Efficient pKa determination in a nonaqueous solvent using chemical shift imaging

Schenck, George, Baj, Krzysztof, Iggo, Jonathan A. and Wallace, Matthew ORCID: https://orcid.org/0000-0002-5751-1827 (2022) Efficient pKa determination in a nonaqueous solvent using chemical shift imaging. Analytical Chemistry, 94 (23). 8115–8119. ISSN 0003-2700

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pKa is an important property of a molecule which impacts many fields, such as drug design, catalysis, reactivity, and environmental toxicity. It is often necessary to measure pKa in nonaqueous media due to the poor solubility of an analyte in water, for example, many compounds of pharmaceutical interest. Although NMR methods to measure pKa in water are well established, determining pKa in organic solvents is laborious and problematic. We present an efficient one-shot method to determine the pKa of an analyte in an organic solvent in a single measurement. Diffusion of an acid into a basic solution of the analyte and a set of pH indicators establishes a pH gradient in the NMR tube. The chemical shift of a pH sensitive resonance of the analyte and the pH of the solution are then determined simultaneously as a function of position along the pH gradient by recording a chemical shift image of the NMR tube. The pKa of the analyte is then determined using the Henderson-Hasselbalch equation. The method can be implemented in any laboratory with a gradient equipped NMR high-field spectrometer and is demonstrated for a range of pharmaceutical compounds and inorganic phosphazene bases.

Item Type: Article
Additional Information: Funding Information: J.A.I. thanks the EPSRC for financial support, Grants EP/F000316/1 and EP/C005643/1. G.S. thanks the EPSRC for a studentship Grant EP/N509693/1. M.W. thanks the Royal Commission for the Exhibition of 1851 for a Research Fellowship and UKRI for a Future Leaders Fellowship (Grant MR/T044020/1). K.B. thanks AstraZeneca (Grant 10045297) and the University of Liverpool for financial support. We thank Miss Megan Carr for experimental assistance.
Uncontrolled Keywords: analytical chemistry ,/dk/atira/pure/subjectarea/asjc/1600/1602
Faculty \ School: Faculty of Science > School of Pharmacy
UEA Research Groups: Faculty of Science > Research Groups > Pharmaceutical Materials and Soft Matter
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Depositing User: LivePure Connector
Date Deposited: 23 Jun 2022 08:32
Last Modified: 22 Oct 2022 18:35
URI: https://ueaeprints.uea.ac.uk/id/eprint/85758
DOI: 10.1021/acs.analchem.2c00200


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