Effect of photo-dimerization of coumarins on their interaction with polymeric β-cyclodextrin

초록

Coumarin and 7-hydroxycoumarin (7HC) were photo-dimerized in an aqueous solution of polymeric beta-cyclodextrin (P beta CD) to investigate the effect of the photo-dimerization on the viscosity of P beta CD solution. P beta CD was prepared by cross-linking beta-cyclodextrin (beta CD) using epichlorohydrin. The content of beta CD residues in P beta CD, determined by a colorimetric method using phenolphthalein as an indicator, was 28.8 wt%. The solubility of coumarin increased with increasing concentration of P beta CD, because the benzene ring of coumarin was included in the hydrophobic cavity of beta CD residue. P beta CD also increased the solubility of 7HC, but the solubilizing effect on 7HC was much less than that on coumarin, possibly because the hydroxy group on the benzene ring was likely to suppress the inclusion in the cavity of beta CD. And, the photo-dimerization degree of 7HC in an aqueous solution of P beta CD was about half than that of coumarin, possibly because the vinyl ether of pyrone group of 7HC could be concealed in the cavity of beta CD. The photo-dimerization of coumarin in an aqueous solution of P beta CD could significantly increase the viscosity of the solution. One coumarin duller would hydrophobically interact with two beta CD residues so it can act as a cross-linker for P beta CD.

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