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

Polarographic and UV-spectrophotometric investigations of Pb(11) complex formation with beta-cyclodextrin have showed that the complexation of Pb(II) ions begins at pH > 10. The formation of lead(11) 1:1 complex with the beta-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 degreesC, ionic strength 1.0), and the molar extinction coefficient value is ca. 5500 (lambda(max) = 260 nm). With further increase in solution pH the Pb-beta-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 beta-cyclodextrin anion activity. Neither Pb(OH)(2) nor Pb(OH)(3)(-) encapsulation into beta-CD cavity was observed. (C) 2002 Elsevier Science Ltd. All rights reserved.