| Popis: |
The reaction of sodium molybdate with o -aminobenzenethiol in acidic aqueous ethanol leads to the isolation of Mo(SNHC 6 H 4 ) 3 , in which each coordinated amino group is singly deprotonated. This result, and others from the literature, are used to illustrate the change in the acidity of ligands coordinated to Mo as a function of both oxidation state and the number of bound oxo-groups. Thus, ligands which may be coordinated to Mo in enzymes may change their p K a values from less than to greater than the physiological pH as the oxidation state decreases. The Mo site may therefore have both proton and electron transfer capacity and since all substrate reactions involve the flow of both protons and electrons it is suggested that the Mo site couples the flow of electrons and protons. In line with this notion, simple mechanistic schemes are presented which explain a number of features of the action of Mo in enzymes. Analogies are drawn between Mo and Re chemistry and it is suggested that Re complexes and Re substituted enzymes (if and when prepared) may provide useful complementary information in the study of Mo chemistry. |
