^14,15N NMR Shielding Constants from Density Functional Theory

Abstract

The prediction of nuclear magnetic resonance (NMR) shielding parameters for the N atom represents a particularly difficult task for most of the Hartree-Fock (HF)-based or density functional theory (DFT)-based methodologies. In fact, for some molecular systems, the effect of the presence of a lone pair and multiple bonds on the N atom makes the use of higher correlated methods absolutely necessary to obtain accurate results. In this article, we present an extensive study covering almost the entire spectrum of nitrogen shielding, from +400 to -50 ppm. The sum-over-states density functional perturbation theory (SOS-DFPT) has been used to calculate the shielding constant of 132 different N atoms. The potential of the various SOS-DFPT local approximations has been assessed through the comparison of N atoms that belong to similar molecular systems to experimental data. This procedure allows us to determine the margin of error to be considered in the SOS-DFPT calculation of the isotropic shieldings for each type of N atom.

Automated Fragmentation Polarizable Embedding Density Functional Theory (PE-DFT) Calculations of Nuclear Magnetic Resonance (NMR) Shielding Constants of Proteins with Application to Chemical Shift Predictions

“…We also include backbone nitrogen NMR shielding constant RMSDs in Table , because they have some importance in protein structure determination. They show much larger RMSDs (>4 ppm for all models) than what was obtained for carbon, but this is not unexpected, since the large variations observed for nitrogen are dependent more heavily on the level of electronic structure theory . Chemical shifts of N atoms also generally exhibits a larger span than C atoms in protein structures…”

“…They show much larger RMSDs (>4 ppm for all models) than what was obtained for carbon, but this is not unexpected, since the large variations observed for nitrogen are dependent more heavily on the level of electronic structure theory. 80 Chemical shifts of N atoms also generally exhibits a larger span than C atoms in protein structures. 81 Based on the above analysis, we conclude that, for the purpose of computing NMR shielding constants of 13 C, model 2 is sufficiently accurate.…”

Aquanitrato Complexes of Palladium, Rhodium, and Platinum: A Comparative15N NMR and DFT Study

“…Recently Leniak and J. Jaźwiński, showed that the non‐relativistic B3PW91/[6‐311++G(2d,p), Stuttgart] computational protocol reproduced the 15 N NMR parameters as good as the more expensive relativistic CGA‐PBE//QZ4P ZORA approaches for a set of model complexes of rhodium(II) tetraformate with nine nitrogenous organic ligands. Fadda et al calculated the shielding constant of 132 different N atoms covering almost the entire spectrum of nitrogen shielding, from +400 to –50 ppm employing the non‐relativistic sum‐over‐states density functional perturbation theory (SOS‐DFPT) and assessed the potential of the SOS‐DFPT local approximations through the comparison of N atoms that belong to similar molecular systems to experimental data.…”

A Photosensitive Liquid Crystal Studied by 14N NMR, 2H NMR, and DFT Calculations

“…In particular, density functional theory (DFT) is a useful tool to calculate both 14 N quadrupolar and chemical shift NMR tensors, as reported in the literature for several solid materials. [31][32][33][34][35][36][37] Herein, we report an original study of diheptylazobenzene (7AB) [38,39] in its nematic and smectic A phases (see Figure 1), based on a combined approach between experimental 14 N and 2 H NMR and DFT ab initio calculations. Previous studies on the 7AB mesogen, based on the sole 2 H NMR study of 7AB selectively deuterated in the aromatic core and/or in the alphamethyl position, [40][41][42][43] are limited to the determination of the main orientational order parameter, S zz , and to studying the impact of UV illumination on both molecular configurational changes and average S zz values.…”