Dioxygen binding reverse

Figure 10.3. The Hr subunit and its diiron site. Dioxygen binds reversibly to the iron labeled Fe2 (Stenkamp 1994). Reprinted with permission from Xiong et al. (2000), copyright 2000 American Chemical Society.

In solution Fe(II)TPP reacts rapidly and irreversibly with oxygen to form a (i-oxo dimer (Equation 13). Fe(II) supported on silica gel does not dimerize (691. On lightly cross-linked polystyrenes dimerization occurs (681. but with 20-30% cross-linked DF 0.01, macroporous copolymers of styrene and 4 aminostyiene, dioxygen binds reversibly (107.1081. Similarly, Fe(in)Pc(COOH)4 bound covalently to linear polystyrene (1091 and to linear poty(styrene-co-2-vinylpyridine) (1101 is active for catalase-like decomposition of hydros peroxide. 

Figure 2.3 Structures of two globin compounds capable of reversible dioxygen binding. From Lippard and Berg, 1994. Reproduced by permission of University Science Books.

Models for haemoglobin and myoglobin. It has been known for a long time that a range of synthetic Co(n) complexes are able to bind reversibly dioxygen in a manner related to the natural systems (Basolo, Hoffman Ibers, 1975 McLendon Martell, 1976). However, similar complexes of iron do not normally function as 02 carriers - rather oxidation to Fe(m)... 

The third group of studies involves attachment of the iron complexes to solid substrates in order to inhibit formation of bridged species. In a very early study, dioxygen was found to bind reversibly to haem diethyl ester embedded in a mixture of polystyrene and l-(2-phenylethyl)imidazole (Wang, 1958). 

Figure 4.13 Co(acacen), an early model compound exhibiting reversible dioxygen binding at low temperatures.

Another gradient-corrected density functional study of reversible dioxygen binding and reversible 0-0 bond cleavage has been carried out for Cu2(p-T 2 r 2... 

Dioxo-L-gulonic acid, 25 751 Dioxygen, reversible binding of, 14 554 Dioxygen binding, by iron, 24 47... 

Another /i- i -peroxo compound able to bind reversibly dioxygen has been structurally characterized, namely [Cu2C>2(L)]2+ (L= 1,2-bis [2-(bis(6-methyl-2-pyridyl)methyl)-6-pyridyl]ethane).30... 

Evidence tom a variety of sources indicates that the active site of tyrosinase is very similar to that of hemocyanin, a dioxygen-binding protein found in molluscs and arthropods (15,16). This type of active site contains two copper ions, which are cuprous in the deoxy state, and which reversibly bind dioxygen, forming the oxy form of the enzyme or protein in which a peroxy ligand bridges between two cupric ions. 

For tricoordinate complexes [Cu2(Nn)]2+ (4a) or tetracoordinate nitrile adducts [Cu2(Nn)(CH3CN)2]2+ (4b), reversible binding can be demonstrated (33, 35). These react with 02 at —80 °C in CH2Cl2 solution, producing deep brown or purple species [Cu2(Nn)(02)]2+ (5) (33, 35). As found for our other copper-dioxygen complexes, reversible 02 or... 

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