On the impossibility of determination of stepwise binding constants for the 1 ∶ 2 complex of (+)-camphor with α-cyclodextrin

Abstract

Knowledge of stepwise binding constants for complexes with higher than 1 ∶ 1 stoichiometry would allow one to study the cooperativity of their formation. However, a detailed analysis of partitioning of the overall binding constant β₁₂ determined by NMR titrations for the 1 ∶ 2 complex of (+)-camphor with α-cyclodextrin into the stepwise ones K₁ and K₂ carried out analogously to published procedures revealed that the partitioning cannot be carried out unequivocally for K₁ << K₂. The programs for partitioning cannot be used as a black box and a satisfactory reproduction of the experimental dependence of relative shifts as a function of relative CD concentration should not be the only criterion of the reliability of the stepwise binding constants obtained using such programs.