HEPES
Title: HEPES
CAS Registry Number: 7365-45-9
CAS Name: 4-(2-Hydroxyethyl)-1-piperazineethanesulfonic acid
Additional Names: N-(2-hydroxyethyl)piperazine-N¢-2-ethanesulfonic acid
Molecular Formula: C8H18N2O4S
Molecular Weight: 238.30
Percent Composition: C 40.32%, H 7.61%, N 11.76%, O 26.86%, S 13.46%
Literature References: One of several zwitterionic N-substituted aminosulfonic acids known as Good Buffers, active in the pH range of 6-8.5. Prepn: N. E. Good et al., Biochemistry 5, 467 (1966). Buffering characteristics: W. J. Ferguson et al., Anal. Biochem. 104, 300 (1980). Temperature effects on pKa and pH: R. N. Roy et al., Cryo-Lett. 6, 285 (1985). Interaction with hydroxyl radicals: M. Hicks, J. M. Gebicki, FEBS Lett. 199, 92 (1986). Interference with Lowry protein determination: H. M. Himmel, W. Heller, J. Clin. Chem. Clin. Biochem. 25, 909 (1987). Use as biological buffer: H. Eagle, Science 174, 500 (1971); K. V. Rao, Indian J. Exp. Biol. 15, 552 (1977); E. D. Lalague et al., J. Microsc. 127, 307 (1982); G. I. McFadden, M. Melkonian, Phycologia 25, 551 (1986).
Properties: Crystals from alcohol + water, mp 234°. pKa1 »3, pKa2 (20°) 7.55. DpKa/°C -0.014. Saturated aqueous soln is 2.25M at 0°.
Melting point: mp 234°
pKa: pKa1 »3, pKa2 (20°) 7.55; pKa/°C -0.014
Use: Biological buffer.

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