Anisotropic water diffusion in neural fibres such as nerve, white matter in spinal cord, or white matter in brain forms the basis for the utilization of diffusion tensor imaging (DTI) to track fibre pathways. The fact that water diffusion is sensitive to the underlying tissue microstructure provides a unique method of assessing the orientation and integrity of these neural fibres, which may be useful in assessing a number of neurological disorders. The purpose of this review is to characterize the relationship of nuclear magnetic resonance measurements of water diffusion and its anisotropy (i.e. directional dependence) with the underlying microstructure of neural fibres. The emphasis of the review will be on model neurological systems both in vitro and in vivo. A systematic discussion of the possible sources of anisotropy and their evaluation will be presented followed by an overview of various studies of restricted diffusion and compartmentation as they relate to anisotropy. Pertinent pathological models, developmental studies and theoretical analyses provide further insight into the basis of anisotropic diffusion and its potential utility in the nervous system.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/nbm.782

The basis of anisotropic water diffusion in the nervous system – a technical review

Publisher Summary This chapter describes many of the techniques employed to study water–macromolecules interactions, their general usefulness, points out areas of mutual support and contradiction. The chapter also presents hydration of other macromolecules and the hydration of small molecules. Four broadly based approaches to operational definitions of hydration include—(1) preferential hydration, (2) hydrodynamic hydration, (3) structural hydration, and (4) low temperature hydration. The use of high resolution X-ray and neutron diffraction data on protein crystals provides an independent approach for estimation of hydration. The chapter presents several proposals for predicting protein hydration based on the amino acid composition of the protein; however, the two main questions concerned include—whether ionic groups are more hydrated than other polar groups, and whether the amide and peptide functions are hydrated or not. Low pH, and to a much smaller degree, high pH should dehydrate proteins. Intermolecular association via ionic mechanisms should be strongly dehydrating; whereas hydrophobic interactions should not have much effect on hydration levels. Although, there is a presumption that both the enthalpy and the entropy are negative for the process of adding water molecules to isolated proteins, which are maintained in their native conformations, but there is no unequivocal evidence for this.

Hydration of Proteins and Polypeptides

Reference LPI-ARTICLE-1999-017View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

/pdf/metal-oxide-surfaces-and-their-interactions-with-aqueous-22jt31pax0.pdf

Metal Oxide Surfaces and Their Interactions with Aqueous Solutions and Microbial Organisms.

Morphology and structure of poly(vinyl alcohol) (PVA) hydrogel prepared by the “repeated freezing-and-melting” method have been investigated by X-ray diffraction, scanning electron microscopy, light-optical microscopy, and simple tension test. The PVA aqueous solution gelled highly by using this method to show rubber-like elasticity, reflecting the gel network in which the amorphous chains are physically cross-linked by the crystallites. The gel morphology was characterized by the porous structure, which was originated from the gelation of continuous PVA-rich solution phase segregated around copious ice crystal phases formed upon freezing. The high gelling ability involved in this method was closely related to the segregation mechanism.

Morphology and structure of highly elastic poly(vinyl alcohol) hydrogel prepared by repeated freezing-and-melting

Diffusion in gels

Pulsed Nmr study of water in agar gels

A large temperature hysteresis is observed in the nmr relaxation times of the water and agar hydrogen nuclei which corresponds to that of the sol-gel transition. Self-diffusion measurements of the water in the gel state indicate that the motions of the great majority of the water molecules are essentially unaffected by the presence of the agar molecules. These results indicate that the major portion of the water molecules in the agar-water system is not in an “icelike” or modified state.

Pulsed Nmr study of the temperature hysteresis in the agar-water system

The study of clay water systems by pulsed nuclear magnetic resonance reveals that natural as well as synthetic clays have associated with them a certain amount of oriented water. Direct experimental evidence of oriented water between natural clay platelets is observed for montmorillonite at room temperature. Doublet splittings in the NMR spectra indicate that the water molecules are preferentially oriented by the clay platelets. The occurrence of the doublet splitting was found to be affected by both particle size and temperature. Experimental evidence indicates that the transverse relaxation process above room temperature is not grossly affected by paramagnetic centers arising from the natural iron content of the clay lattice. Although it is more difficult to observe the doublet splitting in samples with a high iron content, these paramagnetic centers do not preclude its occurrence.

D.E Woessner

Papers

Pulsed Nmr study of water in agar gels

Pulsed Nmr study of the temperature hysteresis in the agar-water system

A study of the orientation of adsorbed water molecules on montmorillonite clays by pulsed NMR

A tetrahedral model for pulsed nuclear magnetic resonance transverse relaxation: Application to the clay-water system

Nuclear spin-lattice relaxation in ammonium chloride and ammonium bromide with special application to interfacial water