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Prediction of ¹H NMR chemical shifts for ionic liquids: strategy and application of a relative reference standard.

ABSTRACT: The computational predictions of ¹H NMR chemical shifts for ionic liquids were investigated. To calculate the chemical shifts more accurately, the approach of relative reference standard (RRS) was proposed. This straightforward computational technique uses organic compounds and ionic liquids that are similar to the studied ionic liquids as standards. The calculated chemical shifts of single ion pairs were strongly influenced by the anion type and the local environment. Using the RRS methodology, the calculated results agreed well with the experimental chemical shifts due to the cancellation of errors caused by the anion. Ionic clusters consisting of 4 ion pairs were also employed to model the ionic liquids with strongly coordinating anions. Large clusters slightly improve the accuracy by reducing systematic errors. Although the experimental ¹H NMR data of the reference ionic liquid should be used, the RRS methodology has been shown to predict ¹H NMR chemical shifts efficiently at different levels of theory.

SUBMITTER: Wang J

PROVIDER: S-EPMC9084412 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature

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Prediction of <sup>1</sup>H NMR chemical shifts for ionic liquids: strategy and application of a relative reference standard.

Wang Juanfang J Liu Ying Y Li Wen W Gao Guanjun G

RSC advances 20180810 50

The computational predictions of <sup>1</sup>H NMR chemical shifts for ionic liquids were investigated. To calculate the chemical shifts more accurately, the approach of relative reference standard (RRS) was proposed. This straightforward computational technique uses organic compounds and ionic liquids that are similar to the studied ionic liquids as standards. The calculated chemical shifts of single ion pairs were strongly influenced by the anion type and the local environment. Using the RRS m ...[more]

PMID: 35548389

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Project description:This work presents an investigation into the effect of including explicit solvent molecules in DFT (Density Functional Theory) calculations of relative energies (ΔErel) and NMR (Nuclear Magnetic Resonance) chemical shifts for organic molecules in chloroform, water, and dimethyl sulfoxide (DMSO) solution using the PCM (Polarizable Continuum Model) approach. The large and flexible molecule of the antibiotic azithromycin (AZM) containing five OH groups and other polar centers susceptible to interacting with solvent molecules was used here as a working example. An increasing number of explicit solvent molecules was used in the geometry optimization of the supermolecule (n = 5, 15, 25, and 50), which accurately reproduces the first solvation shell. We optimized a large AZM trimer (3AZM-75CHCl3) structure at the ωB97x-D/6-31G(d,p)-PCM level, containing 747 atoms, which may roughly simulate a 0.1 M dilute solution, with a good agreement with experimental NMR data. The supermolecule approach offers a robust description of solute-solvent intermolecular interactions, effectively accounting for both short- and long-range effects, making it a reliable method for selecting the predominant conformer in solution. While the effect of including explicit solvent molecules on the DFT calculation of ΔErel and 1H NMR chemical shifts (OH protons) is remarkable, it is only moderate for the evaluation of 13C NMR spectra, providing support for the use of the continuum solvation model in this case. For highly solvated structures, a degree of arbitrariness in the calculation of relative energies is naturally introduced, mainly due to solvent-solvent interaction, causing a strong dependence of total energies on the initial guess structure used in the geometry optimization procedure, with variation in ΔErel around 70 kcal mol-1 being predicted, and, therefore, it may not be quite suitable as a criterion to find the predominant conformer in solution. This does not happen with the DFT calculation of 1H NMR chemical shifts (RMSD variations less than 0.1 ppm were observed for distinct initial guess structures), which are more strongly influenced by the local chemical environment. This is an interesting result regarding the use of an explicit solvent model in DFT calculations for organic molecules.

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Prediction of ¹H NMR chemical shifts for ionic liquids: strategy and application of a relative reference standard.

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Prediction of <sup>1</sup>H NMR chemical shifts for ionic liquids: strategy and application of a relative reference standard.

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Prediction of 1H NMR chemical shifts for ionic liquids: strategy and application of a relative reference standard.

Publications

Prediction of <sup>1</sup>H NMR chemical shifts for ionic liquids: strategy and application of a relative reference standard.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

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Prediction of ¹H NMR chemical shifts for ionic liquids: strategy and application of a relative reference standard.