Abstract
Complexes of β-ionone (BI) with β-cyclodextrin (β-CD), 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and 2-hydroxypropyl-γ-cyclodextrin (HP-γ-CD) were studied by 1 H NMR spectroscopy in aqueous and methanolic solutions. From the dependence of chemical shifts of the BI protons on CD concentration (Job’s plot), it was concluded that BI forms 2:1 inclusion complexes (CD:BI) with β-CD and HP-β-CD, but a 1:1 complex with HP-γ-CD. The stability constants in water are K 21 (BI/β-CD) ≥ 2×10 6 M −2; K 21 (BI/HP-β-CD) = 5×10 6 M −2; K 11 (BI/HP-γ-CD) = 1×10 4 M −1. In 1:1 water/methanol solution the stability constants decrease by about two orders of magnitude compared to those in water. For example, for BI/HP-β-CD complex, K 21=8×10 4 M −2 in this case. Photolysis of trans-β-ionone in water and aqueous CD solutions leads to only one final product, retro-γ-ionone. Other isomers, cis-β-ionone and racemic α-pyran, are formed at earlier stages of the photolysis. The role of cyclodextrin in this process is discussed.
Published Version
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