STUDIES OF HYDROGEN BONDING IN CRYSTALLINE SOLIDS OF CYCLIC DIPEPTIDES. G. Tayhas R. Palmore, Mary T. McBride, Department of Chemistry; University of California, Davis; Davis, CA 95616

Understanding how molecules influence the structure of crystalline solids is essential to the design of new solid-state materials. Researchers have only recently begun to exploit the strength, directionality and selectivity of hydrogen bonds to control the orientation of molecules in the solid state. Although the manipulation of individual molecules into large aggregates with well-defined shapes is masterfully demonstrated in nature, the deliberate control of molecular orientation by researchers is still in its infancy. One promising strategy is to examine the hydrogen-bonding interactions present in crystals of related molecules; such studies define the strengths and weaknesses of a common functional group in controlling the architecture of the solid. Once the organizational properties of a functional group are established, other intermolecular interactions can be systematically introduced and evaluated. We will describe the solid-state packing patterns of cyclic dipeptides that contain hydrogen-bonding functional groups at the 3,6-positions of the diketopiperazine ring. Diketopiperazines contain two amide functional groups within the piperazine ring itself that enable these molecules to self-assemble into hydrogen-bonded "tapes". We will discuss how functional groups at the 3,6-positions of the diketopiperazine ring influence the integrity of these hydrogen-bonded tapes.