Thermochemistry of Microhydration of Sodiated and Potassiated Monosaccharides

The thermochemical properties ΔHon , ΔSon, and ΔGon for the hydration of sodiated and potassiated monosaccharides (Ara = arabinose, Xyl = xylose, Rib = ribose, Glc = glucose, and Gal = galactose) have been experimentally studied in the gas phase at 10 mbar by equilibria measurements using an electrospray high-pressure mass spectrometer equipped with a pulsed ion beam reaction chamber. The hydration enthalpies for sodiated complexes were found to be between −46.4 and −57.7 kJ/mol for the first, and −42.7 and −52.3 kJ/mol for the second water molecule. For potassiated complexes, the water binding enthalpies were similar for all studied systems and varied between −48.5 and −52.7 kJ/mol. The thermochemical values for each system correspond to a mixture of the α and β anomeric forms of monosaccharide structures involved in their cationized complexes

Ab initio anharmonic intermolecular potential of the C2H2-HCl hydrogen bonded complex

International audienceA grid calculation of the intermolecular potential of the hydrogen bonded C2H2-HCl complex has been performed at the CCSD(T)/cc-pVTZ level of theory. The effects of anharmonicity, of coupling between intramolecular and intermolecular motions, and of the basis set superposition error (BSSE) are independently considered. This calculation yields the center of mass separation of the complex, vibrationaly averaged and corrected of BSSE. It also provides the binding energy De and the anharmonic vibrational frequency shift of the νHCL band of the complex correlated with the HCl stretching mode. These properties are compared with experimental results and found to be in very good agreement

Exploring carbohydrate-peptide interactions in the gas phase: structure and selectivity in complexes of pyranosides with N-acetylphenylalanine methylamide.

The physical basis of carbohydrate-peptide interactions has been explored by probing the structures of a series of complexes generated in a solvent-free environment under molecular beam conditions. A combination of double-resonance IR-UV spectroscopy and quantum-chemical calculations has established the structures of complexes of the model, N-acetyl-L-phenylalanine methylamide, bound to the α and β anomers of methyl D-gluco- and D-galactopyranoside as guests. In all cases, the carbohydrates are bound through hydrogen bonding to the dipeptide chain, although with some differing patterns. The amino acid host "engages" with the most suitable pair of neighboring conjugate sites on each carbohydrate; the specific choice depends on the conformation of the peptide backbone and the configuration and conformation of the carbohydrate ligand. None of the structures is supported by "stacking" interactions with the aromatic ring, despite their common occurrence in bound carbohydrate-protein structures

Infrared spectra of the C2H2-HCl complexes: An experimental and ab-initio study

International audienc

Une ligne VUV au Serveur Laser du Centre Laser de l'Université Paris-Sud

Au Centre Laser de l'Université Paris-Sud (CLUPS), un serveur laser (SELA) pour la physico-chimie permet d'accueillir des expérimentateurs autour de sources laser nanoseconde synchronisées à 10 Hz dans des domaines de fréquences variés. Des lasers commerciaux à colorants et OPO pompés par des Nd-YAG couvrent les domaines IR, VIS et UV. Ce domaine a été étendu dans le VUV entre 6 et 19 eV (200–65 nm) par mélange non-linéaire à 4 ondes dans des gaz rares (Xe, Kr, Ar) en suivant les deux schémas résonants ωVUV = 2ω1 ± ω2 qui s'appuient sur un état excité du gaz rare. Un monochromateur sépare le VUV souhaité des autres fréquences et le refocalise au centre de l'expérience. La génération de VUV accordable a été caractérisée en flux (qq 108 à 109 photons/pulse) et en pouvoir résolvant (E/ΔE = 500000 à 15.8 eV), ce dernier étant mesuré sur les raies d'autoionisation très fines de l'argon 3s23p5(2P1/2)ns couramment appelées ns'. Le pouvoir résolvant de cette source laser VUV et la possibilité de la coupler avec les autres lasers dans des expériences à plusieurs couleurs (IR-VIS-UV + VUV) la rend très intéressante et complémentaire des lignes synchrotron VUV, comme DESIRS sur SOLEIL