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Structure of cyclodextrins and their complexes. Part 4. Chromatographic and NMR Study of 1,2,3-tri-t-butylnaphthalene and its complex with γ-cyclodextrin

✍ Scribed by H. Dodziuk; D. Sybilska; S. Miki; Z. Yoshida; J. Sitkowski; M. Asztemborska; A. Bielejewska; J. Kowalczyk; K. Duszczyk; L. Stefaniak

Publisher
Elsevier Science
Year
1994
Tongue
French
Weight
515 KB
Volume
50
Category
Article
ISSN
0040-4020

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✦ Synopsis

The process of complex formation of 1,2,3-tri-t-butyhtaphthalene with y-cyclodextrin was studied by means of gas-liquid chromatography, reversed-phase high performance liquid chromatography and 1H and 13C NMR spectra. In spite of the large volume of the guest molecule, using chromatographic methods, the complex was found to be unusually stable. The stability constant KC+CD was estimated to be ca. 104 M-l in 75 vol% of ethanol in water at 20° C and is greater than 4.4 m-l in glycerin at 900 C. lH and l3C spectra at room temperature exhibit only minor shills of the signals upon complexation and the complex formation manifests itself in carbon spectra at low temperatures by significant broadening of the signals. Both reversed-phase high performance liquid chromatography and room temperature 1H NMR spectra suggest a shallow insertion of the guest into the y-cyclodextrin cavity. There is a surprising inconsistency between the high stability of the complex and the shallow insertion of the guest into the host cavity. Internal rotation of t-butyl groups in the positions 1 and 2 is frozen at 193 K while the remaining group in position 3 rotates almost fkely at this temperature. Molecular mechanics calculations using PCMODEL do not reproduce this trend yielding the smallest barrier hindering the rotation for t-butyl group in position 2.

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