Biological water functions

The great solvent power of water, especially for ionic compounds, is due to its dielectric constant. If this were only, say 10, instead of the actual 80, it would mean that water could dissolve only a trace of sodium chloride. This solvent action of water., naturally. plays an important role in geology. In biology, water functions as a means of conveying salts and other substances which circulate in the bodies of animals and plants. It is outside the scope of this book to discuss any further the function of water on this planet, a subject which could fill many volumes. It is important in this context that we now know water molecules to possess a dipole moment and to discover whether perhaps this fact can provide an explanation of the unique properties of water. 

The hydrogen-bonded dimers with biologically interesting functional groups that have been studied by these methods are the OwH Ow bond in the water dimer and the OH -0=C bond in the formic and acetic acids dimers. They are important because they refer more directly to the intrinsic properties of a particular bond and provide experimental data for comparison with the ab-initio molecular orbital calculations on simple systems described in Chapter 4. 

The interaction between a solute and a solid phase is also influenced by water. Hydration shells or icebergs associated with one or the other phase are destroyed or created in this interaction and often contribute to conformational changes in macromolecular structures — and ultimately to changes in biological and functional properties important in food processing. 

In a series of important studies, Zewail and co-workers examined the SD of exeited tryptophan as a natural probe in several proteins by using the TDFSS teehnique [13]. The advantage of using tryptophan as a probe was twofold. First, it was a natural probe, so the conformation of the protein was not disturbed and the solvation of the native state was explored. Second, one could study proteins where the tryptophan is partly or fully exposed to water, and so SD studies allowed one to directly probe the response of biological water. They found a slow component in the solvation time correlation function, which was in the range 20-40 ps. This was more than an order of magnitude slower than the bulk response. 

If a catalyst is to work well in solution, it (and tire reactants) must be sufficiently soluble and stable. Most polar catalysts (e.g., acids and bases) are used in water and most organometallic catalysts (compounds of metals witli organic ligands bonded to tliem) are used in organic solvents. Some enzymes function in aqueous biological solutions, witli tlieir solubilities detennined by the polar functional groups (R groups) on tlieir outer surfaces. 

In some systems, such as lake and river waters, the suspended inorganic particles may be coated by biological polymers, termed humic substances, which prevent flocculation by either steric or electrostatic mechanisms. These can also interact with added inorganic salts (31) that can neutralize charged functional groups on these polymers. 

These pohcy statements are founded on the existing language and authorities in Clean Water Act Sections 303 (c) (2) (A) and (Bf EPA defined biological criteria as numerical values or narrative expressions used to describe the expected structure and function of the aquatic community. ... 

Toxicity is the ability to cause biological injuiy. Toxicity is a property of all materials, even salt, sugar, and water. It is related to dose and the degree of hazard associated with a material. The amount of a dose is both time and duration dependent. Dose is a function of exposure (concentration) and duration and is sometimes expressed as dose = (concentration) X duration, where n can vaiy from 1 to 4. 

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