>Magister Scientiae - MSc / Magnetosomes, produced by magnetotactic bacteria (MTB), are the most attractive alternative source of non-toxic biocompatible magnetic nanoparticles (MNPs). A magnetosome contains Fe2O4 magnetite with properties superior to MNPs synthesized by the traditional chemical route. However, synthesis of magnetosomes on large scale has not been achieved yet because magnetotactic bacteria are fastidious to grow. In addition, magnetosomes are generally “soft” magnetic materials which can only be used for some applications, while other applications require “hard” magnetic materials. Here at the Institute of Microbial Biotechnology and Metagenomic (IMBM), a study is being conducted on cloning and expression of the magnetosome gene island (MIA), the genetic machinery for magnetosome formation, in an easy to culture E. coli strain. The magnetic properties of the magnetosome can be manipulated by doping with divalent metals such as Ni2+ or Co2+ for a variety of applications. The specific objective of this study was to genetically engineer E. coli strains which accumulate intracellular Ni2+ or Co2+ in order to manipulate the magnetic properties of the magnetosomes. Three E. coli mutants and a wild type strain were transformed with high affinity Ni2+ or Co2+ uptake genes and evaluated for intracellular accumulation at different medium concentrations of NiCl2 or CoCl2. Cellular iron and magnesium were also evaluated because iron is the major component of the magnetosome and magnesium is important for cell growth. The wild type strain, EPI 300 habouring Ni2+ uptake permease the hoxN gene or Co2+ uptake ABC type transporter cbiKMQO operon was found to accumulate the most intracellular Ni2+ or Co2+ in medium conditions most likely to induce magnetosome formation and magnetite manipulation. This strain can be used to co-express the MIA and Ni2+ or Co2+ uptake gene for mass production of magnetosome with altered magnetic properties.

>Magister Scientiae - MSc / Crude extracts from Myrothamnus flabellifolius were fractionated through variouschromatography techniques in order to achieve satisfactory separations. Two compounds, arbutin and lupeol, were isolated from the butanol and ethyl acetate extracts, respectively. Structural elucidation of the compounds was carried out on the basis of 1H and 13C NMR spectroscopy. It was the first time that lupeol had been isolated from M. flabellifolius.The water extract was found to contain heterogeneous pectic polysaccharides. Three polysaccharide fractions were separated from the water extract, namely; MPS, MPS-I and MPS-II. The predominant fraction was found to be MPS, with a molecular weight distribution of 2 X 105 Da. The polysaccharides were made up the following monosaccharides; arabinose, rhamnose, xylose, mannose, galactose and glucose. Monosaccharide composition was determined through acid hydrolysis at high temperatures, followed by GC analysis. The linkage analysis was carried out by GC-MS, following partial methylation of the polysaccharides. The use of human serum albumin (HSA) following its anchoring on magnetic nanoparticles, in order to isolate targeted saponins from Sutherlandia frutescens led to successful isolation of four saponins, namely; sutherlandiosides A-D. The saponins showed great affinity to bind to the HSA.

Les cryptophanes sont des molécules sphériques pouvant encapsuler dans leur cavité lipophile des molécules neutres (halogénométhanes, xénon) mais aussi des espèces ioniques comme les cations césium et thallium. Notre objectif a été d’immobiliser ces cages moléculaires de manière covalente sur un support solide dans le but de créer un matériau capable d’extraire des cations toxiques comme le thallium en milieu aqueux. Différentes stratégies ont été envisagées pour optimiser l’immobilisation de dérivés du cryptophane-A sur des surfaces de silice et d’or (surfaces planes et nanoparticules magnétiques de type coeur-écorce). Les cryptophanes-A mono-acide (1) et hexa-acide(2) ont été immobilisés sur des surfaces de silice préalablement fonctionnalisées par des groupements amines. Le cryptophane-A alcanethiol (3), ainsi que les cryptophanes 1 et 2 modifiés par lacystéamine (respectivement 4 et 5) ont été immobilisés sur des surfaces d’or. La caractérisation des surfaces planes par spectroscopie infrarouge de réflexion-absorption par modulation de polarisation(PM-IRRAS) a permis d’estimer le taux de recouvrement des différentes monocouches de cryptophanes et, ainsi, d’évaluer la méthode d’immobilisation la plus efficace. Un taux de recouvrement proche de 100% a été obtenu pour le cryptophanes 3 immobilisé sur les surfaces d’or.Ce composé a également été immobilisé de façon très efficace sur des nanoparticules magnétiques(γ-Fe2O3/SiO2) enrobées d’une nano-écorce d’or. Ces résultats permettent d’envisager la synthèse d’un cryptophane portant cinq fonctions hydroxyles et une fonction thiol afin de créer des matériaux capables d’extraire des cations toxiques. / Cryptophanes are spherical molecules that can encapsulate neutral molecules(halogenomethanes, xenon), and ionic species like cesium and thallium cations in their lipophiliccavity. Our objective was to covalently immobilize these molecular cages onto solid substrates tocreate a material able to extract toxic cations such as thallium in aqueous media. Different strategieswere considered to optimize the immobilization of cryptophane-A derivatives onto silica and goldsurfaces (flat surfaces and core-shell magnetic nanoparticles). Mono-acid cryptophane-A (1) andhexa-acid cryptophane-A (2) were immobilized onto silica surfaces that were functionalized by aminogroups beforehand. Alcanethiols cryptophane-A (3), 1 and 2 modified by cysteamine (cryptophanes 4and 5 ,respectively) were immobilized onto gold surfaces. Flat surfaces were characterized bypolarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) to estimate thesurface coverage of different cryptophane monolayers and to evaluate the most effective method. Asurface coverage close to 100% was obtained for the cryptophane 3 immobilized onto gold surfaces.This compound has been also immobilized efficiently onto magnetic nanoparticles (γ-Fe2O3/SiO2)coated with gold nano-shell. These results allow to consider the synthesis of cryptophane bearing fivehydroxyl and one thiol functions to create materials able to extract toxic cations