ESSENTIAL CHEMICAL ELEMENTS
Chemical elements essential to life forms can be broken down into four major categories :
- bulk elements (H/H+, C, N, O2– / O2– / O22–, P, S/S2–);
- macrominerals and ions (Na/Na+, K/K+, Mg/Mg2+, Ca/Ca2+, Cl–, PO43–, SO42–);
- trace elements (Fe/FeII /FeIII /FeIV, Zn/ZnII, Cu/CuI /CuII CuIII ); and
- ultratrace elements, comprised of nonmetals (F/F–, I/I–, Se/Se2–, Si/SiIV, As, B) and metals (Mn/ MnII /MnIII /MnIV, Mo/MoIV /MoV /MoVI, Co/CoII /CoIII, Cr/CrIII /CrVI, V/VIII / VIV /VV, NiI /NiII / NiIII, Cd/Cd2+ , Sn/SnII /SnIV , Pb/Pb2+, Li/Li+).
Table 1. Percentage composition of selected elements in the Human Body
| Element | Percentage (by weight) | Element | Percentage (by weight) |
| Oxygen | 53.6 | Silicon, magnesium | 0.04 |
| Carbon | 16.0 | Iron, fluorine | 0.005 |
| Hydrogen | 13.4 | Zinc | 0.003 |
| Nitrogen | 2.4 | Copper, bromine | 2. × 10–4 |
| Sodium, potassium, sulfur | 0.10 | Selenium, manganese, arsenic, nickel | 2. × 10–5 |
| Chlorine | 0.09 | Lead, cobalt | 9. × 10–6 |
Table 2. Metals in Biological Systems : Charge Carriers
| Metal | Coordination Number, Geometry | Preferred Ligands | Functions and Examples |
| Sodium, Na+ | 6, octahedral | O-Ether, hydroxyl, carboxylate | Charge carrier, osmotic balance, nerve impulses |
| Potassium, K+ | 6-8, flexible | O-Ether, hydroxyl, carboxylate | Charge carrier, osmotic balance, nerve impulses |
Table 3. Metals in Biological Systems : Structure, Triggers
| Metal | Coordination Number, Geometry | Preferred Ligands | Functions and Examples |
| Magnesium, Mg2+ | 6, octahedral | O-Carboxylate, phosphate | Structure in hydrolases, isomerases, phosphate |
| Calcium, Ca2+ | 6-8, flexible | O-Carboxylate, carbonyl, phosphate | Structure, charge carrier, phosphate transfer, trigger reactions |
| Zinc, Zn2(d10) | 4, tetrahedral | O-Carboxylate, carbonyl, S-thiolate N-imidazole | Structure in zinc fingers, gene regulation, anhydrases, dehydrogenases |
| Zinc, Zn2(d10) | 5, square pyramid | O-Carboxylate, carbonyl, Nimidazole | Structure in hydrolases, peptidases |
Manganese, Mn2+ (d5) | 6, octahedral | O-carboxylate, phosphate, Nimidazole | Structure in oxidases, photosynthesis |
Manganese, Mn3+ (d4) | 6, tetragonal | O-Carboxylate, phosphate, hydroxide | Structure in oxidases, photosynthesis |
Table 4. Metals in Biological Systems : Dioxygen Transport
| Metal | Coordination Number, Geometry | Preferred Ligands | Functions and Examples | ||
| Copper,Cu (d )2 9 | 5, square pyramid 6, tetragonal | O-Carboxylate, N-imidazole | Type II copper Oxidases, hydroxylases Type III copper Hydroxylases Dioxygen transport In haemocyanin | ||
| Iron,Fe (d )2 6 | 6, octahedral | N-Imidazole, porphyrin | Dioxygen transport in haemoglobin and myoglobin | ||
Table 5. Metals in Biological Systems: Electron Transfer
| Metal | Coordination Number, Geometry | Preferred Ligands | Functions and Examples | |
| Iron, Fe2(d6) | 4, tetrahedral | S-Thiolate | Electron transfer, nitrogen fixation in nitrogenases | |
| Iron, Fe2(d6) | 6, octahedral | O-Carboxylate, alkoxide, oxide, phenolate | Electron transfer in oxidases | |
| Iron, Fe3(d5) | 4, tetrahedral | S-Thiolate | Electron transfer, nitrogen fixation in nitrogenases | |
| 6, octahedral | O-Carboxylate alkoxide, oxide, phenolate | Electron transfer in oxidases | |
Copper, Cu+ (d10), Cu2+ (d9) | 3, trigonal planar | N-Imidazole | Electron transfer in Type III heme-copper oxidases (CuB in cytochrome c oxidase, for example) | |
| Copper, Cu+ (d10), Cu2+ (d9) | 4, tetrahedral | S-Thiolate, thioether, N-imidazole | Electron transfer in Type I blue copper proteins and Type III heme-copper oxidases (CuA in cytochrome c oxidase, for example) |
Table 6. Metals in Biological system : Enzyme Catalysis
| Metal | Coordination Number, Geometry | Preferred Ligands | Functions and Examples | ||
| Copper, Cu2(d9) | 4, square planar | O-Carboxylate, Nimidazole | Type II copper in oxidases | ||
| Cobalt, Co2+ (d7) | 4, tetrahedral | S-Thiolate, thioether, Nimidazole | Alkyl group transfer, oxidases | ||
| Cobalt, Co3+ (d6) | 6, octahedral | O-Carboxylate, Nimidazole | Alkyl group transfer in vitamin B12 | ||
| Cobalt, Co3+ (d7) | 6, octahedral | O-Carboxylate N-imidazole | Alkyl group transfer in vitamin B12r | ||
| Cobalt, Co+ (d8) | 6, octahedral, usually missing the 6th ligand | O-Carboxylate, N-imidazole | Alkyl group transfer in vitamin B12s | ||
| Nickel, Ni2+ (d8) | 4, square planar | S-Thiolate, thioether, Nimidazole, polypyrrole | Hydrogenases, hydrolases | ||
| Nickel, Ni2+ (d8) | 6, octahedral | Uncommon | |||
Molybdenum, Mo4+ (d2), Mo5+ (d1), Mo6+ (d0) | 6, octahedral | O-Oxide, carboxylate, phenolate, S-sulfide, thiolate | Nitrogen fixation in nitrogenases, oxo transfer in oxidases | ||
