Complexations of 2-Aminofluorene and 2-N,N'-Dimethylaminofluorene to b-Cyclodextrin in Presence of Sodium Perchlorate in Aqueous Solution

The complexations of 2-aminofluorene (2-AF) and 2-N,N'-dimethylaminofluorene (DMAF) to b-cyclodextrin (b-CD) have been studied in phosphate buffer (pH = 7.4) in presence of varying concentrations of sodium perchlorate (NaClO₄) in aqueous solution using absorption and fluorescence spectroscopy. In case of DMAF, association constant is about four times higher than that of 2-AF in absence of NaClO₄. The association constant of 2-AF passes through a maximum at around 0.01 M NaClO₄ with increasing concentration of NaClO₄. However, in case of DMAF there is a continuous decrease of association constant with an increase in the concentration of NaClO₄. The variation of association constants with the change in concentration of NaClO₄ for both the molecules is consistent with the variation of fluorescence quantum yields with the change in concentration of NaClO₄. Structures of 2-AF-b-CD and DMAF-b-CD inclusion complexes have been proposed. Aromatic ring without -NH₂ group in case of 2-AF and the same without -N(CH₃)₂ group in case of DMAF enter first into the b-CD cavity from the side of larger rim. The stability of ternary complex formed in the low concentration range of NaClO₄ depends on the hydrogen bond donor ability of the functional group(s) of the substrate explained with the help of the values of total atomic charges on the hydrogen atoms of -NH₂ group of 2-AF molecule obtained from ab initio quantum mechanical calculations by Restricted Hartree-Fock (RHF) method using 6-31G** basis set.