Application Note — Biological and Industrial Coordination Compounds — Notes

Biological Coordination Compounds:

Compound	Metal Ion	Coordination Number	Function
Hemoglobin	$Fe^{2+}$	6	$O_{2}$ transport in blood
Chlorophyll	$Mg^{2+}$	4 (square planar-like)	Photosynthesis (light absorption)
Vitamin $B_{12}$ (cobalamin)	$Co^{3+}$	6	DNA synthesis; nerve function
Carbonic anhydrase	$Zn^{2+}$	4	C $O_{2}$ ⇌ $H_{2}CO_{3}$ equilibrium in blood
Cisplatin	$Pt^{2+}$	4 (square planar)	Anticancer drug (cross-links DNA)

Hemoglobin Detail:

$Fe^{2+}$ centre in porphyrin ring (4 N donor atoms in plane)
One axial position: histidine residue of globin protein
Sixth coordination site: $O_{2}$ (reversible binding) or CO (irreversible → CO poisoning)
CO binds ~200× more strongly than $O_{2}$ , blocking $O_{2}$ transport

Industrial Applications:

Wilkinson's catalyst: RhCl( $PPh_{3}$ )_{3} — alkene hydrogenation
Zeise's salt: K[ $PtCl_{3}$ ( $C_{2}H_{4}$ )] — first organometallic compound
EDTA complexes: used in medicine (heavy metal poisoning chelation therapy), food preservation, analytical chemistry (complexometric titrations)

Cisplatin Anticancer Mechanism: Cis-[Pt( $NH_{3}$ )_{2} $Cl_{2}$ ] crosses the nuclear membrane, hydrolyses the $Cl^{-}$ ligands, and forms cross-links with guanine bases on the same DNA strand (intrastrand crosslinks), preventing DNA replication and inducing apoptosis. The trans isomer cannot form these crosslinks due to geometric constraints.