HEPES

The crystal structure of HEPES [4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, C₈H₁₈N₂O₄S] is presented. This widely used buffer crystallizes as a zwitterion, the N10 atom of the piperazine ring being the protonation site. The molecules form a network of hydrogen bonds involving both nitrogen atoms of the piperazine moiety. The piperazine ring adopts a chair conformation.

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