Radiation chemical studies of porphyrins and metalloporphyrins

Physical and Chemical Properties Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA 

Porphyrins (P) are tetrapyrrole macrocylic compounds with an extended tt-system. The peripheral carbons are numbered as shown below  

Because the four nitrogens form an optimal cavity, porphyrins can bind a wide variety of metal ions to form metalloporphyrins (MP). Iron porphyrins are found in many biological systems and act as electron transfer mediators (cytochromes) or oxygen transfer agents (hemoglobin). Modified porphyrins are found in nature also in the form of chlorophylls and vitamin B,2 and related compounds. 

These natural compounds bear various substituents at the 8-pyrrole positions (2,3,7,8,12,13,17,18). 

Many synthetic porphyrins have been prepared which are substituted at the meso positions (5,10,15,20). Porphyrins that have only alkyl or aryl substituents are insoluble in water. Water soluble porphyrins are made by introducing charged groups, such as carboxylate, sulfonate, trimethylammonium, or pyridinium. Some common synthetic porphyrins and their abbreviated notations are shown below. 

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