The Respective Benefits of X-ray Crystallography and NMR for the Structural Determination of the Inclusion Complex Between Butyl-isothiocyanate and Alpha-cyclodextrin

Isothiocyanates are natural products extracted from plants. These molecules which exhibit very interesting antifungal properties, are insoluble in water. To increase their solubility, we have prepared inclusion complexes with different cyclodextrins. Among all the isothiocyanates studied, we have investigated in more detail the structure of one complex: butyl-isothiocyanate and alpha-cyclodextrin, using two different techniques. Firstly, 1H NMR experiments were performed and revealed the inclusion phenomenon. In parallel, crystals of butyl-isothiocyanate–alpha-cyclodextrin were grown and their crystallographic structure determined. This confirmed the inclusion of the ITC molecules and allowed us to determine the exact position of the guest. Finally, we showed that even though the complex structure was determined separately in solution and in the solid state, the structural characterisations obtained with these two techniques are complementary, enhancing the respective benefits of X-ray crystallography and NMR.