Victor V. Rodin
“Water, Water, Everywhere” begins a famous quatrain by the English poet Samuel Taylor Coleridge. Indeed, there is no chemical compound more ubiquitous or more crucial to all aspects of life on Earth. Most familiar is water in its liquid form, a material that is a near-universal solvent. Sea water, a solution of inorganic salts in water, represents more than 95% of the water on the surface of the planet. While water molecules are essential to life, many aspects of their involvement in biological structures and processes are not fully understood.
Formed from a single oxygen atom and two hydrogens, the physical and chemical properties of water are often anomalous if the hydrogen compounds of the elements surrounding oxygen in the periodic table are considered. For example, water (H2O) is a liquid at room temperature and atmospheric pressure while the compounds NH3, HF and H2S are gases under the same conditions. The anomalous properties of water result from intermolecular dipolar and hydrogen-bonded interactions that are peculiarly potent in pure water and account for this liquid’s ability to function so effectively as a solvent. The same types of interactions often lead to water molecules being found within organized three-dimensional structures of living and inanimate materials where they have specific structural roles that go beyond those of a mere solvent.
Many experimental methods have been applied to the study of water as a solvent or as a part of an assembled structure. Given that water contains hydrogen atoms with their spin ½ nuclei, it is no surprise that proton nuclear magnetic resonance (1H NMR) has been at the forefront of efforts to understand the chemistry of water wherever it is found. Proton NMR can provide information about the stability of organized structures and indications of the time rate(s) of change of these. Such changes might include rearrangement of three-dimensional aspects (such as conformational motions) or change in relative positions through rotational and translational diffusion.
In this volume, Dr. Rodin presents results from his laboratory and those of others that exemplify information that can be obtained about water molecules contained within organized but non-crystalline materials using proton NMR. These efforts appropriately have employed various relaxation, multiple quantum filtered, translational diffusion and imaging experiments. The systems examined range from synthetic (polyacrylates) and natural polymers (collagen and silk) to intact wood and inorganic cements. These reports nicely demonstrate to the reader the current state of the art in applying these powerful NMR experiments to the systems mentioned.