focuses on the functional role of the conserved structures of GSTP1-1. The lock-and-key motif is a highly conserved hydrophobic interaction in the subunit interface of Pi, Mu, and Alpha class GSTs. The key residue (Tyr⁵⁰ in hGSTP1-1) of one subunit is wedged into a hydrophobic pocket of the neighboring subunit. The heterodimer GSTP1/Y50A was constructed from the fully active wild-type GSTP1-1 and the nearly inactive Y50A in order to study how an essentially inactive subunit influences the activity of the neighboring subunit. The results illuminate the vital role of the lock-and-key motif in modulating the GSH binding and the rate of catalysis. Additionally, the two active sites of the dimeric enzyme work synergistically. An observed water network, in hGSTP1-1 structures, connects the two active sites, thereby offering a mechanism for communication between the two active sites.</p><p>Cys⁴⁸ and Tyr⁵⁰ were targeted by mutations and chemical modifications for understanding how the α2 loop residues modulate GSH binding and catalysis. The replacement of Tyr⁵⁰ with different unnatural amino acids showed that the nature of the key residue side-chain influences the interaction with the lock structure and, consequently, the catalytic activity. The K_M^GSH, GSH affinity and protein stability can be modulated by fitting key residue into the lock cavity of the neighbor subunit and, consequently, restriction of the flexibility of the α2 loop. Optimization of the interaction between the key residue and the lock-cavity increases k_cat. Also, the crystal structure of the Cys-free variant was determined. The result indicated that Cys⁴⁸ restricts the flexibility of the α2 loop by interacting with surrounding residues and, consequently, contributes to GSH binding and protein stability.</p>

The glutathione transferases (GSTs) represent a superfamily of dimeric proteins involved in cellular detoxication by catalyzing the nucleophilic addition of the reduced glutathione (GSH) to the hydrophobic electrophiles. The present work focuses on the functional role of the conserved structures of GSTP1-1. The lock-and-key motif is a highly conserved hydrophobic interaction in the subunit interface of Pi, Mu, and Alpha class GSTs. The key residue (Tyr50 in hGSTP1-1) of one subunit is wedged into a hydrophobic pocket of the neighboring subunit. The heterodimer GSTP1/Y50A was constructed from the fully active wild-type GSTP1-1 and the nearly inactive Y50A in order to study how an essentially inactive subunit influences the activity of the neighboring subunit. The results illuminate the vital role of the lock-and-key motif in modulating the GSH binding and the rate of catalysis. Additionally, the two active sites of the dimeric enzyme work synergistically. An observed water network, in hGSTP1-1 structures, connects the two active sites, thereby offering a mechanism for communication between the two active sites. Cys48 and Tyr50 were targeted by mutations and chemical modifications for understanding how the α2 loop residues modulate GSH binding and catalysis. The replacement of Tyr50 with different unnatural amino acids showed that the nature of the key residue side-chain influences the interaction with the lock structure and, consequently, the catalytic activity. The KMGSH, GSH affinity and protein stability can be modulated by fitting key residue into the lock cavity of the neighbor subunit and, consequently, restriction of the flexibility of the α2 loop. Optimization of the interaction between the key residue and the lock-cavity increases kcat. Also, the crystal structure of the Cys-free variant was determined. The result indicated that Cys48 restricts the flexibility of the α2 loop by interacting with surrounding residues and, consequently, contributes to GSH binding and protein stability.

