Side‐chain conformation in poly(γ‐phenethyl‐L‐glutamate)

Abstract

AbstractX‐ray diffraction and energy‐minimization results are reported for poly(γ‐phenethyl‐L‐glutamate). Orthorhombic unit‐cell parameters of drawn fibers are a = 15.4 Å, b = 26.6 Å, c = 54.4 Å. Atomic coordinates are derived for an α‐helix peptide conformation that corresponds to a calculated side‐chain internal energy minimum. The side‐chain conformation correlates well with the electron density projection; the side chains wrap around the α‐helical main chain with the phenethyl ester group directed toward the N‐terminus. The para‐axis of the benzene ring is inclined at an angle nearly nearly normal to the helix axis. The x‐ray structure factors calculated for this model, when compared to the 10 observed structure factors, yield a crystallographic reliability index of R = 0.23.