HEPES

HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) is a zwitterionic sulfonic acid buffering agent; one of the twenty Good's buffers. HEPES is widely used in cell culture, largely because it is better at maintaining physiological pH despite changes in carbon dioxide concentration (produced by aerobic respiration) when compared to bicarbonate buffers, which are also commonly used in cell culture. Lepe-Zuniga et al. reported an unwanted photochemical process wherein HEPES catalyzes a reaction with riboflavin when exposed to ambient light to produce hydrogen peroxide. This is not a problem in bicarbonate-based cell culture buffers. It is therefore strongly advised to keep solutions containing both HEPES and riboflavin in darkness as much as possible to prevent oxidation.

HEPES
Names
Preferred IUPAC name
2-[4-(2-Hydroxyethyl)piperazin-1-yl]ethane-1-sulfonic acid
Other names
HEPES
Identifiers
3D model (JSmol)
883043
ChEBI
ChemSpider
ECHA InfoCard 100.028.098
EC Number
  • 230-907-9
PubChem CID
RTECS number
  • TL6809000
UNII
  • InChI=1S/C8H18N2O4S/c11-7-5-9-1-3-10(4-2-9)6-8-15(12,13)14/h11H,1-8H2,(H,12,13,14) Y
    Key: JKMHFZQWWAIEOD-UHFFFAOYSA-N Y
  • InChI=1/C8H18N2O4S/c11-7-5-9-1-3-10(4-2-9)6-8-15(12,13)14/h11H,1-8H2,(H,12,13,14)
    Key: JKMHFZQWWAIEOD-UHFFFAOYAC
SMILES
  • OCCN1CC[NH+](CCS(=O)([O-])=O)CC1
Properties
C8H18N2O4S
Molar mass 238.3012 g/mol
Appearance white crystalline powder
Density Not applicable
Melting point >234-238°C (453-457K)
40 g/100 ml (20°C)
Acidity (pKa) 3 (pKa1),
7.5 (pKa2)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Eye Irritant
GHS labelling:
Warning
H315, H319, H335
P261, P264, P270, P271, P280, P301+P312, P302+P352, P304+P312, P304+P340, P305+P351+P338, P312, P321, P322, P330, P332+P313, P337+P313, P362, P363, P403+P233, P405, P501
NFPA 704 (fire diamond)
1
0
1
Flash point Non-flammable
Safety data sheet (SDS)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

HEPES has the following characteristics:

  • pKa1 (25 °C) = 3
  • pKa2 (25 °C) = 7.5
  • Useful pH range = 2.5 to 3.5 or 6.8 to 8.2

HEPES has negligible metal ion binding, making it a good choice as a buffer for enzymes which might be inhibited by metal chelation.

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