X-RAY STUDIES ON CRYSTALLINE COMPLEXES INVOLVING AMINO-ACIDS AND PEPTIDES .32. EFFECT OF CHIRALITY ON IONIZATION STATE, STOICHIOMETRY AND AGGREGATION IN THE COMPLEXES OF OXALIC-ACID WITH DL-LYSINE AND L-LYSINE

Crystals of the oxalic acid complex of DL-lysine (triclinic P (1) over bar; a = 5.540(1), b = 10.764(2), c = 12.056(2) Angstrom, a = 77.8(1) , beta = 80.6(1), gamma = 75.6(1)degrees; R = 4.7% for 2023 observed r eflections) contain lysine and semioxalate ions in the I:I ratio, wher eas the ratio of lysine and semioxalate/oxalate ions is 2:3 in the cry stals of the L-lysine complex (monoclinic P2(1); a = 4.906(1), b = 20. 145(4), c = 12.455(1) Angstrom, beta = 92.5(1)degrees; R = 4.4% for 14 94 observed reflections). The amino acid molecule in the L-lysine comp lex has an unusual ionisation state with positively charged ex-and sid e-chain amino groups and a neutral carboxyl group. The unlike molecule s aggregate into separate alternating layers in the DL-lysine complex in a manner similar to that observed in several of the amino acid comp lexes. The L-lysine complex exhibits a new aggregation pattern which c annot be easily explained in terms of planar features, thus emphasizin g the fundamental dependence of aggregation on molecular characteristi cs. Despite the differences in stoichiometry, ionisation state and lon g-range aggregation patterns, the basic element of aggregation in the two complexes exhibits considerable similarity. (C) Munksgaard 1997.