Properties of cyclo-β-tetrapeptide assemblies investigated by means of DFT calculations

We present a theoretical study of structural, energetic, and electronic properties of hollow tubular structures of cyclo-β-tetrapeptides using density functional theory methods. Our calculations consider first a cyclic subunit made of four β-peptide residues, which is fully optimized with gradient-corrected exchange-correlation functionals. Second, we completely optimize the structures of dimer and trimer composed of these ring-shaped subunits. It is found that these tubular structures form strongly hydrogen-bonded systems with interaction energy of −0.86 and −1.68 eV, respectively, after correcting for basis set superposition error. Also, we evaluate the cooperative effects in the trimer formation. This is obtained as ∼19% of the total interaction energy. Considering a decomposition energy scheme, the calculated three-body term corresponds to ∼13% of the total binding energy.