Inclusion complexes of 2-phenoxyethanol and alkoxyethanols in cyclodextrins: an H-1 NMR study


The association in aqueous solutions of small amphiphilic molecules [2-phenoxyethanol, PhE1, and some alpha-n-alkyl-omega-hydroxyoligo(oxiethylenes], C4E1, C4E2 and C6E2) with beta-cyclodextrin (beta CD), heptakis(2,6-di-O-methyl)-beta-cyclodextrin (DIMEB) and heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TRIMEB) was investigated by H-1 NMR spectroscopy. The upfield shifts observed for the H3 and H5 NMR signals due to anisotropic shielding confirm that the host-guest associations are of inclusion type. The stoichiometries and the apparent inclusion constants, K (app), were determined by H-1 NMR spectroscopy using the H5 and H3 signals. The relative differences in the K (app) values for beta CD inclusion complexes seem to reflect the hydrophobic/hydrophilic balance of the guests. The K (app) values for the PhE1 inclusion complexes can be related to the degree of methylation and hydrophobicity variation within the considered hosts. In addition, a comparative study between beta CD and TRIMEB inclusion complexes using 2D ROESY (Rotating-frame Overhauser Enhancement SpectroscopY) NMR spectra provides structural features for these complexes which are inaccessible by other experimental methods.



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Andrade-Dias, C; Goodfellow, BJ; Cunha-Silva, L; Teixeira-Dias, JJC

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