Incipient type II β-turn, internal water bridge and head-to-tail sequence in the structure of tri-α-aminoisobutyric acid dihydrate

Abstract

C₁₂H₂₃N₃O₄.2H₂O, M_r = 309, monoclinic, P2₁, a =8.504 (2), b = 11.287 (2), c = 8.922 (2) Å, β = 108.65 (1)Å, V= 811.4 (4), ų, Z = 2, D_x = 1.27 (2), D_m = l.26Mg m^-3, λ(Cu Kα)= 1.5418Å, μ = 8.53 cm^-1, F(000) = 336, T= 293 K, final R = 0.040 for 1499 observed reflections. The bond angles in the central residue exhibit conformation-dependent -asymmetry about C^α. The conformation of the molecule corresponds to an incipient type II' (or type II) β-turn. The structure contains an internal water bridge, involving two water molecules, which connects the terminal amino group and the carbonyl group of the second residue. An interesting feature of the crystal is a zigzag head-to-tail sequence centred around a 2₁ screw axis.