Microionization constants: novel approach for the determination of the zwitterionic equilibrium of hydroxyphenylalkylamines by photometric titration.
The record of the formation of the phenolate and the zwitterionic form in the course of titration by photometry makes it possible to estimate the tautomeric equilibrium, K(Z), between the zwitterionic and the uncharged form of an ampholyte, provided that (1) the absorptivity of the phenolate and the zwitterionic form are identical and (2) the absorptivities of both forms are distinct from the absorptivities of the protonated and the uncharged form. The relation between the absorbance and K(Z), the degree of titration and the degree of overlapping of the basic and the acid ionization constant is given.
Institute of Pharmaceutical Chemistry, Faculty of Pharmacy, Martin-Luther-University Halle-Wittenberg, D-06108 (Saale), Halle, Germany. peinhardt@pharmazie.uni-halle.de
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G
Peinhardt
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Wiese
D000465:Algorithms; D000588:Amines / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D007202:Indicators and Reagents; D010783:Photometry
D000588:Amines; D007202:Indicators and Reagents