MOLECULAR RECOGNITION OF DIHOMOOXACALIX[4]-ARENE IN THE CRYSTAL STRUCTURES OF (1:1) COMPLEXES WITH XYLENE ISOMERS. Ken-ichi Tomita*,Kenji Suzuki#,Isao Nakanishi+, Anthony E. Armah*,Zouhair Asfari@, Jacques Vicens@, *Faculty of Pharmaceutical Sciences, Osaka University, Suita, Osaka 565, #Dainihon Pharmaceutical Co., Enokicho, Suita, Osaka 564, +Fujisawa Pharmaceutical Co., Kashima, Yodogawa-ku, Osaka 532, Japan, @Laboratoire de Chimie Minerale et Analytique, E.H.I.C.S., Strasbourg, France

Dihomooxacalix[4]arenes(1) are macrocycles made from four phenolic units meta-linked by three methylene and one methylene oxy-methylene bridges at positions ortho to the hydroxy groups, and the hydrogen atom at the position para to the hydroxy group of phenolic residues was replaced with bulky aliphatic groups (p-isopropyl or p-tert-butyl). Recently, we have reported our results on the isomer separation of the xylenes by extractive crystallization with calix[4]arenes including dihomooxacalix[4]arene(2), and p-isopropyldihomooxacalix[4]arene extracted o-xylene with 84 % selectivity while para-xylene with only 16 % selectivity. This fact may indicate the difference and strength of molecular recognition of xylene isomers by dihomooxacalix[4]arene. Therefore, we solved the crystal structures of (l:l) complexes of dihomooxacalix[4]arenes with xylene isomers(3) and we tried to simulate the specific molecular recognition mechanism exhibited between the host and guest molecules by the computational method (electrostatic surface charge distribution, heat of formation and so on) and we found the important contribution of CH--[[pi]] interactions which probably act to stabilize the guest molecule inside the cavity of host molecule.

(l)C. D. Gutsche et al., J. Amer. Chem. Soc., 103, 3782 (1981).

(2)J. Vicens et al., J. Inc. Phenom., 10, 159 (1991).

(3)K. Suzuki et al., Chem. Letters, l991, 1699.

K. Suzuki, Doctor thesis, Osaka University (1991).

A. E. Armah et al., Acta Cryst., C48, 1474 (1992).