Discuss briefly giving an example in each case the role of co-ordination compounds in.
(i) Biological systems
(ii) Medicinal chemistry
(iii) Analytical Chemistry

Explanation

(i) Role of co-ordination compounds in biological systems.
(a) Haemoglobin, the oxygen carrier in blood, is a complex of `Fe^(2+)` with porphyrin.
(b) The pigment chlorophyll in plants, responsible for photosynthesis, is a complex of `Mg^(2+)` with porphyrin.
(c) Vitamin `B_(12)` (cyanocobalamine) the antipernicious anaemia factor, is a complex of cobalt.
(ii) Role of co-ordination compounds in medicinal chemistry
(a) the platinum complex cis-`[Pt(NH_3)_2 Cl_2]` (cis-platin) is used in the treatment of cancer.
(b) EDTA complex of calcium is used in the treatment of lead poisoning. Ca-EDTA is a weak complex , when it is administered, calcium in the complex is replaced by the lead present in the body and is eliminated in the urine.
(c) The excess of copper and iron present in animal system are removed by the chelating ligands D-penicillamine and desferroxime B via the formation of complexes.
(iii) Role of co-ordination compounds in analytical chemistry : Complex formation is frequently encountered in qualitative and quantitative chemical analysis.