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 amine groups, no metal chelation, near physiologic pH range.

  • pKa at 25C of 7.55 (a second one at pH 3 is not of interest)
  • usable buffering range of 6.8 to 8.2
  • molecular weight 238.3
  • ΔpKa/ΔT = -.014

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