title: Preparation and unique circular dichroism phenomena of urea-functionalized self-folding resorcinarenes bearing chiral termini through asymmetric hydrogen-bonding belts.
abstract: Chiral macrocycles with eight (R)- and (S)-methylbenzylurea residues on the resorcinarene skeleton linked through a hexyl or dodecyl spacer having amide linkages have been prepared by the reactions of the corresponding octaamine derivative with (R)- and (S)-alpha-methylbenzylisocyanate, respectively. In chloroform, the urea-functionalized resorcinarenes with hexyl spacers form intramolecular hydrogen bonds by bundling the urea and amide residues in a cyclic fashion to give a self-folding cavitand. The urea and amide residues are cooperatively oriented in the same direction to result in asymmetric hydrogen-bonding belts. Unique circular dichroism (CD) bands are induced in the absorption wavelength ranges of the macrocyclic skeleton, caused by a chirality transmission from their chiral urea termini through hexyl spacers in the self-folded conformation. On the other hand, urea-functionalized resorcinarenes with a longer dodecyl spacer do not show such unique CD bands on the macrocycle, because of their weaker propensity for hydrogen bond formation. The characteristic CD bands of the urea-functionalized self-folding macrocycles disappeared upon complexation with anions such as chloride and bromide, reflecting breaking of the intramolecular hydrogen-bonding belts.
authors.affiliation: Institute for Materials Chemistry and Engineering, Graduate School of Engineering, Kyushu University, Higashi-ku, Fukuoka 812-8581, Japan. ohaya@ms.ifoc.kyushu-u.ac.jp
authors.forename: Osamu
authors.initials: O
authors.lastname: Hayashida
authors.forename: Jun-ichi
authors.initials: J
authors.lastname: Ito
authors.forename: Shinji
authors.initials: S
authors.lastname: Matsumoto
authors.forename: Itaru
authors.initials: I
authors.lastname: Hamachi