Engineering Crystalline Architecture with Supramolecular Tapes: Studies on Secondary Donor−Acceptor Interactions in Cocrystals of the Cyclic Dipeptide of Glycine

In this study, we examine the noncovalent interactions that occur between the cyclic dipeptide of
glycine (GLYDKP) and a carboxylic acid guest. This study complements our earlier studies on the cyclic dipeptide
of aspartic acid by exploring further the possibility of using hydrogen-bonded tapes comprised of molecules of
GLYDKP, as a scaffold with which to control the location of guest molecules in a crystalline lattice. On the basis of
the 11 cocrystals of GLYDKP reported herein, we conclude that guest molecules will be positioned between tapes of
GLYDKP if the guest molecules meet the following criteria. First, the width of the guest molecule should be between
4.5 and 8.5 Å. Second, interactions between adjacent guest molecules should be stronger than a van der Waals
contact. Third, a hydrogen-bond donor (hydroxyl group) and a hydrogen-bond acceptor (carbonyl group) should be
present in the structure of the guest with their separation no greater than two bonds between the carbon atom of
the carbonyl group and the oxygen atom of the hydroxyl group. Fourth, the strength of interactions between molecules
in the cocrystal should be of the following order:  host−host > host−guest > guest−guest. This order ensures the
tape superstructure dictates the location of guest molecules in the host lattice.