Résumé
The first part of this work is dedicated to reactions relevant to prebiotic chemistry. In view of applicative purposes, we first examined the preparation of amino acid N-carboxyanhydrides (NCA) through nitrosation of N-carbamoylamino acids (CAA) by NO+O2. We evidenced a new, potentially prebiotic route to NCA and peptides in aqueous medium, as a result of CAA decomposition. Finally this pathway is equivalent to amino acid activation by cyanate, and is also observed in the presence of urea. Concerning prebiotic chirality, we examined several reactions involved in a theoretical model of homochirality emergence (through rendering the racemic state dynamically unstable): epimerisation of CAA and N-terminal residues of peptides, reactivity of NCA on an [alpha]-alkyl amino acid. Our results underline the complexity of such problem, and lead us to re-consider prebiotic amino acid activation by proposing several possibilities derived from cyanate reactions. The second part of this work presents analytical developments in capillary electrophoresis (CE): new stacking (preconcentration) methods suitable for peptides embedded in high ionic strength samples; and new methods for the modulation of electro-osmotic flow (EOF) through non-covalent grafting of polymers and/or polyelectrolytes in the capillary. Applied to a model sample, stacking methods involving electric field amplification and transient isotachophoresis, resulted into stacking factors ranging from 30 to 80. Under certain conditions, the coupling of stacking and EOF modulation resulted in doubled sensitivity compared to classical stacking methods.