Ligand deprotonation curves

A binuclear zinc complex of the 2,6-bis [(2-pyridylmethyl)(2-hydroxyethyl) amino]methyl -4-methylphenol ligand (L33, Fig. 63) catalyzes the hydrolysis of bis(4-nitrophenyl) phosphate in aqueous buffer solution to yield 4-nitrophenol and 4-nitrophenyl phosphate.246 Analysis of the pH-rate profile revealed a sigmoidalshaped curve with a pKa = 7.13. This value is similar to a deprotonation event characterized by potentiometric titration and has been assigned to deprotonation of... 

It is noteworthy that the corresponding f(a) parts of the titration curves of the acid, Hj B,(f(a)=Eiaj) with NaOH and the base, the totally deprotonated B(f(a)=E(N-i)aj or njj) with HCl are, complementary. The first is a measure of the extent of removal of protons from the acid, and the second, addition of protons to the base. The term, iTn, represents the average number of bound protons per base. The addition of protons to a base is strongly analogous to metal complex formation where, n, the average number of ligands bound to the metal ion, will be introduced. 

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