The Biologic Importance of Coordination Complexes

A protein is a large molecule assembled from a-amino acids, which have the general structure 

The First-Row Transition Metals and Their Biological Significance 

Chromium Assists insulin in the control of blood sugar may also be involved in the control of cholesterol 

Iron Component of hemoglobin and myoglobin involved in the electron transport chain 

Cobalt Component of vitamin Bj2, which is essential for the metabolism of carbohydrates, fats, and proteins 

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On coordination, the porphyrin macrocycle loses two protons (to yield a neutral complex when the central metal ion is divalent). The extensive electron delocalization throughout the ligand will normally extend to the central metal when the latter is covalently bound to the porphyrin. As expected, such complexes are extremely stable this is undoubtedly important to the biological role of these complexes. 

There is a particularly extensive and rich coordination chemistry associated with iron(II) N donor macrocycles. The coordination chemistry of the biologically important iron porphyrin complexes has been of interest since the classic studies of Fischer, and over recent years there has been a resurgence of work on these and also on a wide range of related synthetic macrocyclic complexes. This section concentrates on their coordination chemistry, and where appropriate highlights enhanced ligand reactivity specifically induced by the iron(II) centre. First saturated ligands are discussed and then the unsaturated systems, with the particularly well-studied porphyrins and phthalocyanines being dealt with in separate subsections. 

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