5 Water Chemistry and Biochemistry 121plus the equilibrium due to the self-ionization of
water stabilize the pH of the solution. Buffer solu-
tions abound in nature: milk, juice, soft drinks, soup,
fluid contained in food, and water in the ocean, for
example.
Hydrophilic and Hydrophobic Effects
The hydrophilic effectrefers to the hydrogen bond-
ing, polar-ionic and polar-polar interactions with
water molecules, which lower the energy of the sys-
tem and make ionic and polar substances soluble.
The lack of strong interactions between water mole-
cules and lipophilic molecules or the nonpolar por-
tions of amphiphilic molecules is called the hydro-
phobic effect, a term coined by Charles Tanford
(1980).
When mixed with water, ionic and polar mole-
cules dissolve and disperse in the solution, whereas
the nonpolar or hydrophobic molecules huddle to-
gether, forming groups. At the proper temperature,
groups of small and nonpolar molecules surrounded
by water cages form stable phases calledhydratesor
clathrates. For example, the clathrate of methane
forms stable crystals at temperatures below 300 K
(Sloan 1998). The hydrophobic effect causes the for-
mation of micelles and the folding of proteins in
enzymes so that the hydrophobic parts of the long
chain huddle together on the inside, exposing the
hydrophilic parts to the outside to interact with water.
Hydrophilic and hydrophobic effects together sta-
bilize three-dimensional structures of large mole-
cules such as enzymes, proteins, and lipids. Hydro-
phobic portions of these molecules stay together,
forming pockets in globular proteins. These bio-
polymers minimize their hydrophobic surface to
reduce their interactions with water molecules.
Biological membranes often have proteins bonded
to them, and the hydrophilic portions extend to the
intra- and intercellular aqueous solutions. These
membrane-bound proteins often transport specific
nutrients in and out of cells. For example, water,
amino acid, and potassium-sodium ion transporting
channels are membrane-bound proteins (Garrett and
Grisham 2002).
Hydrophilic and hydrophobic effects, together
with the ionic interaction, cause long-chain proteins
called enzymesto fold in specific conformations
(three-dimensional structures) that catalyze specific
reactions. The pH of the medium affects the charges
of the proteins. Therefore, the pH may alter enzyme
conformations and affect their functions. At a spe-
cific pH, some enzymes consist of several subunits
that aggregate into one complex structure in order to
minimize the hydrophobic surface in contact with
water. Thus, the chemistry of water is intimately
mingled with the chemistry of life.
During food processing, proteins are denatured
by heat, acid, base, and salt. These treatments alter
the conformation of the proteins and enzymes. De-
natured proteins lose their life-maintaining function-
ality. Molecules containing hydrophilic and hydro-
phobic parts are emulsifiers that are widely used in
the food industry.
Hydrophilic and hydrophobic effects cause non-
polar portions of phospholipids, proteins, and cho-
lesterol to assemble into micelles and bilayers, or
biological membranes (Sloan 1998). The membrane
conformations are stable due to their low energy,
and they enclose compartments with components to
perform biological functions. Proteins and enzymes
attached to the membranes communicate and trans-
port nutrients and wastes for cells, keeping them
alive and growing.Hard Waters and Their TreatmentsWaters containing dissolved CO 2 (same as H 2 CO 3 )
are acidic due to the equilibriaH(aq) HCO 3 (aq) ↔H 2 CO 3 (aq) H 2 O
CO 2 (g)HCO 3 (aq) ↔H(aq) CO 3 2-(aq).Acidic waters dissolve CaCO 3 and MgCO 3 , and
waters containing Ca^2 , Mg^2 , HCO 3 , and CO 3 2-
are temporary hard waters,as the hardness is
removable by boiling, which reduces the solubility
of CO 2. When CO 2 is driven off, the solution be-
comes less acidic due to the above equilibria.
Furthermore, reducing the acidity increases the con-
centration of CO 3 2-, and solids CaCO 3 and MgCO 3
precipitate:Ca^2 (aq) CO 3 2-(aq) ↔CaCO 3 (s)Mg^2 (aq) CO 3 2-(aq) ↔MgCO 3 (s)Water containing less than 50 mg/L of these sub-
stances is considered soft; 50–150 mg/L moderately
hard; 150–300 mg/L hard; and more than 300 mg/L
very hard.