Investigation on the inclusion behavior of neutral red with β-cyclodextrin, hydroxypropyl-β-cyclodextrin and sulfobutylether-β-cyclodextrin Original Research Article

The formation of the inclusion complexes of neutral red (NR) with cyclodextrins (CDs) including β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and sulfobutylether-β-cyclodextrin (SBE-β-CD) was studied by fluorescence and UV-Vis absorption spectroscopy and the binding constants (K) of the inclusion complexes were obtained by steady-state fluorescence measurements. Experimental conditions including the concentrations of various CDs and media acidity were investigated in detail. The results suggested that NR exists in two molecular forms in aqueous solution (the acidic form and the neutral form). CDs were most suitable for inclusion of the neutral form of NR and could cause enhanced fluorescence emission and absorption by NR. Moreover, the effect of the charged CD (SBE-β-CD) was quite different from that of the uncharged CDs (β-CD and HP-β-CD). A mechanism is proposed to explain the inclusion process.