Core directed self-assemblies in the solid state of retro Aib bis-peptide dicarboxylic acids; a design strategy for...

Self-assembly patterns as a function of the central core insert in the retro bis-peptide dicarboxylic acids HO-Aib-X-Aib-OH, containing oxalyl (-CO-CO-; 1), fumaryl (-CO-CH = CH-CO-; 2), and adipoyl [-CO-(CH2)4-CO-; 3], have been characterized by single crystal x-ray diffraction analyses. Extensive hydrogen bonding occurs in each crystal but there are no OH ... O binds between acid groups. Only two types of hydrogen bonds occur in all the crystals: NH ... O (acid terminal), 2.84-2.98 A and OH (acid terminal) ... O (core carbonyl), 2.55-2.67 A (except for an additional intramolecular C5 type bond in the oxalyl moiety in 1). The self-assembly patterns are a beta-network in 1, separate layer assemblies (beta-networks) for two independent molecules in 2 that combine into a three-dimensional gamma network, and separate ribbon assembles (alpha networks) for two independent molecules in 3 that combine into an extended beta-network sheet with hydrophobic faces.