Aggregation studies in crystals of apolar helical peptides: Boc-Aib-Val-Ala-Leu-Aib-Val-Ala-Leu-Aib-OMe

Abstract

In the crystal, the backbone of Boc-(Aib-Val-Ala-Leu)₂-Aib-OMc adopts a helical form with four α-type hydrogen bonds in the middle, flanked by 3₁₀-type hydrogen bonds at either end. The helical molecules stack in columns with head-to-tail hydrogen bonds, either directly between NH and CO, or bridged by solvent molecules. The packing of the helices is parallel, even in space group P2₁. Cell parameters are a = 9.837(2) Å. b = 15.565(3) Å. c = 20.087(5) Å, β= 96.42(2)°. d_calc= 1.091 g/cm³ for C₄₆H₈₃,N₉O₁₂· 1.5H₂O·0.67CH₃OH. There appears to be some hydration of the backbone in this apolar helix.