betadex and 2-aminofluorene

The molecular recognition interaction of beta-cyclodextrin (beta-CDx) was investigated using 2-amino-9-fluorenone (2AFN) by UV, steady-state fluorescence and time-resolved fluorescence measurements in aqueous solution at various pH. The effect of acidity on the ground and excited state equilibria between the neutral and the monocationic forms of 2AFN in water and in beta-CDx environments are studied. Based on the change in the fluorescence spectrum and lifetimes of 2AFN by the addition of beta-CDx, it is found that the unsubstituted part of the 2AFN is encapsulated in the hydrophobic cavity of beta-CDx. The unusual red shift obtained for the protonation of amino group in water and beta-CDx solution is due to large solvent relaxation of the monocation. The structure of the 1:1 inclusion complex between 2AFN and beta-CDx has been proposed on the basis of ground and excited state pKa values and the bond distances obtained by MOPAC/AM 1 data.

Topics: beta-Cyclodextrins; Fluorenes; Fluorometry; Hydrogen-Ion Concentration; Molecular Structure; Spectrometry, Fluorescence; Spectrophotometry, Ultraviolet; Water

Beta-cyclodextrin (beta-CDx) forms inclusion complexes with 2-aminofluorene (2AF) and 2-amino-9-hydroxyfluorene (2AHF) in different stoichiometries (Guest-host ratio 1:1 and 1:2 respectively) which is discussed on the basis of study by absorption and fluorescence spectroscopy. The ground and the excited state acidity constants for the neutral-monocation equilibrium of the two fluorophores in aqueous beta-CDx medium are determined by spectrophotometric and fluorimetric titration methods respectively. The dual fluorescence observed for 2AHF monocation in aqueous solution is due to the formation of monocation-water exciplex. This monocation-water exciplex formation is hindered in beta-CDx solution by the inclusion complexation. Based on the results obtained, the structures of the inclusion complexes are proposed.

Topics: beta-Cyclodextrins; Fluorenes; Spectrometry, Fluorescence