Oxygen-binding, reaction, affinity

Nakamura H, Kumita H, Imai K, lizuka T, Shiro Y. 2004. ADP reduces the oxygen-binding affinity of a sensory histidine kinase, FixL The possibility of an enhanced reciprocating kinase reaction. Proc Natl Acad Sci USA 101 2742-2746,... 

The main factors determining the efficiency of different oxides as catalysts for lower alkanes oxidation are the H-atom affinity of strong oxidizing surface sites and the oxygen binding energy. These thermochemical factors cause the rates and directions of free-radical reactions and, as a result, the catalytic activity and selectivity to certain products. 

An obvious choice for the construction of artificial oxygen binding mimics is the use of oxidisible transition metal (particularly iron) complexes of porphyrin ligands such as 12.23, as in the natural system. In such cases, the O2 affinity is governed essentially by the reduction potential of the metal centre (Ej) as in the reaction + e = M +. Iron(ll) and cobalt(ll) are particularly favourable in... 

The oxygen-binding affinity (P50), or oxygen-binding equilibrium constant K), of the reaction [see Eq. (1)] is moderate (P50 = UK = 27 mm Hg P50 is the oxygen partial pressure at which half of the iron—porphyrin is bound... 

The oxygen affinity of the derivative was shown to be about half that of unmodified hemoglobin under similar conditions, but a degree of cooperativity was preserved. Kquilihrium and kinetic ligand-binding studies on this derivative have been interpreted (62) to show a perturbed R state. It is beheved that although the reaction is between the two P-chains, aP-dimers function independentiy, probably through a flexible connection. 

In spite of the low affinity for binding to oxygen, gold(III) alkoxo, hydroxo and even 0X0 complexes have been obtained [6, 7]. These are valuable models for Au-O(H) species which are likely to be involved in oxidation reactions catalyzed by metal-oxide-supported gold [8]. All these complexes have displayed interesting chemical reactivity and, in some cases, remarkable catalytic activity. 

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