Biomedical Engineering Reference
In-Depth Information
7.5.3 Applications in Bioorganic Chemistry
7.5.3.1  Smell
Carvone exists as a pair of enantiomers. (R)-(−)-carvone smells like spear-
ment, whereas (S)-(+)-carvone smells like caraway. Why do these enantio-
mers have different smells (i.e., different biological activity)? Olfactory
receptors in the cell membranes of humans apparently possess the ability to
respond differently to the two carvone enantiomers. Considering each cell
as an analog computer, processing fuzzy logic [13], the reaction of the recep-
tor proteins in the olfactory complex has the ability to regulate ion transport
through the cell membrane differentially for the two carvone enantiomers,
thereby producing a different electrochemical signal to the brain. Perhaps,
the selection processes in mitochondrial evolution resulted in certain specific
cellular logic functions for smell, and specific abilities of species to distin-
guish and differentiate enantiomers such as carvone [14]. The two enantio-
mers “present themselves” differently to the olfactory receptors, resulting
in a differential response. It is also possible that the two enantiomers pres-
ent a different fit to the hydrogen-bonded water networks that play such an
important role in “presenting” molecules to one another in biological solu-
tion. Complementary shapes are thus selected for a specific reaction.
7.5.3.2   Protein Structure and Folding and the Influence 
of the Aqueous Environment
Analysis and characterization of proteins represent an important branch of
biotechnology. The theories of hydrogen bonding are proving of great impor-
tance to the understanding of protein behavior. Martin Chapman's site [15]
describes extended hydrogen-bonded water molecules, such as icosahedrals,
which should be visible under a 1000× or 2000× microscope, if indeed they
are stable and exist for more than the expected femtosecond duration.
Further experimentation is needed to properly characterize these struc-
tures. It may be possible for water to remain in an aggregate represented by
one of Chaplin's “magic numbers” for more than a very short duration. This
is a bit controversial in the literature. Some of the abstracts from a recent con-
ference on water [16] indicate that indeed this occurs. If so, perhaps we can
control the behavior of protein folding in “conditioned” structured aqueous
environments. Another site also discusses water as a “designer fluid” that
helps proteins change shape [17].
Protein folding helps determine the functionality of the biomacromolecule.
Aspartic acid, for example, is considered acidic hydrophilic [18]. When the
protein folds, the side chains can be transferred from a solution-like environ-
ment to one determined by the 3-D structure of the folded protein. So, expo-
sure to solvents could be impacted differentially on one side of the protein
versus the other. Differential interaction of the aspartic acid side chain with
permanent charges and protein dipoles will also affect the pH of the side
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