X-Ray Studies on Crystalline Complexes Involving Amino Acids and Peptides. Part XX. Crystal Structures of DL-Arginine Acetate Monohydrate and DL-Lysine Acetate and a Comparison with the Corresponding L-Amino Acid Complexes

Abstract

Crystals of DL-arginine acetate monohydrate, C6H15N4O2+C2H3O2-.H2O, are monoclinic, P2(1)/c, with a = 13.552(2), b = 5.048(2), c = 18.837(3) A, beta = 101.34(2) degrees and Z = 4, and those of DL-lysine acetate, C6H15N2O2+.C2H3O2- are triclinic, P1, with a = 5.471(2), b = 7.656(2), c = 12.841(2) A, alpha = 94.48(1), beta = 94.59(2), gamma = 98.83(2) degrees and Z = 2. The structures have been solved by direct methods and refined to R = 0.058 and 0.077 for 1522 and 1259 observed reflections respectively. The difference in the number and the nature of proton donors leads to a difference in hydrogen bond density in the two structures. The basic elements of aggregation in both the structures are pairs of amino acid molecules, each pair stabilized by two centrosymmetrically related hydrogen bonds involving alpha-amino and alpha-carboxylate groups, stacked along the shortest dimension to form columns. The pairs are held together in each column by head-to-tail sequences. The columns stack along a crystallographic axis to form layers. Adjacent layers are bridged by acetate ions. The amino acid-acetate interactions are primarily through side chains and involve specific interactions and characteristic interaction patterns. The gross features of molecular aggregation are nearly the same in DL-arginine acetate monohydrate and L-arginine acetate whereas they are substantially different in the lysine complexes. In both cases, one of the two head-to-tail sequences in the L complex is replaced by a hydrogen bonded loop involving alpha-amino and alpha-carboxylate groups, in the DL complex. This may have implications for prebiotic condensation during chemical evolution.

X-ray studies on crystalline complexes involving amino acids and peptides. XXV. Structures of DL-proline hemisuccinic acid and glycyl-L-histidinium semisuccinate monohydrate and a comparative study of amino-acid and peptide complexes of succinic acid

“…Earlier work in this laboratory (Vijayan, 1988;Soman, Rao, Radhakrishnan & Vijayan, 1989;Soman & Vijayan, 1989) and the present work also demonstrate that amino acids, peptides, and other relevant molecules in different combinations give rise to different, often predictable, aggregation patterns with characteristic features. The elucidation of the geometrical features of several possible specific interactions, characteristic interaction patterns and aggregation patterns is a precondition for understanding the self-assembly processes that may have led to the first multimolecular systems.…”

Environment-induced stabilization of hydrogen-bonded dimers in crystal of lysine (5-methyl-1H-[1,2,4]triazol-3ylsulfanyl)-acetate

“…The salts of lysine with various organic acids were extensively studied [7][8][9][10][11][12][13][14][15][16][17][18]. These studies provide essential information about molecular structure, tautomeric properties of AA and intermolecular interaction patterns.…”

X-ray studies on crystalline complexes involving amino acids and peptides. XXX. Structural invariance and optical resolution through interactions with an achiral molecule in the histidine complexes of glycolic acid

“…The glycolate complex of OL-histidine could not be compared with the corresponding acetate complex as the structure of the latter is not available. However, it may be mentioned that the relative invariance of aggregation patterns with respect to changes in the size and nature of molecules present in the system is a recurring theme in the study of crystalline complexes involving amino acids (Suresh & Vijayan, 1983b;Soman, Rao, Radhakrishnan & Vijayan, 1989;. Such patterns involving hydrogen bonding have been a feature of aggregation of other organic molecules as well (Bernstein, Davis, Shimoni & Chang, 1995).…”

“…As in many other binary complexes involving amino acids (Vijayan, 1988;Soman, Rao, Radhakrishnan & Vijayan, 1989;Prasad & Vijayan, 1991;, the unlike molecules aggregate into separate alternating layers in DL-histidine glycolate. Two sets of hydrogen bonds stabilize the histidine layer parallel to the ab plane.…”

“…The present focus of the programme is on complexes of amino © 1996 International Union of Crystallography Printed in Great Britain -all rights reserved acids with simple molecules that are believed to have existed on the primitive earth (Kvenvolden, Lawless & Ponnamperuma, 1971;Miller & Orgel, 1974). Complexes of this type analysed so far involve succinic, acetic and formic acids (Suresh & Vijayan, 1983a,c;Soman, Rao, Radhakrishnan & Vijayan, 1989;Prasad & Vijayan, 1990, 1993aSuresh, Prasad & Vijayan, 1994;Suresh, Padmanabhan & Vijayan, 1994;. These analyses have provided useful information on the effect of simple carboxylic acids on amino acid aggregation, amino acid-carboxylic acid interactions and the structural behaviour of the two types of molecules in the presence of each other.…”