The crystal structure of L-arginine monohydrobromide monohydrate

Abstract

The crystal of L-arginine monohydrobromide monohydrate belong to space group P2₁, with four molecules of C₆H₁₄O₂N₄HBr·H₂O in the unit cell of dimensions a=11.26Å, b=8.65Å, c=11.25Å, and β=91.5°. The positions of the two bromine atoms in the asymmetric unit were determined from the Patterson projections. A three-dimensional β synthesis based upon these atoms was calculated and this yielded the rest of the structure. The structure was refined by the three-dimensional least-squares method using about 1956 reflections. The final R factor is 0.102. The estimated standard deviations are 0.032 to 0.035Å in bond lengths and about 2° in bond angles. The two crystallographically independent molecules in the asymmetric unit have a pseudotranslation of about c/2 when viewed along the b axis. The bond lengths and bond angles for the two molecules are normal. The two molecules differ in their configurations in the orientation of the guanidyl groups with respect to the aliphatic chain. The arginine molecules occur as zwitterions, both the guanidyl and the amino groups accepting protons from the acid groupings present in the structure.