The structure and function of biomolecules are strongly influenced by their hydration shells. Structural fluctuations and molecular excitations of hydrating water molecules cover a broad range in space and time, from individual water molecules to larger pools and from femtosecond to microsecond time scales. Recent progress in theory and molecular dynamics simulations as well as in ultrafast vibrational spectroscopy has led to new and detailed insight into fluctuations of water structure, elementary water motions, electric fields at hydrated biointerfaces, and processes of vibrational relaxation and energy dissipation. Here, we review recent advances in both theory and experiment, focusing on hydrated DNA, proteins, and phospholipids, and compare dynamics in the hydration shells to bulk water.

http://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.6b00765

Water Dynamics in the Hydration Shells of Biomolecules

Biomimetic water-collecting materials inspired by nature

From the point of view of intermolecular interactions, the cytoplasmic space is more like a crowded party in a house full of furniture than a game of tag in an empty field. Understanding the physical chemical properties of cytoplasm is thus of key importance for understanding cellular function. This article attempts to provide an entree into the current literature on this subject and offers some general guidelines for thinking about intracellular biochemistry.

The physical chemistry of cytoplasm and its influence on cell function: an update.

The general trend in soft matter is to study systems of increasing complexity which are more technologically and biologically relevant. This is facilitated by the capability of quasielastic neutron scattering (QENS) to selectively probe spatially resolved dynamical modes at a molecular level. The large number of recent publications using QENS for investigating complex and multi-component soft matter systems, serves as recognition of the suitability of this technique by the scientific community. Exploiting its complementarity with molecular dynamics (MD) simulations and other experimental techniques is the basis of a successful methodology for this scientific challenge. We illustrate the potential of QENS with three kinds of soft materials whose structural units increase in size/complexity: lipids, polymers and biomolecules.

Quasielastic neutron scattering in soft matter

Understanding adaptation to extreme environments remains a challenge of high biotechnological potential for fundamental molecular biology. The cytosol of many microorganisms, isolated from saline environments, reversibly accumulates molar concentrations of the osmolyte ectoine to counterbalance fluctuating external salt concentrations. Although they have been studied extensively by thermodynamic and spectroscopic methods, direct experimental structural data have, so far, been lacking on ectoine-water-protein interactions. In this paper, in vivo deuterium labeling, small angle neutron scattering, neutron membrane diffraction and inelastic scattering are combined with neutron liquids diffraction to characterize the extreme ectoine-containing solvent and its effects on purple membrane of H. salinarum and E. coli maltose binding protein. The data reveal that ectoine is excluded from the hydration layer at the membrane surface and does not affect membrane molecular dynamics, and prove a previous hypothesis that ectoine is excluded from a monolayer of dense hydration water around the soluble protein. Neutron liquids diffraction to atomic resolution shows how ectoine enhances the remarkable properties of H-bonds in water—properties that are essential for the proper organization, stabilization and dynamics of biological structures.

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Neutrons describe ectoine effects on water H-bonding and hydration around a soluble protein and a cell membrane.

The dynamics of water in human red blood cells was measured with quasielastic incoherent neutron scattering in the temperature range between 290 and 320 K. Neutron spectrometers with time resolutions of 40, 13, and 7 ps were combined to cover time scales of bulk water dynamics to reduced mobility interfacial water motions. A major fraction of ∼90% of cell water is characterized by a translational diffusion coefficient similar to bulk water. A minor fraction of ∼10% of cellular water exhibits reduced dynamics. This slow water fraction was attributed to dynamically bound water on the surface of hemoglobin which accounts for approximately half of the hydration layer.

Giuseppe Zaccai

Papers

Cytoplasmic water and hydration layer dynamics in human red blood cells.