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Inclusion Complexes of Cyclodextrins with Methylene Blue and α -Naphthol Orange and Temperature Dependence of the Inclusion Complexation in Aqueous Solutions

2002; Oxford University Press; Volume: 75; Issue: 1 Linguagem: Inglês

10.1246/bcsj.75.77

1348-0634

Sanyo Hamai, Hideyuki Satou,

Photochemistry and Electron Transfer Studies

Abstract Methylene Blue (MB) has been found to form a complex with α-Naphthol Orange (αNO) in aqueous solution. From a simulation concerning the fluorescence quenching of MB by αNO, an equilibrium constant for the formation of the 1 : 1 MB–αNO complex has been estimated to be 79900 mol-1 dm3. Upon the addition of γ-CD to MB solution containing αNO, the absorption of the MB monomer band is enhanced in intensity without an appearance of the MB dimer band, indicating the formation of a ternary γ-CD–MB–αNO inclusion complex. To determine a stoichiometry of the ternary inclusion complex, a continuous variation method using the fluorescence intensities has been performed under the condition that the sum of the initial concentrations of γ-CD and αNO has been kept constant. The result of the continuous variation method indicates the formation of a 2 : 1 : 1 γ-CD–MB–αNO inclusion complex. The equilibrium constant for the formation of the γ-CD–MB–αNO inclusion complex from γ-CD and the 1 : 1 MB–αNO complex has been evaluated to be 1.86 × 109 mol-2 dm6 from a simulation concerning the absorbance change. From the temperature dependence of the equilibrium constants, ΔH and ΔS values have been evaluated for the γ-CD–MB–αNO and γ-CD–MB–Acid Orange 7 systems. The ΔH and ΔS values for the formation of the γ-CD–MB–αNO inclusion complex have been positive in sign, in contrast to those for the formation of the MB–αNO and γ-CD–αNO complexes.