Studies on Synthetic and Natural Melanin and Its Affinity for Fe(III) Ion

Table 2

Dissociation constants of major groups in natural melanin*.

Equilibria	−logK𝑎 (SD)
[Ac^−][H^+]/[HAc]	4.35 (0.10)
[Qi^−][H^+]/[HQi]	6.30 (0.08)
[HCat^−][H^+]/[H2Cat]	10.50 (0.12)
[Cat^2−][H^+]/[HCat^−]	12.81 (0.09)

*Obtained by fitting the average of three or more titrations.