HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid ) is a zwitterionic organic chemical buffering agent. HEPES is widely used in cell culture, largely because tests indicate it is better at maintaining physiological pH despite changes in carbon dioxide when compared to bicarbonate buffers.

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The dissociation of water decreases with falling temperature, but the dissociation constants (pK) of phosphate and bicarbonate buffers do not change much with temperature. HEPES is like water in that dissociation decreases as the as temperature decreases. This makes HEPES a preferred 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. For best repeatability of results it is then strongly advised to keep any HEPES containing solution in darkness as much as possible.

Fears that HEPES may serve as a nutrient source for aerobic bacteria have been shown to be unfounded.

References

^ 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. PMID 12445548.

Toxicity of light-exposed Hepes media. Lepe-Zuniga JL, Zigler JS Jr, Gery I. Journal of Immunological Methods. 1987 Oct 23;103(1):145.
Analysis of the cytotoxic effects of light-exposed HEPES-containing culture medium.
Zigler JS Jr, Lepe-Zuniga JL, Vistica B, Gery I., In Vitro Cell Dev Biol. 1985 May;21(5):282-7.

Categories: Alcohols | Amines | Buffers | Sulfonic acids

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "HEPES". A list of authors is available in Wikipedia.