The Experts below are selected from a list of 12666 Experts worldwide ranked by ideXlab platform
Jochen Autschbach - One of the best experts on this subject based on the ideXlab platform.
-
modeling of heavy atom ligand nmr spin spin Coupling in solution molecular dynamics study and natural bond orbital analysis of hg c Coupling constants
Chemistry: A European Journal, 2011Co-Authors: Shaohui Zheng, Jochen AutschbachAbstract:Ab initio molecular dynamics (MD) and relativistic density functional NMR methods were applied to calculate the one-bond Hg-C NMR indirect Nuclear Spin-Spin Coupling constants (J) of [Hg(CN)(2) ] and [CH(3) HgCl] in solution. The MD averages were obtained as J((199) Hg-(13) C)=3200 and 1575 Hz, respectively. The experimental Hg-C Spin-Spin Coupling constants of [Hg(CN)(2) ] in methanol and [CH(3) HgCl] in DMSO are 3143 and 1674 Hz, respectively. To deal with solvent effects in the calculations, finite "droplet" models of the two systems were set up. Solvent effects in both systems lead to a strong increase of the Hg-C Coupling constant. From a relativistic natural localized molecular orbital (NLMO) analysis, it was found that the degree of delocalization of the Hg 5d(σ) nonbonding orbital and of the HgC bonding orbital between the two coupled atoms, the nature of the trans Hg-C/Cl bonding orbital, and the s character of these orbitals, exhibit trends upon solvation of the complexes that, when combined, lead to the strong increase of J(Hg-C).
-
relativistic zeroth order regular approximation combined with nonhybrid and hybrid density functional theory performance for nmr indirect Nuclear spin spin Coupling in heavy metal compounds
Journal of Chemical Theory and Computation, 2010Co-Authors: Salvador Moncho, Jochen AutschbachAbstract:A benchmark study for relativistic density functional calculations of NMR Spin-Spin Coupling constants has been performed. The test set contained 47 complexes with heavy metal atoms (W, Pt, Hg, Tl, Pb) with a total of 88 Coupling constants involving one or two heavy metal atoms. One-, two-, three-, and four-bond Spin-Spin Couplings have been computed at different levels of theory (nonhybrid vs hybrid DFT, scalar vs two-component relativistic). The computational model was based on geometries fully optimized at the BP/TZP scalar relativistic zeroth-order regular approximation (ZORA) and the conductor-like screening model (COSMO) to include solvent effects. The NMR computations also employed the continuum solvent model. Computations in the gas phase were performed in order to assess the importance of the solvation model. The relative median deviations between various computational models and experiment were found to range between 13% and 21%, with the highest-level computational model (hybrid density functional computations including scalar plus spin-orbit relativistic effects, the COSMO solvent model, and a Gaussian finite-nucleus model) performing best.
-
two component relativistic hybrid density functional computations of Nuclear spin spin Coupling tensors using slater type basis sets and density fitting techniques
Journal of Chemical Physics, 2008Co-Authors: Jochen AutschbachAbstract:Computations of indirect Nuclear Spin-Spin Coupling constants using two-component relativistic density functional theory with a hybrid functional are reported. The program implementation makes use of a Slater-type orbital expansion of the molecular orbitals and the zeroth-order regular approximation for the treatment of relativistic effects. Exact exchange terms in the Kohn–Sham response kernel were computed using a fitting procedure. Computations with the PBE0 hybrid functional were carried out for heavy-atom-ligand-one-bond Couplings in PbH4, Pb(CH3)2H2, Pb(CH3)3H, three platinum complexes, the interhalogen diatomics such as ClF, ClBr, ClI, BrF, BrI, IF, and the series Tl-X with X=F, Cl, Br, I. The hybrid functional computations performed very well. In particular, for the isotropic Coupling and the Coupling anisotropy of Tl-X, the PBE0 hybrid functional yielded considerably improved agreement with experiment.
