Thermodynamic Properties of Alanylpeptide Buffer Systems and Their Potential as Standards in Biological Applications

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• 作者：Sooboo Singh ; J.A. Nevines ; Moganavelli Singh ; Mario Ariatti and Munessar Sankar
• 关键词：Peptides ; amines ; amino acids ; acid– ; base ; second dissociation constant ; thermodynamic constants ; ampholytes ; zwitterions ; alanylglutamine ; alanylleucine ; alanylglycine ; DL ; alanyl ; DL ; methionine ; buffers ; calorimetry ; solvation ; mixtur
• 刊名：Journal of Solution Chemistry
• 出版年：2003
• 出版时间：2003
• 年：2003
• 卷：32
• 期：5
• 页码：435-450
• 全文大小：170 KB

文摘

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, Ho, So, and C_powere 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 -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)