Sweet switches: Azobenzene glycosides as photosensitive lectin inhibitors in solution and on surfaces

Non-covalent interactions between carbohydrate ligands and their lectin receptors are accompanied by conformational changes between the interacting partners. Such changes might reflect a principal conformational control of carbohydrate-protein interactions, which has received only little attention until to date. Hence, the central focus of this thesis is to synthesize photoswitchable glycomimetics and investigate the role of light-induced conformational changes in carbohydrate recognition. Thus azobenzene glycoconjugates are principal target molecules of our research. Photoirradiation of azobenzene glycosides at ~ 365 nm induces E→Z isomerization leading to a certain E/Z ratio in the photostationary state (PSS). The special features of azobenzene glycoconjugates featuring an E→Z→E isomerization option in solution will eventually allow us to utilise this type of molecules with -D-mannose-specific lectins. In this context, a new class of azobenzene glycosides were synthesized and their photochromic properties were studied in solution by 1H NMR and UV-Vis spectroscopy and they were tested as inhibitors for type 1 fimbriae-mediated bacterial adhesion, such as the bacterial lectin FimH.. To mimic the cell surface glycocalyx, azobenzene glycosides were immobilised on gold surfaces to form photoswitchable glyco-SAMs. Photoisomerization was performed on the gold surface and monitored by IRRAS and UV-Vis spectroscopy. To get insight in the conformational control of carbohydrate recognition in a multivalence context, photosensitive glyconanopartices were also prepared and binding efficiency of different isomers was tested with the lectin ConA

Inhibition of bacterial adhesion to live human cells: Activity and cytotoxicity of synthetic mannosides

AbstractBacterial adhesion to glycosylated surfaces is a key issue in human health and disease. Inhibition of bacterial adhesion by suitable carbohydrates could lead to an anti-adhesion therapy as a novel approach against bacterial infections. A selection of five α-mannosides has been evaluated as inhibitors of bacterial adhesion to the polysaccharide mannan, as well as to the surface of live human HT-29 cells. Cell toxicity studies were performed to identify the therapeutic window for a potential in vivo-application of the tested carbohydrates. A previously published mannosidic squaric acid diamide was shown to be exceptionally effective as inhibitor of the bacterial lectin FimH

Spectroscopie infrarouge, cinétique et caractérisation de molécules aromatiques (implications astrophysiques)

This thesis is devoted to the investigation of the spectroscopy, kinetics and characterization of aromatic molecules. The manuscript is organized accordingly in three parts. In the first part, we report the first direct absorption infrared spectroscopy of the benzene dimer in the 3.3 micron region corresponding to the C-H fundamental stretch of the benzene monomer. The presence of new bands in the spectrum and the red shift of the C-H fundamental stretch are analyzed in detail. We extend this work to benzene clusters and benzene-argon complexes. For benzene clusters, the results are discussed in terms of solid phase of the clusters. For benzene-argon complexes, we measured high resolution spectra in the 3.3 micron region which are under analysis. In the second section of the thesis, the kinetics of anthracene dimerization at 60 K, 80 K, 120 K, 235 K and 470 K using the CRESU (Kinetics of Reactions in Supersonic Uniform Flows) technique has been studied. The rate constant of dimerization at 60 K has been obtained. Our findings are employed to assess the role of PAH nucleation in haze formation in Jupiter s polar atmosphere. Finally the carbonaceous material formed by pyrolysis of acetylene in a unique high temperature reactor has been explored. A variety of techniques such as H-NMR, IR and XRD have been used to unravel the intimate chemical and physical structures of the material.Cette thèse est consacrée à la spectroscopie, à la cinétique réactionnelle et à la caractérisation de molécules aromatiques. Le manuscrit est organisé en trois parties. La première partie traite de la première étude spectroscopique jamais réalisée sur le dimère du benzène par absorption directe. Elle est menée dans la région à 3,3 microns qui correspond aux modes vibrationnels d élongation C-H. L observation de nouvelles bandes dans le spectre et le décalage vers le rouge du mode C-H sont analysés en détail. Cette étude est étendue aux agrégats de benzène et aux complexes benzène-argon. En ce qui concerne les agrégats de benzène, l interprétation des résultats conduit à une phase solide des agrégats. Pour les agrégats mixtes benzène-argon, des spectres à haute résolution, en cours d analyse, ont été obtenus dans la région à 3,3 microns. Dans la deuxième partie de la thèse, la cinétique de dimérisation de l anthracène a été étudiée à 60 K, 80 K, 120 K, 235 K et 470 K en utilisant le procédé CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme). Le taux de la réaction de dimérisation à 60 K a été obtenu. Ces résultats ont été utilisés afin d évaluer le rôle tenu par la nucléation des Hydrocarbures Aromatiques Polycycliques dans la formation de la brume détectée dans l atmosphère polaire de Jupiter. Enfin, les particules carbonées formées par pyrolyse de l acétylène dans un réacteur à haute température original ont été analysées. Un ensemble de techniques telles que H-NMR, IR et XRD ont été utilisées pour explorer les structures chimiques et physiques de ce matériau carboné.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Structural and electrical properties of new core-shell silver poly(m-toluidine-co-2-bromoaniline) nanocomposites

