화학공학소재연구정보센터
Journal of Physical Chemistry B, Vol.108, No.37, 14154-14162, 2004
Site-specific interaction between 2-dibenzofuran carboxylate and beta-and gamma-cyclodextrins determined by intermolecular NOE and molecular modeling
The topologies of the complexes between 2-dibenzofuran carboxylate (DBFC) and beta- and gamma-cyclodextrins (CDs) have been studied by NMR methods (H-1 NMR and 2D ROESY) and by molecular modeling strategies. The analysis of the spectra and the molar ratio plots reveal the formation of complexes of 1: 1 stoichiometry with beta-CD. The stability constants have been calculated by multivariable nonlinear least-squares regression from the changes in the chemical shifts of the protons of both host and guest molecules. For the beta-CD complex, the interproton distances between the host and guest have been deduced from the NOE enhancements. Rigid docking calculations using the geometrical restraints given by the NMR experiments, together with molecular dynamics simulations assuming a continuum solvent model, indicate that DBFC is oriented with the carboxylate group at the narrow rim of the CD. The radial distribution functions obtained by considering explicit water molecules with periodic boundary conditions indicate that the solvation degree of the charged group of DBFC in its free or bound form is the same. In the case of gamma-CD, the NMR data indicate the presence of 1: 1 and 2:1 complexes [(DBFC)(2)/gamma-CD], with a constant for the second binding step higher than that of the first. The stoichiometry and binding constants, apparently in disagreement with previously reported fluorescence experiments, are satisfactorily explained by considering the range of working concentrations.