B. Sridhar

l-Valinium picrate

In the title compound, C5H12NO2+·C6H2N3O7−, the carboxyl group of the valinium residue is engaged in a strong hydrogen bond with the picrate anion. The amino group of the l-valinium cation and the picrate anion are held together by an intermolecular hydrogen bond. The valine residue is involved in a zigzag (Z1) head-to-tail sequence.

l-Aspartic acid monohydrate

In the title compound, C4H7NO4·H2O, the screw-related aspartic acid molecules are linked along the a axis by N—H⋯O hydrogen bonds to form helical structures. The adjacent helices are inter-linked through O—H⋯O hydrogen bonds and also by the water molxadecules through N—H⋯O(W) and O(W)—H⋯O hydrogen bonds, to form a three-dimensional network.

Bis(l‐proline) hydrogen nitrate

In the title compound, 2C5H9NO2·H+·NO3−, the two proline residues are linked by a strong O—H⋯O hydrogen bond, with an O⋯O distance of 2.414u2005(3)u2005A. In one of the residues, the pyrrolidine ring adopts an envelope conformation, while in the other it adopts a half-chair conformation. N—H⋯O hydrogen bonds link the two residues to form double-chain structures down the a axis, which are interlinked by N—H⋯O hydrogen bonds involving the O atoms of the nitrate ions.

Bis(l-proline) hydrogen(1+) perchlorate

In the title compound, 2C5H9NO2·H+·ClO4−, two proline residues are linked by a strong O—H⋯O hydrogen bond with an O⋯O distance of 2.474u2005(6)u2005A. Conformational disorder is observed in the pyrrolidine rings of the two proline residues. In one of the residues, both the major and minor conformers adopt conformations intermediate between half-chair and envelope, whereas in the other residue, they adopt envelope conformations. The crystal structure is stabilized by a number of N—H⋯O hydrogen bonds.

β-Alanine β-alaninium picrate

In the title compound, C3H7NO2·C3H8NO2+·C6H2N3O7−, each β-alanine residue forms an asymmetric O—H⋯O hydrogen bond with its inversion-related partner [O⋯O = 2.477u2005(4) and 2.472u2005(4)u2005A], involving disorder of carboxylic acid and carboxylate groups. The crystal structure is further stabilized by N—H⋯O hydrogen bonds.

DL -Valine DL -valinium picrate

The title compound, C5H12NO2+·C6H2N3O7−·C5H11NO2, crystallizes in the monoclinic system with one valinium cation, one valine molxadecule and one picrate anion in the asymmetric unit. In the crystal structure, the valinium cation is linked to the picrate anion via O—H⋯O hydrogen bonds.

l-Me­thionine l-me­thioninium perchlorate monohydrate

In the title compound, C5H12NO2S+·ClO4−·C5H11NO2S·H2O, the l-mexadthionine and l-mexadthioninium residues are linked by a strong O⋯O hydrogen bond [2.500u2005(1)u2005A]. The mexadthionine residue adopts a trans–gauche I–gauche I conformation, while the mexadthioninium residue has a gauche II–trans–gauche I conformation. The mexadthioninium residues in the crystal are engaged in straight (S1) head-to-tail hydrogen bonding, thus forming infinite chains along the b axis.

l-Valine l-valinium perchlorate monohydrate

In the title compound, C5H12NO2+·ClO4−·C5H11NO2·H2O, the valine as a zwitterion and valinium are bonded through a strong O—H⋯O hydrogen bond. Their ammonium groups and the perchlorate ion are held together by hydrogen bonds. Both valine and valinium show gauche-II forms.

l‐Lysine l‐lysinium dichloride nitrate

In the title compound, 2C6H15N2O2+·H+·NO3−·2Cl−, both the monoprotonated lysinium molxadecules are bonded through a strong, nearly symmetric, O—H⋯O hydrogen bond forming a dimer. The O⋯O distance is 2.425u2005(8)u2005A. Molecule I is engaged in a zigzag (Z1) head-to-tail sequence. Both chloride anions link molxadecules I and II through the α- and ∊-amino groups in an infinite chain along the a axis. The nitrate ion shows orientational disorder.

A triclinic polymorph of l‐argininium chloride

The title compound, C6H15N4O2+·Cl−, crystallizes in the triclinic system with two crystallographically independent argininium residues and two chloride ions in the P1 unit cell. In an earlier study, the structure of l-arginine chloride [Mazumdar et al. (1969). Z. Kristallogr. 130, 328–339] was determined in the monoclinic space group P21. In our work, the side-chain conformation has an all-trans form in one of the residues, whereas in the other residue, it is in the gauche I-trans-trans-trans form. All the N atoms, carboxylxadate groups and chloride ions are involved in a hydrogen-bonding network.