Nuclear magnetic resonance , hydration dynamics

A review is given of the application of Molecular Dynamics (MD) computer simulation to complex molecular systems. Three topics are treated in particular the computation of free energy from simulations, applied to the prediction of the binding constant of an inhibitor to the enzyme dihydrofolate reductase the use of MD simulations in structural refinements based on two-dimensional high-resolution nuclear magnetic resonance data, applied to the lac repressor headpiece the simulation of a hydrated lipid bilayer in atomic detail. The latter shows a rather diffuse structure of the hydrophilic head group layer with considerable local compensation of charge density. 

This review article is concerned with the structure, bonding, and dynamic processes of water molecules in crystalline solid hydrates. The most important experimental techniques in this field are structural analyses by both X-ray and neutron diffraction as well as infrared and Raman spectroscopic measurements. However, nuclear magnetic resonance, inelastic and quasi elastic neutron scattering, and certain less frequently used techniques, such as nuclear quadrupole resonance, electron paramagnetic resonance, and conductivity and permittivity measurements, are also relevant to solid hydrate research. 

Proton and deuteron nuclear magnetic resonance techniques are applied in solid hydrate research both for determining the hydrogen positions and for studying the dynamic processes of the water molecules ". ... 

Water dynamics in clays has been studied for Na and Li montmoril-lonites, vermiculites and hectorites . Quasi-elastic neutron scattering and nuclear magnetic resonance indicate the existence of slow and fast motions of water molecules. The fastest motion (tr 10 s) has the same value as in normal water and is almost temperature independent. The slow motion is anisotropic and associated with the hydrated cation shell. In materials with high water content (interparticular liquid-like phase) the distinction between rotational and translational motions appears possible . 

J.H. Han, K.W. Lee, G.W. Jeon, C.E. Lee, W.K. Park, E.H. Choi, H nuclear magnetic resonance study of hydrated water dynamics in perfluorosulfonic acid ionomer NAFION, Appl. Phys. Lett. 106 (2015) 023104. 

Spectroscopic methods for hydration of ions were reviewed for structural aspects and dynamic aspects of ionic hydration by Ohtaki and Radnai (150). They discussed X-ray diffraction, neutron diffraction, electron diffraction, small-angle X-ray (SAXS) and neutron-scattering (SANS), quasi-elastic neutron-scattering (QENS) methods, extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES) spectroscopies, nuclear magnetic resonance (NMR), Mdssbauer, infrared (IR), Raman, and Raleigh-Brillouin spectroscopies. The clay interlayer molecular modeling where clay surface is interfaced with aqueous solution also includes ions that are also solvated by interlayer water. 

The open lattice of the gas hydrate structure has long been known as a matrix for isolation of molecules. The dynamics of the encaged guests can be studied by nuclear magnetic resonance (NMR) or dielectric spectroscopy. ... 

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