Thermodynamics of the first and second proton dissociations from aqueous l-aspartic acid and l-glutamic acid at temperatures from (278.15 to 393.15) K and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of zwitterionic, protonated cationic, and deprotonated anionic forms at molalities from (0.002 to 1.0) mol · kg −1

• Published in: The Journal of chemical thermodynamics Vol. 39; no. 4; pp. 645 - 666
• Main Authors: Ziemer, S.P., Woolley, E.M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 2007; Elsevier
• Subjects: 2-Aminobutanedioic acid; 2-Aminoglutaric acid; 2-Aminopentanedioic acid; 2-Aminosuccinic acid; Acidity; Apparent molar heat capacity; Apparent molar volume; Chemical thermodynamics; Chemistry; Exact sciences and technology; General and physical chemistry; l-Aspartic acid; l-Aspartinium chloride; l-Glutamic acid; l-Glutaminium chloride; Mixtures; Monosodium l-aspartate; Monosodium l-glutamate; Proton dissociations; Thermodynamic properties; Young’s Rule; Zwitterion; 2-Aminosuccinic acid; Young’s Rule; Apparent molar heat capacity; Monosodium l-glutamate; 2-Aminoglutaric acid; Zwitterion; Acidity; l-Aspartic acid; 2-Aminopentanedioic acid; l-Glutamic acid; l-Glutaminium chloride; Proton dissociations; Monosodium l-aspartate; l-Aspartinium chloride; Apparent molar volume; 2-Aminobutanedioic acid; Glutamic acid; Molar volume; Dissociation constant; Density; Thermodynamics; Chlorides; L-Aspartinium chloride; L-Glutaminium chloride; Aspartic acid; Molality; Chemical properties; L-Glutamic acid; Heat capacity; Sodium compound; Young's Rule; Thermal properties; α-Aminoacid; Monosodium L-aspartate; Monosodium L-glutamate; Apparent quantity; L-Aspartic acid; Aqueous solution; Thermodynamic properties; Betaines
• ISSN: 0021-9614; 1096-3626
• DOI: 10.1016/j.jct.2006.08.008

We have measured the densities of aqueous solutions of l-aspartic acid, l-glutamic acid, and equimolal solutions of these two amino acids with HCl and with NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, at molalities 0.002 ⩽ m/mol · kg −1 ⩽ 1.0 as solubity of the solutes allowed, and at p = 0.35 MPa using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a twin fixed-cell differential temperature-scanning calorimeter. We used the densities to calculate apparent molar volumes V ϕ and the heat capacities to calculate apparent molar heat capacities C p, ϕ for these solutions. We used our results and values from the literature for V ϕ ( T, m) and C p, ϕ ( T, m) for HCl(aq), NaOH(aq), and NaCl(aq) and the molar heat capacity change Δ r C p,m ( T, m) for ionization of water to calculate parameters for Δ r C p,m ( T, m) for the first two proton dissociations from each of the protonated aqueous cationic amino acids. We used Young’s Rule and integrated these results iteratively to account for the effects of equilibrium speciation and chemical relaxation on V ϕ ( T, m) and C p, ϕ ( T, m). This procedure gave parameters for V ϕ ( T, m) and C p, ϕ ( T, m) for l-aspartinium and l-glutaminium chlorides and for monosodium l-aspartate and l-glutamate which modeled our observed results within experimental uncertainties. We report values for Δ r C p,m , Δ r H m, pQ a, Δ r S m, and Δ r V m for the first and second proton dissociations from protonated aqueous l-aspartic acid and l-glutamic acid as functions of T and m.