The association of Nile Red (NR) with b-, and g-cyclodextrins (CDs) was analyzed by semiempirical parametric method 3 (PM3), density functional theory-Becke, three-parameter, Lee-Yang-Parr hybrid functional (DFT-B3LYP/6-31G), and molecular dynamics (MD) and Langevin dynamics (LD) calculations, including annealing and molecular mechanics (MM) geometry optimization. Our results suggest that inclusion complexes of NR and both CD are possible but occlusion complexes are more favourable. Differences in the intermolecular H-bonding yielded by the DFT-level of treatment could explain the distinct behaviour regarding deactivation to the ground state of NR in presence of b-, andg-CD in fluorescence experiments. DFT optimization of NR in gaseous state rendered lower twisting angles and larger pyramidalization of the amino group than reported elsewhere.
Key words: Molecular modeling, cyclodextrins, Nile Red complexes.
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