Domain Swapping in Abiotic Foldamers.

Foldamer sequences that adopt tertiary helix-turn-helix folds mediated by helix-helix hydrogen bonding in organic solvents have been previously reported. In an attempt to create genuine abiotic quaternary structures, i.e. assemblies of tertiary structures, new sequences were prepared that possess additional hydrogen bond donors at positions that may promote an association between the tertiary folds. However, a solid state structure and extensive solution state investigations by Nuclear Magnetic Resonance (NMR) and Circular dichroism (CD) show that, instead of forming a quaternary structure, the tertiary folds assemble into stable swapped-domain dimer motifs. Domain swapping entails a complete reorganization of the arrays of hydrogen bonds and changes in relative helix orientation and handedness that can all be rationalized.