title: Hydration profiles of aromatic amino acids: conformations and vibrations of L-phenylalanine-(H2O)n clusters.
abstract: IR-UV double resonance spectroscopy and ab initio calculations were employed to investigate the structures and vibrations of the aromatic amino acid, L-phenylalanine-(H(2)O)(n) clusters formed in a supersonic free jet. Our results indicate that up to three water molecules are preferentially bound to both the carbonyl oxygen and the carboxyl hydrogen of L-phenylalanine (L-Phe) in a bridged hydrogen-bonded conformation. As the number of water molecules is increased, the bridge becomes longer. Two isomers are found for L-Phe-(H(2)O)(1), and both of them form a cyclic hydrogen-bond between the carboxyl group and the water molecule. In L-Phe-(H(2)O)(2), only one isomer was identified, in which two water molecules form extended cyclic hydrogen bonds with the carboxyl group. In the calculated structure of L-Phe-(H(2)O)(3) the bridge of water molecules becomes larger and exhibits an extended hydrogen-bond to the pi-system. Finally, in isolated L-Phe, the D conformer was found to be the most stable conformer by the experiment and by the ab initio calculation.
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan. tebata@hiroshima-u.ac.jp
authors.forename: Takayuki
authors.initials: T
authors.lastname: Ebata
authors.forename: Takayo
authors.initials: T
authors.lastname: Hashimoto
authors.forename: Takafumi
authors.initials: T
authors.lastname: Ito
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Inokuchi
authors.forename: Fuat
authors.initials: F
authors.lastname: Altunsu
authors.forename: Bernhard
authors.initials: B
authors.lastname: Brutschy
authors.forename: P
authors.initials: P
authors.lastname: Tarakeshwar
mesh_terms: D000465:Algorithms; D006860:Hydrogen Bonding; D008968:Molecular Conformation; D010649:Phenylalanine / Q000737:chemistry*; D013055:Spectrophotometry, Infrared / Q000379:methods; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*; D013816:Thermodynamics; D014732:Vibration; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D010649:Phenylalanine