Tetrapyrroles biology

As a class, metal-ion derivatives of tetrapyrrole macrocyclic rings, such as the corrins or porphyrins (see Chapter 1 for the parent ring structures), are of major biological importance. 

Smith, A. Transport of Tetrapyrroles Mechanisms and Biological and Regulatory Consequences Dailey, H. A., Jr., Ed. McGraw-Hill Publishing Co. New York, 1990, pp. 435-490. 

Nickel porphyrins are of interest because of their occurrance in coal, shale, and petroleum deposits (1) and because of their key role in biological conversion of COg to methane (2--5). The enzyme methylreductase is the nickel-tetrapyrrole-containing enzyme that catalyses the final step, and possibly other steps, in the 6-electron reduction of CO2 to methane (6). The active site of the methylreductase enzyme contains a nickel-sirochlorin derivative called F 3q (6-8). Understanding the involvement of in methane... 

Warren, M. J., and A. I. Scott, Tetrapyrrole assembly and modification into the ligands of biologically functional cofactors. Trends Biol. Sci. 51 486-491, 1990. 

Several tetrapyrroles are employed by Nature to carry out fundamental biological functions and synthetic models compounds have been extensively used in order to understand the mechanisms of action of natural systems. 

Biologically essential tetrapyrrolic macrocycles of two main types exist the porphyrins, the prosthetic group of heme proteins, and the corrins, most representative among which is the coenzyme of Vitamin B12. 

In this review we will focus on synthetic derivatives of the macrocycles where a tetrapyrrolic skeleton is maintained and on their metal complexes without taking into account their biologically active counterparts. 

Excited-state chemistry of tetrapyrroles and their complexes is a branch of chemistry with a strong linking to other chemical disciplines, biology and physics. This branch draws motivations for the own development from the above areas of science and technology and it itself acts as a rich source of stimulation for these and further areas. 

Explain why tetrapyrrole macrocycles feature highly as cation binding hosts in biological systems (Chapter 2) while expanded porphyrins such as (4.14) are more suited to anion binding. 

Section M Smil, V. (1997) Global population and the nitrogen cycle. Sci. Amer. 277(7), 58-63. Warren, M.J., Cooper, J.B., Wood, S.P. and Shoolingan-Jordan, P.M. (1998) Lead poisoning, haem synthesis and 5-aminolaevulinic acid dehydratase. Trends Biochem. Sci. 23, 217-221. Warren, M.J. and Scott, A.I. (1990) Tetrapyrrole assembly and modification into the ligands of biologically functional cofactors. Trends Biochem. Sci. 15, 486-491. 

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