Oxygen Antioxidant: Role of Oxygen to Reduce Free Radicals

The Importance of Oxygen – in Antioxidants

The element Oxygen exists as a double molecule (2 Oxygen atoms join together to give O2). It is colorless, odorless and tasteless gas. It is the second most abundant element in the atmosphere and comprises 21% of the total air. It is one of the most common-element on the earth’s crust and is also found in water and mineral ores. In water, oxygen has limited solubility. However it is important for the survival of water organisms and even essential for the respiratory functions of human beings.

To reach the transport organisms of the blood, oxygen has to dissolve in water and then cross the alveoli of the lungs.

1. Oxidation
Organic molecules like human-tissue, food, fuel, plastic; rubber and paint are all oxidized by oxygen. When a molecule is oxidized, it is attacked by oxygen and forms an oxide. Rusting in metal machines, oil tasting or smelling bad and apple slices turning brown are all common examples of oxidation. And the oxygen molecules that are responsible for oxidation are called oxidants. The oxidant either takes electrons, takes hydrogen or adds oxygen and oxidizes other molecules.

Thereby oxidation results in the formation of more free radicals or oxidants. These free radicals or oxidants break the body down, cell-by-cell and tissue-by-tissue.

At normal temperatures the rates of oxidation are very slow. However, heat or the presence of enzymes increases the rate of oxidation. Antioxidants (substances that fight against oxidants that cause free radicals) remove catalysts to prevent oxidation. They also protect the important cell components by repairing the damage caused by oxygen, or by being oxidized themselves. Even though molecular oxygen is required to produce the fuel that is essential for cell life, it also poses as a threat. Oxygen has 2 electrons, but it is regarded as a free radical because it contains 2 unpaired electrons. Oxygen is present as a free radical, though under ideal conditions, oxygen maybe tightly coupled as in water.

2. Oxygen Reduction 
Oxygen Radicals are the most common and most damaging and so seeks more attention in biological systems. The Reduction of oxygen produces 2 important radicals Superoxide and Hydroxyl. Reduction is a process similar to oxidation and produces free radicals. By removal of oxygen, or by addition of Hydrogen or electrons to a molecule reduction takes place. And reducing agent is the chemical that actually does the reduction.

CO2 + C —— 2CO is an example for reduction.
The equation has to be read as ‘Carbon dioxide (Co2) is reduced to Carbon monoxide and Carbon is oxidized to Carbon monoxide (CO)’. When the processes function, oxidation and reduction can change a Carbon dioxide molecule and a Carbon atom into 2 molecules of Carbon monoxide.

Another example that can be mentioned is the change in the chemical make-up of an atom by the addition of electrons through reduction.
O2 + e- —— O2-
Here O2 is reduced to Superoxide radical that is a free radical.

3. Superoxide Radical 
When one radical is added to an oxygen molecule, a radical of superoxide is formed. The added electron pairs with one of the unpaired oxygen electrons leaving behind one unpaired electron. By accepting 1 more electron, the resultant radical acts as a weak oxidizing agent. For Example – Ascorbic acid can be oxidized by it. Depending on the medium in which it is dissolved the chemical behavior of superoxide varies. Superoxide is more reactive and dangerous in organic solvents, whereas in water superoxide is not very reactive. In fact, considerable damage maybe caused if any superoxide is produced within the body.

4. Hydroxyl Radical 
The most reactive among oxygen radical is hydroxyl radical. It attacks anything that comes in contact with it, as it is highly reactive. Hydroxyl converts itself back into water by pulling off hydrogen atoms from whatever it can. It can set different types of free radical chain reactions and cause damage. When DNA constituents are paired off with hydroxyl, danger starts. Normal pairing is prevented which leads to the formation of DNA mutations that can cause diseases like cancer.

5. Singlet Oxygen 
Oxygen has 2 unpaired electrons, but they are paired in such a way that at room temperature Oxygen oxidizes things very slowly. According to theory of aging, slow, cumulative oxidation of body tissue over a period of time causes aging. However, heat and catalysts speed up oxidation and oxygen can be converted into more reactive and powerful oxidizing agents by making a simple change in its electron pattern. Lipids (fats) oxidize and change into liquid peroxides in the presence of singlet oxygen.