Any of a group of organic pigments characterized by the possession of a cyclic group of four linked nitrogen-containing rings (a tetrapyrrole nucleus), the nitrogen atoms of which are often coordinated to metal ions. Porphyrins differ in the nature of their side-chain groups. They include the chlorophylls, which contain magnesium; and haem, which contains iron and forms the prosthetic group of haemoglobin, myoglobin, and the cytochromes. Porphyrins are also used in host-guest chemistry. See supramolecular chemistry.
Porphyrin
Any of a group of organic pigments characterized by the possession of a cyclic group of four linked nitrogen-containing rings (a tetrapyrrole nucleus), the nitrogen atoms of which are often coordinated to metal ions. Porphyrins differ in the nature of their side-chain groups. They include the chlorophylls, which contain magnesium; and haem, which contains iron and forms the prosthetic group of haemoglobin, myoglobin, and the cytochromes.
Generalized structure of a porphyrin
Heterocyclic derivative of a porphin, which is composed of four linked rings, each containing nitrogen (a tetrapyrrole ring structure). As such it is capable of combining with a variety of metals and so forms part of the structure of many important biological molecules, including haemoproteins, chlorophyll, cytochromes, and vitamin B12.
- radon
- radula
- Raeder, Erich (1876–1960)
- Raffaello
- raffinate
- raffinose
- Raffles, Sir Stamford (1781–1826)
- Rafsanjani, Ali Akbar Hashemi (1934–2017)
- raft foundation
- ragged array
- ragged right
- Raglan, FitzRoy James Henry Somerset, 1st Baron (1788–1855)
- ragwort
- Rahman
- rahmonic
- RAID
- rail
- rail transport, Australia
- railway
- railways, history of
- rain
- rainbow
- RainCube
- raindrop
- raindrop erosion