The crystal and molecular structure ofl-ornithine hydrochloride

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Abstract
Crystals of ornithine hydrochloride, C 5 H 12 N 2 O 2 · HCl belong to the monoclinic space group P 2 1 with cell dimensions a = 4.99 Å, b = 8.00 Å, c = 10.00 Å and β = 97°. The number of molecules per unit cell is two. The structure has been solved by three-dimensional Patterson and heavy-atom Fourier syntheses. The hydrogen positions have been located from a three-dimensional difference Fourier synthesis. The positional coordinates of all the atoms, together with their temperature factors (anisotropic for non-hydrogen atoms and isotropic for hydrogen atoms), have been refined by three-dimensional least-squares method. The R value at the end of the refinement is 0.064. The bond lengths and bond angles of ornithine hydrochloride have been compared with those of other amino acids, particularly arginine dihydrate and lysine hydrochloride. The molecule is a zwitterion, with both the alpha and terminal amino nitrogen atoms accepting an extra proton each. The side chain of this molecule has a fully extended configuration. Both the amino nitrogen atoms assume tetrahedral configuration and interlink the molecules in the crystal by a three-dimensional network of hydrogen bonds of the types N–H···Cl − and N–H···O.