Bis(L-proline) hydrogen nitrate

In the title compound, 2C(5)H(9)NO(2).H+.NO3-, the two proline residues are linked by a strong O-H...O hydrogen bond, with an O...O distance of 2.414 (3) Angstrom. 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.