title: Determination of acid-base dissociation constants of azahelicenes by capillary zone electrophoresis.
abstract: CZE was employed to determine acid-base dissociation constants (pK(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 pK(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 pK(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 pK(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 pK(a) of these compounds was estimated.
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
authors.forename: Sille
authors.initials: S
authors.lastname: Ehala
authors.forename: Jirí
authors.initials: J
authors.lastname: Mísek
authors.forename: Irena G
authors.initials: IG
authors.lastname: Stará
authors.forename: Ivo
authors.initials: I
authors.lastname: Starý
authors.forename: Václav
authors.initials: V
authors.lastname: Kasicka
mesh_terms: D000136:Acid-Base Equilibrium; D001372:Aza Compounds / Q000032:analysis*; D019075:Electrophoresis, Capillary / Q000295:instrumentation / Q000379:methods; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D011083:Polycyclic Compounds / Q000032:analysis*; D012680:Sensitivity and Specificity; D013237:Stereoisomerism; D013997:Time Factors
chemical_list: D001372:Aza Compounds; D011083:Polycyclic Compounds; C031660:helicenes