Chemistry Reference
In-Depth Information
manufactured are usually formed by steaming the bones and the hides under pressure and then
treating them with hot water in several cycles. This degrades the collagen and make is soluble.
The aqueous solution is concentrated by vacuum evaporation of the water. The material that gels is
dried and pulverized. Milder hydrolysis yields gelatin that is used commercially in foods.
Casein, the milk protein (less readily available casein from vegetable sources is hardly ever used),
is also used in adhesives. Here too, synthetics are gradually taking over. At one time it was used to
produce a fiber and a plastic that was formed by cross-linking with formaldehyde. The cross-linking
reaction was carried out by immersing the proteins in a formaldehyde solution (4-5%) at 55-65
C for
long periods of time, such as days and even months, depending upon the size of the article. The cross-
linking reaction involved pendant amino groups and is quite similar to the reactions of urea- and
bridges may also involve amide nitrogens. It does not appear likely that casein fibers or plastics are
still being produced anywhere.
Extensive research work has gone into modification of proteins, not for commercial applications
but for academic reasons. Thus, for instance, Frances et al. developed a new reaction that introduces
single reactive ketones or aldehydes at the N-terminal groups of protein when the proteins are mixed
with pyridoxal phosphate [
44
]. The researchers also developed a palladium-catalyzed allylic alkyl-
ation that attaches long lipid tails to proteins, a process that can be used to customize the solubility of
enzymes, antibodies, viral capsids, and other proteins.
8.6 Nucleic Acids
These are protein-bound polymers that are essential in many biological processes. They perform such
functions as directing the syntheses of proteins in living cells and constitute the chemical basis of
heredity [
56
,
57
]. The polymers are polyphosphate esters of sugars that contain pendant heterocyclic
amines, called “bases”:
O
sugar
O
P
O
n
base
There are two principle types of nucleic acids with two different sugars. One is
D
-2-deoxyribose
found in
deoxyribonucleic acid (DNA)
:
OH
2
3
1
4
O
OH
CH
2
OH
5
