NMR Studies of Cyclodextrin Inclusion Complex with Ethyl Hexanoate in Ethanol Solution

Abstract

The formation of a βCD inclusion complex for aliphatic ethyl ester, with ethyl hexanoate as a guest molecule was investigated. Proton T1 measurements by the IR method and 1D difference nuclear Overhauser enhancement experiments showed that ethyl hexanoate exists with the groups (H-2 and H-3) around the ester bond nearer to the narrower βCD cavity and the other protons are proximal to the H(CD)-3 and H(CD)-5 protons within the cavity with a folded structure. The complexation of βCD was greatly affected by the addition of ethanol. With increasing ethanol concentration, a marked increase in volatility of ethyl hexanoate from the βCD solution was observed; the volatility in 30% ethanol was about 3 times larger than in 0% one. On the basis of the observed NOE and T1 values, the lowering of the abilitys of βCD complexation in ethanol solution is assumed to be caused by the situation shift of guest molecule toward the narrower side or outside of the cavity.