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1. Solvent effect on the 195 Pt NMR properties in pyridonate-bridged Pt III dinuclear complex derivatives investigated by ab initio molecular dynamics and localized orbital analysis

   https://doi.org/10.1039/D0CP05849A  

   Batista, Patrick R. ; Ducati, Lucas C. ; Autschbach, Jochen ( June 2021 , Physical Chemistry Chemical Physics)

   null (Ed.)

   An ab initio molecular dynamics investigation of the solvent effect (water) on the structural parameters, 195 Pt NMR spin–spin coupling constants (SSCCs) and chemical shifts of a series of pyridonate-bridged Pt III dinuclear complexes is performed using Kohn–Sham (KS) Car–Parrinello molecular dynamics (CPMD) and relativistic hybrid KS NMR calculations. The indirect solvent effect ( via structural changes) has a dramatic effect on the 1 J PtPt SSCCs. The complexes exhibit a strong trans influence in solution, where the Pt–Pt bond lengthens with increasing axial ligand σ-donor strength. In the diaqua complex, where the solvent effect is more pronounced, the SSCCs averaged for CPMD configurations with explicit plus implicit solvation agree much better with the experimental data, while the calculations for static geometry and CPMD unsolvated configurations show large deviations with respect to experiment. The combination of CPMD with hybrid KS NMR calculations provides a much more realistic computational model that reproduces the large magnitudes of 1 J PtPt and 195 Pt chemical shifts. An analysis of 1 J PtPt in terms of localized and canonical orbitals shows that the SSCCs are driven by changes in the s-character of the natural atomic orbitals of Pt atoms, which affect the 'Fermi contact' mechanism. 

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2. The Search for Molecular Corks Beyond Carbon Monoxide: A Quantum Mechanical Study of N-Heterocyclic Carbene Adsorption on Pd/Cu(111) and Pt/Cu(111)

   Simpson, Scott ( March 2022 , ACS Spring 2022)

   Periodic Density Functional Theory calculations reveal the potential application of 10 imidazole based N-heterocyclic carbenes (NHCs) to behave as “molecular corks” for hydrogen storage on single atom alloys, comprised of Pd/Cu(111) or Pt/Cu(111). Calculations show that functionalizing the NHC with different electron withdrawing/donating functional groups results in different binding energies of the NHC with the alloy surfaces. The results are compared to DFT calculations of carbon monoxide bound to these alloys. The Huynh electronic parameter (HEP) is calculated for several simple imidazole NHCs to gauge σ-donor ability, while Se-NMR and P-NMR calculations of selenourea derivatives and carbene-phosphinidene adducts, respectively, have been utilized to gauge π-acidity of the NHCs. It is demonstrated that consideration of both σ and π donating/accepting ability must be considered when predicting the surface-adsorbate binding energy. It was found that electron withdrawing groups tend to weaken the NHC-surface interaction while electron donating substituents tend to strengthen the interaction. 

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3. Search for molecular corks beyond carbon monoxide: A quantum mechanical study of N-heterocyclic carbene adsorption on Pd/Cu(111) and Pt/Cu(111) single atom alloys

   Simpson, Scott ( December 2021 , Pacifichem 2021)

   Periodic Density Functional Theory calculations reveal the potential application of 10 imidazole based N-heterocyclic carbenes to behave as “molecular corks” for hydrogen storage on single atom alloys, comprised of Pd/Cu(111) or Pt/Cu(111). Calculations show that functionalizing the NHC with different electron withdrawing/donating functional groups results in different binding energies of the NHC with the alloy surfaces. The results are compared to DFT calculations of carbon monoxide bound to these alloys. The Huynh electronic parameter (is calculated for several simple imidazole NHCs to gauge σ-donor ability, while Se-NMR of and P-NMR calculations of selenourea derivatives and carbene-phosphinidene adducts, respectively, have been utilized to gauge π-acidity of the NHCs. It is demonstrated that consideration of both σ and π donating/accepting ability must be considered when predicting the surface-adsorbate binding energy. It was found that electron withdrawing groups tend to weaken the NHC-surface interaction while electron withdrawing substituents tend to strengthen the interaction. 

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4. J -Driven dynamic nuclear polarization for sensitizing high field solution state NMR

   https://doi.org/10.1039/d1cp04186j  

   Concilio, Maria Grazia ; Kuprov, Ilya ; Frydman, Lucio ( January 2022 , Physical Chemistry Chemical Physics)

   Dynamic nuclear polarization (DNP) is widely used to enhance solid state nuclear magnetic resonance (NMR) sensitivity. Its efficiency as a generic signal-enhancing approach for liquid state NMR, however, decays rapidly with magnetic field B 0 , unless mediated by scalar interactions arising only in exceptional cases. This has prevented a more widespread use of DNP in structural and dynamical solution NMR analyses. This study introduces a potential solution to this problem, relying on biradicals with exchange couplings J ex of the order of the electron Larmor frequency ω E . Numerical and analytical calculations show that in such J ex ≈ ± ω E cases a phenomenon akin to that occurring in chemically induced DNP (CIDNP) happens, leading to different relaxation rates for the biradical singlet and triplet states which are hyperfine-coupled to the nuclear α or β states. Microwave irradiation can then generate a transient nuclear polarization build-up with high efficiency, at all magnetic fields that are relevant in contemporary NMR, and for all rotational diffusion correlation times that occur in small- and medium-sized molecules in conventional solvents. 

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5. Large Volume Liquid State Scalar Overhauser Dynamic Nuclear Polarization at High Magnetic Field

   https://doi.org/10.1039/C9CP02997D  

   dubroca, thierry ; Wi, Sungsool ; van Tol, Johan ; Frydman, Lucio ; Hill, Stephen ( January 2019 , Physical Chemistry Chemical Physics)

   Dynamic Nuclear Polarization (DNP) can increase the sensitivity of Nuclear Magnetic Resonance (NMR), but it is challenging in the liquid state at high magnetic fields. In this study we demonstrate significant enhancements of NMR signals (up to 70 on 13C) in the liquid state by scalar Overhauser DNP at 14.1 T, with high resolution (~0.1 ppm) and relatively large sample volume (~100 µL). 

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