Today, enzymes are extensively used for many industrial applications, this includes bulk and fine-chemical synthesis, pharmaceuticals and consumer products. Though Nature has perfected enzymes for many millions of years, they seldom reach industrial performance targets. Natural enzymes could benefit from protein redesign experiments to gain novel functions or optimize existing functions. Glutathione transferases (GSTs) are detoxification enzymes, they also display disparate functions. Two Mu-class GSTs, M1-1 and M2-2, are closely related but display dissimilar substrate selectivity profiles. Saturation mutagenesis of a previously recognized hypervariable amino acid in GST M2-2, generated twenty enzyme variants with altered substrate selectivity profiles, as well as modified thermostabilities and expressivities. This indicates an evolutionary significance; GST Mu-class enzymes could easily alter functions in a duplicate gene by a single-point mutation. To further identify residues responsible for substrate selectivity in the GST M2-2 active site, three residues were chosen for iterative saturation mutagenesis. Mutations in position10, identified as highly conserved, rendered enzyme variants with substrate selectivity profiles resembling that of specialist enzymes. Ile10 could be conserved to sustain the broad substrate acceptance displayed by GST Mu-class enzymes. Enzymes are constructed from primarily twenty amino acids, it is a reasonable assumption that expansion of the amino acid repertoire could result in functional properties that cannot be accomplished with the natural set of building blocks. A combination approach of site-directed mutagenesis and chemical modifications in GST M2-2 and GST M1-1 resulted in novel enzyme variants that displayed altered substrate selectivity patterns as well as improved enantioselectivities. The results presented in this thesis demonstrate the use of different protein redesign techniques to modulate various functions in Mu-class GSTs. These techniques could be useful in search of optimized enzyme variants for industrial targets. / biokemi och organisk kemi

Les nanocelluloses connaissent un fort développement depuis ces dernières décennies et font l’objet de nombreuses études menées par les industriels et/ou consortiums académiques. Cette étude s’insère dans le cadre d’un projet européen (SUNPAP) visant à l’industrialisation des nanofibrilles de cellulose (NFC). La présente thèse fait l’état de nouveaux procédés de modification chimique de surface des NFC dans une optique de chimie verte. Plusieurs stratégies ont été développées telle que l’emploi de liquides ioniques comme solvant de réaction (décrit comme solvants verts) ou l’utilisation d’une nanoemulsion en phase aqueuse permettant le greffage de surface des NFC. Dans le but d’étudier l’impact de ces modifications chimiques, les substrats ainsi traités ont été par la suite utilisés dans diverses applications. Ainsi, des bionanocomposites ont pu être produits, l’impact sur l’introduction de NFC (modifiées ou non) dans du papier a également été étudié. Une étude sur les propriétés antibactériennes et la biodégradabilité des NFC modifiées est également proposée. Une caractérisation approfondie des NFC vierges et modifiées a été réalisée. Des techniques puissantes et innovantes ont été utilisées pour caractériser ces substrats tels que l’XPS (X-ray Photoelectron Spectroscopy) ou encore la SIMS (Secondary Ion Mass Spectrometry). Toutes ces modifications, applications et caractérisations proposées constituent une avancée et des perspectives prometteuses dans le monde des nanocelluloses. / Nanocelluloses know a strong interest since last decades and they are the subject of many studies led by industrials and / or academic consortia. This study is a part of a European project (SUNPAP) for the industrialization of nanofibrillated cellulose (NFC). This thesis is the state of new methods for the chemical surface modification of NFC with a view of green chemistry. Several strategies have been developed such as the use of ionic liquids as reaction solvent (described as green solvents) or the use of an aqueous medium in order to graft the surface of NFCs. Thus, the treated substrates were then used in various applications. Also, bionanocomposites were produced, the impact of the introduction of NFC (modified or not) in paper sheets has also been studied. A study on the antibacterial properties and biodegradability of modified NFC is also proposed. Several characterizations of neat and modified NFC were performed. Powerful and innovative techniques have been used to characterize these substrates such as XPS (X-ray Photoelectron Spectroscopy) or SIMS (Secondary Ion Mass Spectrometry). All these chemical modifications, applications and characterizations are offered promising prospects in the world of nanocelluloses.

