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Vibrio harveyi is a bioluminescent bacterium and the organism in which quorum sensing was discovered. It was recently found that a class of molecules, cyclic dipeptides, may be a new kind of quorum sensing signal that may affect other species in the genus. The purpose of this study was to determine if V. harveyi produced one of these molecules, cyclo(Phe-Pro) or cFP, and the effects it has on bioluminescence, growth and gene expression. Electrospray Mass Spectrometry was used to detect cFP, and it was found. While growth and gene expression were not significantly affected by cFP, bioluminescence was slightly induced at low concentrations. It appears that V. harveyi does not produce cFP and it does not significantly affect the luminescence quorum sensing controlled genes, and is most likely not a true signal, in V. harveyi.

As antimicrobial resistance persistently disrupts the treatment of microbial infection, natural product chemistry has played a significant role in identifying novel drugs with novel modes of action critical to getting ahead of resistance. The primary goal of this project is to extract and identify potential novel antimicrobial natural products produced by Arthrobacter sp. Although underexplored, Arthrobacter sps. have been known to produce bioactive compounds with versatility; one such is a depsipeptide with quorum-sensing inhibitory activity.1 In this research, an Arthrobacter sp. TAJX1902, isolated from a soil sample, showed inhibitory activity against a filamentous indicator bacterium and a violacein-producing Janthinobacterium sp. Arthrobacter sp. TAJX1902 was cultured using rich medium broth and agar to extract and isolate metabolites. Isolated compounds were characterized via spectroscopic techniques, including 1D and 2D-NMR spectroscopy and GCMS analysis. Arthrobacter sp. TAJX1902 produces Pyrrolo[1,2-a]pyrazine-1,4-dione, hexahydro-3-(phenylmethyl), and five other bioactive cyclic dipeptides (CDPs).

Cyclodipeptides (CDPs) are the smallest, most stable cyclic peptides that are synthesized as secondary metabolites by bacteria. The aim of this study was to investigate the effect of the Pseudomonas argentinensis (SA190) and four (CDPs), named as cis-cyclo-(Pro-Phe) (Cyclo2), cis-cyclo-(Pro-Leu) (Cyclo3), cis-cyclo-(Pro-Tyr) (Cyclo4) and cis-cyclo-(Pro-Val) (Cyclo5), with three concentrations (1µM, 100nM, and 10nM), on the growth of Arabidopsis thaliana under normal plant growth conditions [1/2MS media], salt conditions [125 mM NaCl] and drought conditions [25% PEG]. Moreover, we determined the most effective CDPs with optimal concentration. It was found that cis-cyclo-(Pro-Tyr) (Cyclo4) at a concentration of 100nM had an effect on the plant growth and can mimic the effect of SA190 under normal [1/2MS media] conditions. Also, cis-cyclo-(Pro-Tyr) (Cyclo4) at a concentration of 1µM can mimic the effect of SA190 under salt conditions [125mM NaCl]. Finally, cis-cyclo-(Pro-Val) (Cyclo5) at a concentration of 1µM can mimic the effect of SA190 under drought conditions [25% PEG].

