Theoretical study of sheets formed by beta-peptides

Structural and thermodynamic features of the sheets formed by beta-peptides have been studied by quantum mechanics calculations using peptide models. Calculations using dipeptide models indicate that the intrinsic hydrogen bond strength is great for both parallel and antiparallel sheets and that it is little affected by proper substituents. Heterochiral-beta(2,3)-peptides have much stronger sheet-forming propensity than other types of peptides because their favored backbone conformation is ideal for sheet formation. A planar or ideally pleated strand has a curved geometry, which is unfavorable for the formation of sheets. Thus, sheets have to adopt twisted geometries. There is a large cooperativity in the formation of the hydrogen bond network in the sheets of beta-peptides in the perpendicular direction due to long-range electrostatic attractions because all carbonyl groups are roughly in the same direction, in contrast to the situation in beta-sheets of alpha-peptides.