The Sutherland group recently demonstrated that from a mixture of oligoribonucleotide-2'- or 3'-phosphates the latter is chemoselectively acetylated. This is shown to mediate a template-directed ligation to give predominantly 3',5'-linked RNA that is acetylated at the ligation junction (acetyl-RNA). It was suggested that RNA emerged prebiotically via acetyl-RNA and also is proposed to have favourable genotypic properties due to greater propensity to form duplex structure. To study the properties of acetyl-RNA, their synthesis by solid-phase chemistry was required and described is the design of a 2'/3'-O-acetyl orthogonal protecting group strategy. Key to the orthogonal protecting group strategy is the use of (2-cyanoethoxy)carbonyl for the protection of the nucleobase exocyclic amines and a photolabile solid-phase linker group that allowed partial on-column deprotection. The synthesis of the 2'/3'-O-acetyl and 2'/3'-O-TBDMS phosphoramidites, in addition to preparation of a photolabile solid-phase support, are described. With the materials to hand the procedures for an automated synthesis of acetyl-RNA were optimised and several acetyl-RNA oligonucleotides were synthesised. The duplex stability of acetyl-RNA with up to four sites of 2'-O-acetylation were assessed by UV melting curve analysis. Remarkably, the acetyl groups caused a consistent decrease in Tm of between 3.0-3.2 °C. Thermodynamic parameters indicated a decrease in duplex stability that was consistent with a decrease in hydration of the minor groove resulting in a reduction of the stabilising hydrogen bonding network. The stability of a tetraloop was also found to decrease on acetylation. The acetylated- tetraloop it is able to form duplex at lower concentrations than the natural tetraloop. Additionally, it is more stable at high concentrations, indicating that acetyl-RNA favours duplex over other secondary structure. These properties are considered to give acetyl-RNA competitive advantage for their non-enzymatic replication. Aminoacylation of RNA is an important process in modern biology but the intermediacy of aminoacyl-adenylates is considered to be prebiotically implausible. A potentially prebiotic aminoacylation of nucleoside-3'-phosphates, selective for the 2'-hydroxyl, is presented. However, it was thought the aminoacylation yields could be improved and so a search for an alternative activator was conducted. Oligoribonucleotide-3'-phosphates were exposed to the aminoacylation conditions and selective aminoacylation at only the 2'-hydroxyl of the 3'-end was observed. In particular, the aminoacylation of a trimer lends support to Sutherland’s theory of a linked origin of RNA and coded peptide synthesis.

Les aptamères correspondent à de courtes séquences d'oligonucléotides possédant une forte affinité et spécificité envers un ligand (petites molécules organiques, peptides, acides nucléiques, protéines, cellules). Du fait de leurs remarquables propriétés, ils sont utilisés comme alternative aux anticorps dans les dispositifs de type biocapteur/biopuce, notamment pour la détection de petites molécules (PM < 2000 Da). L'imagerie de résonance des plasmons de surface (SPRi) est une technique de détection optique qui a gagné une attention croissante ces dernières années. Elle est basée sur un principe de variation de l'indice de réfraction d'une surface sélective lors de l'interaction sonde/cible. Sa sensibilité est néanmoins limitée aux molécules de poids moléculaire supérieur à 2000 Da. Dans le cadre de ces travaux, nous avons développé une biopuce à aptamères pour à la détection d'une petite molécule, l'adénosine, au moyen de la technique de résonance des plasmons de surface (SPR). Pour cela, deux différentes stratégies ont été développées. La première combine l'utilisation de nanoparticules d'or (AuNPs) pour l'amplification du signal SPRi avec l'ingénierie des séquences d'aptamères. La seconde stratégie est basée sur l'exploitation de la stabilité thermodynamique apportée par l'interaction de la cible (adénosine) avec les séquences d'aptamères. Le dispositif SPR est alors couplé à un système de régulation de température, permettant ainsi d'assurer la dissociation des complexes et d'établir des profils de dénaturation caractéristiques. Nos résultats initient ainsi une nouvelle approche dans la détection de petites molécules par SPRi et ouvrent de nouvelles perspectives de développement des biocapteurs à aptamères. / Aptamers are single-stranded DNA (ssDNA) or RNA molecules capable of binding to target molecules, including proteins, metal ions and drugs. Because of their specific binding abilities and many advantages over antibodies (higher stability, lower cost, easy chemical modification…), they provide a great opportunity to produce sensing surfaces for effective and selective detection of small molecules. Surface Plasmon Resonance imaging (SPRi) has become one of the most widely used label-free method for the study of biorecognition events on sensor surfaces. This technique provides a rapid approach, however, limited by low refractive index changes occurring when small molecules (<2000 Da) are captured on the sensor. Whereas significant reflectivity variation is observed upon the interaction of large molecules like proteins with the sensing interface, for small molecules targets such adenosine, the reflectivity variation is often too small to be detected by SPRi. Thereby, only few studies have been reported so far on SPRi-based biosensor for small molecules detection using aptamers. In this work, we developed two bioassay strategies for the detection of a model small molecule, adenosine, using Surface Plasmon Resonance imaging. The first one combines the SPRi signal enhancement effect induced by gold nanoparticles (AuNPs) with the advantage of using engineered DNA aptamers. The experimental results have demonstrated that the presence of gold nanoparticles and adenosine, which works as a molecular linker between engineered aptamer fragments, can significantly increase the SPRi response. The second strategy is based on the thermodynamics of binding between adenosine and its aptamer. To that end, SPRi technique was coupled with rigorous temperature control and aptamer duplex stability was monitored (affected by target binding) by quantification of melting transitions. Our results initiate a new approach for small molecule detection using SPRi with the aim to validate future prospects for integration in parallelized platform.

