Hydration profiles of aromatic amino acids : conformations and vibrations of L-phenylalanine–(H2O)n clusters
PhysChemChemPhys_2006_8_4783.pdf 1.62 MB
IR-UV double resonance spectroscopy
IR-UV double resonance spectroscopy and ab initio calculations were employed to investigate the structures and vibrations of the aromatic amino acid, L-phenylalanine–(H2O)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–(H2O)1, and both of them form a cyclic hydrogen-bond between the carboxyl group and the water molecule. In L-Phe–(H2O)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–(H2O)3 the bridge of water molecules becomes larger and exhibits an extended hydrogen-bond to the π-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.
The authors would like to acknowledge the support from the Grant-in-Aids for Scientific Research (18205003) by the Ministry of Education, Science, Sports, and Culture, Japan and from the French-German CNRS-DFG binational project. T. E. gratefully acknowledges financial support from Satake foundation.
Physical Chemistry Chemical Physics
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Royal Society of Chemistry
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Graduate School of Science