Conclusions
The lysine amino acid was cocrystallized with an important antiseptic
agent mandelic acid. Single crystal X-ray analysis revealed that there
was a proton transfer from the carboxylic acid group of mandelic acid to
the lysine side chain and lysine also exhibits a zwitterionic form due
to the proton transfer from the carboxylic acid of lysine to the
backbone amino group. The inclusion of water molecules in the crystal
lattice facilitates the formation of intermolecular N–H···O and
O–H···O interactions. The strength and stabilizing/destabilizing nature
of different dimeric complexes were evaluated by the PIXEL energy
analysis. The relative contribution of different inter-contacts was
qualitatively analyzed using Hirshfeld surface analysis and 2D
fingerprint plots. Topological analysis suggested that
N–H+···O- interactions which
emanated from proton transfer between the side chain N2 of lysine and
the carboxylate of the mandelate and between atom backbone N1 and the
carboxylate group of lysine showed intermediate bonding character
between closed and shared shell interactions. Other interactions that
exist in the title complex are closed shell in nature.