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<p>The protolytic and complexation properties of selected isomeric aromatic amino acids in aqueous solution were studied by a combination of potentiometric and UV-spectrophotometric titration at <i>I</i> = 0.1 mol/L (KCl/NaClO<sub>4</sub>) and <i>T</i> = (25 ± 1)°C. Acid dissociation constants were determined for ammonium (p<i>Ka</i><sub>0</sub>) and carboxy groups (p<i>Ka</i><sub>1</sub>) in isomeric benzenecarboxylic amino acids: for anthranilic acid (<Emphasis Type="BoldUnderline">L1</Emphasis>), <i>meta</i>-aminobenzoic acid (<Emphasis Type="BoldUnderline">L2</Emphasis>), and <i>para</i>-aminobenzoic acid (<Emphasis Type="BoldUnderline">L3</Emphasis>); and for ammonium groups (p<i>Ka</i><sub>1</sub>) in isomeric benzenesulfonic amino acids: for orthanilic acid (<Emphasis Type="BoldUnderline">L4</Emphasis>), methanilic acid (<Emphasis Type="BoldUnderline">L5</Emphasis>), and sulfanilic acid (<Emphasis Type="BoldUnderline">L6</Emphasis>). The amino group basicity in the reagents decreased in the series of <i>meta</i>-, <i>para</i>-, and <i>ortho</i>-isomers. Despite the lower basicity of the amino group in <i>ortho</i>-isomers, their metal complexes have the highest stability. Anthranilic acid exhibits selective properties towards copper(II) ions, and orthanilic acid towards silver(I) ions. The spectroscopic characteristics of transition-metal complexes of isomeric benzenesulfonic amino acids with silver(I), copper(II), nickel(II), and cobalt(II) ions were determined.</p>

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Protolytic and Complexation Properties of Some Isomeric Aromatic Amino Acids in Aqueous Solution

  • 期刊论文

  • 发表日期：

    2025年6月1日

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  • G. P. Zharkov,
  • N. N. Yunusov,
  • Yu. S. Petrova,
  • A. V. Pestov,
  • L. K. Neudachina

摘要

The protolytic and complexation properties of selected isomeric aromatic amino acids in aqueous solution were studied by a combination of potentiometric and UV-spectrophotometric titration at I = 0.1 mol/L (KCl/NaClO4) and T = (25 ± 1)°C. Acid dissociation constants were determined for ammonium (pKa0) and carboxy groups (pKa1) in isomeric benzenecarboxylic amino acids: for anthranilic acid (L1), meta-aminobenzoic acid (L2), and para-aminobenzoic acid (L3); and for ammonium groups (pKa1) in isomeric benzenesulfonic amino acids: for orthanilic acid (L4), methanilic acid (L5), and sulfanilic acid (L6). The amino group basicity in the reagents decreased in the series of meta-, para-, and ortho-isomers. Despite the lower basicity of the amino group in ortho-isomers, their metal complexes have the highest stability. Anthranilic acid exhibits selective properties towards copper(II) ions, and orthanilic acid towards silver(I) ions. The spectroscopic characteristics of transition-metal complexes of isomeric benzenesulfonic amino acids with silver(I), copper(II), nickel(II), and cobalt(II) ions were determined.