Abstract
The second dissociation constants pK 2of the NH3 +charge center of the alanylpeptides, alanylglutamine (Ala–Gln), alanylleucine (Ala–Leu), alanylglycine (Ala–Gly), and DL-alanyl–DL-methionine (DL-Ala–DL-Met) were determined at ten temperatures in the range, 5–50°C. These pK 2values were calculated from the emf of cells containing buffer solutions of these dipeptides. A cell of the type described by Harned and Ehlers,(1)utilizing hydrogen and silver–silver bromide electrodes was used. The thermodynamic quantities, ΔHo, ΔSo, and ΔCp owere derived from the temperature coefficients of the dissociation constants. The pK 2values at 25°C, 8.2105 ( Ala–Gln), 8.2668 ( Ala–Leu), 8.2940 ( Ala–Gly), and 8.3054 ( DL-Ala–DL-Met). These values show that different substituent groups on the α-carbon atom (which include polar and nonpolar groups), have a small effect on the dissociation of the NH3 +charge center. These compounds were also found to be suitable as buffers in the pH range(7–9). The thermodynamics of the solute–solvent interaction is interpreted in terms of the mixture model.(2)
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Singh, S., Nevines, J., Singh, M. et al. Thermodynamic Properties of Alanylpeptide Buffer Systems and Their Potential as Standards in Biological Applications. Journal of Solution Chemistry 32, 435–450 (2003). https://doi.org/10.1023/A:1024572811929
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DOI: https://doi.org/10.1023/A:1024572811929