Spectroscopic and crystallographic data are presented for a series of tetrapeptides and analogous depsipeptides that can form a minimal β-hairpin (two intramolecular hydrogen bonds). These model compounds have been used to test the hypothesis that “mirror image” β-turns promote β-hairpin formation. This hypothesis was inspired by a statistical survey of β- hairpins in globular proteins (Sibanda, BL; Thornton, JM Nature 1985, 316, 170), which ...