If you took NaCl and cooled it to freezing the liquid to solid transition will get denser as the atoms align into the crystal lattice since this is the most efficient packing and is at lower energy. Water aligns into a tetrahedral state as it changes phase to solid. The main difference is the partial covalent nature of hydrogen bonds. For the atomic orbitals to align properly the covalent aspect of the bonding needs to spread out to get the wave functions at minimum energy.
Even in liquid water, at any given temperature, high density water zones are at higher energy than low density water. This seems counter intuitive but is explained because low density water has better tetrahedral structuring. But it needs to spread out to make this work. This indicates that although H-bonds are both ionic and covalent the covalent appears to create the most energy advantage. In the high density all the electrostatic distances are lower yet it is as higher energy. Below is a practical use by cells for this difference in energy. The energy is high enough in the water to turn cells off and on.
ScienceDirect - Cell Biology International : HIGH AND LOW DENSITY WATER AND RESTING, ACTIVE AND TRANSFORMED CELLS
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Resting and active states of cells are described in terms of the expectation, derived from experiments with aqueous polymers, that they contain two modified forms of water: high density, reactive, fluid water and low density, inert, viscous water. Low density water predominates in a resting cell and is converted to high density water in an active cell. It is proposed that switching from one state to another is an integral part of cellular function. When this ability is lost cells are transformed either to a state of rigor or to a hyperactive state in which they no longer depend upon external signals.
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Low density tetrahedral water can freeze cells into inactivity because it does not provide enough energy to get everything into gear. If we froze the DNA, at room temperature, with low density water, it would become sluggish. If you want mutations you need high density water near the DNA, to give the DNA an extra energy boost.
