On the energetic and structure of 2-piperidinic acid

In this paper we investigate, by means of ab initio (RHF) and density functional theory calculations, the energetic, electronic and structural properties of the 2-piperidinic acid, in gas phase and explicitly interacting with a number of water molecules. We find that two water molecules, placed in the vicinity of the amino acid, are needed in order to stabilize the zwitterionic structure. These two water molecules and the amino acid form a cyclic structure that maximizes the hydrogen bond cooperativity. These results are compared with the crystal structure of the 2-piperidinic acid.