Calorimetric investigations of aqueous amino acid and dipeptide systems from 288. 15 to 328. 15 K

Abstract

Densities and heat capacities have been measured for aqueous solutions of L-asparagine, L-glutamine, glycylglycine, glycyl-L-valine, glycyl-L-asparagine, and glycyl-DL-leucine at 288. 15,298.15, 313.15, and 328.15 K. These data have been used to calculate apparent molar volumes, V2,0, and apparent molar heat capacities, Cp,2,0, which in turn have been used to obtain standard state volumes, v;, and heat capacities, c;,,.The semi-empirical modelling procedures of Helgeson, Kirkham, and Flowers have been used to subdivide the calculated standard state volume and heat capacity data into solvation and nonsolvation contributions. The nonsolvation components of the standard state properties are used in group additivity analyses. These analyses yield structural contributions to standard state volumes and heat capacities for the CH(NH,)CO,H, CH,, OH, COOH, CH, CONH,, and CONH groups. The temperature dependences of these contributions are discussed. Some comments are reported concerning the practicality of using the thermodynamic properties of aqueous amino acid and peptide systems as the basis for modelling standard state thermodynamic properties of aqueous protein systems.Key words: heat capacities, densities, volumes, amino acids, peptides, group additivity. On rapporte quelques commentaires relatifs au caractere pratique de l'utilisation des propriCtCs thermodynamiques des systemes aqueux d'acides aminCs et de peptides pour la modClisation des propriCtCs thermodynamiques standard des systkmes aqueux de protkines.

Ionization constants of aqueous amino acids at temperatures up to 250°C using hydrothermal pH indicators and UV-visible spectroscopy: Glycine, α-alanine, and proline

“…Heat-of-mixing flow calorimetry has been used to determine ionization constants and enthalpies of reaction for the protonation of the amino and carboxylate groups of several amino acids at temperatures of up to 125°C (Izatt et al, 1992;Gillespie et al, 1995;Wang et al, 1996). Vibrating-tube densimeters and a Picker-type flow microcalorimeter have recently been used to determine experimental values for the standard partial molar volumes and heat capacities of glycine, ␣-alanine, ␤-alanine, proline, and the dipeptide glycyl-gylcine, at temperatures as high as 275°C (Hakin et al, 1995(Hakin et al, , 1998Clarke and Tremaine, 1999;. We are aware of no other experimental studies on the thermodynamic properties of aqueous amino acids or peptides above 100°C.…”

The partial molar heat capacities of glycine and glycylglycine in aqueous solution at elevated temperatures and atp= 10.0 MPa

“…The values of C ∞ p,m,φ for aqueous solutions of glycine and glycylglycine used in these fits were those obtained at p = 0.1 MPa by Hakin et al (48,49) and the values of C ∞ p,m,φ (corr) reported in table 4. Estimates of the c 1 and c 2 coefficients and their standard errors for aqueous glycine and glycylglycine solutions are contained in table 6 together with estimates of the other coefficients for equation (20).…”

“…(25,48,49) To compare the present results with those previously reported, the following thermodynamic relation can be used:…”

“…The literature V ∞ m,φ and S v values for glycine (25) and glycylglycine (26) used in the calculations were chosen to cover, as closely as possible, the molality range used in this work. The apparent molar volumes were then converted to a pressure of 10.0 MPa using apparent molar isothermal compressibilities, κ T,m,φ , at p = 0.1 MPa that were obtained using the equation: where κ ∞ T,m,φ is the partial molar isothermal compressibility of the solute at infinite dilution and S κ is the experimental slope.…”

“…The values obtained for the quantity (∂ 2 V ∞ m,φ /∂ T 2 ) p were −(1.8 ± 0.2) · 10 −3 cm 6 · mol −1 · K −2 and −(2.9 ± 0.7) · 10 −3 cm 6 · mol −1 · K −2 for glycine and glycylglycine, respectively. The C p,m,φ values for glycine and glycylglycine in aqueous solution obtained at p = 0.1 MPa (48,49) were corrected to a pressure of 10.0 MPa using equation (18). The results obtained are reported in table 4 and shown in figures 2 and 3.…”