Precision neutron diffraction structure determination of protein and nucleic acid components. VIII: the crystal and molecular structure of the β-form of the amino acidl-glutamic acid

Abstract

A neutron diffraction study of the β-form of L-glutamic acid, C₅H₉NO₄, has been carried out. The structure is orthorhombic: space groupP2₁2₁2₁,a= 5·159(5),b= 17·30(2),c= 6·948(7) Å andz = 4. Least-squares refinements based on 803 reflexions led to a final conventionalR value of 0·026, and bond lengths involving hydrogen atoms have been determined with an average precision of 0·004 Å. The molecule is in the zwitterion form, and no intramolecular hydrogen bonds have been found. The hydrogen atom involved in a strong hydrogen bond between two carboxyl groups in adjacent molecules (0 ... 0 distance 2·519(2) Å) is covalently bonded to the carboxyl group belonging to the side chain of the amino acid. This side chain is buckled with C^δ gauche to C^α with respect to the C^β—C^γ bond. The bond angles involving carbon atoms in the side chain are accordingly strained.