Porphyrin tetrapyrrole

Keywords Field effect transistors (FETs) Organic semiconductor Phthalocyanine Porphyrin Tetrapyrrole... 

Compounds of iron complexed in a porphyrin (tetrapyrrole) ring differ in side chain composition. Haems are the prosthetic groups of cytochromes and are found in most oxygen carrier proteins. 

With the catalysis of strong Lewis acids, such as tin(IV) chloride, dipyrromethenes may aiso be alkylated. A very successful porphyrin synthesis involves 5-bromo-S -bromomethyl and 5 -unsubstituted 5-methyl-dipyrromethenes. In the first alkylation step a tetrapyrrolic intermediate is formed which cyclizes to produce the porphyrin in DMSO in the presence of pyridine. This reaction sequence is useful for the synthesis of completely unsymmetrical porphyrins (K.M. Smith, 1975). 

The Ni and V concentrated into the vacuum resid appear to occur in two forms. Erom 10 to 14% of each of these two metals can be distilled in the 565—705°C boiling range, where they exhibit the strong visible Soret bands associated with the porphyrin stmcture. This tetrapyrrole stmcture (48,49), possibly derived from ancient chlorophyll, has been confirmed by a variety of analytical techniques. 

A sequence of an ozonolysis-PK reaction has been used to convert functionalized cyclohexenes to pyrroles (for example 49 and 50) that are important precursors to natural tetrapyrroles, hemes, and porphyrins ... 

Cyclization of l-bromo-19-methyl-1.19-dideoxybiladicnes-ac 11 to porphyrins 12 occurs simply by heating the tetrapyrrole in 1,2-dichlorobenzene solution or in few cases in dimethyl sulfoxide. 

The formation of a cyclic tetrapyrrole—ie, a porphyrin—occurs by condensation of four molecules of PEG (Figure 32-6). These four molecules condense in a head-to-tail manner to form a linear tetrapyrrole, hy-... 

Porphyrinogens are cyclic tetrapyrrole precursors which give rise to three basic groups of molecules, discriminated by their state of oxidation porphyrins, dihydroporphyrins and tetrahydroporphryins the basic structures are depicted in Figure 2.1.1. 

The biosynthesis of the tetrapyrrole macrocycle and its branches leading to haem and chlorophylls has been covered in detail in several reviews - - and will be concisely described in this section. Tetrapyrrole biosynthesis occurs entirely in the plastids and is composed of several enzymatic steps starting from 5-aminolevulinic acid (ALA), which is the key precursor of porphyrins and the source of their carbon and nitrogen. 

A porphyrinogen is a reduced tetrapyrrole parent compound of a porphyrin... 

Fig. 3 illustrates schematically the structures of some well characterized hemoproteins. In the cytochrome series the desired range of redox potentials is achieved by variations in the axial ligands, contributed by the porphyrin moiety, as well as by substitutions around the periphery of the tetrapyrrole nucleus with groups of differing electron-attracting ability. 

As demonstrated above, lanthanide complexes containing phthalocyanines and various porphyrins as ligands have been studied in great detail. In contrast, the number of studies on analogous complexes containing phthalocyaninato and tetrapyrrole ligands like tetrabenzoporphyrinato-, tetraazaporphyrinato- or N-confused porphyrinato-, is rather limited [151-155], though such compounds also attract considerable interest. 

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. 

Coordination compounds composed of tetrapyrrole macrocyclic ligands encompassing a large metal ion in a sandwich-like fashion have been known since 1936 when Linstead and co-workers (67) reported the first synthesis of Sn(IV) bis(phthalocyanine). Numerous homoleptic and heteroleptic sandwich-type or double-decker metal complexes with phthalocyanines (68-70) and porphyrins (71-75) have been studied and structurally characterized. The electrochromic properties of the lanthanide pc sandwich complexes (76) have been investigated and the stable radical bis(phthalocyaninato)lutetium has been found to be the first example of an intrinsic molecular semiconductor (77). In contrast to the wealth of literature describing porphyrin and pc sandwich complexes, re-... 

As we will see in subsequent chapters, many metalloproteins have their metal centres located in organic cofactors (Lippard and Berg, 1994), such as the tetrapyrrole porphyrins and corrins, or in metal clusters, such as the Fe-S clusters in Fe-S proteins or the FeMo-cofactor of nitrogenase. Here we discuss briefly how metals are incorporated into porphyrins and corrins to form haem and other metallated tetrapyrroles, how Fe-S clusters are synthesized and how copper is inserted into superoxide dismutase. 

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