Coded Amino Acids in Gas Phase:  The Shape of Isoleucine

The solid α-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 mo...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2005-09, Vol.127 (37), p.12952-12956
Main Authors: Lesarri, Alberto, Sánchez, Raquel, Cocinero, Emilio J, López, Juan C, Alonso, José L
Format: Article
Language:English
Subjects:
Atomic and molecular physics
Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
Exact sciences and technology
Hydrogen Bonding
Isoleucine - chemistry
Lasers
Microwaves
Models, Chemical
Molecular Conformation
Molecular properties and interactions with photons
Optical Rotation
Physics
Properties of molecules and molecular ions
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Summary:The solid α-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 Cβ similar to that observed in valine and a trans arrangement of Cα and Cδ. Ab initio calculations at MP2/6-311++G(d,p) level reproduce satisfactorily the experimental results.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja0528073