Polymorphism of L-nitroargininium bromide monohydrate

We have found that L-nitroargininium bromide monohydrate (L-NNA center dot HBr center dot H2O) has two polymorphic (a and (3) forms. Vibrational spectra of L-NNA center dot HBr center dot H2O (alpha and beta forms) and the previously known L-NNA center dot HCl center dot H2O are reported. On the basis of vibrational spectra it is concluded that alpha-form L-NNA center dot HBr center dot H2O is isostructural with L-NNA center dot HCl center dot H2O, in the structure of which carboxyl groups form hydrogen bonds with chloride ions. We have determined crystal and molecular structures of beta-form L-NNA center dot HBr center dot H2O. Unlike L-NNA center dot HCl center dot H2O and therefore a-form L-NNA center dot HBr center dot H2O, in the structure of beta-form carboxyl group forms strong hydrogen bond with water molecule. Similarity of the structure of beta-form L-NNA center dot HBr center dot H2O with the structure of anhydrous L-nitroarginine methyl ester hydrochloride is revealed, which happens because OH3 grouping serves as methyl group. IR spectra of anhydrous specimens L-NNA center dot HCl and L-NNA center dot HBr (alpha and beta forms) are reported as well. (c) 2007 Elsevier B.V. All rights reserved.