On the behaviour of water hydrogen bonds at biomolecular sites: Dependences on temperature and on network dimensionality Daniela Russo a, * , John R.D. Copley b , Jacques Ollivier c , José Teixeira d a CNR-INFM & CRS/Soft, c/o Institut Laue Langevin, 6 rue J. Horowitz BP156, F-38042 Grenoble, France b National Institute of Standards and Technology, Gaithersburg, MD 20899-6102, USA c Institut Laue Langevin, 6 rue J. Horowitz BP156, F-38042 Grenoble, France d Laboratoire Léon Brillouin (CEA/CNRS), Saclay CEA, 91191 Gif-sur Yvette Cedex, France article info Article history: Received 5 November 2009 Received in revised form 3 December 2009 Accepted 5 December 2009 Available online 8 January 2010 Keywords: Hydration water dynamics Hydrophobic interaction Hydrophilic interaction Protein dynamics Neutron scattering Hydrogen bond network abstract Neutron scattering experiments have been used to investigate the effects of temperature and network dimensionality (from hydrated powders to highly concentrated solutions) on the hydrogen bond dynam- ics of hydration water molecules at specific sites in selected biomolecules. With this aim in view, the evolution of hydration water dynamics of a prototypical hydrophobic amino acid with polar backbone, N-acetyl-leucine-methylamide (NALMA), and a hydrophilic amino acid, N-acetyl-glycine-methylamide (NAGMA), has been investigated as a function of temperature. We show that the temperature dependence of the diffusive dynamics of water molecules is the same for both hydrophilic and hydrophobic peptides. A comparison between hydrated powders and high con- centrated solutions reveals a similar behaviour, particularly for the hydrophobic peptide. On the other hand we find a distinct difference in the behaviour with temperature of the hydrogen bond lifetime in solutions and hydrated powders. Whereas at room temperature the hydrogen bond lifetime is longer in solution than in the hydrated powder, the reverse situation obtains at low temperatures. This result suggests a change in the plasticity of the hydrogen bond network depending on its extension. Differences in the densities of states lend support to this concept. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Most of the literature on hydration of biomolecules focus on the structure and dynamics of the first layer of hydrated powders [1– 4], ‘‘first layer” means the collection of water molecules required in order to cover the exposed surface of the biomolecule. In such cases, the role of hydrophilic sites is generally dominant so that most of the water molecules of the first layer form relatively stable bonds with the substrate, limiting their translational diffusion and influencing the structure and dynamics of the biomolecules. More detailed studies [5–8] can better discriminate between the behav- iour of individual water molecules at the vicinity of specific hydro- philic sites or hydrophobic regions of the surface of biomolecules, as well as between, translational diffusion, molecular rotations and hydrogen bond lifetime effects. In a sense such studies may be interpreted within the context of other general studies of water under confinement. To a large extent it has been demonstrated that the dynamics of biomolecules depends on the hydration level of the molecule. Both the details of the water binding sites and the extension of the hydration water network influence the intrinsic motions as has been observed by Zanotti and coworkers [9] for myoglobin and lysozyme proteins, by Zaccai and coworkers for human hemoglo- bin and macromolecules in Escherichia coli [10,11] and by Russo and coworkers [12,13] on small bio model peptides. Despite the fact that the dynamic time scale of water molecules at the biomo- lecular interface remains comparable to the dynamics of super- cooled water [3,7,8,14,15], both in hydrated powders and in highly concentrated solutions, distinct patterns of biomolecular dynamical behaviour can be observed. This is probably due to the fact that in solution the hydration water molecules interact not only with the biomolecular interface but with other water molecules within an extended hydrogen bond network. Thus the interaction among water molecules takes place in an extended three-dimensional space. In contrast, the hydration water of hy- drated powders interacts almost exclusively with the biomolecular interface, given the small number of neighbouring water molecules (probably none at low hydration levels), so the interaction range is limited to a surface and the first hydration layer is probably less structured than in solutions. Since the ultimate goal of hydration studies in biology is an understanding of relatively concentrated aqueous solutions, as close as possible to the situation of living cells, it seems necessary to establish a connection between studies 0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2009.12.020 * Corresponding author. E-mail address: russo@ill.fr (D. Russo). Journal of Molecular Structure 972 (2010) 81–86 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc