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On the helical conformation of un-ionized poly(gamma-D-glutamic acid).

The conformational preferences of the naturally occurring poly(gamma-D-glutamic acid) in the un-ionized state were investigated using a combination of molecular dynamics and quantum mechanical calculations. Results indicated that a left-handed helix with 19-membered ring hydrogen bonds set between the CO of the amide group i and the NH of amide group i + 3 is the most stable conformation for this poly(gamma-amino acid). Weak intramolecular interactions between the oxygens of the carboxyl side groups and the NH of the backbone amide groups were detected. They are assumed to be responsible for the unexpected handedness exhibited by the helix with regards to the stereochemistry of the compound.