HEPES

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. Hydrogen ion buffers for biological research. Biochemistry. 1966 Feb;5(2):467-77. DOI:10.1021/bi00866a011 |
2. Good NE and Izawa S. Hydrogen ion buffers. Methods Enzymol. 1972;24:53-68. DOI:10.1016/0076-6879(72)24054-x |
3. Blanchard JS. Buffers for enzymes. Methods Enzymol. 1984;104:404-14. DOI:10.1016/s0076-6879(84)04107-0 |