Porphins Tetrapyrroles

An important exception to this rule is provided by the magnesium complexes of tetrapyrrole systems, the parent compound of which is porphine (7-II). These conjugated heterocycles provide a rigid planar environment for Mg2+ (and similar) ions. The most important of such derivatives are the chlorophylls and related compounds,28 which are of transcendental importance in photosynthesis in plants.29 The structure of chlorophyll-a, one of the many chlorophylls, is (7-III). 

Porphyrins are heteroaromatic compounds characterised by a tetrapyrrolic structure that consists of four pentagonal pyrroles linked by four methylene bridges, the porphine structure (Figure 1). 

The abbreviations for porphyrins and other tetrapyrroles, axial ligands and other species that will be used in this article are listed in Sect. E. A generalized description of the porphine nucleus is given in Fig. 1. The generalized notation for the atoms of the porphine nucleus shown was originally suggested by Hoard Structural parameters of interest include bond distances and angles, the size of the central hole (Ct"-N), the position of the metal atom with respect to the mean plane of the core and a conformational description of the core itself. 

Porphyrins. Collective name derived from Greek porphyra=purple, purple snail, for the widely distributed purple (red) natural pigments formally prepared from the parent skeleton of porphine by substitution of the macrocylic tetrapyrrole framework with methyl, vinyl, acetic acid, propanoic acid units, or other substituents. 

Porphin the parent tetrapyrrole of the Porphyrins (see). Porphin is a term from the original Fischer nomenclature. It is synonymous with porphyrin. See also Chlorin. 

Figure 1 (a) Typical porphyrins porphine, chlorin, and corrole. (b) Some common porph3Tmoids. Note the tetrapyrrole skeleton... 

A number of biologically important compounds contain substituted pyrroles in cyclic or linear array. With the exception of the corrin nucleus of vitamin 8 2 in which one methylene bridge is missing, the. cyclic tetrapyrroles can be regarded as derivatives of the parent porphin, the structure of which is given in Figure 38. The porphyrins... 

The macrocyclic tetrapyrrole skeletons of a range of natural substances can act as ligands that bind metals to form complexes. In foods, the main important types of macrocycKc tetrapyrroles are porphin (see Section 9.2) and corrin (see Section 5.13.1) derivatives. 

Figure 8.1.1 depicts (a) the structure of protoporphyrin IX, and (b) the structure of porphin from which porphyrins are derived. Porphin is an unsubstituted tetrapyrrole connected at a-carbons by CH bridges. Porphyrins are substituted porphins, among which protoporphyrin IX is one of the most important because it is a constituent of hemoglobin and myoglobin. 

Accessory pigments in photosynthesis ( ) Phycoerythrin Phycocyania Red and blue-green algae Red and blue-green algae Tetrapyrrole related to proto-porphin (7) Tetrapyrrole 290.000 275.000 (83,119) (129b)... 

In addition to chlorophyll a, one also finds chlorophyll c, that is specific to the brown lineage and comprises a mixture of two very closely related forms, chlorophylls Cl and C2- Two essential differences allow us to distinguish between chlorophyll a and chlorophylls c - the tetrapyrrole system of the porphin (dehydrochlorin) and the replacement of the phytyl chains by crotonic add. 

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