HEPES

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

A Good buffer [Good'66 PMID 5942950, Good'74 PMID 4206745, Blanchard'84 PMID 6717292]. 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.

• 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 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. and