COMPLEXATION OF METHYL-ORANGE AND TROPAEOLIN-000 NO-2 BY BETA-CYCLODEXTRIN DIMERS

Spectrophotometric studies of the complexation of Methyl Orange (MO(-) ) and Tropaeolin 000 No. 2 (TR(-)) anions by dimeric N,N'-bis(6(A)-deo xy-6(A)-beta-cyclodextrin)urea (beta CD)(2)ur and its oxalamide and su ccinamide analogues, (beta CD)(2)ox and (beta CD)(2)su, respectively, are consistent with the predominant formation of complexes of the gene ral formulae (beta CD)(2)x . MO(-) characterized by stability constant s K-1=(1.05+/-0.04) x 10(5), (1.92+/-0.04) x 10(5) and (2.50+/-0.02) x 10(4) dm(3) mol(-1) and (beta CD)(2)x . TR(-) characterized by K-1=(1 .39+/-0.03) x 10(4), (7.4+/-0.1) x 10(3) and (4.60+/-0.05) x 10(3) dm( 3) mol(-1), in aqueous phosphate buffer at pH 9.0 and 5.5 and 298.2 K. These values are significantly greater than K-1=2160 and 710 dm(3) mo l(-1) for the beta-cyclodextrin complexes, beta CD . MO(-) and beta CD . TR(-) and are indicative of cooperative binding in (beta CD)(2)x . MO(-) and (beta CD)(2)x . TR(-). The factors affecting complex stabili ty are discussed and comparisons are made with related systems.