The impact of hydration water on the dynamics of side chains of hydrophobic peptides: from dry powder to highly concentrated solutions.
Elastic and quasielastic neutron scattering experiments are used to investigate the dynamics of side chains in proteins, using hydrophobic peptides, from dry and hydrated powders up to solutions, as models. The changes of the internal dynamics of a prototypical hydrophobic amino acid, N-acetyl-leucine-methylamide, and alanine amino acids are investigated as a function of water/peptide molecular ratio. While previous results have shown that, in concentrated solution, when the hydrophobic side chains are hydrated by a single hydration water layer, the only allowed motions are confined and can be attributed to librational/rotational movements associated with the methyl groups. In the present work we observe a dynamical evolution from dry to highly hydrated powder. We also observe rotational and diffusive motions and a dynamical transition at approximately 250 K for long side chain peptides while for peptides with short side chains, there is no dynamical transition but only rotational motions. With a local measurement of the influence of hydration water dynamics on the amino acid side chains dynamics, we provide unique experimental evidence that the structural and dynamical properties of interfacial water strongly influence the side chain dynamics and the activation of diffusive motions. We also emphasize that the side chain length has a role on the onset of dynamical transition.
Russo
Daniela
D
Institut Laue Langevin, CNR-INFM and CRS/Soft, 6 rue J. Horowitz BP156, F-38042 Grenoble, France. russo@ill.fr
Teixeira
José
J
Ollivier
Jacques
J
D004548:Elasticity; D057927:Hydrophobic and Hydrophilic Interactions; D033363:Neutron Diffraction; D010455:Peptides / Q000737:chemistry*; D012996:Solutions; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
D010455:Peptides; D012996:Solutions; D014867:Water