Benchmark of Density Functional Theory in the Prediction of C Chemical Shielding Anisotropies for Anisotropic Nuclear Magnetic Resonance-Based Structural Elucidation.

Density functional theory (DFT) calculations have emerged as a powerful theoretical toolbox for interpreting and analyzing the experimental nuclear magnetic resonance (NMR) spectra of chemical compounds. While DFT has been extensively used and benchmarked for isotropic NMR observables, the evaluation of the full chemical shielding tensor, which is necessary for interpreting residual chemical shift anisotropy (RCSA), has received much less attention, despite its recent applications in the structural elucidation of organic molecules. In this study, we present a comprehensive benchmark of carbon shielding anisotropies based on coupled cluster reference tensors taken from the NS372 benchmark data set.

Structural Insights Into the Opening Mechanism of C1C2 Channelrhodopsin.

Channelrhodopsins, light-gated cation channels, enable precise control of neural cell depolarization or hyperpolarization with light in the field of optogenetics. This study integrates time-resolved serial crystallography and atomistic molecular dynamics (MD) simulations to resolve the structural changes during C1C2 channelrhodopsin activation. Our observations reveal that within the crystal environment, C1C2 predominantly remains in a light-activated state with characteristics of the M intermediate.

Toward the Next Generation of Density Functionals: Escaping the Zero-Sum Game by Using the Exact-Exchange Energy Density.

ConspectusKohn-Sham density functional theory (KS DFT) is arguably the most widely applied electronic-structure method with tens of thousands of publications each year in a wide variety of fields. Its importance and usefulness can thus hardly be overstated. The central quantity that determines the accuracy of KS DFT calculations is the exchange-correlation functional.

Deuteration as a General Strategy to Enhance Azobenzene-Based Photopharmacology.

Chemical photoswitches have become a widely used approach for the remote control of biological functions with spatiotemporal precision. Several molecular scaffolds have been implemented to improve photoswitch characteristics, ranging from the nature of the photoswitch itself (e.g.

Implementation and First Evaluation of Strong-Correlation-Corrected Local Hybrid Functionals for the Calculation of NMR Shieldings and Shifts.

Local hybrid functionals containing strong-correlation factors (scLHs) and range-separated local hybrids (RSLHs) have been integrated into an efficient coupled-perturbed Kohn-Sham implementation for the calculation of nuclear shielding constants. Several scLHs and the ωLH22t RSLH have then been evaluated for the first time for the extended NS372 benchmark set of main-group shieldings and shifts and the TM70 benchmark of 3d transition-metal shifts. The effects of the strong-correlation corrections have been analyzed with respect to the spatial distribution of the sc-factors, which locally diminish exact-exchange admixture at certain regions in a molecule.

Revisiting Gauge-Independent Kinetic Energy Densities in Meta-GGAs and Local Hybrid Calculations of Magnetizabilities.

In a recent study [J. Chem. Theory Comput.

Unusually Large Effects of Charge-assisted C-H⋅⋅⋅F Hydrogen Bonds to Anionic Fluorine in Organic Solvents: Computational Study of F NMR Shifts versus Thermochemistry.

A comparison of computed F NMR chemical shifts and experiment provides evidence for large specific solvent effects for fluoride-type anions interacting with the σ*(C-H) orbitals in organic solvents like MeCN or CH Cl . We show this for systems ranging from the fluoride ion and the bifluoride ion [FHF] to polyhalogen anions [ClF ] . Discrepancies between computed and experimental shifts when using continuum solvent models like COSMO or force-field-based descriptions like the 3D-RISM-SCF model show specific orbital interactions that require a quantum-mechanical treatment of the solvent molecules.

Systematic Evaluation of Modern Density Functional Methods for the Computation of NMR Shifts of 3d Transition-Metal Nuclei.

