Acta Crystallographica Section B

Structural Science

Volume 56, Part 4 (August 2000)

research papers

Acta Cryst. (2000). B56, 690-696 [ doi:10.1107/S0108768100002202 ]

X-ray studies on crystalline complexes involving amino acids and peptides. XXXV. Invariance and variability in amino acid aggregation in the complexes of maleic acid with L-histidine and L-lysine

J. V. Pratap, R. Ravishankar and M. Vijayan

Abstract: The crystal structures of complexes of maleic acid with L-histidine and L-lysine have been determined. The two crystallographically independent amino acid molecules in the L-histidine complex have different closed conformations, while the lysine molecule in its complex has the most favourable conformation sterically with an all-trans sidechain trans to the [alpha] -carboxylate group. The maleic acid molecules exist as semi-maleate ions of similar conformation and contain a symmetric OHO hydrogen bond. Amino acid cations and semi-maleate anions aggregate into alternate layers in both the structures. The arrangement of molecules in the histidine layer in L-histidine semi-maleate is closer to that in the crystals of the free amino acid than in other L-histidine complexes. On the other hand, the arrangement of lysine molecules in its semi-maleate complex is different from any observed so far. However, the well established characteristic interaction patterns involving amino and carboxylate groups still play a major role in holding the molecules together in the crystal of the complex.

Keywords: Amino acids; Peptides; Aggregation; Histidine and lysine complexes.