PIPES

PIPES (piperazine-N,N′-bis(2-ethanesulfonic acid)) is a Good's buffer of the ethanesulfonic acid series. Its pKa at 25 °C is 6.8, and its useful buffering range is pH 6.1–7.5. Buffers can be prepared by titrating the free acid with a base to the required pH, or by mixing equimolar solutions of the monosodium and disodium salts.

One study states that, of the 20 well-known buffers proposed by Good, all except MES, MOPS and PIPES form metal-ion complexes, which can interfere seriously, particularly in protein analyses. In a separate study, oxidative deposition of iron in ferritin, or autoxidation of iron without protein, produced radicals from the piperazine-ring buffers PIPES, HEPES and EPPS, but not from MES. The authors concluded that piperazine-ring Good's buffers should be avoided in studies of redox processes in biochemistry.

Fixation for electron microscopy. In one study of mammalian and marine tissues, PIPES gave better ultrastructural detail than some common inorganic buffers, especially with long fixation times.

PHEM buffer. PIPES is a component of PHEM buffer (PIPES, HEPES, EGTA and MgCl₂). In one study on mussel gill tissue, PHEM-based fixatives preserved ultrastructure as well as or better than routine fixatives for marine specimens.

Microtubule assembly. PIPES buffer has been used to study the ionic and nucleotide requirements of microtubule polymerisation from purified brain tubulin.

Caspase assays. One study recommended a buffer of PIPES with NaCl, dithiothreitol, EDTA, CHAPS and sucrose, at defined concentrations and pH, as optimal for studying caspases-3, -6, -7 and -8 in vitro.