A wide range of density functionals from all rungs of Jacob's ladder have been evaluated systematically for a set of experimental 3d transition-metal NMR shifts of 70 complexes encompassing 12 × Ti, 10 × V, 10 × Cr, 11 × Mn, 9 × Fe, 9 × Co, and 9 × Ni shift values, as well as a diverse range of electronic structure characteristics. The overall 39 functionals evaluated include one LDA, eight GGAs, seven meta-GGAs (including their current-density-functional─CDFT─versions), nine global hybrids, four range-separated hybrids, eight local hybrids, and two double hybrids, and we also include Hartree-Fock and MP2 calculations. While recent evaluations of the same functionals for a very large coupled-cluster-based benchmark of main-group shieldings and shifts achieved in some cases aggregate percentage mean absolute errors clearly below 2%, the best results for the present 3d-nuclei set are in the range between 4 and 5%.

Extended Benchmark Set of Main-Group Nuclear Shielding Constants and NMR Chemical Shifts and Its Use to Evaluate Modern DFT Methods.

An extended theoretical benchmark set, NS372, for light main-group nuclear shieldings and NMR shifts has been constructed based on high-level GIAO-CCSD(T)/pcSseg-3//CCSD(T)/cc-pVQZ reference data. After removal of the large static-correlation cases O, F, and BH from the statistical evaluations for the O, F, and B subsets, the benchmark comprises overall 372 shielding values in 117 molecules with a wide range of electronic-structure situations, containing 124 H, 14 B, 93 C, 43 N, 31 O, 47 F, 14 P, and 6 S shielding constants. The CCSD(T)/pcSseg-3 data are shown to be close to the basis-set and method limit and thus provide an excellent benchmark to evaluate more approximate methods, such as density functional approaches.

Implementation and Validation of Local Hybrid Functionals with Calibrated Exchange-Energy Densities for Nuclear Shielding Constants.

A recently reported coupled-perturbed Kohn-Sham implementation to compute nuclear shielding constants with gauge-including atomic orbitals and local hybrid functionals has been extended to cover higher derivatives of the density in the local mixing function (LMF) of the local hybrid as well as the calibration function (CF) needed to deal with the ambiguity of exchange-energy densities. This allowed the first evaluation of state-of-the-art local hybrids with "calibrated" exchange-energy densities for nuclear shieldings. Compared to previously evaluated simpler local hybrids without a CF, appreciable improvements are found for proton shieldings.

Effect of the Current Dependence of Tau-Dependent Exchange-Correlation Functionals on Nuclear Shielding Calculations.

Exchange-correlation functionals that depend on the local kinetic energy τ are widely used in many fields. This includes meta-generalized gradient approximation (GGA) functionals and their global hybrid versions as well as local hybrid functionals with τ-dependent local mixing functions to determine position-dependent exact-exchange admixture. Under the influence of an external magnetic field, τ becomes dependent on the gauge of the magnetic vector potential and should thus be extended to a gauge-invariant formulation.

Nuclear Spin-Spin Couplings: Efficient Evaluation of Exact Exchange and Extension to Local Hybrid Functionals.

We present an efficient implementation for the computation of nuclear spin-spin coupling tensors within density functional theory into the TURBOMOLE software suite. Emphasis is put on methods to efficiently evaluate the Hartree-Fock exchange needed for hybrid functionals: resolution of the identity and seminumerical evaluation on a grid. Our algorithm allows for the selection of specific nuclei for the reduction of calculation times.

An Efficient Coupled-Perturbed Kohn-Sham Implementation of NMR Chemical Shift Computations with Local Hybrid Functionals and Gauge-Including Atomic Orbitals.

Nuclear shielding calculations for local hybrid (LH) functionals with position-dependent exact-exchange admixtures within a coupled-perturbed Kohn-Sham (CPKS) framework have been implemented into the Turbomole code using efficient seminumerical integration techniques to deal with two-electron integrals. When using gauge-including atomic orbitals, LHs generate additional terms within the "pre-loop" section of the CPKS scheme compared to global hybrid (GH) functionals, related to perturbed electron-repulsion integrals. These terms have been implemented and tested in detail, together with dependencies on grid sizes and integral screening procedures.

