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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 |
| UEA Research Groups: | Faculty of Science > Research Groups > Pharmaceutical Materials and Soft Matter |
| Depositing User: | LivePure Connector |
| Date Deposited: | 27 Jul 2022 09:32 |
| Last Modified: | 21 Oct 2022 01:33 |
| URI: | https://ueaeprints.uea.ac.uk/id/eprint/86936 |
| DOI: | 10.1021/acs.analchem.2c01166 |
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