BIO COORDINATION COMPOUNDS
Coordination compounds play an important role in many biological processes in plants and animals.
The following table gives some of the important bio coordination compounds.
1. Haemoglobin Transport and storage of oxygen
2. Chlorophyll Photosynthesis 3. Ferredoxins Rubredoxins Electron Transfer
Among the Bio-coordination compounds function and nature of haemoglobin and chlorophyll play dominant role in natural process.
Haemoglobin in the red blood cells carries oxygen from the lungs to the tissues. It delivers the oxygen molecule to myoglobin in the tissues. When the oxygen has been released for cell respiration, haemoglobin loses its bright red colour and becomes purple. It then combines with the waste carbon dioxide produced by the cells and deposits in the lungs so that the gas can be exhaled.
Nature of haemoglobin and myoglobin
Both are having the same structure excepting the fact that myoglobin is a monomer and haemoglobin is a tetramer. Both are iron-porphyrin complex.
These are biocoordination complexes formed between porphyrin and iron in its +2 oxidation state (Fe2+). The iron-porphyrin complex is called the heme group, which is a part of haemoglobin. Each haemoglobin molecule consists of four subunits, each unit is being a folded chain.
The working part of haemoglobin is a hemegroup containing an Fe2+ cation coordinated to four nitrogen atoms of porphyrin group and one nitrogen atom of histidine group. The sixth octahedral site is available to bind oxygen molecule.
Chlorophyll is a magnesium - porphyrin complex. The magnesium is at the centre of the modified porphyrin ring septeon (corrin). The oxidation state of magnesium is +2 (Mg2+). The modified porphyrin acts as the ligand.
There are several kinds of chlorophyll that vary slightly in their molecular structure.
In plants, chlorophyll 'a' is the pigment directly responsible for the transformation of light energy to chemical energy. Hence in plants, the green pigment chlorophyll helps photosynthesis. The conversion of atmospheric carbondioxide and atmospheric moisture into carbohydrate and molecular oxygen in the presence of sunlight, by the plant is called as photosynthesis. Chlorophyll acts as a light sensitiser in this important process.
xCO2 + yH2O ⎯chlorophyll sunlight ®Cx(H2O)y + O2
Photosynthesis requires, in addition to chlorophyll, the help of four other metal complexes, a manganese complexes, two iron complexes and a copper complex.
All oxygenated animals take molecular oxygen through haemoglobin and release CO2. But chlorophyll helps in the conversion of atmosphere CO2 into molecular oxygen which act as a fuel for human cell.