Precision neutron diffraction structure determination of protein and nucleic acid components. XIII

A neutron diffraction study of L-glutamine, C s H I o N 2 O a , has been carried out. Space group P212121; Z= 4; a = 16.020 (10), b = 7.762 (6), c = 5 119 (4) ,~. Full-matrix least-squares refinements, including anisotropic temperature factors for all atoms and an extinction correction, have led to a conventional R value of 0.032. The neutron-diffraction results confirm the structure found by X-ray diffraction [Cochran, W. & Penfold, B. R. (1952). Acta Cryst. 5, 644-653] to be essentially correct; the main new feature here is the location of all hydrogen atoms with a precision of 0005/~. The glutamine zwitterions are in the keto form, as expected, and the crystal structure is stabilized by a three-dimensional network of N H . . . O hydrogen bonds. One such hydrogen bond is formed by each of the five hydrogens attached to nitrogen.