-
Nuclear spin spin Coupling constants from regular approximate relativistic density functional calculations i formalism and scalar relativistic results for heavy metal compounds
Journal of Chemical Physics, 2000Co-Authors: Jochen Autschbach, Tom ZieglerAbstract:We present a relativistic formulation of the spin–spin Coupling hyperfine terms based on the two component zeroth-order regular approximate Hamiltonian. The scalar relativistic parts of the resulting operators were used for an implementation into the Amsterdam density functional program. Application of the code for the calculation of one-bond metal-ligand Couplings of systems containing 183W, 195Pt, 199Hg, and 207Pb shows that scalar relativistic calculations are able to reproduce major parts of the relativistic effects on the Coupling constants, which can be even larger in magnitude than the respective total nonrelativistic values. The spatial origin of the regular approximate relativistic analogue of the Fermi-contact contribution, which is usually responsible for the strong relativistic increase of the Couplings, is analyzed. Its relativistic effects can be described by the relativistic increase of valence orbital density in the very vicinity of the heavy nucleus.
Stephan P A Sauer - One of the best experts on this subject based on the ideXlab platform.
-
the anomalous deuterium isotope effect in the nmr spectrum of methane an analysis in localized molecular orbitals
ChemPhysChem, 2008Co-Authors: Stephan P A Sauer, Patricio Federico ProvasiAbstract:Isotope effects on NMR indirect Nuclear spin–spin Coupling constants (SSCC) are less frequently studied than the corresponding effects on chemical shifts. Nevertheless, unusual effects have been observed for them and still lack a satisfying explanation. Raynes and co-workers measured the temperature dependence of the SSCC of the isotopomers of methane and found it puzzling that the reduced one-bond carbon–deuterium SSCC is larger than the carbon–proton Coupling constant for all mixed isotopomers. This implies that the secondary isotope effect [Eq. (1)] on the carbon–hydrogen SSCC
-
Interaction energies and NMR indirect Nuclear Spin-Spin Coupling constants in linear HCN and HNC complexes.
The Journal of Physical Chemistry A, 2005Co-Authors: Patricio Federico Provasi, Gustavo A. Aucar, Marina Sanchez, Ibon Alkorta, José Elguero, Stephan P A SauerAbstract:The cooperativity effects on both the electronic energy and NMR indirect Nuclear Spin-Spin Coupling constants J of the linear complexes (HCN) n and (HNC) n (n = 1-6) are discussed. The geometries of the complexes were optimized at the MP2 level by using the cc-pVTZ basis sets. The Spin-Spin Coupling constants were calculated at the level of the second-order polarization propagator approximation with use of the local dense basis set scheme based on the cc-pVTZ-J basis sets. We find strong correlations in the patterns of different properties such as interaction energy, hydrogen bond distances, and Spin-Spin Coupling constants for both series of compounds. The intramolecular Spin-Spin Couplings are with two exceptions dominated by the Fermi contact (FC) mechanism, while the FC term is the only nonvanishing contribution for the intermolecular Couplings. The latter do not follow the Dirac vector model and are important only between nearest neighbors.
-
the effect of lone pairs and electronegativity on the indirect Nuclear spin spin Coupling constants in ch2x x ch2 nh o s ab initio calculations using optimized contracted basis sets
Journal of Chemical Physics, 2001Co-Authors: Patricio Federico Provasi, Gustavo A. Aucar, Stephan P A SauerAbstract:The indirect Nuclear spin–spin Coupling constants of C2H4, CH2NH, CH2O, and CH2S were investigated by means of correlated ab initio calculations at the level of the second order polarization propagator approximation (SOPPA) and the second order polarization propagator approximation with coupled cluster singles and doubles amplitudes—SOPPA(CCSD) using large basis sets, which are optimized for the calculation of Coupling constants. It is found that at the self-consistent-field (SCF) level CH2NH and CH2S exhibit triplet instabilities whereas CH2CH2 and CH2O show triplet quasi-instabilities, which renders the SCF results meaningless. Our best results deviate between 0.3 and 2.7 Hz from the experimental values. We find that although the one-bond C–H and Y–H Couplings as well as the two- and three-bond H–H Couplings are dominated by the Fermi contact term, significant contributions of the orbital paramagnetic and sometimes even spin–dipolar terms are observed for the one-bond C–Y and two-bond C–H and Y–H coupli...
