Spectroscopic Studies of Cyclodextrin Complexes with 2,5-Bis-(4-Methylphenyl)Oxazole

Abstract

The complexation of γ-cyclodextrins (γ-CDs) with the guest molecule 2,5-bis-(4-methylphenyl)oxazole (MPPO) has been studied by use of fluorescence spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and dynamic light scattering (DLS). The changes in the 1H NMR aromatic signals of MPPO in aqueous γ-CD provide evidence of complexation and inclusion. DLS was used to confirm the existence of a distribution of the aggregates in the nanometer range. Excimer fluorescence was pronounced in the presence of γ-CD. The evidence of the existence of two species was shown through fluorescence lifetime data. The emission intensities of the steady state fluorescence and the fluorescence anisotropies of the linear aggregates revealed a phase transition temperature of 60 °C.

The Determination of the Stoichiometry of Cyclodextrin Inclusion Complexes by Spectral Methods: Possibilities and Limitations

“…In some cases, the obtained complexes form extended linear aggregates, revealed mostly from the unexpectedly large value of the fluorescence anisotropy, e.g. 2,5-diphenyl-oxazole with -CD (Agbaria & Gill, 1988), 2,5-diphenyl-1,3,4-oxadiazole, 2-phenyl-5-(4-biphenyl)-1,3,4-oxadiazole and 2,5-biphenyl-1,3,4-oxadiazole with -CD (Agbaria & Gill, 1994), 2,5-bis-(4-methylphenyl)-oxazole with -CD and -CD (Yarabe et al, 2002), 1,4-diphenyl-1,3-butadiene with -CD and -CD (De La Pena et al, 1997), trans-1,6-diphenyl-1,3,5-hexatriene with -CD and -CD (Li & McGown, 1994), 4,4′-bis(2-benzoxazolyl) stilbene with -CD and -CD (Wu et al, 2006) and coumarin 153 with -CD (Mandal et al, 2011).…”