Constants and thermodynamics of the acid-base equilibria of triglycine in water–ethanol solutions containing sodium perchlorate at 298 K


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The acid−base equilibrium constants for glycyl-glycyl-glycine (triglycine) in water–ethanol solvents containing 0.0, 0.1, 0.3, and 0.5 mole fractions of ethanol are determined by potentiometric titration at 298.15 K and an ionic strength of 0.1, maintained with sodium perchlorate. It is established that an increase in the ethanol content in the solvent reduces the dissociation constant of the carboxyl group of triglycine (increases pK1) and increases the dissociation constant of the amino group of triglycine (decreases pK2). It is noted that the weakening of the acidic properties of a triglycinium ion upon an increase of the ethanol content in the solvent is due to the attenuation of the solvation shell of the zwitterionic form of triglycine, and to the increased solvation of triglycinium ions. It is concluded that the acid strength of triglycine increases along with a rise in the EtOH content in the solvent, due to the desolvation of the tripeptide zwitterion and the enhanced solvation of protons.

Sobre autores

L. Pham Tkhi

Ivanovo State University of Chemistry and Technology

Autor responsável pela correspondência
Email: oxt@isuct.ru
Rússia, Ivanovo, 153000

T. Usacheva

Ivanovo State University of Chemistry and Technology

Email: oxt@isuct.ru
Rússia, Ivanovo, 153000

N. Tukumova

Ivanovo State University of Chemistry and Technology

Email: oxt@isuct.ru
Rússia, Ivanovo, 153000

N. Koryshev

Email: oxt@isuct.ru

T. Khrenova

Ivanovo State University of Chemistry and Technology

Email: oxt@isuct.ru
Rússia, Ivanovo, 153000

V. Sharnin

Ivanovo State University of Chemistry and Technology; Krestov Institute of Solution Chemistry

Email: oxt@isuct.ru
Rússia, Ivanovo, 153000; Ivanovo, 153045

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