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 | Chapter 1 | Chemistry and Biochemistry: Research Progress Vol. 1

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.

These results (slight increase in ∆Cp° 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 ∆Cp°), and 2) some changes in the solvation pattern, that is, progressively greater steric hindrance (tending to increase ∆Cp° value by exclusion of solvent).

 

Author (s) Details

 

Rabindra N. Roy
Hoffman Department of Chemistry, Drury University, Springfield, MO, USA.

 

Lakshmi N. Roy
Hoffman Department of Chemistry, Drury University, Springfield, MO, USA.

 

Katherine E. Hundley
Hoffman Department of Chemistry, Drury University, Springfield, MO, USA.

 

Taylor R. Wehmeyer
Hoffman Department of Chemistry, Drury University, Springfield, MO, USA.

 

Lucas S. Tebbe
Hoffman Department of Chemistry, Drury University, Springfield, MO, USA.

 

Please see the book here:- https://doi.org/10.9734/bpi/cbrp/v1/3470