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chemical structure of HEPES
CAS number 7365-45-9 YesY
PubChem 23831
ChemSpider 22278 YesY
ChEBI CHEBI:42334 YesY
RTECS number TY2900000
Jmol-3D images Image 1
Molecular formula C8H18N2O4S
Molar mass 238.30 g mol−1
Appearance white crystalline powder
Density Not applicable
Melting point >234-238°C (453-457K)
Solubility in water 40 g/100 ml (20°C)
MSDS External MSDS
R-phrases R36, R37, R38.
S-phrases S26, S36.
Main hazards Irritant.
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid ) is a zwitterionic organic chemical 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 cellular respiration) when compared to bicarbonate buffers, which are also commonly used in cell culture. The dissociation of water decreases with falling temperature, but the dissociation constants (pK) of many other buffers do not change much with temperature. HEPES is like water in that its dissociation decreases as the temperature decreases. This makes HEPES a more effective buffering agent for maintaining enzyme structure and function at low temperatures.[1] Lepe-Zuniga et al. reported a phototoxicity of HEPES when exposed to ambient light by the production of hydrogen peroxide,[2][3] which is not a problem in bicarbonate-based cell culture buffers. It is therefore strongly advised to keep HEPES-containing solutions in darkness as much as possible. Fears that HEPES may serve as a nutrient source for aerobic bacteria have been shown to be unfounded.[citation needed]

HEPES has the following characteristics:

  • pKa (25 °C) = 7.5
  • Useful pH range = 6.8 to 8.2

See also[edit]


  1. ^ Baicu SC, Taylor MJ. (2002). "Acid-base buffering in organ preservation solutions as a function of temperature: new parameters for comparing buffer capacity and efficiency". Cryobiology 45 (1): 33–48. doi:10.1016/S0011-2240(02)00104-9. PMID 12445548. 
  2. ^ Lepe-Zuniga JL, Zigler JS, Gery I (October 1987). "Toxicity of light-exposed Hepes media". J. Immunol. Methods 103 (1): 145. doi:10.1016/0022-1759(87)90253-5. PMID 3655381. 
  3. ^ Zigler JS, Lepe-Zuniga JL, Vistica B, Gery I (May 1985). "Analysis of the cytotoxic effects of light-exposed HEPES-containing culture medium". In Vitro Cell. Dev. Biol. 21 (5): 282–7. doi:10.1007/BF02620943. PMID 4019356. 

External links[edit]

http://www.sigmaaldrich.com/catalog/product/sigma/h3375 https://www.avantormaterials.com/commerce/product.aspx?id=2147508501