La structure et le processus de formation des traces latentes dans le poly (allyl diglycol carbonate), PADC, ont été étudiés par spectroscopie FT-IR et par simulation Monte Carlo. La quantité de groupes OH formés est équivalente à la quantité de disparition des groupes éther. L’utilisation de radiations à faible TLE a prouvé que les fonctions carbonyle ne disparaissent que lorsque deux électrons au minimum interagissent avec une seule unité de répétition du polymère. Les résultats obtenus avec des protons de haute énergie permettent de comprendre la différence entre des traces révélables et non-révélables. Sur la base de ces résultats, un nouveau concept physique de Fluence Electronique Radiale autour de la Trace d’un Ion, défini comme la densité d'électrons secondaires qui traversent une surface cylindrique de rayon donné, est proposé pour décrire le seuil de détection du PADC en utilisant le code Geant4-DNA. Les connaissances acquises sont utiles pour trouver des agencements moléculaires appropriés pour de nouveaux détecteurs de sensibilités désirées. / The structure and formation process of latent tracks in poly(allyl diglycol carbonate), PADC, have been examined using the combination of FT-IR spectrometry and a Monte Carlo simulation. The generation amount of OH groups is almost equivalent to the loss amount of ether. An important role of the secondary electron that the carbonyl can be broken only when more than two electrons pass through a single repeat unit is clarified by experiments using low LET radiations. Results of high energy protons lead us to the elucidation of the difference between etchable and un-etchable tracks. Based on these results, a new physical concept of Radial Electron Fluence around Ion Tracks, which is defined as the number density of secondary electron that pass through the cylinder surface with a certain radius is proposed for the detection threshold of PADC using Geant4-DNA. Obtained knowledge is helpful to find appropriate molecule arrangements for new etched track detector with desired sensitivities

Orientadores: Sergio Marangoni, Luis Alberto Ponce-Soto / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-10T16:19:54Z (GMT). No. of bitstreams: 1 RomeroVargas_FreyFrancisco_M.pdf: 1233125 bytes, checksum: 85502fc7f4b2dd6cdb2a6fc0c220c5b2 (MD5) Previous issue date: 2007 / Resumo: As serpentes do gênero Crotalus incluem várias espécies amplamente distribuídas nocontinente Americano. Os venenos crotálicos das serpentes encontradas no Brasil apresentam características próprias. Entre os componentes bioativos, as fosfolipases A2 (E.C. 3.1.1.4.) destacam-se por ser a principal componente, tais enzimas são dependentes de cálcio e hidrolisam a ligação sn-2 éster dos fosfolipídios e alem disso induz uma variedade de efeitos. Nesta tese, primeiramente nos desenvolvemos um novo protocolo de purificação com uma coluna C18 µ-Bondapack em HPLC de fase reversa destas toxinas, Os perfis obtidos mostraram que o veneno total da espécie Crotalus durissus cumanensis foi fracionado em quatorze picos, onde as frações 9 e 10 apresentam atividade PLA2. Do veneno de Crotalus durissus ruruima foram obtidos dezoito picos, sendo que as frações 12 e 13 apresentaram atividade PLA2 também. Assim, neste trabalho, nos apresentamos o isolamento, purificação determinação de sua estrutura primaria de duas isoformas fosfolipase A2 para cada espécie crotálica: Crotalus durissus cumanensis e Crotalus durissus ruruima denominados como Cdc-9, Cdc-10, Cdr-12 e Cdr-13, respectivamente. Todas elas são formadas por 122 resíduos de aminoácidos. O alinhamento dos aminoácidos, das isoformas Cdc-9, Cdc-10, Cdr-12 e Cdr-13 mostram um alto nível 93.4 % de homologia seqüencial para as duas primeiras e 92.6% para as outras, observaram-se com respeito a distintas PLA2 que diminuíram para cerca de 50 % de homologia. Todas elas foram identificadas como miotoxinas e apresentaram atividade fosfolipásica. Foi possível realizar, a partir das isoformas nativas um processo de modificação química, utilizando-se reagentes seletivos para amino ácidos específicos (His, Tyr e Lys) os quais estão envolvidos na rede catalítica ou na interação com sua interface, logo após, foram analisadas quanto a suas características físico-químicas e biológicas. Nossos estudos de miotoxicidade local e sistêmica de