Crystal structure of heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin complexes with m-iodophenol and 4-biphenylacetic acid. Guest-induced conformational change of a pyranose ring

Abstract

Crystal structures of heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TM-β-CDx) complexes with m-iodophenol (MIP) and 4-biphenylacetic acid (BPA) have been determined by X-ray analysis. The macrocylic ring of TM-β-CDx is elliptically distorted in both complexes. The 2,3,6-tri-O-methylglucose residues incline against the plane through seven glycosidic oxygen atoms to relieve the steric hindrance involving methyl groups at the O(2), O(3) side. In the MIP complex, one glucose residue exhibits the skew (twist boat) conformation. The MIP molecule is fully included within the TM-β-CDx cavity, both ends of which are blocked by adjacent molecules, and the hydroxy group is hydrogen-bonded to O(2) of the host TM-β-CDx. In the BPA complex, the phenyl group is located at the centre of the cavity while half a molecule protrudes from the O(2), O(3) side. The carboxy group of BPA is located in intermolecular space to form a hydrogen bond with an adjacent TM-β-CDx molecule. The complex formation induces the chiral conformation in BPA. The biphenyl group is in the R-configuration with an angle of 42.4° between the two benzene rings.