Structural Characterization of a Cyclodextrin/l-menthol Inclusion Complex in the Solid-state by Solid-state NMR and Vibrational Circular Dichroism

Abstract

Hydrophobic and volatile flavor molecules can be encapsulated inside cyclodextrins (CyDs). Inclusion complexes are frequently used in solid or dispersed states in preserved food and cosmetics. In this study, the solid-state structures of spray-dried inclusion complexes of l-menthol in α-CyD and β-CyD were analyzed using 13 C solid-state NMR and vibrational circular dichroism (VCD). The NMR signals of l-menthol and CyDs were identified in the physical mixture and the l-menthol inclusion complex of αand β-CyD. The NMR signal of the isopropyl-methyl group of menthol in the α-CyD inclusion complex exhibited a large low-field shift, which suggested a steric hindrance between menthol and α-CyD. VCD exhibited specific changes in the intensity of bands corresponding to CC vibrations in α-CyD and O-C stretching vibrations in l-menthol. Our results indicated that l-menthol specifically fitted the narrow space within α-CyD. The combined solid-state NMR and VCD analysis provided structural insights into the flavor inclusion complex in the solid-state.

A Review of Applications of Solid-State Nuclear Magnetic Resonance (ssNMR) for the Analysis of Cyclodextrin-Including Systems

“…CD complexes in solid state are used also as enantioseparators [ 32 ], food and flavor-encapsulating agents [ 62 , 96 ], as part of the antimicrobial packaging materials [ 19 , 46 ], etc. Thanks to ssNMR, the inner structure, complexation process, CD-guest molar ratio, etc., are defined.…”

Quantitative NMR in Analytical Chemistry

“…Therefore, if high-precision quantitativeness is added the NMR ability, it will be very effective not only in determining the structure of organic molecules, but also in the physicochemical property analysis of a system. [1][2][3][4][5][6][7][8] Futhermore, NMR can analyze solid-liquid coexistence systems (samples containing precipitates, agglutinates, sludge, etc.). 9 Moreover, since NMR can be observed in a very wide concentration range, pretreatment, such as dilution or concentration of the sample solution is not required.…”