STRUCTURE OF CYCLODEXTRINS AND THEIR COMPLEXES .4. CHROMATOGRAPHIC AND NMR-STUDY OF 1,2,3-TRI-T-BUTYLNAPHTHALENE AND ITS COMPLEX WITH GAMMA-CYCLODEXTRIN

The process of complex formation of 1,2,3-tri-t-butylnaphthalene with gamma-cyclodextrin was studied by means of gas-liquid chromatography, reversed-phase high performance liquid chromatography and H-1 and C-13 NMR spectra. In spite of the large volume of the guest molecule, usin g chromatographic methods, the complex was found to be unusually stabl e. The stability constant K-G,K-gamma-CD was estimated to be ca. 10(4) M(-1) in 75 vol% of ethanol in water at 20 degrees C and is greater t han 4.4 m(-1) in glycerin at 90 degrees C. H-1 and C-13 spectra at roo m temperature exhibit only minor shifts of the signals upon complexati on 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 H-1 NMR spectra suggest a shallow insertion of the guest into the gamma-cy clodextrin cavity. There is a surprising inconsistency between the hig h 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 ro tates almost freely at this temperature. Molecular mechanics calculati ons using PCMODEL do not reproduce this trend yielding the smallest ba rrier hindering the rotation for t-butyl group in position 2.