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Analytical applications of retinoid—cyclodextrin inclusion complexes:1. Characterization of a retinal—β—cyclodextrin complex

Authors
Journal
Journal of Pharmaceutical and Biomedical Analysis
0731-7085
Publisher
Elsevier
Publication Date
Volume
14
Identifiers
DOI: 10.1016/0731-7085(95)01672-4
Keywords
  • Retinoids
  • Cyclodextrins
  • Inclusion Complexes
Disciplines
  • Chemistry

Abstract

Abstract In studies in these laboratories on the supramolecular chemistry of the retinoids, it has been recently confirmed that inclusion of these substances within the cavity of cyclodextrins protects their excited states, thus improving their photochemical stability. In the present paper, the isolation is described of a crystalline stable complex between retinal and β-cyclodextrin, which has been characterized by means of several techniques including atomic force microscopy (AFM). The complex shows distinct spectroscopic differences from both retinal and β-cyclodextrin. Thus, it absorbs at λ max = 380 nm in water whereas retinal is insoluble; it shows room-temperature luminescence, which retinal does not; finally, it gives 1H-NMR and 13C-NMR spectra in d 6-DMSO with clear differences in chemical shifts with respect to those of β-cyclodextrin. Besides these studies in solution, the behaviour of the complex in the solid state has been compared with that of physical mixtures of retinal and β-cyclodextrin. IR spectroscopy shows clear differences, particularly a shift in the retinal carbonyl absorption (1644–1672 cm −1). AFM studies reveal the existence of aggregates; X-ray diffractometry also supports the formation of a cyclodextrin—retinal complex.

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