Conformations of a monodisperse homohexapeptide, Nps‐[Glu(OBzl)]₆‐NHEt, and its critical concentration of β‐form formation in solution

Nps‐[Glu(OBzl)] 6 ‐NHEt has been prepared by coupling Nps‐[Glu(OBzl)] 2 ‐OH with HCl,H‐[Glu(OBzl)] 4 ‐NHEt by means of dicyclohexylcarbodiimide. The ir spectra of its nujol mull show that the hexapeptide has the β‐structure of antiparallel chains. When it is dissolved in dioxane or ethylene dichloride, the hexapeptide consists of a mixture of the β‐form and the solvated σ‐form, but the β‐form can exist only above a certain critical concentration. The critical concentration is about 0.4g dl −1 in dioxane and 0.08g dl −1 in ethylene dichloride, and the content of β‐form increases with increasing concentration above it. The CD of the dioxane and ethylene dichloride solutions shows concentration dependence in visible and uv regions.