Sheet structure of an L,D-dipeptide aggregate:: Inclusion compounds of (S)-phenylglycyl-(R)-phenylglycine with amides

A simple dipeptide, (S)-phenylglycyl-(R)-phenylglycine (S,R-1), formed inclusion compounds with a small amide such as formamide, acetamide, N,N-dimethylformamide (DMF), or N,N-dimethylacetamide. By single-crystal X-ray analysis, the inclusion compounds were shown to have a wavy layer structure. The molecules of S,R-1 are arranged in parallel via ionic pairing of the carboxyl and amino groups to construct the wavy layers. The guest molecules were accommodated in a, channel cavity between the layers by means of hydrogen bonding with +NH3 Of S,R-1. The cavity, is surrounded by the phenyl groups of S,R-1 that conformationally rotate so as to make the cavity size fit the guest amide.