STRUCTURAL FEATURE AND MOLECULAR INTERACTION OF BASIC-AMINO-ACID PICRIC ACID COMPLEXES BY X-RAY CRYSTAL ANALYSES

As a part of elucidating the structural features of a host molecule ne cessary for the recognition of basic amino acids, the crystal structur es of the picrates of DL-arginine (1), L-arginine (2), L-lysine (3) an d L-ornitine (4) have been determined by X-ray analyses, The molecular packing pattern is found to be common in these crystal structures, Th e picric acids themselves form layers perpendicular to a crystallograp hic axis, and respective basic amino acids are packed into these layer s, where the amino acids themselves also form singly or doubly arrange d layers in a head-to-tail fashion and are stabilized by hydrogen bond s between the alpha-carboxyl and guanidyl or terminal amino groups, Th e picric acid interacts with the amino acid by three to seven NH(amino acid)... O(picric acid) hydrogen bonds, A notable feature of the mole cular interaction commonly found in complexes 1-4 is the simultaneous fixation at three portions of the amino acid (alpha-amino, alpha-carbo xyl and terminal amino or guanidyl groups) by a hydrogen bond and/or e lectrostatic interactions, In conclusion, it was shown that both the c rystal packing and the molecular interaction modes are important for t he complex formation between the basic amino acid and picric acid mole cules.