Thermodynamics of proton dissociations from aqueous threonine and isoleucine at temperatures from (278.15 to 393.15)K, molalities from (0.01 to 1.0)mol·kg−1, and at the pressure 0.35MPa: Apparent molar heat capacities and apparent molar volumes of zwitterionic, protonated cationic, and deprotonated anionic forms

Thermodynamics of proton dissociations from aqueous l-methionine at temperatures from (278.15 to 393.15)K, molalities from (0.0125 to 1.0)mol·kg−1, and at the pressure 0.35MPa: Apparent molar heat capacities and apparent molar volumes of l-methionine, methioninium chloride, and sodium methioninate

“…Our iterative Young's Rule results lead to calculated values of D r C p,m , D r H m , pQ a , D r S m , and D r V m for reactions (5) and (6) as functions of T and m as described by Ziemer et al [1]. Figure 7 shows D r C p,m (T, m) for reactions (5) and (6).…”

“…Figure 7 shows D r C p,m (T, m) for reactions (5) and (6). We are unable to find in the literature any previous measurements of D r C p,m for either reaction (5) or (6).…”

“…where Y /,tot is the apparent molar property of the mixture, Y rel results from shifts in the equilibrium position by reaction (5) or (8) from perturbation of T or p during the measurement (or calculation) of the property Y /,tot , m is the stoichiometric molality of the limiting reagent in the solution [m = m{HMet ± (aq)} < m{HCl(aq)} for reaction (5) and m = m{HMet ± (aq)} < m{NaOH(aq)} for reaction (8)}], m(i) is the molality of species i, Y / (i) is the apparent molar property C p,/ (i) or V / (i) of species i, and m t is given by equation (10):…”

“…Reference values at T = 298.15 K used as integration constants in this report are pK a = (2.2 6 ± 0.2 0 ) and D r H m ¼ ð1:2 7 AE 0:5 5 Þ kJ Á mol À1 for reaction (5), and pK a = (9.2 1 ± 0.2 1 ) and D r H m ¼ ð43:4 1 AE 0:4 1 Þ kJ Á mol À1 for reaction (6). The value used for pK a of reaction (5) is the average of the values reported at T = 298.15 K in references [26][27][28][29][30][31][32][33].…”

“…We have studied the most simple amino acid glycine [1], the aliphatic amino acids valine [2], L-2-aminobutanoic acid [2], proline [3], alanine [4], and isoleucine [5], as well as the heteroatomic threonine [5], serine [6], and histidine [7,8]. Our current work focuses on aqueous L-methionine.…”