The role of H-bonding in the structure of the 4-piperidinecarboxylic acid monohydrate

In this work we have investigated the hydrogen bond scheme of 4-piperidinecarboxylic (isonipecotic) acid by means of X-ray diffraction, NMR spectroscopy and semi-empirical calculations. The 4-piperidinecarboxylic acid displays a three-dimensional assembly of hydrogen bonds. Hence, infinite chains of amino acid molecules linked by amino-carboxylate intermolecular hydrogen bonds run parallel to the b and c axes; additionally, chains of amino acid molecules intercalated with water molecules held together by water-carboxylate hydrogen bonds run parallel to the a axis. The theoretical calculations show large cooperative effects for the first of the amino acid chains mentioned above, which is manifested as shortening on the amino-carboxylate hydrogen bond distances and decreasing of the hydrogen bond enthalpies per monomer of the hydrogen bonded clusters, with increment of monomers in the chain.