title: Redetermination of 2-[4-(2-hydroxy-ethyl)piperazin-1-ium-1-yl]ethanesul-fonate at 100 K.
abstract: The crystal structure of the title compound (common name HEPES), C(8)H(18)N(2)O(4)S, has been redetermined at 100 K in order to properly elucidate the protonation state of the HEPES molecule. The piperazine ring has a chair conformation and one of the N atoms in the ring is protonated, which was not previously reported [Gao, Yin, Yang, & Xue (2004). Acta Cryst. E60, o1328-o1329]. The change of protonation state of the nitrogen atom significantly affects the intermolecular interactions in the HEPES crystal. The structure is stabilized by N-H⋯O and O-H⋯O hydrogen bonds and ionic inter-actions, as the title compound in solid state is a zwitterion. HEPES mol-ecules pack in layers that are held together by ionic and weak inter-actions, while a hydrogen-bonded network connects the layers.
authors.affiliation: University of Virginia, Department of Molecular Physiology & Biological Physics, 1340 Jefferson Park Avenue, Charlottesville, VA 22908, USA.
authors.forename: Pawel
authors.initials: P
authors.lastname: Sledz
authors.forename: Thomas
authors.initials: T
authors.lastname: Minor
authors.forename: Maksymilian
authors.initials: M
authors.lastname: Chruszcz