How Do Nuclei Couple to the Magnetic Moment of a Paramagnetic Center? A New Theory at the Gauntlet of the Experiments

Abstract

The recent derivation, based on pure quantum chemistry (QC) first-principles, of the pseudocontact shifts (PCSs) caused by a paramagnetic metal center on far away nuclei has cast doubts on the validity of the semiempirical (SE) theory, predicting PCSs to arise from the metal magnetic susceptibility anisotropy. The SE theory has been used and applied countless times, especially in the last 2 decades, to obtain structural information on proteins containing paramagnetic metal ions. We show here that the QC and SE predictions can be directly tested against experiments, provided a suitable macromolecular system is used. The SE approach yields a good prediction of the experimental PCSs while the QC one does not. It appears that the classic theory is able to grasp satisfactorily the underlying physics.

A dysprosium single molecule magnet outperforming current pseudocontact shift agents

“…The above treatment relies on the assumption 68,69 of a direct relation between PCS and the magnetic susceptibility tensor, which was recently confirmed by a rigorous quantum chemistry treatment. 70 …”

Design and applications of lanthanide chelating tags for pseudocontact shift NMR spectroscopy with biomacromolecules

“…density functional theory (DFT) calculations allow to predict the structure and conformational bias of lanthanide complexes in vacuo and in solution as well as the anisotropy tensor for electron paramagnetic resonance (EPR) studies and are therefore under current investigation in order to facilitate the use of paramagnetic effects by decreasing the experimental work associated with the development of new LCTs [23,[76][77][78][79][80][81][82][83]. Very recent work proves the semi-empirical approach to be superior in reproducing PCS compared to a quantum chemistry approach [84].…”

Observability of Paramagnetic NMR Signals at over 10 000 ppm Chemical Shifts

“…[28][29][30][31] The use of electronic structure theory in the analysis of paramagnetic NMR data remains a growing field of research, and the clarification of its fundamental aspects remains a focus of current investigations. [32][33][34][35][36][37][38][39][40][41][42] Paramagnetic relaxation enhancement (PRE) is a useful source of information about electron-nucleus distances and also provides estimates of electron relaxation rates. [43] Currently, the analysis of PRE is mostly based on complementary models derived by Solomon, Bloembergen, and Morgan (contact and dipolar mechanism, referred to here as SBM mechanism), [44][45][46] and GuØron (Curie mechanism).…”

“…[ 28 , 29 , 30 , 31 ] The use of electronic structure theory in the analysis of paramagnetic NMR data remains a growing field of research, and the clarification of its fundamental aspects remains a focus of current investigations. [ 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ]…”