THE LINEAR TRIPEPTIDE L-ALANYLGLYCYL-L-ALANINE

L-Alanylglycyl-L-alanine, C8H15N3O4, exists as zwitter-ion in the crys tal with the N terminus protonated and the C terminus in an ionized fo rm, Both the peptide units are in trans configurations and deviate sig nificantly from planarity. Backbone torsion angles are psi(1)=172.7(2) , omega(1)=-178.2(2), phi(2)=91.7(2), phi(2)=-151.9(2), omega(2)=-176. 9(2), phi(3)=-71.3(2), phi(31)=-7.0(3) and psi(32) 172.4(2)degrees. Th e protonated NH3+ group forms three hydrogen bonds with atoms of symme try-related molecules.