NMR pD-variation method to determine the proper stabilities of organic electrolyte complexes: case of histidine complexes with a cyclophane acid

Rosa Elena Navarro, Yedith Soberanes, Motomichi Inoue*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The complexation of organic electrolytes, like carboxylic acids and amines, is studied usually by spectrometric titration at a constant pH. Obtained stability constants are, however, conditional and dependent on the pH selected, differing from the proper constants. In nuclear magnetic resonance (NMR) titration in D2O, a stability constant determined at a given pD is not directly correlated to other properties observed at a pH in H2O because of difference between acid dissociations in the solvents. To overcome these problems, this report proposes pD-variable NMR spectrometry, which monitors NMR signals of a mixture of the reactants with the variation of pD. This method identifies complexes formed in different pD ranges, and determines the proper stability constants, to yield the species distribution, which can be replotted in pH scale. The usefulness and limitation are examined by simulation of titration curves. An experimental example is presented for complexation of histidine with a cyclophane acid. Excel® files for calculations are available in Supplementary material.

Original languageEnglish
Pages (from-to)598-604
Number of pages7
JournalSupramolecular Chemistry
Volume33
Issue number10
DOIs
StatePublished - 2021

Bibliographical note

Funding Information:
This work was supported by División de Ingeniería de la Universidad de Sonora (Grant no. USO316007870). The authors thank Universidad de Sonora for the support of operating the NMR facilities.

Publisher Copyright:
© 2022 Informa UK Limited, trading as Taylor & Francis Group.

Keywords

  • NMR titration
  • histidine
  • molecular complex
  • pH–pD correlation
  • stability constant

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