Oxine Stability constants

Malley and Mellor (17) have shown that for a given ligand the stability constants depend on the central metal. For convenience the values of the constants are frequently quoted on a logarithmic scale. Thus, for 8-hydroxyquinoline, the logarithmic stability constants, log K2, of some divalent, first-row transition metal oxinates are ... 

The stability constants for the 8-hydroxyquinoline (oxine) complexes have been questioned owing to the ease with which the V complexes undergo oxidation, even by atmospheric 02. However, adducts [VO(oxine)2L] (L = py or other nitrogen bases) were more stable towards oxidation. The oxine complex gradually turns magenta black when extracted into a nonpolar solvent, indicating formation of the V oxine complex in air, but in... 

Table 13 Stability constant data for silver compounds Ligand Oxine... 

What is the explanation of this protective action of cobalt At first it might seem that the cobalt combined with the oxine and thus denied it to the iron. But if this were so, nickel would be still more effective because the stability constant of nickel—oxine is much higher than that of cobalt—oxine (Table 11.2 also Albert, 1953). Yet nickel has no protective action at low concentrations. 

Because of the inductive effect of the second nitrogen atom, neither the high stability constant nor the high antibacterial action of oxine is quite reached (the latter falls short by only one twofold serial dilution). However, the last seven substances in Table 11.9 all have stability constants of the same order. For these seven substances, the antibacterial action runs parallel to the partition coefficient, which establishes the correlation. 

Experiments similar to those mentioned in the preceding sections were performed to show that oxine is weakly adsorbed while the Tb-oxine complex is adsorbed more strongly (Jiao et al., 1983). By a method suggested by Yatsimirskii et al. (1962), the stability constant of the Tb-oxine complex was found to be log = 10.35. The... 

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