Odd-even effects in supramolecular assemblies of diamide bolaamphiphiles

Bolaamphiphiles ("bolas") containing two secondary amide groups at the ends of an oligomethylene chain and two amino acid type headgroups were synthes ized. The structures of crystals, of noncovalent fibers, and of surface mon olayers on gold strongly depended on odd-even effects. In the crystal struc tures of alanine-alanine dipeptides with C-11- and C-12-alpha,omega -amino acid linkers, helical (even number of methylene groups in the chain) or she etlike (odd) arrangements of the headgroups were found. Bolas containing tw o different amino acid end groups, namely, D- or L-alanine and L-lysine, co nnected by the same C-11- and C-12 linkers did not crystallize. Only the ev en-numbered bolas gave fibers. L- and D- configurations of alanine headgrou ps affected the curvature of the fibers. Diamido bolas with terminal SK-gro ups self-assembled on gold. Only those with even-numbered chains gave rigid monolayers. Simple stereochemical arguments concerning the fitting of amid e hydrogen bond chains on both ends of the bolas are given to explain the o bserved differences in crystals, fibers, and monolayers.