Determination of acid–base dissociation constants of azahelicenes by capillary zone electrophoresis

✍ Scribed by Sille Ehala; Jiří Míšek; Irena G. Stará; Ivo Starý; Václav Kašička

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 590 KB
• Volume: 31
• Category: Article
• ISSN: 1615-9306
• DOI: 10.1002/jssc.200800227

✦ Synopsis

Abstract

CZE was employed to determine acid–base dissociation constants (p__K__~a~) of ionogenic groups of azahelicenes in methanol (MeOH). Azahelicenes are unique 3‐D aromatic systems, which consist of ortho‐fused benzene/pyridine units and exhibit helical chirality. The p__K__~a~ values of pyridinium groups of the studied azahelicenes were determined from the dependence of their effective electrophoretic mobility on pH by a nonlinear regression analysis. The effective mobilities of azahelicenes were determined by CZE at pH range between 2.1 and 10.5. Thermodynamic p__K__~a~ values of monobasic 1‐aza[6]helicene and 2‐aza[6]helicene in MeOH were determined to be 4.94 ± 0.05 and 5.68 ± 0.05, respectively, and p__K__~a~ values of dibasic 1,14‐diaza[5]helicene were found to be equal to 7.56 ± 0.38 and 8.85 ± 0.26. From these values, the aqueous p__K__~a~ of these compounds was estimated.