X-ray Studies on Crystalline Complexes Involving Amino Acids and Peptides. XXVII. Effect of Chirality, Specific Interactions and Characteristic Aggregation Patterns in the Structures of Arginine and its Complexes with Formic Acid

Abstract

The crystal structures of DL-arginine dihydrate, DL-arginine formate dihydrate and L-arginine formate have been determined and refined using X-ray crystallographic techniques. The three structures, along with other related ones, demonstrate the conformational variability of arginine. The amino acid molecules aggregate essentially in a similar manner in DL-arginine dihydrate and in the known structure of L-arginine dihydrate; the effects arising out of the reversal of the chirality of half the amino acid molecules are absorbed by small local adjustments. However, such a reversal leads to profound differences in aggregation in DL-arginine and L-arginine formates, in contrast to the situation in the corresponding acetates. Thus the effect of chirality on biomolecular aggregation cannot be easily predicted or even rationalized. Arginine-carboxylate interactions in the complexes primarily involve the guanidyl groups and contain specific interactions. Indeed the primary mode of arginine-carboxylic acid aggregation is substantially invariant in the arginine complexes of succinic, acetic and formic acids.

A molecular orbital study of C–H···Cl– and N–H···Cl– hydrogen bonds. Inferences on selected metal complexes and on protein ClC Cl– channels

“…The corresponding bond lengths and bond angle found at solid state in the structure of DL-arginine dihydrate[46] are 1.461, 1.320, 1.333, 1.335 Å and 118.7, 122.5, 118.8°. This shows that the levels of theory are accurate to compute reliable structures for this type of molecules.…”

X-ray studies on crystalline complexes involving amino acids and peptides. XXXV. Invariance and variability in amino acid aggregation in the complexes of maleic acid with L-histidine and L-lysine

“…The current focus of the program is on complexes of basic amino acids with carboxylic acids which are believed to have existed in the prebiotic milieu (Miller & Orgel, 1974). Complexes involving succinic acid, acetic acid, formic acid, glycolic acid and oxalic acid have already been analysed (Prasad & Vijayan, 1993b;Suresh, Padmanabhan & Vijayan, 1994;Suresh, Prasad & Vijayan, 1994;Suresh & Vijayan, 1995a. These studies yielded unexpectedly interesting results on the variability of the ionization state of the component molecules when they are brought together and its effect on stoichiometry and molecular aggregation, in addition to enriching the general results obtained in previous studies.…”

Amino Acid Structures

“…As far as the racemate of arginine is concerned, there are two crystal phases, both hydrates: DL-arginine monohydrate (Kingsford-Adaboh et al 2000, 2002, measured at 100 K) and DL-arginine dihydrate (Suresh et al 1994). To date, no anhydrous phase of DL-arginine has been reported.…”