title: Coded amino acids in gas phase: the shape of isoleucine.
abstract: The solid alpha-amino acid isoleucine has been vaporized by laser ablation and expanded in a supersonic jet, where the molecular conformations of the isolated molecule were probed using Fourier transform microwave spectroscopy. Two conformers of neutral isoleucine have been detected in gas phase, the most stable being stabilized by an intramolecular hydrogen bond N-H...O=C and a cis-COOH arrangement. The higher energy form is stabilized by an intramolecular hydrogen bond N...H-O. The sec-butyl side chain of the amino acid adopts the same configuration in the two observed conformers, with a staggered configuration at Cbeta similar to that observed in valine and a trans arrangement of Calpha and Cdelta. Ab initio calculations at MP2/6-311++G(d,p) level reproduce satisfactorily the experimental results.
authors.affiliation: Grupo de Espectroscopía Molecular (GEM), Departamento de Química Física y Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, 47005 Valladolid, Spain.
authors.forename: Alberto
authors.initials: A
authors.lastname: Lesarri
authors.forename: Raquel
authors.initials: R
authors.lastname: Sánchez
authors.forename: Emilio J
authors.initials: EJ
authors.lastname: Cocinero
authors.forename: Juan C
authors.initials: JC
authors.lastname: López
authors.forename: José L
authors.initials: JL
authors.lastname: Alonso
mesh_terms: D006860:Hydrogen Bonding; D007532:Isoleucine / Q000737:chemistry*; D007834:Lasers; D008872:Microwaves; D008956:Models, Chemical; D008968:Molecular Conformation; D009904:Optical Rotation
chemical_list: D007532:Isoleucine