Molecular recognition study on a supramolecular system. Part 21. Inclusion complexation thermodynamics of aliphatic alcohols by organoselenium modified β-cyclodextrins

The spectrophotometric titrations have been performed at 25-40 °C in aqueous solution to give the complex stability constants and the thermodynamic parameters for the stoichiometric 1 : 1 inclusion complexation of various aliphatic alcohols with mono[6-(phenylseleno)-6-deoxy]-β-cyclodextrin (2), mono[6-(o-, m-, p-tolylseleno)-6-deoxy]-β-cyclodextrin (3-5), mono[6-(p-chlorophenyl-seleno)-6-deoxy]-β-cyclodextrin (6), mono[6-(benzylseleno)-6-deoxy]-β-cyclodextrin (7) and mono[6-(naphthaleneseleno)-6-deoxy]-β-cyclodextrin (8). On the basis of the present and previous results, the molecular binding abilities and selectivities for guest aliphatic alcohols of the host β-cyclodextrin derivatives (2-8) are discussed comparatively and globally from the thermodynamic point of view. The thermodynamic parameters obtained are critical functions of the size/shape of aliphatic alcohols, and the position and type of the substituent introduced to the aromatic ring of β-cyclodextrin's sidearm, which are elucidated in terms of the conformational, electrostatic, hydrogen-bonding, and hydrophobic effects.