L-histidine iodides

In the present work we investigated salt formation in the L-histidine(L-His) + HI + H2O system. Single crystals of six salts have been obtained and their crystal and molecular structures have been determined: monoclinic (L-HisH)I (I), monoclinic (L-HisH)I (II), orthorhombic (L-HisH)I (III), (L-HisH2)I2 (V), (L-HisH2)I2·H2O (VI) and (L-HisH···L-HisH2)I3 (VII). One more, a triclinic polymorph (L-HisH)I (IV) has been obtained from aqueous solution containing L-histidine and HI in presence of L-proline. Infrared spectra of all seven crystals are showed and compared. Salts formed in this system differ from the salts formed in the previously investigated L-His + HF + H2O, L-His + HCl + H2O and L-His + HBr + H2O systems. Particularly, in addition to the salts formed by singly (L-HisH) and doubly (L-HisH2) charged cations we obtained a salt with (A+···A2+) type dimeric cation. Previously salts with (A+···A2+) type dimeric cation were obtained only for mixed salts with different anions. This finding may lead to reinvestigation of salts formation with ornithine, lysine, arginine and histidine capable forming singly and doubly charged cations.