Abstract: | The tripeptide, L-prolyl-glycyl-glycine, crystallizes in the trigonal space group P32, with a = b = 8.682(2)Å, c= 12.008(2) and Z = 3. The structure was solved by direct methods and refined to an R-value of 0.07 for 727 reflections (I > 1.0s?). The molecule exists as a zwitterion in the crystal. The peptide units and trans and show significant deviations from planarity (ω1 = 169.7o, ω2=-170.1o). The peptide backbone adopts a left-handed helical conformation similar to that of polyglycine II and polyproline II. |