Au cours de la dernière phase d’accrétion, les planètes terrestres ont connu des impacts géants violents et très énergétiques. A la suite du chauffage causé par les impacts, la Terre primitive était partiellement ou totalement fondue, et un océan magmatique a été formé dans la couche externe de la Terre. Le refroidissement successif de l’océan magmatique a causé la cristallisation fractionnée du manteau primitif. Cependant, il reste beaucoup d’incertitudes à propos de l’accrétion de la Terre primitive, comme la profondeur et la durée de vie d’un (ou plusieurs) océan(s) magmatique(s), l’effet de la recristallisation du manteau sur la ségrégation chimique entre les différents réservoirs de la Terre et ainsi de suite. La connaissance des propriétés de fusion du manteau profond est important aussi pour examiner la possibilité d’une fusion partielle actuellement. L’objectif était d’aborder quelques problèmes concernant le manteau inférieur terrestre : Quelle est la séquence de fusion entre les phases dominantes dans le manteau inférieur ? Est-ce qu’on peut expliquer la zone à ultra-basse vélocité (ULVZ) avec la fusion partielle d’un manteau pyrolytique (ou chondritique) ? Quel est le partage du fer entre les phases silicatées liquides et solides dans le manteau profond ? Est-ce qu’on peut donner des informations nouvelles sur les propriétés d’un océan magmatique profond à partir des courbes de fusion du manteau primitif ? Dans cette étude les courbes de fusion et les relations de fusion ont été analysées en utilisant la cellule à enclume de diamant chauffé au laser (LH-DAC) pour des pressions entre 25 et 135 GPa et des températures jusqu’à plus que 4000 K, i.e. pour des conditions de P-T qui correspondent au manteau inférieur terrestre entier. Les compositions utilisées ont été le raccord entre MgO et MgSiO3 et une composition de type chondritique pour le manteau terrestre. J’ai utilisé deux techniques in-situ de radiation-synchrotron pour déduire les propriétés de fusion à hautes pressions ; la diffractométrie au rayons-X et la fluorescence au rayons-X. Les nouveaux résultats obtenus dans cette étude sont : (...) / During the final stage of accretion, terrestrial planets experienced violent and highly energetic giant impacts. As a consequence of impact heating, the early Earth was partially or wholly molten, forming a magma ocean in the outer layer of Earth. Subsequent cooling of the magma ocean has led to fractional crystallization of the primitive mantle. Many unknowns remain about accretion of the early Earth, such as extension depth and life time of the magma ocean(s), role of mantle recrystallization on the chemical segregation between the different Earth reservoirs, and so on. The knowledge of melting properties of the deep mantle is also important to investigate the possibility of partial melting at the present time. The aim of this study was to tackle a few major questions concerning the Earth lower mantle : What is the melting sequence between the main lower mantle phases ? Can we explain the ultra-low-velocity zones (ULVZ) by partial melting of pyrolitic (or chondritic) mantle ? How does iron partition between liquid and solid silicate phases in the deep mantle ? Can we provide new information on the properties of the deep magma ocean based on the melting curve of the primitive mantle ? Melting curves and melting relations have been investigated using the laser-heated diamond anvil cell (LH-DAC) for pressure between 25 and 135 GPa and temperature up more than 4000 K, i.e. at P-T conditions corresponding to the entire Earth’s lower mantle. Compositions investigated were the join between MgO and MgSiO3 and a model chondritic-composition for the Earth mantle. Two different in situ synchrotron radiation techniques have been used to infer melting properties at high pressures ; X-ray diffraction and X-ray fluorescence spectroscopy. The new results obtained in this study include : (...)