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Protonation behavior of dextran amino acid esters

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Dextran esters of different amino acids (glycine, β-alanine, L-ornithine, L-lysine) are investigated regarding their pKa values by potentiometric titration. The pKa values of the dextran derivatives are generally dependent on the position of the amino group in relation to the ester group, i.e. the nearer they are located in the molecule, the lower the resulting pKa values are, L-ornithine ester being the exception. An influence of the polymer backbone is ruled out. Stability against hydrolysis at different pH values and over longer periods at constant pH value is measured by potentiometric and polyelectrolyte titration. |