HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) is a

zwitterion In chemistry, a zwitterion ( ; ), also called an inner salt or dipolar ion, is a molecule that contains an equal number of positively and negatively charged functional groups. : (1,2- dipolar compounds, such as ylides, are sometimes excluded from ...

sulfonic acid In organic chemistry, sulfonic acid (or sulphonic acid) refers to a member of the class of organosulfur compounds with the general formula , where R is an organic alkyl or aryl group and the group a sulfonyl hydroxide. As a substituent, it is kn ...

buffering agent A buffer solution is a solution where the pH does not change significantly on dilution or if an acid or base is added at constant temperature. Its pH changes very little when a small amount of strong acid or base is added to it. Buffer solution ...

. It is one of the twenty

Good's buffers Good's buffers (also Good buffers) are twenty buffering agents for biochemistry, biochemical and biology, biological research selected and described by Norman Good and colleagues during 1966–1980. Most of the buffers were new zwitterionic compoun ...

. HEPES is widely used in

cell culture Cell culture or tissue culture is the process by which cell (biology), cells are grown under controlled conditions, generally outside of their natural environment. After cells of interest have been Cell isolation, isolated from living tissue, ...

, largely because it is better at maintaining physiological pH despite changes in

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

concentration (produced by

aerobic respiration Cellular respiration is the process of oxidizing biological fuels using an inorganic electron acceptor, such as oxygen, to drive production of adenosine triphosphate (ATP), which stores chemical energy in a biologically accessible form. Cellu ...

) 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 Riboflavin, also known as vitamin B2, is a vitamin found in food and sold as a dietary supplement. It is essential to the formation of two major coenzymes, flavin mononucleotide and flavin adenine dinucleotide. These coenzymes are involved in ...

when exposed to ambient light to produce

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

. 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 Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

. HEPES has the following characteristics: * p''K''_a1 (25 °C) = 3 * p''K''_a2 (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.

References

{{DEFAULTSORT:Hepes Hydroxyethyl compounds Piperazines Buffer solutions Sulfonic acids Ethanolamines

See also

References