Magnetic Resonance in Chemistry

doi: 10.1002/mrc.5458pmid: N/A

No abstract is available for this article.

Jimmink, Bono O.; Tessari, Marco; Kentgens, Arno P. M.

doi: 10.1002/mrc.5510pmid: 39842446

Parahydrogen induced polarisation (PHIP) is often used to enhance the sensitivity of NMR, with the purpose of extending the applicability of the technique. Nuclear spin hyperpolarisation obtained via PHIP is generally localised on the protons derived from the addition of para‐enriched hydrogen to an unsaturated substrate. This limitation has been previously addressed by pulse schemes that can spread this hyperpolarised magnetisation through the entire network of J‐coupled protons in the product molecule. Here, we extend this approach, by implementing 2D NMR spectroscopy on such network of hyperpolarised protons. This novel approach to 2D acquisition during parahydrogenation allows information to be gained from the entirety of a molecule, quicker and/or at lower concentrations than by conventional NMR. The efficacy of the method is exemplified by performing a 2D TOCSY experiment during hydrogenative PHIP, using 2‐pentyn‐1‐ol as a substrate. A 2D spectrum was obtained in a few minutes at micromolar concentration, demonstrating the applicability of this methodology.

Martínez‐Gómez, Fabián; Caroli Rezende, Marcos; Rodríguez‐Huenchún, Valentina; Ormazábal‐Toledo, Rodrigo

doi: 10.1002/mrc.5512pmid: 39854026

The 1H‐ and 13C‐NMR spectra of three substituted N‐(4‐hydroxyphenyl)pyridinium perchlorates, precursors of solvatochromic 4‐pyridiniophenolate betaines, were recorded in deuterated acetone, dimethylsulfoxide, and acetonitrile, and their spectral behavior in these solvents was analyzed as evidence of the solute–solvent interactions present in solution. The effect of the increasing orthogonality between the phenolic and pyridinium fragments was clearly evident from the obtained spectra, thus shedding light on the ground‐state structures of their deprotonated solvatochromic derivatives and their interactions with the solvent.

Da Silva, Haroldo C.; Hernandes, Isabel S.; De Almeida, Wagner B.

doi: 10.1002/mrc.5511pmid: 39865421

We present a DFT‐PCM NMR study of 3‐indoleacetic acid (3‐IAA), used as a working example, including explicit solvent molecules, named PCM‐nCHCl3, PCM‐nDMSO (n = 0, 2, 4, 8, 14, 20, and 25), to investigate the dimer formation in solution. Apart from well‐known cyclic (I) and open (II) acetic acid (AA) dimers, two new structures were located on DFT‐PCM potential energy surface (PES) for 3‐IAA named quasicyclic A (III) and quasicyclic B (IV), the last one having N–H…O hydrogen bond (instead of O–H…O). In addition, four other structures having π–π type interactions named V, VI, VII, and VIII were also obtained completing the sample on the PES. Our theoretical results and experimental 1H NMR data (CDCl3) strongly indicate that 3‐IAA should exist in a quasicyclic form (III) in a chloroform solution different from AA. Solute–solvent interactions play a key role in O–H and N–H chemical shifts. The strong H‐bond formation between the S=O and O–H and N–H groups produces large chemical shift value THAT masquerades the identification of dimer formation in DMSO solution based on 1H NMR chemical shift changes. However, analysis of 13C NMR and relative energy DFT‐PCM‐nDMSO results strongly indicate the presence of parallel ring interacting dimer having OH…benzene ring bond (VI). There can be a competition between solute–solute and solute–solvent interactions, and polar DMSO solvent can break the quasicyclic dimers (III and IV) intermolecular O–H…O and N–H…O bonds yielding two solvated monomeric species hydrogen bonded to O=S(CH3)2 groups, what may take place for other organic molecules in solution. However, it did not happen for the π–π interacting dimers and structure VI survived in DMSO solution.

Zhao, Xiaojian; Liang, Yan; Tian, Ruizhen; Li, Guijin; Zhou, Xilin; Zhou, Zifa; Zhang, Xiaolan

doi: 10.1002/mrc.5509pmid: 39888055

The defect structures of the orthorhombical and tetragonal Cu2+ centers in Cu1−xHxZr2(PO4)3 are theoretically studied by analyzing their experimental electron paramagnetic resonance (EPR) parameters, based on the perturbation formulas of these parameters for a 3d9 ion in orthorhombically and tetragonally elongated octahedra, respectively. The above centers are attributed to the Cu2+ ions locating at M(1) site, and the crystal field parameters (CFPs) are quantitatively determined from the superposition model and the local structures of the Cu2+ sites. Based on the calculation, the parallel Cu‐O bonds may undergo the relative elongations ΔZO (≈ 0.113 Å) and ΔZT (≈ 0.102 Å) for the orthorhombical and tetragonal Cu2+ centers in Cu1−xHxZr2(PO4)3 along z‐axis, respectively. Meanwhile, the planar Cu‐O bonds are found to experience the relative variation δr (≈ 0.056 Å) along the x‐ and y‐axes for the orthorhombical Cu2+ center because of the Jahn–Teller (JT) effect. The theoretical EPR parameters based on the above local structures agree well with the observed values.

Matveev, Mikhail V.; Lunkov, Sergei S.; Chumakova, Natalia A.

doi: 10.1002/mrc.5513pmid: 39900458

Spin trap method allows receiving important information about the structure of short‐living intermediate radicals involved in chemical processes. Commonly, the product of a spin trap reaction with an intermediate radical is identified based on the hyperfine structure of its EPR spectrum. However, such identification can be significantly complicated for novel radicals whose spectra are unknown. In this work, we propose a semiquantitative low‐cost computation method that allows predicting the hyperfine structure of EPR spectra of the α‐phenyl‐N‐tert‐butylnitrone (PBN) adducts with fluorine‐containing radicals. The scheme was tested for several radicals containing from 0 to 4 fluorine atoms.

Møller, Christoffer H. S.; Sauer, Stephan P. A.

doi: 10.1002/mrc.5514pmid: 39950736

In the pursuit of computational methods which boast both low computational cost and a high degree of accuracy, the SOPPA‐derived methods RPA(D) and HRPA(D) are showing great promise. This study aims to further the benchmarking of these two methods in comparison with both the original SOPPA and the CCSD method by calculating NMR spin–spin coupling constants in the backbone structure of free amino acid residues. Based on a small basis set study, the relative performance of the methods was not found to be heavily dependent on the size of the basis set. While HRPA(D) was found to reproduce the SOPPA results to a consistently high degree of accuracy, RPA(D) reproduced the CCSD results for the one‐bond coupling constants more accurately than both HRPA(D) and SOPPA.