HEPES is a common buffering chemical similar to Tris in Tris-HCl buffers and phosphates in PBS. Buffers are used to keep the pH at a certain value and can "buffer" the addition of small amounts of acids/bases.
Property of HEPES
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.
- Chemical formula: C8H18N2O4S
Buffers are typically 1 M, prepared by neutralizing HEPES with sodium hydroxide. HEPES is essentially insoluble until it is neutralized.