( S )-2-Carb-oxy-ethyl l-cysteinyl sulfone.

The title compound {systematic name: (2 S )-2-aza-niumyl-3-[(2-carb-oxy-ethane)-sulfon-yl]propano-ate}, C 6 H 11 NO 6 S, forms enanti-opure crystals in the monoclinic space group P 2 1 and exists as a zwitterion, with a protonated α-amino group and a deprotonated α-carboxyl group. Both the carboxyl groups and the amino group are involved in an extensive multicentered inter-molecular hydrogen-bonding scheme. In the crystal, the diperiodic network of hydrogen bonds propagates parallel to (101) and involves inter-connected heterodromic R 4 3 (10) rings. Electrostatic forces are major contributors to the structure energy, which was estimated by DFT calculations as E total = -333.5 kJ mol -1 .