Bioinorganic chemistry

Bioinorganic chemistry is a specialized field that spans the chemistry of metal-containing molecules within biological systems. This field is concerned with the control and use of metal ions in biochemical processes. Although bioinorganic chemistry includes the study of artificially introduced metals (e.g. medicinally), many natural occurring biological processes (such as respiration) depend upon molecules containing inorganic elements, such as metalloproteins, and these natural processes are also studied by bioinorganic chemistry. Bioinorganic chemistry has developed from the continuing research in inorganic chemistry and its important associations in biological chemistry.

As a mix of biochemistry and inorganic chemistry, bioinorganic chemistry is important in realizing the implications of electron-transfer proteins, substrate bindings and activation, atom and group transfer chemistry as well as metal properties in biological chemistry.

History
Paul Ehrlich used organoarsenic (“arsenicals”) for the treatment of syphilis, demonstrating the relevance of metals, or at least metalloids, to medicine, that blossomed with Rosenberg’s discovery of the anti-cancer activity of “cisplatin (cis-PtCl2(NH3)2). The first protein ever crystallized (see James B. Sumner) was urease, later shown to contain nickel at its active site. Vitamin B12, the cure for pernicious anemia was shown crystallographically by Dorothy Crowfoot Hodgkin to consist of a cobalt in a corrin macrocycle. The Watson-Crick structure for DNA demonstrated the key structural role played by phosphate-containing polymers.

Research areas
There are several distinct systems of interest in bioinorganic chemistry. These areas include metal ion transport and storage, metallohydrolase enzymes, metal-containing electron transfer proteins, oxygen transport and activation proteins, bioorganometallic systems such as hydrogenases and alkyltransferases, and enzymes involved in nitrogen metabolism pathways.

Metal ion transport and storage covers a diverse collection of ion channels, ion pumps (e.g. NaKATPase), vacuoles, siderophores, and other proteins and small molecules whose aim is to carefully control the concentration of metal ions in the cell.

Hydrolase enzymes include a diverse collection of proteins that interact with water and substrates. Examples of this class of metalloproteins are carbonic anhydrase, metallophosphatases, and metalloproteinases.

Metal-containing electron transfer proteins are comprised of three major classes: These electron transport proteins are complementary to the non-metal electron transporters nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD).
 * iron-sulfur proteins such as rubredoxins, ferredoxins, Rieske proteins, and aconitases
 * blue copper proteins
 * cytochromes

Oxygen transport and activation proteins make extensive use of metals such as iron, copper, and manganese. Heme is utilized by red blood cells in the form of hemoglobin for oxygen transport and is perhaps the most recognized metal system in biology. Other oxygen transport systems include myoglobin, hemocyanin, and hemerythrin. Oxidases and oxygenases are metal systems found throughout nature that take advantage of oxygen to carry out important reactions such as energy generation in cytochrome c oxidase or small molecule oxidation in cytochrome P450 oxidases or methane monooxygenase. Some metalloproteins are designed to protect a biological system from the potentially harmful effects of oxygen and other reactive oxygen-containing molecules such as hydrogen peroxide. These systems include peroxidases, catalases, and superoxide dismutases. A complementary metalloprotein to those that react with oxygen is the oxygen evolving complex present in plants. This system is part of the complex protein machinery that produces oxygen as plants perform photosynthesis.

Bioorganometallic systems such as hydrogenases and methylcobalamin are biological examples of organometallic chemistry.

The nitrogen metabolism pathways make extensive use of metals. Nitrogenase is one of the more famous metalloproteins associated with nitrogen metabolism. More recently, the cardiovascular and nueronal importance of nitric oxide has been examined, including the enzyme nitric oxide synthase. (See also: nitrogen assimilation.)

Metals in medicine is the study of the design and mechanism of action of metal-containing pharmaceuticals, and compounds that interact with endogenous metal ions in enzyme active sites. This diverse field includes the platinum and ruthenium anti-cancer drugs, chelating agents, gold drug chaperones, and gadolinium contrast agents.