Theoretical study of the secondary structures of unionized Poly(gamma-D-glutamic acid)

Poly(gamma-D-glutamic acid), 1, the only natural gamma-peptides, have many important biological functions. The secondary structures of a hexamer model of unionized gammaDPGA, 3, have been studied by a quantum mechanical method (B3LYP/6-31G*), including the solvent effect using the SCIPCM model. Frequency calculations were carried out using the HF/6-31G* method. Calculations indicate that a right-handed 19-helix is the most stable secondary structure. The calculated electronic circular dichroism spectrum of the right-handed 19-helix agrees with the experimental spectrum quite well, which further supports the above prediction. A right-handed 14-helical structure is also found to be quite stable in the gas phase.Physics, Atomic, Molecular & ChemicalSCI(E)EI0ARTICLE23-242491-249810