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.

• pK_a at 25C of 7.55 (7.31 at 37C)
• a second pK_a at pH 3 is not of interest
• usable buffering range of 6.8 to 8.2
• molecular weight 238.3
• ΔpK_a/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. . pmid:5942950. PubMed HubMed [Good66]
2. Good NE and Izawa S. . pmid:4206745. PubMed HubMed [Good74]
3. Blanchard JS. . pmid:6717292. PubMed HubMed [Blanchard84]