Interaction of lead(II) with β-cyclodextrin in alkaline solutions Original Research Article

Polarographic and UV-spectrophotometric investigations of Pb(II) complex formation with β-cyclodextrin have showed that the complexation of Pb(II) ions begins at pH >10. The formation of lead(II) 1:1 complex with the β-cyclodextrin anion was observed at pH 10–11.5. The logarithm of the stability constant of this complex compound is 15.9±0.3 (20 °C, ionic strength 1.0), and the molar extinction coefficient value is ca. 5500 (λmax=260 nm). With further increase in solution pH the Pb–β-cyclodextrin complex decomposes and converts to Pb(OH)2 or Pb(OH)3− hydroxy-complexes. This process occurs with a decrease in Pb(II) complexation degree. The latter result could be explained by a decrease in the β-cyclodextrin anion activity. Neither Pb(OH)2 nor Pb(OH)3− encapsulation into β-CD cavity was observed.