Substitutions on metalloporphyrins

If no acid or alkali is extra added to methanolic solutions, the methoxo-methanol species (2) widely predominates, as revealed by its absorption spectra Soret, 416 nm a, 531 nm p, 565 nm. Stage (8.4.6) shows the importance of the protons of the protic solvent in the oxidation of cobalt(II) and elimination of superoxide radical (HO2 ). 

Methanolic solutions of [Co (PP)(CH30)(CH30H)] can be also prepared by dissolving [Co (PP)(Cl)] (dark violet-red ci stals) in methanol. Upon dissolution, the complex releases its chloride practically instantaneously and equilibrates, as shown by (8.4.8) where species 2 predominates. The spectra of [Co (PP)(CH30)(CH30H)] prepared either from [Co (PP)] in methanol in the presence of O2 or from [Co (PP)(Cl)] in methanol are identical. 

The imidazole ring is an essential component of many biological systems in proteins as part of the side chain of the amino acid histidine (hemoglobin and myoglobin), in nucleic acids as part of the purine ring of adenine and 

Imidazole is a ligand electron donor in the a and n sense. It is a much better electron donor than are most of the other nitrogen heterocycles. The majority of imidazoles are especially good a donors, and moderately good n donors. It has been recently shown that imidazole with an aldehyde group in 2-position, (2-CHOimH) is a very strong n acceptor, comparable to 

Imidazole has different roles in the mentioned biological systems, e.g., as proton donor or proton acceptor in hydrogen bonding imidazole can function as a specific base or a nucleophilic catalyst, or it can function as a ligand for metal coordination. Imidazole is the bonding site for various metallo-proteins, such as Mn , Fe , Fe + Cu, Cu , and It is known that 

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