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Physicochemical Characterization of Sildenafil: Ionization, Lipophilicity Behavior, and Ionic‐Partition Diagram Studied by Two‐Phase Titration and Electrochemistry

DOI

64

Citations

0

References

2000

Year

Véronique Gobry, Géraldine Bouchard, Pierre‐Alain Carrupt, Bernard Testa, Hubert H. Girault
Helvetica Chimica Acta

Abstract

Sildenafil (ViagraTM) was examined for its ionization and lipophilicity by two-phase titration and electrochemistry at the interface between two immiscible electrolyte solutions (ITIES) in the 1,2-dichloroethane/H2O system. The dissociation constants (basic pKa=6.78, acidic pKa=9.12) and partition coefficients of the various species, together with the effects of electrical potential, were used to construct an ionic partition diagram (pH-potential representation). This allowed to interpret the transfer mechanisms of sildenafil at liquid/liquid interfaces, suggesting in particular that an intramolecular H-bond influences the lipophilicity of the neutral and cationic species. Conformational calculations confirmed this hypothesis.