Abstract
The second dissociation constants pK2of 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 pK2values 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 ΔCpowere derived from the temperature coefficients of the dissociation constants. The pK2values 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)
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call