Manganese(II) Complex Compounds with Apple Pectin Modified with Amino Acids (L-Phenylalanine, L-Histidine, and L-Tryptophan)

New polymer complexes of manganese(II) based of apple pectin modified with amino acids (L-histidine, L-phenylalanine and L-tryptophan) were synthesized. The stability constants of the complexes with the composition pectin–manganese(II) (2 : 1) and the standard thermodynamic characteristics (Δ H° , Δ G° , and Δ S° ) of the complex formation were determined by spectrophotometric methods. Compared to the manganese complex based on native pectin, the polymer complexes with pectin modified with amino acids have greater stability, which increases in the series Phe < His < Trp. Features of the thermal behavior of manganese complexes with pectin ligands were revealed. The stability of the metal complexes was confirmed by testing in a medium simulating gastric juice.