Determination of the appropriate valence of 1,4-piperazinediethanesulfonic acid (PIPES) in physiological pH.
1,4-Piperazinediethanesulfonic acid (PIPES), a zwitterion buffer, was titrated with KOH to measure its pH and osmolality. Both pH and osmolality changes showed three phases, and two transition points coincided with pH 5.1 and 10.2. The second phase is important in biological reactions, and from the present results, the pK1 is 3.3 while pK2 is 6.85 at 20 degrees C. The slope of the osmolality curve was 2 mOsm per 1 mM KOH addition in the first and third phases, while it was 1 mOsm per 1 mM KOH in the second phase. The first phase indicates that +/- PIPES +/- changes to -PIPES +/- by the addition of KOH. In the second phase, additional KOH produces -PIPES-. PIPES acts as a divalent ion, at least, in the physiological pH range of around 7.0. Concentrations of -PIPES +/- and -PIPES- around the physiological pH range are calculated as follows. [formula: see text] The ionic strength of PIPES is calculated as follows. [formula: see text]
Hatae
J
J
Department of Physiology, School of Medicine, Fukuoka University, Japan.
Fujishiro
N
N
Kawata
H
H
D017738:Alkanesulfonic Acids / Q000737:chemistry*; D002021:Buffers; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides; D009994:Osmolar Concentration; D010879:Piperazines / Q000737:chemistry*; D017680:Potassium Compounds
D017738:Alkanesulfonic Acids; D002021:Buffers; D006878:Hydroxides; D010879:Piperazines; D017680:Potassium Compounds; C008916:piperazine-N,N'-bis(2-ethanesulfonic acid); C029943:potassium hydroxide