X-RAY STUDIES ON CRYSTALLINE COMPLEXES INVOLVING AMINO-ACIDS .1. CRYSTAL-STRUCTURE OF L-LYSINE L-ASPARTATE

Lysine aspartate, a crystalline complex of lysine and aspartic acid, crystallizes in the monoclinic space group P21 with 2 formula units in a unit cell of dimensions a = 5.539 (3), b = 7.848 (4), c = 15.324 (15) .ANG., .beta. = 99.1 (1).degree.. The structure was solved by direct methods and Fourier techniques and refined to an R value of 0.069 for 1134 photographically observed reflections. The dimensions and the conformation of the lysine molecule are similar to those observed in lysine monohydrochloride dihydrate. The side-chain carboxyl group of the aspartate ion is deprotonated unlike that in L- and DL-aspartic acid. The bond lengths and angles in the aspartate ion, except those in the side-chain and carboxylate group, are comparable with those in L- and DL-aspartic acid. Considerable differences exist in the conformation of the molecule in these structures. The crystal structure of lysine aspartate consists of alternating layers, 1 layer comprising lysine molecules and the other, aspartate ions. The 2 layers are interconnected primarily by H-bonds between the side-chain amino group of lysine and carboxylate O atoms belonging to neighboring aspartate ions.