In this article, we report the synthesis and characterization of silver dispersed poly(m-toluidine-co-2-bromoaniline) copolymer synthesized by chemical oxidative polymerization method. The synthesized copolymer composites were subjected to different analytical characterization methods, such as FT-IR, UV, XRD, SEM, photoluminescence and electrical conductivity studies. All the polymer samples are found to be soluble in common organic solvents. UV absorption spectra show a red shift when silver nanoparticles are dispersed in the copolymer. The characteristic peaks observed in FT-IR spectra confirm the formation of the copolymer. XRD pattern reveals the crystalline nature of the copolymer composites and sharp peaks in the spectra confirm the presence of silver particles. The silver nanoparticles change the surface morphology in the form of perfect encapsulation. The electrical conductivity of the polymer composites is found to vary from 10−4 S/cm to 10−6 S/cm. PL study reveals the charge transfer between the copolymer and the silver particles

Kinetic Stability of Si2C5H2 Isomer with a Planar Tetracoordinate Carbon Atom

Dissociation pathways of the global minimum geometry of Si2C5H2 with a planar tetracoordinate carbon (ptC) atom, 2,7-disilatricyclo[4.1.0.01,3]hept-2,4,6-trien-2,7-diyl (1), have been theoretically investigated using density functional theory and coupled-cluster (CC) methods. Dissociation of Si-C bond connected to the ptC atom leads to the formation of 4,7-disilabicyclo[4.1.0]hept-1(6),4(5)-dien-2-yn-7-ylidene (4) through a single transition state. Dissociation of C-C bond connected to the ptC atom leads to an intermediate with two identical transition states and leads back to 1 itself. Simultaneous breaking of both Si-C and C-C bonds leads to an acyclic transition state, which forms an acyclic product, cis-1,7-disilahept-1,2,3,5,6-pentaen-1,7-diylidene (19). Overall, two different products, four transition states, and an intermediate have been identified at the B3LYP/6-311++G(2d,2p) level of theory. Intrinsic reaction coordinate calculations have also been done at the latter level to confirm the isomerization pathways. CC calculations have been done at the CCSD(T)/cc-pVTZ level of theory for all minima. Importantly, all reaction profiles for 1 are found be endothermic in Si2C5H2. These results are in stark contrast compared to the structurally similar and isovalent lowest-energy isomer of C7H2 with a ptC atom as the overall reaction profiles there have been found to be exothermic. The activation energies for Si-C, C-C, and Si-C/C-C breaking are found to be 30.51, 64.05, and 61.85 kcal mol−1, respectively. Thus, it is emphasized here that 1 is a kinetically stable molecule. However, it remains elusive in the laboratory to date. Therefore, energetic and spectroscopic parameters have been documented here, which may be of relevance to molecular spectroscopists in identifying this key anti-van’t-Hoff-Le Bel molecule

Fe<inline-formula><math display="inline"><semantics><mrow><msub><mi mathvariant="bold">C</mi><mn mathvariant="bold">4</mn></msub><msubsup><mi mathvariant="bold">H</mi><mn mathvariant="bold">2</mn><mrow><mrow><mn mathvariant="bold">2</mn><mo mathvariant="bold">+</mo></mrow></mrow></msubsup></mrow></semantics></math></inline-formula> Encompassing Planar Tetracoordinate Iron: Structure and Bonding Patterns

The singlet, triplet, and quintet electronic states of the FeC4H22+ system are theoretically explored using quantum chemical methods, and 39 isomers are identified in the singlet electronic state and 4 isomers in both triplet and quintet electronic states. A molecule with a planar tetracoordinate iron (ptFe) is found on the potential energy surface of singlet and triplet electronic states. The bonding features of ptFe in the singlet electronic state are analyzed with natural bond orbital (NBO) analysis, adaptive natural density partitioning (AdNDP), and molecular orbital analysis. The resultant data delineate that the ptFe is stabilized through electron delocalization in the ptFe system

Direct Infrared Absorption Spectroscopy of Benzene Dimer

The direct infrared (IR) absorption spectrum of benzene dimer formed in a free-jet expansion was recorded in the 3.3 mu m region for the first time. This has led to the observation of the C H stretching fundamental mode nu(13) (B(1u)), which is both IR and Raman forbidden in the monomer. Moreover, the IR forbidden and Raman allowed nu(7) (E(2g)) mode has been observed as well. These two modes were found to be red-shifted along with the IR allowed nu(20) (E(1u)) mode, as previously reported by Erlekam et al. [Erlekam; Frankowski; Meijer; Gert von Helden J. Chem. Phys. 2006, 124, 171101], using ion-dip spectroscopy, contrary to the blue-shift predicted earlier by theoretical studies. The observation of the nu(13) band indicates that the symmetry is reduced in the dimer, confirming the T-shaped structure observed by Erlekam et al. Our experimental results have not provided any direct evidence for the presence of the parallel displaced geometry, the main objective of the present work, as predicted by theoretical calculations