%0 Journal Article %T Thermodynamics of the Second Dissociation Constants (pK<sub>2</sub>) of Piperazine-N,N′-bis-2-hydroxypropanesulfonic Acid (POPSO Sesquisodium Salt) and Associated Thermodynamic Functions from (278.15 to 328.15) K %A Rabindra N. Roy %A Lakshmi N. Roy %A Katherine E. Hundley %A Taylor R. Wehmeyer %A Lucas S. Tebbe %J Journal of Biophysical Chemistry %P 143-151 %@ 2153-0378 %D 2014 %I Scientific Research Publishing %R 10.4236/jbpc.2014.54016 %X The second acidic dissociation constants of protonated piperazine-N,N′-bis-2-hydroxypropane-sulfonic acid (POPSO sesquisodium salt) have been determined at 12 different temperatures from (278.15 to 328.15) K including 310.15 K. Electromotive-force measurement technique was used employing hydrogen-silver chloride cells without liquid junction. The results of pK₂ are given by the equation: pK₂ = -1041.77/T + 51.0459 - 6.97646lnT. The uncertainty of the fit is ±0.0008. At 289.15 K, pK₂ = 7.8029; whereas, at 310.15 K (body temperature), pK₂ = 7.6862. Thus, the buffer solutions of POPSO and its sodium salt are useful for pH control in the physiological pH region of (7.0 to 8.5). The changes of Gibbs free energy ( $\"\"$ G°), enthalpy ( $\"\"$ H°), entropy ( $\"\"$ S°) and heat capacity $\"\"$ Cp° were computed from the temperature derivative of the pK₂ for the dissociation of the zwitterionic acid POPSO^±-3 = POPSO^-4 + H⁺ in the standard state. At 298.15 K, these results are compared with those of similar components, which are the derivatives of the parent compounds TAURINE, PIPERAZINE and MORPHOLINE. %K pH %K Buffer Compound %K Liquid Junction %K Thermodynamic Functions %K Activity Coefficients %K Electromotive-Force %K pK< %K sub> %K 2< %K /sub> %U http://www.scirp.org/journal/PaperInformation.aspx?PaperID=51670