Determining Thermodynamics of the Second Dissociation Constants of Protonated Piperazine-N, N'-bis-2-Hydroxypropane-Sulfonic Acid POPSO at Different Temperatures from 278.15 to 328.15 K
Chemistry and Biochemistry: Research Progress Vol. 1,
24 January 2025,
Page 1-13
https://doi.org/10.9734/bpi/cbrp/v1/3470
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 \(\pm\)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 ( Go), enthalpy ( Ho), entropy ( So) and heat capacity Cpo were computed from the temperature derivative of the pK2 for the dissociation of the zwitterionic acid POPSO\(\pm\)-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.
These results (slight increase in \(\Delta\)Cpo of POPSO) suggest that the substitution and the presence of an extra monosodium POPSO molecule in POPSO disodium salt apparently have two effects: 1) progressive increase of hydrophobic characters (tending to increase \(\Delta\)Cpo), and 2) some changes in the solvation pattern, that is, progressively greater steric hindrance (tending to increase \(\Delta\)Cpo value by exclusion of solvent).