HEPES

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N-(2-hydroxyethyl)piperazine-N’-(2-ethanesulfonic acid); 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; CAS NUMBER: 7365-45-9

A Good buffer [1][2][3]. Stable pH vs. temperature, no primary amine groups, no metal chelation, near physiologic pH range.

  • pKa at 25C of 7.55 (7.31 at 37C)
  • a second pKa at pH 3 is not of interest
  • usable buffering range of 6.8 to 8.2
  • molecular weight 238.3
  • ΔpKa/ΔT = -.014
  • HEPES contains tertiary amines, which are reactive under certain conditions. See its structure in the Sigma catalog.
  • Chemical formula: C8H18N2O4S

Buffers are typically 1 M, prepared by neutralizing HEPES with sodium hydroxide. HEPES is essentially insoluble until it is neutralized.

  1. Good NE, Winget GD, Winter W, Connolly TN, Izawa S, and Singh RM. Hydrogen ion buffers for biological research. Biochemistry 1966 Feb; 5(2) 467-77. pmid:5942950. PubMed HubMed [Good66]
  2. Good NE and Izawa S. Hydrogen ion buffers. Methods Enzymol 1972; 24 53-68. pmid:4206745. PubMed HubMed [Good74]
  3. Blanchard JS. Buffers for enzymes. Methods Enzymol 1984; 104 404-14. pmid:6717292. PubMed HubMed [Blanchard84]
All Medline abstracts: PubMed HubMed and
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