Search Results (3)

In the present study, we benchmark computational protocols for predicting Co-59 NMR chemical shift. Quantum mechanical calculations based on density functional theory were used, in conjunction with our NMR-DKH basis sets for all atoms, including Co, which were developed in the present study. The best protocol included the geometry optimization at BLYP/def2-SVP/def2-SVP/IEF-PCM(UFF) and shielding constant calculation at GIAO-LC-ωPBE/NMR-DKH/IEF-PCM(UFF). This computational scheme was applied to a set of 34 Co(III) complexes, in which, Co-59 NMR chemical shift ranges from +1162 ppm to +15,100 ppm, and these were obtained in distinct solvents (water and organic solvents). The resulting mean absolute deviation (MAD), mean relative deviation (MRD), and coefficient of determination (R²) were 158 ppm, 3.0%, and 0.9966, respectively, suggesting an excellent alternative for studying Co-59 NMR. Full article

The absence of adequate force field (FF) parameters to describe certain metallic complexes makes new and deeper analyses impossible. In this context, after a group of researchers developed and validated an AMBER FF for a platinum complex (PC) conjugated with AHBT, new possibilities emerged. Thus, in this work, we propose an improved path to obtain NMR spectroscopic parameters, starting from a specific FF for PC, allowing to obtain more reliable information and a longer simulation time. Initially, a docking study was carried out between a PC and PI3K enzyme, aiming to find the most favorable orientation and, from this pose, to carry out a simulation of classical molecular dynamics (MD) with an explicit solvent and simulation time of 50 ns. To explore a new PC environment, a second MD simulation was performed only between the complex and water molecules, under the same conditions as the first MD. After the results of the two MDs, we proposed strategies to select the best amino acid residues (first MD) and water molecules (second MD) through the analyses of hydrogen bonds and minimum distance distribution functions (MDDFs), respectively. In addition, we also selected the best frames from the two MDs through the OWSCA algorithm. From these resources, it was possible to reduce the amount and computational cost of subsequent quantum calculations. Thus, we performed NMR calculations in two chemical environments, enzymatic and aqueous, with theory level GIAO–PBEPBE/NMR-DKH. So, from a strategic path, we were able to obtain more reliable chemical shifts and, therefore, propose safer spectroscopic probes, showing a large difference between the values of chemical shifts in the enzymatic and aqueous environments. Full article

Pt(0) complexes have been widely used as catalysts for important reactions, such as the hydrosilylation of olefins. In this context, nuclear magnetic resonance (NMR) spectroscopy plays an important role in characterising of new structures and elucidating reaction mechanisms. In particular, the Pt-195 NMR is fundamental, as it is very sensitive to the ligand type and the oxidation state of the metal. In the present study, quantum mechanics computational schemes are proposed for the theoretical prediction of the Pt-195 NMR chemical shift and ¹J(¹⁹⁵Pt–³¹P) in Pt(0) complexes. The protocols were constructed using the B3LYP/LANL2DZ/def2-SVP/IEF-PCM(UFF) level for geometry optimization and the GIAO-PBE/NMR-DKH/IEF-PCM(UFF) level for NMR calculation. The NMR fundamental quantities were then scaled by empirical procedures using linear correlations. For a set of 30 Pt(0) complexes, the results showed a mean absolute deviation (MAD) and mean relative deviation (MRD) of only 107 ppm and 2.3%, respectively, for the Pt-195 NMR chemical shift. When the coupling constant is taken into account, the MAD and MRD for a set of 33 coupling constants in 26 Pt(0) complexes were of 127 Hz and 3.3%, respectively. In addition, the models were validated for a group of 17 Pt(0) complexes not included in the original group that had MAD/MRD of 92 ppm/1.7% for the Pt-195 NMR chemical shift and 146 Hz/3.6% for the ¹J(¹⁹⁵Pt–³¹P). Full article