Formation of Copper(II) Complexes with Low- and High-Methoxylated Pectins Modified with Salicylic and Anthranylic Acids
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ation of Copper(II) Complexes with Low- and High-Methoxylated Pectins Modified with Salicylic and Anthranylic Acids R. Kh. Mudarisovaa,*, O. S. Kukovinetsb, and S. V. Kolesova a Ufa
Institute of Chemistry, Ufa Research Center, Russian Academy of Sciences, Ufa, 450054 Russia b Bashkir State University, Ufa, 450014 Russia *e-mail: [email protected] Received July 15, 2020; revised July 15, 2020; accepted July 29, 2020
Abstract—Low- and high-methoxylated pectins were synthesized and modified with anthranilic and salicylic acids to obtain effective polymeric ligands. On their basis, new copper(II) metal-polymer complexes were obtained, their composition was determined, stability constants and thermodynamic characteristics of the complex formation process were calculated. The efficiency of the metal binding to the polymer ligand depends mainly on the degree of pectin methoxylation, the acidity of the medium, the temperature of the process, and also on the structure of the pharmacologically active modifier acid. The thermal stability of polymeric copper(II) complexes increases with the introduction of an organic complexone into the polysaccharide and with a decrease in the degree of pectin methoxylation. Keywords: complex formation, apple pectin, methoxylation degree, copper(II), pharmacophores, stability constants
DOI: 10.1134/S1070363220110183 Polymeric metal complexes based on polysaccharides have multifold biological activity. In particular, this was noted for metal complexes obtained with the use of native pectin as a high-molecular ligand [1–6]. It is known that pectin substances are acidic polysaccharides, the state of carboxyl groups of which determines their properties— the ability to interact with metal cations, amines, and other complexing agents of organic and inorganic natures. Depending on the relative amount of carboxyl groups in the residues of galacturonic acid esterified with methyl alcohol, high-methoxylated (with the esterification degree > 50%) and low-methoxylated (with the esterification degree < 50%) pectins are distiquished. These structural features of polysaccharide molecules create a variety of physicochemical pectin parameters, which is reflected in their complexing, biological, and pharmacological properties [7–10]. Strengthening the complexing power of biopolymers in respect to metal ions is also possible by modifying the polysaccharide with organic compounds containing active nucleophilic groups [11–14]. The aim of this work was to study the effect of the methoxylation degree of apple pectin modified with pharmacologically active carboxylic acids on the features
of complex formation with copper(II) ions. The main interest in copper(II) complexes with pectins is associated with the possibility of creating on their basis new effective drugs that have, in particular, an antianemic effect [1, 5], and also with their use as models of copper proteides (for example, hemocyanin) that can transport oxygen, or as catalysts for redox processes in the body [15]. Anthranilic (1) and salicylic (2) aci
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