todas as isoformas nativas e modificadas dos venenos crotálicos in vivo, evidenciaram o incremento nos níveis de creatina cinase (CK) séricos e nas isoformas modificadas foram inibidas na sua atividade catalítica ou devido às mudanças estruturais que afetam outras regiões alem do sitio catalítico, revelando a importância de conhecer a relação estrutura-função. Em contraste, o efeito indutor de edema, não pode ser rapidamente correlacionado com suas diferenças estruturais. Os resultados apresentados neste trabalho proporcionam a obtenção de uma ferramenta bioquímica útil para acrescentar nosso conhecimento da relação dos sítios farmacológicos alem da região catalítica nas fosfolipases A2 / Abstract: The serpents of the genus Crotalus include several species widely distributed in the American continent. The poisons crotálicos of the serpents found in Brazil, they present own characteristics. Among the components bioativos, the phospholipases A2 (E.C. 3.1.1.4.) standing out to be the main component, such enzymes are dependents of calcium and hidrolise the bond sn-2 éster of the fosfolipídios and besides that induced a variety of effects. In this thesis, firstly we develop a new purification protocol with a column C18 µ- Bondapack in HPLC of reverse phase of these toxins, The obtained profiles showed that the total poison of the species Crotalus durissus cumanensis was fractioned in fourteen picks, where the fractions 9 and 10 present activity PLA2. Of the poison of Crotalus durissus ruruima they were obtained eighteen picks, and the fractions 12 and 13 also presented activity PLA2. This way, in this work, we present the isolation, purification, determination of his primary structure of two isoforms fosfolipase A2 for each species crotálics: Crotalus durissus cumanensis and Crotalus durissus ruruima denominated like Cdc-9, Cdc-10, Cdr-12 and Cdr-13, respectively. All of them are formed by 122 residues of amino acids. The alignment of amino acids of the isoforms Cdc-9, Cdc-10, Cdr-12 and Cdr-13 it shows a high level of sequential homology 93.4% for the first two and 92.6% for the other ones, they were observed with regard to different PLA2 that decreased for about 50% of homology. All of them were identified as miotoxins and they presented phospholipasic activity. it was possible to carry out starting from the native isoforms a process of chemical modification, being used selective reagents for amino specific acids (His, Tyr and Lys) which are involved in the catalytic net or in the interaction with his interface, soon after, they were analyzed as for their physio-chemical and biological characteristics. Our studies of local and systemic miotoxicity of all the native and modified isoforms in vivo of the poisons crotálicos, evidenced the increment in the levels of creatine kinase (CK) séricos and in the modified isoformas they were inhibited in his activity catalytic or due the structural changes that they affect other regions besides the catalytic place, revealing the importance of knowing the relationship structure-function. In contrast, the effect producing edema, it cannot be correlated quickly with their structural differences. The results presented in this work provide the obtaining of an useful biochemical tool to increase our knowledge of the relationship of the pharmacological sites also of the catalytic region in the phopholipases A2 / Mestrado / Bioquimica / Mestre em Biologia Funcional e Molecular

Made available in DSpace on 2017-07-10T18:01:57Z (GMT). No. of bitstreams: 1 Cristiana Rocker.pdf: 2541583 bytes, checksum: a2c9e3fe99f71c1640b23b9fa0f61899 (MD5) Previous issue date: 2015-07-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Effluent containing toxic metals present serious risks to the environment and to living beings due to their persistence in the environment bioacumulam on trophic chain. The biosorption method has been widely tested in the treatment of these effluents, by presenting itself as a low-cost alternative and effective. The objective of this work was to analyze the process of biosorption of Cr(III) from aqueous solutions and synthetic tanning effluent using inactive biomass of aquatic macrophytes Pistia stratiotes in natura (PN) and chemically modified (PM), Salvinia molesta in natura (SN) and chemically modified (SM). The characterization