Перегляд за Автор "Михалюк, Андрій Петрович"

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Особливості комплексоутворення та аналітичні характеристики ациклічних поліетерів
(2024) Кроніковський, Олег Ігоревич; Михалюк, Андрій Петрович; Кроніковська, Олена Петрівна; Стаднічук, Наталія Олександрівна
The complex formation of neutral ligands such as polyethylene glycol (PEG) with metal cations can be represented as follows. The flexible molecule of polyethylene glycol sequentially fills the solvation sphere of the cation, like the behavior observed in crown ethers. Evidently, the polymer chain itself becomes multiply charged in the process, as in the limiting case, every 6-8 oxygen atoms bind one cation. This leads to certain conformational changes in the chain. For example, in the case of polyethylene glycol binding salts, a decrease in intrinsic viscosity and an increase in polymer chain rigidity are observed, indicating an expansion of the ligand macromolecule coil during complex formation due to electrostatic repulsion between the metal cations. As the charge accumulates, the polymer molecule unfolds, attempting to adopt an extended chain conformation with crown-like complexes arranged along it. The electrostatic repulsion forces are partially offset by the screening effect of counterions, but at low salt concentrations, the anionic screening effect is insufficient to reduce the electrostatic potential that arises from cation binding, and the cations cannot be placed closely together on the chain. The stoichiometry of metal salt complexes with polypodands is quite varied. For instance, the composition of PEG complexes with HgCl2 corresponds to a molar ratio of 1:1 (salt: monomer unit). The number of monomer units per binding site for salts such as Na+, K+, Rb+, Cs+ in methanol are 16.8, 12.3, 13.2, and 14.5, respectively, and increase with decreasing salt concentration. The binding constant of the salt significantly depends on the molar mass of PEG. Generally, the binding constant initially increases and then remains practically unchanged when the polymer's molar mass reaches around 1000-2000