1-Piperazineethanesulfonic acid, 4-(2-hydroxyethyl)- 4-(2-Hydroxyethyl)-1-piperazineethanesulfonic acid 7365-45-9 HEPES N-2-Hydroxyethylpiperazine N',2'-ethanesulfonic acid N-2-Hydroxyethylpiperazine-N'-ethanesulfonate N-2-Hydroxyethylpiperazine-N'-ethanesulfonic acid N-2-Hydroxyethylpiperazine-N-ethane sulfonic acid NSC166663