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Interaction of lead(II) with beta-cyclodextrin in alkaline solutions
Eugenijus Norkus1, Giedre Grinciene, Rimantas Vaitkus
1Institute of Chemistry, A Gostauto 9, LT-2600, Vilnius, Lithuania. norkus@ktl.mii.lt
Carbohydrate Research
|November 9, 2002
Summary
Lead(II) ions form a 1:1 complex with beta-cyclodextrin anions above pH 10, with a stability constant of 15.9. This complex decomposes at higher pH, forming lead hydroxy-complexes.
Area of Science:
- Coordination Chemistry
- Supramolecular Chemistry
Background:
- Beta-cyclodextrin (beta-CD) is a cyclic oligosaccharide with a hydrophobic cavity and hydrophilic exterior.
- Lead(II) ions are environmentally significant and their complexation behavior is of interest.
Purpose of the Study:
- To investigate the complex formation between lead(II) ions and beta-cyclodextrin.
- To determine the conditions and stability of the formed complex.
Main Methods:
- Polarographic investigations
- UV-spectrophotometric analysis
Main Results:
- Pb(II) complexation with beta-cyclodextrin begins at pH >10.
- A 1:1 lead(II)-beta-cyclodextrin complex forms between pH 10-11.5 with a stability constant (log K) of 15.9 ± 0.3.
- The complex decomposes at higher pH, forming lead hydroxy-complexes, due to decreased beta-cyclodextrin anion activity.
Conclusions:
- The formation and decomposition of Pb(II)-beta-cyclodextrin complexes are pH-dependent.
- Lead hydroxy-complexes do not encapsulate within the beta-cyclodextrin cavity.