Behavior of Dioxygen Bound to Metals

The triplet ground state (OkJ/mol) for the O2 molecule is represented by the term symbol Eg and has two unpaired electrons, one each in the rr or the K level. The first excited state (92kJ/mol above the ground state) is a singlet (electrons spin paired with both electrons in either the irf or the Kf level). The singlet state with paired spin electrons, one each in the rr and K levels, is the next excited level 155 kJ/mol above the ground state. Reduction of O2 by one electron yields the superoxide ion (O2) a radical anion. Reduction by two electrons yields the peroxide ion, (02 ). As noted in equation 7.1, the reduction potential for O2 in the presence of protons is thermodynamically favorable. Therefore reversible binding of O2 to a metal can only be achieved if competition with protons and further reduction to superoxide and peroxide are both controlled.  

4 Structure of the Active Site in Myoglobin and Hemoglobin Comparison to Model Compounds 

Despite the many model compounds that have been prepared, picket fence porphyrin and its many cogeners, first reported by the CoUman research group in 1974, remains the only porphyrin-type ligand system yielding 

TABLE 7.1 Deoxy-Heme Stereochemistry for Mb, Hb, and Model Compounds 

Fe(Tpiv)PP-(l-MeIm)02, works better as a model for Hb02 and Mb02 than does model 3, Fe(Tpiv)PP-(2-MeIm)02, although the ( ) and tilt values are not good matches with Mb02 in either model. 

IRON-CONTAINING OXYGEN CARRIERS AND THEIR SYNTHETIC MODELS 

7 STRUCTURE OF THE ACTIVE SITE IN MYOGLOBIN AND HEMOGLOBIN COMPARISON TO MODEL COMPOUNDS 

X-ray crystallographic structures of myoglobin and hemoglobin were first completed in 19662 and 19753, respectively. Since then, many other X-ray crystallographic studies of deoxy- and oxy- as well as met-myoglobin and hemoglobin have been carried out.22,24 Additionally, researchers have studied the carbon monoxide bound moieties MbCO and HbCO as well as MbNO. Site-directed mutagenesis of residues near the active sites of Mb and Hb have yielded 

The information of Tables 4.3 and 4.4 indicates that a water molecule is found in the binding cavity of a chains of hemoglobin A (HbA) even though this cavity has been called hydrophobic. Indeed, although many hydrophobic groups such as 

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