MOLECULAR MECHANICS STUDIES ON INCLUSION-COMPOUNDS OF CYANINE DYE MONOMERS AND DIMERS IN CYCLODEXTRIN CAVITIES

Molecular mechanics calculations were applied to monomers and dimers of cyanine dyes (3,3′-diethyloxacarbocyanine iodide (DOC), 3,3′-diethyloxadicarbocyanine iodide (DODC), and 3,3′-diethyloxatricarbocyanine iodide (DOTC)) in β and Γ-cyclodextrin (CD) cavities, to explain the experimental findings that DODC and DOTC dimers are included both in β and Γ-CD cavities and that the DOC dimer is included only in a Γ-CD cavity. The calculations show that the inclusion of dye dimers into cyclodextrin leads to stabilization of the total system; however, the (DOC)2-β-CD system is much less stable than the others, in agreement with experimental findings. Except for DOC and β-CD, the dimer dye (D2)-CD systems are found to be more stable than the corresponding monomer dye (D)-CD systems. This seemingly puzzling result can be rationalized in terms of the important role of the van der Waals stabilization energy in the inclusion compounds. The present study shows the usefulness of molecular mechanics calculations in the investigation of inclusion compounds. © 1990, American Chemical Society. All rights reserved.