Inclusion complexes of cyclodextrins with 4-amino-1,8-naphthalimides (part 2)

Fluorescence spectroscopy was used to characterize inclusion compounds between 4-amino-1,8-naphthalimides (ANI) derivatives and different cyclodextrins (CDs). The ANI derivatives employed were N-(12-aminododecyl)-4-amino-1,8-naphthalimide (mono-C₁₂ANI) and N,N′-(1,12-dodecanediyl)bis-4-amino-1,8-naphthalimide (bis-C₁₂ANI). The CDs used here were α-CD, β-CD, γ-CD, HP-α-CD, HP-β-CD and HP-γ-CD. The presence of CDs resulted in pronounced blue-shifts in the emission spectra of the ANI derivatives, with increases in emission intensity. This behavior was parallel to that observed for the dyes in apolar solvents, indicating that inclusion complexes were formed between the ANI and the CDs. Mono-C₁₂ANI formed inclusion complexes of 1:1 stoichiometry with all the CDs studied. Complexes with the larger CDs (HP-β-CD, HP-γ-CD and γ-CD) were formed by inclusion of the chromophoric ANI ring system, whereas the smaller CDs (α-CD, HP-α-CD and β-CD) formed complexes with mono-C₁₂ANI by inclusion of the dodecyl chain. Bis-C₁₂ANI formed inclusion complexes of 1:2 stoichiometry with HP-β-CD, HP-γ-CD and γ-CD, but did not form inclusion complexes with α-CD, HP-α-CD and β-CD. The data were treated in the case of the large CDs using a Benesi-Hildebrand like equation, giving the following equilibrium constants: mono-C₁₂ANI:HP-β-CD (K ₁₁ = 50 M^?1), mono-C₁₂ANI:HP-γ-CD (K ₁₁ = 180 M^?1), bis-C₁₂ANI:HP-β-CD (K ₁₂ = 146 M^?2), bis-C₁₂ANI:HP-γ-CD (K ₁₂ = 280 M^?2).