Cooperative Multipoint Recognition of Organic Dyes by Bis(-cyclodextrin)s with 2,2′-Bipyridine-4,4′-dicarboxy Tethers

Abstract

A series of novel 6,6'-bis(beta-cyclodextrin)s linked by 2,2'-bipyridine-4,4'-dicarboxy tethers; that is, 2,2'-bipyridine-4,4'-dicarboxy-bridged bis(6-O-beta-cyclodextrin) (2) and N,N'-bis(2-aminoethyl )-2,2'-bipyridine-4,4'-dicarboxamide-bridged (3), N,N'-bis(5-amino-3-azapentyl)-2,2'-bipyridine-4,4'-dicarboxamide-bridged (4) and N,N'-bis(8-amino-3,6-diazaoctyl)-2,2'-bipyridine-4,4'-dicarboxamide-bridged bis(6-amino-6-deoxy-beta-cyclodextrin) (5), has been synthesized as cooperative multipoint-recognition receptor models. The inclusion complexation behavior of 2-5 with organic dyes; that is, ammonium 8-anilino-1-naphthalenesulfonate, Brilliant Green, Methyl Orange, Acridine Red, and Rhodamine B, has been investigated in aqueous phosphate buffer solutions (pH 7.20) at 25 degrees C by means of ultraviolet, fluorescence, and circular dichroism spectrometry as well as by fluorescence lifetime measurements. The spectral titrations gave the complex stability constants (Ks) and Gibbs' free energy changes (deltaG degrees) for the inclusion complexation of 2-5 with the organic dyes and other thermodynamic parameters (deltaH degrees and deltaS degrees) for the inclusion complexation of 2-4 with the fluorescent dyes Acridine Red and Rhodamine B. Bis(beta-cyclodextrin)s 2-5 displayed higher binding abilities toward most of the examined dye molecules than native beta-cyclodextrin 1; this is discussed from the viewpoints of the size/shape-fit concept, the induced-fit interaction, and cooperative, multipoint recognition by the bridging chain and the dual hydrophobic cavities. Thermodynamically, the inclusion complexation of 2-4 with Acridine Red is totally enthalpy driven with a negative or minor positive entropic contribution, but the inclusion complexation with Rhodamine B is mainly entropy-driven with a mostly positive, but occasionally negative, enthalpic contribution; in some cases this determines the complex stability.

Water / Methyl isobutyl ketone (MIBK) Biphasic System in Slug Flow under High Temperature and Pressure Conditions

“…The compensation was observed regardless of the V MIBK /V water value and the types of partitioning system, suggesting that the partitioning behavior of substrates was thermodynamically driven by the same mechanism. The y-intercept obtained by the extrapolation of H to 0, TS 0 , is the index for the desolvation of the molecule [23]. TS 0 was thereby estimated to be -0.14 kJ/mol.…”

Cyclodextrin Polymers and Cyclodextrin-Containing Polysaccharides for Water Remediation

“…This polymer presents high adsorption removal efficiencies for congo red (CR) and rhodamine B (RB), above 80%, with q max equal to 712 and 175 mg g −1 , respectively. Here, in contrast to the metal ion adsorption mechanism, the dyes interact with the CD cavities by forming stable host-guest supramolecular complexes, characterized by stability constants of 1667 and 4266 M −1 [141,142], respectively. However, whilst hydrophobic and π-π interactions are the predominant mechanism for RB adsorption, for CR, electrostatic interactions between the sulfonate groups of the dye also occur [52].…”

Mono-6-Substituted Cyclodextrins—Synthesis and Applications

“…Liu et al [ 97 ] mixed 2,2’-bipyridine-4,4’-dicarboxylic dichloride and β-CD in DMF/pyridine mixture. The authors added DCC and let the reaction run for 18 h at 0 °C and another 48 h at room temperature.…”