Lessons from the Spin-Polarization/Spin-Contamination Dilemma of Transition-Metal Hyperfine Couplings for the Construction of Exchange-Correlation Functionals.

Hyperfine couplings (HFCs) of open-shell transition-metal centers are known to often depend crucially on core-shell spin polarization (CSSP). The latter is typically underestimated by semilocal density functionals, while admixture of exact exchange (EXX) in (global) hybrid functionals enhances CSSP. Unfortunately, a metal-ligand antibonding character of one or more of the singly occupied molecular orbitals of the complex will cause substantial valence-shell spin polarization (VSSP), which for global hybrids with higher EXX admixtures may lead to substantial spin contamination, thereby deteriorating the overall electronic structure and the dipolar couplings.

A Computational Modeling Approach Predicts Interaction of the Antifungal Protein AFP from with Fungal Membranes via Its γ-Core Motif.

Fungal pathogens kill more people per year globally than malaria or tuberculosis and threaten international food security through crop destruction. New sophisticated strategies to inhibit fungal growth are thus urgently needed. Among the potential candidate molecules that strongly inhibit fungal spore germination are small cationic, cysteine-stabilized proteins of the AFP family secreted by a group of filamentous Ascomycetes.

Reactivity of the Sterically Demanding Siloxanediol Mes Si(OH)(μ-O)Si(OH)Mes Towards Water and Ether Molecules.

A series of isotopologues of the siloxanediol Mes Si(OH)(μ-O)Si(OH)Mes (3 a) (Mes=2,4,6-trimethylphenyl) were synthesized by reactions of the corresponding disiloxane precursors Mes Si(μ-O) SiMes (2 a), Mes Si(μ- O) SiMes (2 b) or Mes Si(μ- O) SiMes (2 c) with an excess of H O, H O or H O. NMR and IR signal assignments for the siloxanediols in benzene are supported by quantum-chemical calculations, which indicate small energy differences between trans and cis conformers, the latter of which exhibits an intramolecular hydrogen bond. H NMR as well as IR data suggest the presence of a mixture of both conformers in C D .

Taming Silicon Congeners of CO and CO : Synthesis of Monomeric Si and Si Chalcogenide Complexes.

The synthesis of the unprecedented monomeric Si selenide complex (bis-NHC)Si=Se→GaCl 2 (bis-NHC=bis-N heterocyclic carbene, H C[{NC(H)=C(H)N(Dipp)}C:] , Dipp=2,6-iPr C H ), bearing the elusive SiSe ligand as a heavy CO homologue by the reaction of the silylone-GaCl adduct (bis-NHC)Si→GaCl 1 with elemental selenium in acetonitrile, is reported. The similar conversion of 1 with excess selenium conducted in THF afforded the SiSe complex (bis-NHC)Si(=Se)Se→GaCl 3. Remarkably, the reaction of 1 with Te=P(nBu) as a gentle Te transfer reagent led to the isolation of the monomeric SiTe complex (bis-NHC)SiTe 4, the first structurally characterized Lewis acid free heavy CO homologue complex.

An Isolable Silicon Dicarbonate Complex from Carbon Dioxide Activation with a Silylone.

The first isolable molecular silicon dicarbonate complex (bis-NHC)Si(CO ) 2 (bis-NHC=H C[{NC(H)=C(H)N(Dipp)}C:] , Dipp=2,6-iPr C H ) was synthesized by facile reaction of the bis-N-heterocyclic carbene stabilized silylone (bis-NHC)Si 1, bearing a zero-valent silicon atom, with carbon dioxide. The monomeric silicon dioxide complex (bis-NHC)SiO 3 supported by the bis-NHC ligand was proposed as a key intermediate resulting from double oxygenation of the zero-valent silicon atom in 1 by two molar equivalents of CO under liberation of CO; its subsequent Lewis acid-base reaction with CO leads to 2 which has been fully characterized including an single-crystal X-ray diffraction analysis. Its electronic structure, spectroscopic data and the thermochemistry of the formation have been studied quantum-chemically.