Molecular Recognition Studies on Supramolecular Systems 34. Synthesis of Aromatic Diamino-bridged Bis(β-cyclodextrin)s and their Inclusion Complexation with Dye Molecules

Abstract

A series of 6,6'-bis( g -cyclodextrin)s with rigid aromatic diamino tethers, i.e. p -phenylenediamino-bridged-bis(6-amino-6-deoxy- g -cyclodextrin) ( 3 ), 4,4'-bianilino-bridged-bis(6-amino-6-deoxy- g -cyclodextrin) ( 4 ) and 3,3'-bianilino-bridged-bis(6-amino-6-deoxy- g -cyclodextrin) ( 5 ), have been synthesized by the reaction of mono[6- O -( p -toluenesulfonyl)]-( g -cyclodextrin) with corresponding materials. The inclusion complexation behavior of native g -cyclodextrin ( 1 ), mono-(6-anilino-6-deoxy)- g -cyclodextrin ( 2 ), and novel bis( g -cyclodextrin) 3 - 5 with some representative dyes, i.e. ammonium 8-anilino-1-naphthalenesulfonate (ANS), Brilliant Green, Methyl Orange, Acridine Red and Rhodamine B, was investigated at 25C in aqueous phosphate buffer solution (pH 7.20) by means of fluorescence, ultraviolet, circular dichroism spectrometry as well as fluorescence lifetime measurement. The spectrophotometric titrations gave the complex stability constants ( K S ) and Gibbs free energy changes ( j G 0 ) for the stoichiometric 1:1 inclusion complexation of hosts examined with dye molecules. As compared with 1 or 2 , bridged bis( g -cyclodextrin)s displayed significantly enhanced binding abilities towards these dyes. Typically, dimer 3 showed the highest binding ability upon inclusion complexation with acridine red affording 17 times higher K S for 3 than for 1 . The molecular binding abilities and selectivities of dyes by bridged bis( g -cyclodextrin)s have been discussed from the viewpoint of induced-fit interaction and multipoint recognition mechanism.