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.