Ce travail est consacré à l’étude des effets de chiralité dans des dipeptides cycliques construits sur un cycle dikétopiperazine (DKP) et comportant deux résidus de chiralités identiques ou opposées, LL et LD. Les mêmes systèmes sont étudiés dans différents environnements par spectroscopie optique couplée à des calculs de chimie quantique. Les molécules neutres sont isolées et refroidies en jet supersonique et caractérisées par spectroscopie laser UV et IR sélective en conformère. La structure des systèmes protonés, isolés dans un spectromètre de masse ICR, est déterminée par spectroscopie de dissociation induite par absorption de multiples photons IR. Enfin, le dichroïsme circulaire vibrationnel (VCD) est appliqué aux échantillons en phase solide. Les systèmes étudiés comportent un résidu aromatique tyrosine (cyclo Tyr-Pro) ou phénylalanine (cyclo Phe-Phe et Phe-His). Le diastéréomère LD est en général moins stable et plus flexible que LL, et ils ne diffèrent structurellement que par des interactions faibles de type NH…π ou CH…π. Le conformère le plus stable correspond en général à une structure où le chromophore aromatique est replié sur le cycle peptidique, l’autre partie étant étendue. Un effet très important de la chiralité est observé dans certains dimères protonés. Enfin, les expériences de VCD en phase condensée montrent que la phase cristalline de cyclo LPhe-DPhe formée par déshydratation du dipeptide linéaire en phase solide est chirale à cause de la synchronisation des chiralités transitoires des monomères. / This work focuses on the study of chirality effects on the structure of cyclic dipeptides built on a diketopiperazine (DKP) ring with residues of identical (LL) or opposite (LD) chirality. The same systems are studied in different environments by means of optical spectroscopy coupled to quantum chemical calculations. The neutral molecules are isolated and cooled down to a few K in a supersonic expansion and characterized by UV and conformer-specific IR laser spectroscopy. The structure of the protonated systems, isolated in an ICR mass spectrometer, is determined by infrared multiple photon dissociation spectroscopy. Last, vibrational circular dichroism (VCD) is applied to the solid-state samples.The studied systems possess an aromatic residue, either tyrosine (cyclo Tyr-Pro) or phenylalanine (cyclo Phe-Phe and Phe-His). The LD diastereomer is in most of the cases less stable and more flexible than LL. LL and LD differ from each other by weak interactions like NH…π or CH…π interactions. The most stable conformer usually corresponds to a structure with the aromatic chromophore folded over the DKP ring, the other part being extended. A dramatic effect of chirality is observed for some of the protonated dimers. Last, VCD experiments in the condensed phase show that the crystal phase of LPhe-DPhe formed by solid-state dehydration of the linear dipeptide is chiral due to synchronization of the transient chirality of the monomers.

Ce travail vise à comprendre l’effet de la chiralité sur la structure et la photoréactivité de biomolécules, isolées en phase gazeuse. Pour cela, nous combinons des méthodes de spectroscopie laser couplées à la spectrométrie de masse avec des calculs de chimie quantique. La comparaison entre spectres expérimentaux et simulés permet de déterminer la structure des espèces étudiées et de comprendre leur photoréactivité. La première partie étudie la différence de structure entre les deux diastéréoisomères d’un dipeptide cyclique (cyclo Tyr-Tyr). Une seule forme est observée quand les deux résidus tyrosine n’ont pas la même chiralité. Dans cette structure, un des cycles aromatiques est replié sur le cycle peptidique et l’autre est étendu à l’extérieur. Dans le stéréoisomère où les deux résidus ont la même chiralité, cette forme coexiste avec une autre, dans laquelle les deux cycles aromatiques interagissent par une liaison hydrogène. La deuxième partie concerne la structure et la nature des états excités de complexes d’alcaloïdes dérivés de la quinine avec l’acide sulfurique. Les complexes sont formés par l’ajout de l’ion bisulfate sur l’alcaloïde doublement protoné. L’ion bisulfate protège l’alcaloïde de la photodissociation UV grâce à un effet de cage, qui est identique pour la quinine et son pseudoénantiomère la quinidine. / This thesis aims at understanding chirality effects on the structure and photoreactivity of biomolecules in the gas phase by combining laser spectroscopy coupled to mass spectrometry and quantum chemical calculations. Comparison between experimental and simulated spectra allows determining the structure of the species under study and understanding their photoreactivity. The first part of this work focuses on the structural differences between the two diastereoisomers of a cyclic dipeptide, cyclo Tyr-Tyr. Only one form is observed when the two residues have different chirality. In this form, one of the aromatic rings is folded over the dipeptide ring and the other one is extended outwards. For the diastereomer with residues of identical chirality, this form coexists with a structure in which the two aromatic rings are in a stacked position, stabilized by hydrogen bond formation. The second part of this thesis deals with the structure and the nature of the excited states of complexes of cinchona alkaloids with sulfuric acid. An important finding is that the complexes are formed by adding the bisulfate ions to doubly-protonated alkaloid. The presence of the bisulfate ion has a protective effect towards photodissociation thanks to the cage effect, which is identical for quinine and its pseudo enantiomer quinidine.