Publication details

Interpreting the paramagnetic NMR spectra of potential Ru(III) metallodrugs: Synergy between experiment and relativistic DFT calculations



Year of publication 2016
Type Article in Periodical
Magazine / Source Journal of the American Chemical Society
MU Faculty or unit

Central European Institute of Technology

Web DOI: 10.1021/jacs.6b02749
Field Physical chemistry and theoretical chemistry
Keywords paramagnetic NMR; ruthenium; chemical shift; contact shift; hyperfine coupling; DFT; spin density;
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Description Ruthenium-based compounds are potential candidates for use as anticancer metallodrugs. The central ruthenium atom can be in the oxidation state +2 (e.g., RAPTA, RAED) or +3 (e.g., NAMI, KP). In this study we focus on paramagnetic NAMI analogs of a general structure [4-R-pyH]+trans-[RuIIICl4(DMSO)(4-R-py)]-, where 4-R-py stands for a 4-substituted pyridine. As paramagnetic systems are generally considered difficult to characterize in detail by NMR spectroscopy, we performed a systematic structural and methodological NMR study of complexes containing variously substituted pyridines. The effect of the paramagnetic nature of these complexes on the 1H and 13C NMR chemical shifts was systematically investigated by temperature-dependent NMR experiments and density-functional theory (DFT) calculations. To understand the electronic factors influencing the orbital (delta(orb), temperature-independent) and paramagnetic (delta(para), temperature-dependent) contributions to the total NMR chemical shifts, a relativistic two-component DFT approach was used. The paramagnetic contributions to the 13C NMR chemical shifts are correlated with the distribution of spin density in the ligand moiety and the 13C isotropic hyperfine coupling constants, Aiso(13C), for the individual carbon atoms. To analyze the mechanism of spin distribution in the ligand, the contributions of molecular spin-orbitals (MSOs) to the hyperfine coupling constants and the spatial distribution of the z-component of the spin density in the MSOs calculated at the relativistic four-component DFT level are discussed and rationalized. The significant effects of the substituent and the solvent on delta(para), particularly the contact contribution, are demonstrated. This work should contribute to further understanding of the link between the electronic structure and the NMR chemical shifts in open-shell systems, including the ruthenium-based metallodrugs investigated in this account.
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