Raman and Solid State NMR Study on an Inclusion Compound of Aspartame with Cyclodextrin

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Abstract
A crystal of inclusion compound of Aspartame (α-L-aspartyl-L-phenylalanine methyl ester, APM) with β-cyclodextrin (β-CD) was obtained from their aqueous solution. The Raman spectrum of this crystal indicates some differences from the spectral sum of APM and β-CD. An analysis of these spectral differences suggests that the phenyl moiety of APM is included in the cavity of β-CD in the inclusion compound. In addition, a Raman spectroscopic study of APM with 15N-substitution and N-deuteration indicates that the peptide backbone of APM undergoes some conformational change on APM going into the inclusion compound. Solid state 13C CP MAS- and gated-decoupling MAS–NMR spectra for the inclusion compound indicate that the phenyl ring rotates at a higher frequency than 270 MHz, that the Phe Cβ and phenyl ring Cl move at the frequency of about 270 MHz, and that the molecular motion of the other parts of APM occurs at lower frequency than 270 MHz.