Natural Oxygen Carriers

The two most important metalloprotein, other than hemoglobin and myoglobin are hemerythrins and hemocyanin which act as natural oxygen carrier. Hemocyanin is discussed in previous question. 

Tsuchida et al. [33], synthesized Poly(l-vinyl and l-vinyl-2-methyl-imidazole) bound heme (iron-porphyrin) complexes as models for mimicking natural oxygen carriers such as hemoglobin. The reaction between AIBN polymerized poly(l-vinyl)imidazole, or poly(l-vinyl-2-methylimidazole) and Fe(III) protoporphyrin IX diethyl ester in DMF and small amount of Na2S204 yields the Fe(III) complex (Fig. 15),... 

Despite differences in the chemical nature of the active sites, three classes of natural oxygen carriers display amazing similarities in thermodynamic and kinetic parameters that characterize dioxygen binding. All noncooperative proteins or isolated subunits of oligomeric oxygen carriers show reversible 1 1 02 binding (Equation 4.5). 

Dioxygen dissociation from the oxy forms of natural oxygen carriers is characterized by a fairly large activation enthalpy and large positive activation entropy and activation volume. For example, = 92 kJ/mol, A5 ff =117 J/K mol, and AV ff=... 

Newton and Hall [175] performed ab initio calculations on dioxygen complexes of Co and Fe porphyrins, which are models for natural oxygen carriers. The Co-O system is best described as a superoxocobalt(III)... 

As models for natural oxygen carriers, many co-balt(II) complexes coordinated with nitrogen-bases have been shown to reversibly interact with molecular oxygen to form C0O2 or C02O2 complexes depending upon the nature of the ligands. 

Stimulated largely by the existence of important biochemical systems, a number of cobalt complexes which are considered to be models for the natural oxygen carriers have been prepared and studied. One of the most extensively investigated complexes is [2,2 -ethylenbis(nitrilomethylidene)diphenolato] cobalt(II), Co(salen), I, and its... 

Consequently, the synthetic hemopolymer has properties closely resembling those of natural oxygen carriers, although the basic polymer is completely different. This demonstrates that specificity and reactivity are by no means privileges of naturally occurring polymers. Such findings could have been obtained only from model studies. 

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