of the biomasses and biosorption experiments as a function of pH, time, concentration of ion Cr(III), and desorption temperature for the purpose of determining the maximum capability of biosorption. By means of the scanning electron microscopy images of biosorbents showed uneven surfaces and heterogeneous, and in the infrared spectroscopy indicated that the chemical modification with sodium hydroxide and citric acid removed soluble phenolics and increased the carboxyl groups involved in the biosorption process. Kinetic studies showed that the average time required for the system come into balance is from 240 minutes, and all the biosorbents tested were adjusted by the pseudo-segunda order model, the biosorbents also modified adjusted intraparticle diffusion model. The results of biosorption in function of the concentration of the ion Cr(III), indicated the maximum capacity of each biosorbent. Of biosorbents in natura, SN presented the highest capacity of biosorption, with 25.70 mg g-1, on the other hand, the biomass modified PM reached capacity with 58.16 mg g-1. The results were adjusted the Freundlich isotherm, and the Langmuir model presented good adjustment to the modified biosorbents. Using the thermodynamic studies, it was found that these are spontaneous and exothermic reactions, and the results of desorption were higher for PM. The tests using raw effluent from tannery and biological treatment pond, SN proved to be more advantageous for use in the treatment of raw sewage and biological treatment pond, for presenting the highest rate of removal of Cr(III). Whereas the biomass of aquatic macrophytes P. stratiotes and S. molesta are abundant in the environment, the use of the same as biosorbent is favourable for the treatment of effluents. / Efluentes contendo metais tóxicos apresentam sérios riscos ao meio ambiente e aos seres vivos, devido sua persistência no ambiente bioacumulam-se na cadeia trófica. O método de biossorção vem sendo amplamente testado no tratamento destes efluentes, por apresentar-se como uma alternativa de baixo custo e eficaz. O objetivo do trabalho foi analisar o processo de biossorção de Cr(III) de soluções aquosas sintéticas e de efluente de curtume utilizando a biomassa inativa das macrófitas aquáticas Pistia stratiotes in natura (PN) e quimicamente modificada (PM), Salvinia molesta in natura (SN) e quimicamente modificada (SM). Realizou-se a caracterização das biomassas e experimentos de biossorção em função do pH, tempo, concentração do íon Cr(III), temperatura e dessorção com a finalidade de se determinar a capacidade máxima de biossorção. Por meio das imagens de microscopia eletrônica de varredura dos biossorventes observou-se superfícies irregulares e heterogêneas, e a espectroscopia na região do infravermelho indicou que a modificação química com hidróxido de sódio e ácido cítrico removeu compostos fenólicos solúveis e aumentou os grupamentos carboxila envolvidos no processo de biossorção. Os estudos cinéticos demonstraram que o tempo médio necessário para o sistema entrar em equilíbrio é a partir de 240 minutos, e todos os biossorventes testados foram ajustados pelo modelo de pseudo-segunda ordem, sendo que os biossorventes modificados também se ajustaram ao modelo de difusão intrapartícula. Os resultados de biossorção em função da concentração do íon Cr(III), indicaram a capacidade máxima de cada biossorvente. Dos biossorventes in natura, SN apresentou a maior capacidade de biossorção, com 25,70 mg g-1, por outro lado, nas biomassas modificadas, PM atingiu maior capacidade com 58,16 mg g-1. Os resultados foram ajustados a isoterma de Freundlich, sendo que o modelo de Langmuir apresentou bons ajustes aos biossorventes modificados. Por meio dos estudos termodinâmicos, constatou-se que tratam-se de reações espontâneas e exotérmicas, e os resultados de dessorção foram maiores para PM. Nos testes utilizando o efluente bruto de curtume e da lagoa de tratamento biológico, SN mostrou-se mais vantajosa para a utilização no tratamento do efluente bruto e da lagoa de tratamento biológico, por apresentar a maior taxa de remoção de Cr(III). Considerando que a biomassa das macrófitas aquáticas P. stratiotes e S. molesta encontram-se abundantes no meio ambiente, a utilização das mesmas como biossorvente é favorável para o tratamento de efluentes.

