HEPES

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N-(2-hydroxyethyl)piperazine-Nā€™-(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. HEPES is often used to maintain protein solubility in biochemical experiments.

  • 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 the structure of HEPES.
  • 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. PubMed ID:5942950 | HubMed [Good66]
  2. Good NE and Izawa S. Hydrogen ion buffers. Methods Enzymol. 1972;24:53-68. PubMed ID:4206745 | HubMed [Good74]
  3. Blanchard JS. Buffers for enzymes. Methods Enzymol. 1984;104:404-14. PubMed ID:6717292 | HubMed [Blanchard84]
All Medline abstracts: PubMed | HubMed and