X-ray studies on crystalline complexes involving amino acids and peptides. XVI. Structure of L-ornithine D-aspartate monohydrate

Abstract

C₅H₁₃N₂O₂⁺· C₄H₆NO₄^-·H₂O, M_r = 283, monoclinic, P2₁, a = 5.118 (1), b = 7.881 (2), c = 16.025 (2) Å, β = 91.78 (2) °, V = 646.1 (4) ų, Z = 2, D_m = 1.46(2), D_x = 1.45 g cm^-3, λ(Mo Kα) = 0.7107 Å μ = 1.376 cm^-1, F(000) = 304, final R = 0.055 for 1370 observed reflections. The aggregation pattern in the present structure is entirely different from that in L-ornithine L-aspartate hemihydrate. It is similar to that in L-lysine D-aspartate monohydrate in that the unlike molecules aggregate into separate alternating layers, but is different from that in the other LD amino acid-amino acid complexes analysed so far. An interesting feature of the structure is an internal hydrogn bond between the α-amino group and one of the side-chain carboxyl O atoms in the separate ion. The structure contains a closed hydrogen-bonded loop made up of alternating amino and carboxylate groups.