Various patterns of foldameric oligomers formed by trans-ABHC ((1S,2S,3S, 5S)-2-amino-6,6-dimethylbicyclo-[3.3.1]heptane-3-carboxylic
acid) and beta(3)-hSer residues were studied. NMR, ECD and molecular modelling demonstrated
that octameric and nonameric sequences with multiple i-i+3 ABHC pair repulsions attain
the beta-H18 helix in CD3OH. As a close relative of the alpha-helix, this helix type
is stabilized by i-i+4 backbone H-bond interactions. The formation of the beta-H18
helix was found to be solvent-and concentration-dependent. Upon dilution, the beta-H18
-> beta-H12 helix transition was revealed by concentration-dependent ECD, DOSY-NMR
and TEM measurements.