Supramolecular Walls from Cyclic Peptides: Modulating Nature and Strength of Weak Interactions

Both macrolactams cyclo-[NH-CH2-C C-CH2-C(Me)(2)-CO](n) (n = 3 and n = 2) have been synthesized and crystallized. They have respectively one intramolecular hydrogen bond and no such bond. Both macrocycles self-assemble as parallel supramolecular walls with or without inclusion of solvent between them. The units of the former (n = 3) are held together by NH center dot center dot center dot pi/NH center dot center dot center dot OC interactions, whereas they are glued by a very dense network of classical parallel-oriented hydrogen bonds, involving all the amides of the rings, in the latter (n = 2). In that case, the bulky C(Me)(2) groups are located on the surface of the walls and can be held responsible for the piling process of the layers, by means of attractive van der Waals interactions. This spatial arrangement recalls the 3D structure of cellulose, where all constitutive sheets stack mostly via van der Waals forces.