Fat goes rancid over time if no
antioxidants are added. Our bodies also contain
fat
molecules, called
lipids. They are essential for our
cell membranes. These
too must be protected from excessive peroxidation; left unchecked, it can cause
atherosclerosis or various autoimmune and
neurodegenerative diseases, such as
Alzheimer's disease, to set in. Nature's most important weapon in defense of
lipid peroxidation is
vitamin E (alpha-
tocopherol). An international team of
researchers working with Derek A.
Pratt (
Vanderbilt University, USA) has now
developed a new class of
antioxidants that are up to 100 times more effective
than vitamin E.
The trouble with the peroxidation of
lipids is that it is a chain reaction. In
the first step, an
oxygen radical -- a molecule with an unpaired electron on an
oxygen atom, removes a
hydrogen atom from a lipid. This leaves behind a lipid
radical, which has an unpaired electron on a
carbon atom, which reacts with an
oxygen molecule to form a lipid peroxyl radical. This is an oxygen radical that
can then attack another lipid in turn -- in order to steal a
hydrogen atom --
resulting in yet another lipid radical.The vicious circle starts all over again
and is difficult to stop. This is where antioxidants like alpha-tocopherol come
into the picture; they intercept the lipid peroxyl
radicals. Radical
scavengers
like tocopherol are
phenols/order_t/'>phenols, they consist of a six-membered aromatic
carbon ring
with an attached oxygen atom, and this oxygen atom carries a hydrogen atom (an
OH group). This hydrogen atom is stripped away by the peroxyl radical. In
contrast to the lipid
radicals, the resulting phenolic radical is relatively
unreactive, and the chain reaction stops. In order to find an even better
radical interceptor, the chemists searched for a phenolic compound, whose OH
group gives up its hydrogen atom more easily than vitamin E. However, most of
these super radical scavengers are much to readily attacked by oxygen in the air
to be useful.
computer simulations enabled Pratt and his co-workers to develop a new class of
air-stable phenolic antioxidants. Subsequent experiments have demonstrated that
two of these amino pyridinol compounds, as they are called, are particularly
effective radical scavengers. They consist of a
phenol ring, in which one of the
carbon atoms has been replaced with a
nitrogen atom. This aromatic (containing
three
double bonds) ring is fused with another, aliphatic (containing only
single bonds) carbon ring, which also contains a
nitrogen atom. "These amino
pyridinols are, to the best of our knowledge, the fastest
peroxyl-radical-trapping antioxidants ever reported," says Pratt.