Does it bind? A method to determine the affinity of calcium and magnesium ions for polymers using 1H NMR spectroscopy

Wallace, Matthew ORCID: https://orcid.org/0000-0002-5751-1827, Holroyd, Joshua, Kuraite, Agne and Hussain, Haider (2022) Does it bind? A method to determine the affinity of calcium and magnesium ions for polymers using 1H NMR spectroscopy. Analytical Chemistry, 94 (31). 10976–10983. ISSN 0003-2700

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Abstract

The binding of calcium and magnesium ions (M2+) by polymers and other macromolecules in aqueous solution is ubiquitous across chemistry and biology. At present, it is difficult to assess the binding affinity of macromolecules for M2+ without recourse to potentiometric titrations and/or isothermal titration calorimetry. Both of these techniques require specialized equipment, and the measurements can be difficult to perform and interpret. Here, we present a new method based on 1H NMR chemical shift imaging (CSI) that enables the binding affinity of polymers to be assessed in a single experiment on standard high-field NMR equipment. In our method, M2+ acetate salt is weighed into a standard 5 mm NMR tube and a solution of polymer layered on top. Dissolution and diffusion of the salt carry the M2+ and acetate ions up through the solution. The concentrations of acetate, [Ac], and free (unbound) M2+, [M2+]f, are measured at different positions along the sample by CSI. Binding of M2+ to the polymer reduces [M2+]f and hinders the upward diffusion of M2+. A discrepancy is thus observed between [Ac] and [M2+]f from which the binding affinity of the polymer can be assessed. For systems which form insoluble complexes with M2+, such as sodium polyacrylate or carboxylate-functionalized nanocellulose (CNC), we can determine the concentration of M2+ at which the polymer will precipitate. We can also predict [M2+]f when a solution of polymer is mixed homogeneously with M2+ salt. We assess the binding properties of sodium polyacrylate, alginate, polystyrene sulfonate, CNC, polyethyleneimine, ethylenediamenetetraacetic acid, and maleate.

Item Type: Article
Faculty \ School: Faculty of Science > School of Pharmacy
Depositing User: LivePure Connector
Date Deposited: 27 Jul 2022 09:32
Last Modified: 12 Aug 2022 01:06
URI: https://ueaeprints.uea.ac.uk/id/eprint/86936
DOI: 10.1021/acs.analchem.2c01166

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