The Thermodynamics of Ionization of Amino Acids. I. The Ionization Constants of γ-Aminobutyric Acid

Abstract

The electromotive forces of cells with hydrogen and silver-silver chloride electrodes which contained buffer mixtures either of -aminobutyric acid and hydrochloric acid or of the amino acid, its sodium salt, and sodium chloride were measured at 5°i ntervals from 10 to 50°. From these data the thermodynamic ionization constants, K¡ for the ionization of the carboxyl group and K2 for the ionization of the ammonium group, were calculated. The changes in free energy, enthalpy, entropy and heat capacity associated with the ionization in the standard state can be obtained from the equations -log K¡ = (1209.

GABA-Controlled Synthesis of the Metastable Polymorphic Form and Crystallization Behavior with a Chiral Malic Acid

“…Furthermore, the proton transfer between GABA and GABA-H + (Figure ) is at equilibrium at a p K a 1 value of 4.038 . Thus, at pH 4 the zwitterionic form and the protonated form are balanced.…”

“…At molar fraction 0.5, the pH is defined as p K a 1 4.038. The plotted data are based on equations stated in the Supporting Information, eq S1 …”

“…Malic acid (p K a 3.4), which, in contrast to tartaric acid (p K a 2.9), has one less hydroxyl group, was chosen. Applying this rule of thumb to GABA (p K a 4.038) and the malic acid results in a Δp K a around 0.6. At this range, the probability of cocrystal formation is quite high .…”

Surprising Effect of Carbon Chain Length on Inducing Ability of Additives: Elusive Form-II of γ-Aminobutyric Acid (GABA) Induced by Sodium Carboxylate Additives

“…Distribution curves of different ionic species of GABA at different pH values (blue area: pH range of GABA supersaturated solution contained 2–10% sodium acetate; 20 °C: p K a 1 = 4.038, p K a 2 = 10.706; corresponding calculation formulas are displayed in the Supporting Information S3). …”