Page 262 - MODERN ELECTROCHEMISTRY

198 CHAPTER 2

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changes in the protein structure. Much of the water present in a biological cell would
be associated with the cell surface and hence have an oriented or rigid structure. Thus,
the interior of biological cells contains an interconnecting network of cellular organ-
elles: there is little space inside for free water.
Water in biological systems does indeed have a structure different from that of
the bulk, as it does at all interfaces, and the appropriate way to look at the alleged
difference in its structure is to realize that there is a large surface-to-volume ratio in
cell-like structures so that the fraction of water associated with surfaces is large, and;
by definition, under electric fields that are characteristic of the surface of double layers
at surface–solution interfaces. Hence, the icelike structure that Szent-Györgyi saw as
characteristic of biological systems would be a description of any near-surface water
and becomes the norm for biological cell water because most water is near a surface
and hence has abnormal structure (Ling and Drost-Hansen, 1975).

2.25.2. Spectroscopic Studies of Hydration of Biological Systems
Zundel reports on the hydration of thin polyelectrolyte ion-exchange membranes
subject to progressive increases in water sorption. Spectroscopic observations of these
systems reflect the hydration of polyion charge centers in the membranes but in the
presence of associated counterions, which in turn are progressively hydrated.
Zundel worked with polysulfonates and found the spectra of unhydrated polymer salts:
the cation is attached unsymmetrically to the groups. This mode of attachment
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leads to a loss of degeneracy in the antisymmetric vibrations.
The fact that this is so allows one to follow the hydration of cation–polyanion
association. This also affects the assignment of changes of band frequency in the water
molecule as it dissociates with the counterion groups.
In the region of 2000–4000 it is possible to obtain Spectroscopic results that
reflect the bound water at polyions. These occur at 3000–3700 in and
2200–2750 for As the radius of the bound counteranion and polystyrene
sulfonate decreases, the OH stretching vibration of the hydration water molecule
increases (e.g., from to and from to
These Spectroscopic results are consistent with corresponding thermodynamic
results obtained by Gluckauf and Kitt. They found that the greatest values of and
for sorption occurred during the first water molecule aggregation per ion pair and
decreased for subsequent ones.

2.25.3. Molecular Dynamic Simulations of Biowater

So far there have been few in-depth MD simulations of water at the interfaces of
cells. As indicated earlier, the results of general studies and Spectroscopic data suggest
that much of the water in biological cells is affected by the interface. The fact that the

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Degeneracy = more than one state having the same energy.