BIOINORGANIC CHEMISTRY
Bioinorganic chemistry deals with the role of metals and non metals in biological systems. The inorganic elements, other than carbon, especially the metals are also vital to the functioning of bio- systems. Many biological processes such as photosynthesis, respiration, metal ion transport, enzymatic actions etc., fall into the realm of bioinorganic chemistry. It is highly advanced interdisciplinary science.
The two major components of bioinorganic chemistry are: i) the study of naturally occurring inorganic elements in bio-systems and ii) introduction of these elements as probes or drugs into biological systems and studying inorganic models that mimic the behavior of various metallo-proteins. It also investigates the nutritional aspects, toxicity, therapeutic action, transport & storage of metals and non metals in plants and animals including micro organisms.
The organisms uptake elements in different forms from the earth crust and the surrounding atmosphere. However, it is evident from the following table that there is rather a weak correlation between the distribution of various elements in the earth crust to that in the biological systems. Hence certain efficient and optimized systems and mechanisms are evolved for the uptake, utilization and storage of essential elements; all of which fall into the scope of Bioinorganic chemistry.
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DISTRIBUTION OF ELEMENTS |
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| Earth crust | Human body | |||
| Element | % | Element | % | |
| O | 47 | O | 63 | |
| Si | 28 | C | 25.5 | |
| Al | 7.9 | H | 9.5 | |
| Fe | 4.5 | N | 1.4 | |
| Ca | 3.5 | Ca | 0.31 | |
| Na | 2.5 | P | 0.22 | |
| K | 2.5 | K | 0.08 | |
| Mg | 2.2 | S | 0.06 | |
The inorganic elements, especially the metals play an important role in biological systems. Based on the relative concentrations in the biological systems, the metals are divided into:
Bulk metals - Na, K, Mg & Ca
Trace metals - Zn, Fe, Co, Ni, Cu, Mo, V etc., which are present in low concentration and are used for biocatalysis.
Find the summary of biological functions metals and non metals in the following tables.
| Bulk Metal | Biological functions |
| Na+ & K+ | * As electrolytes. * Maintain the concentration gradient in living cells (osmotic balance). * Helps in active and passive transport. * Charge carriers. |
| Mg2+ | * Present in chlorophyll and helps in photosynthesis. * In energy production (ATP --->ADP); * Activation of enzymes. * Information carrier. * Present in endo and exo skeletons. |
| Ca2+ | * Charge carrier. * In muscle and nerve functions - cell signalling. * It acts as second messenger and sentinel at synapse. * Present in teeth as Ca5(PO4)3(OH) (hydroxylapatite). * CaCO3 is present in endo and exo skeletons. * In activation of enzymes. * In blood coagulation. |
| Trace Metal | Biological functions |
| Zn2+ | * Hydrolytic enzymes: carboxypeptidase * Metal storage: e.g., metallothionein. * zinc finger proteins (genetic transcription), stabilization of proteins. |
| CuI/II | * Electron transfer. * Transport and storage of dioxygen. |
| FeII/III | * Electron transfer. * Transport and storage of dioxygen. * Fe3O4 is used to store iron, and, as it is magnetic, is used by magnetotactic bacteria to sense the direction of the Earth s magnetic field. * Conversion of N2 to ammonia (nitrogen fixation). |
| CoIII | * Cobalamine ( e.g. Vitamin-B12 ) |
| MnII/III/IV | * Electron transfer. * In photosynthesis, generation of dioxygen by splitting water. It is part of OEC (Oxygen Evolving Complex) in PS-II system. |
| NiI/II/III | * Electron transfer. * Hydrogenase and hydrolases (urease). |
| MoIV/VI, VIV/V | * Electron transfer. * Conversion of N2 to ammonia (nitrogen fixation). |
Not only metals, but some non metals are also found in biological systems. The biological functions of some of non metals are given below.
| Non metal | Biological functions |
| P5+ | * Found in Hydroxylapatite, ATP, cell membrane and DNA. |
| Se(II) | * Selenocysteine |
| F- | * As fluorapatite, Ca5(PO4)3F in teeth. |
| Cl- | * Most important free anion, besides HCO3- |
| I- | * functioning of hormones of the thyroid; in radiation therapy. |
The importance of bioinorganic chemistry can be realized from the following applications of metals and their compounds in medical field.
* cisplatin (containing platinum) and budotitane (containing Titanium) are used in treatment of cancer.
* Iron in the form of ferrous sulfate or ferrous gluconate is used in treatment of iron deficiency anemia.
* Li+, in the form of Li2CO3, is used in the treatment of depression, hypertension.
* Sb(III) salts are used in eczema (inflammatory condition of skin).
* Bi(III) salts (as Bismuth subsalicylate ) are used in gastric ulcer.
* BaSO4 is used as contrast agent in radiography.
* Gd3+ is used as contrast agent in NMR.
* 99mTc (in Cardiolyte) is used in radio diagnostics. 99mTc is a metastable isotope of Technetium, an artificially made element. Its half life is 6 hrs only and emits gamma rays.
* Silver sulfadiazine is used to treat and prevent bacterial or fungal infections of the skin.
* Selenium sulfide used to treat seborrheic dermatitis and Tinea versicolor.
* MoS42- (tetrathiomolybdate) is used as anti copper agent in Wilsons disease (excess of copper accumulation in liver - a genetic disorder). It is also used as an antitumor agent.