Determination of the Appropriate Valence of 1, 4-Piperazinediethanesulfonic Acid (PIPES) in Physiological pH

抄録

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°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. [chemical formula], [chemical formula] The ionic strength of PIPES is calculated as follows. [chemical formula]