Cette thèse a pour objectif de développer une nouvelle approche bio-inspirée des processus de polymérisation conduisant à la formation de polyterpènes et ultérieurement du caoutchouc naturel, un polyisoprène de structure purement 1,4-cis de forte masse molaire dont les propriétés sont encore inégalées par ses homologues synthétiques. Pour cette raison la production mondiale de caoutchouc naturel demeure stratégique et est toujours proche de 10 millions de tonnes, soit environ 45% de la demande mondiale annuelle en élastomères. Alors que les voies de synthèse développées jusqu’à présent pour accéder à des homologues du caoutchouc naturel sont basées sur la polymérisation par voie anionique ou par coordination de l’isoprène,l’approche suivie par la nature pour synthétiser les polyterpènes est basée sur la polymérisation à caractère cationique d’un autre monomère, le pyrophosphate d’isopentényle (IPP) qui est la brique de construction universelle de la famille des terpènes. Le projet a pour objet de tenter de reproduire au plus près le procédé naturel et d’utiliser, d’une part, la voie cationique pour polymériser des modèles de l’IPP et l’isoprène en utilisant des homologues du pyrophosphate dediméthylallyle (DMAPP, amorceur employé par la nature) comme amorceurs et des acides de Lewis pour mimer les cations divalents (Zn2+, Mg2+ or Mn2+) qui assistent les enzymes au cours des étapes d’ionisation et d’activation mises en jeu au cours de la biosynthèse, afin d’accéder à des polyterpènes approchant la structure des produits naturels. Contrairement à la nature, nous avons obtenus des oligomères de structure 1,4-trans avec de plus, de nombreuses structures cyclisées. D’autre part, nous avons également cherché à améliorer les propriétés d’un polyisoprène 1,4-cis obtenu par polymérisation anionique afin d’approcher celles du caoutchouc naturel. Nous avons développé une fonctionnalisation des chaines de polyisoprène 1,4-cis permettant d’ancrer des groupements urées susceptibles d’établir un réseau physique de liaisons hydrogènes. Nous avons montré que les polyisoprènes modifiés possèdent des propriétés viscoélastiques comparables à celles du caoutchouc naturel non vulcanisé obtenu par coagulation du latex. / Although synthetic rubbers, including high cis-content polyisoprene (PIP), are used in a broad range ofapplications, they are far from achieving the performances of natural rubber (NR), a 100% 1,4-cis polyisoprenewith very high molar mass. Therefore, NR produced exclusively by hevea (whereas more than 2,500 plant species are known to produce polyterpene-based polymers) is still dominant in many engineering applications since its exceptional properties grants this polymer a strategic resource material which holds a significant marketshare (about 45%).. The only alternative plant species under cultivation, Parthenium argentatum, also calledguayule, produces a latex yielding rubber with properties close to those of hevea rubber, and marketed as “non allergenic natural rubber” but with a higher cost complex extraction processes The NR biosynthesis process isdescribed as a polymerization process involving a series of enzymatic reactions using isopentenyl pyrophosphate(IPP) as elementary building brick. Besides, synthetic PIPs with high cis-content were already produced fromisoprene monomer by Ziegler-Natta, lanthanide-based or anionic-type polymerizations. Currently, no syntheticPIPs mimics the performance of NR, maybe because 100% 1,4-cis PIP could so far not been produced synthetically. A close inspection of the NR biosynthesis process led us to postulate that this latter is consistent with a transferless, stereospecific carbocationic-type polymerization mechanism. We then propose to develop this new bio-inspired cationic-like polymerization approach with the aim to produce polyterpenes and then NR homologues of tailored molar mass and microstructure that could exhibit properties close to natural polyterpenes by using IPP homologues and isoprene as monomers, DMAPP homologues asinitiators and Lewis acids to mimick the divalent cations (Zn2+, Mg2+ or Mn2+) that assist the enzymes during the initiation end activation steps. For the cationic polymerization of isoprene, oligomers with 1,4-trans and cyclized structures were obtained. We also develop new routes to modify polyisoprenes obtained by anionic polymerization in order to establish hydrogen interaction. To this end, different urea groups were grafted and the modified polyisoprene exhibite delastomeric properties close to the one of a non-vulcanized NR obtained by latex coagulation