X-ray studies on crystalline complexes involving amino acids and peptides. XXVIII. Recurrence of characteristic aggregation and interaction patterns in the crystal structures of DL- and L-lysine formate

Abstract

The crystal structures of L-lysine formate [P2_j, a = 5.431 (1), b = 7.546 (1), c = 12.095 (2)Å, β = 93.42 (1) °, Z = 2] and DL-lysine formate [P2₁/c, a = 10.205(2), b= 11.152 (2), c = 8.491 (1)Å, β = 97.51 (1) °, Z=4] have been determined and refined to R = 0.039 and 0.054 for 1060 and 1689 observed reflections, respectively. Both the structures consist of alternating layers of unlike molecules. The aggregation pattern in the lysine layer in the L-lysine complex, with a straight and a zigzag head-to-tail sequence interconnecting the molecules, is almost the same as that observed in L-lysine acetate, L-lysine L-aspartate and L-lysine D-aspartate. In the DL-lysine complex, hydrogen-bonded dimers of lysine are interconnected by head-to-tail sequences, as in DL-lysine hydrochloride. The structures thus demonstrate the relative invariance of certain aggregation and interaction patterns involving lysine. The relative invariance also extends to interactions between the side-chain amino group and the formate ions.