-
correlated calculations of indirect Nuclear spin spin Coupling constants using second order polarization propagator approximations soppa and soppa ccsd
Theoretical Chemistry Accounts, 1998Co-Authors: Thomas Enevoldsen, Jens Oddershede, Stephan P A SauerAbstract:We present correlated calculations of the indirect Nuclear Spin-Spin Coupling constants of HD, HF, H2O, CH4, C2H2, BH, AlH, CO and N2 at the level of the second-order polarization propagator approximation (SOPPA) and the second-order polarization propagator approximation with coupled-cluster singles and doubles amplitudes – SOPPA(CCSD). Attention is given to the effect of the so-called W 4 term, which has not been included in previous SOPPA Spin-Spin Coupling constant studies of these molecules. Large sets of Gaussian basis functions, optimized for the calculation of indirect Nuclear Spin-Spin Coupling constants, were used instead of the in general rather small basis sets used in previous studies. We find that for nearly all Couplings the SOPPA(CCSD) method performs better than SOPPA.
Trygve Helgaker - One of the best experts on this subject based on the ideXlab platform.
-
calculation of nmr spin spin Coupling constants in strychnine
Journal of Organic Chemistry, 2016Co-Authors: Trygve Helgaker, Michal Jaszunski, Pawel świderAbstract:We compare the NMR indirect Nuclear spin–spin Coupling constants in strychnine calculated using density functional theory (DFT) with the semiempirical relativistic force field (RFF) method of Kutateladze and Mukhina (KM) (J. Org. Chem. 2015, 80, 10838–10848). DFT values significantly more accurate than those obtained by KM for their comparison with RFF values can be obtained, at a lower cost, by an appropriate selection of basis set.
-
the nmr indirect Nuclear spin spin Coupling constants for some small rigid hydrocarbons molecular equilibrium values and vibrational corrections
Chemical Physics, 2004Co-Authors: Torgeir A Ruden, Trygve Helgaker, Michal JaszunskiAbstract:The indirect Nuclear spin–spin Coupling constants of allene and of two sterically strained hydrocarbons – cyclopropane and cyclopropene – calculated at different levels of electronic-structure theory are compared with each other and with experimental equilibrium constants, obtained from experiment by subtracting calculated vibrational contributions. It is found that, even in a relatively small basis set, the coupled-cluster singles-and-doubles (CCSD) method provides very good results, outperforming the other ab initio methods considered in this work – namely, the second-order polarization propagator approximation (SOPPA) and the multiconfigurational self-consistent field (MCSCF) approach. Calculations in the same basis set are also carried out at the hybrid level of density functional theory (DFT). Compared with the experimental equilibrium values the CCSD method gives the best results for the ab initio methods, while SOPPA consistently performs better than RASSCF. Hybrid DFT performs as well as SOPPA for the one-bond Coupling constants, while, for the other constants, it provides results of similar quality as CCSD. The DFT approximation is also used to evaluate the indirect Nuclear spin–spin Coupling constants and their vibrational corrections for the larger cyclobutene and cyclobutane molecules. 2003 Elsevier B.V. All rights reserved.
-
analytical calculation of Nuclear magnetic resonance indirect spin spin Coupling constants at the generalized gradient approximation and hybrid levels of density functional theory
Journal of Chemical Physics, 2000Co-Authors: Trygve Helgaker, Mark D Watson, Nicholas C HandyAbstract:A fully analytical implementation of the Nuclear magnetic resonance (NMR) indirect Nuclear spin–spin Coupling constants at the density-functional theory (DFT) level is presented. The implementation involves all four contributions of the nonrelativistic Ramsey theory: The dia- and para-magnetic spin–orbit contributions as well as the paramagnetic Fermi-contact and spin–dipole contributions. Three different exchange-correlation functionals—LDA (local density approximation), BLYP (Becke–Lee–Yang–Parr), and B3LYP (hybrid BLYP)—are tested by comparison with experiment and high-level ab initio calculations for a series of molecules containing first-row elements. All three levels of theory represent a significant improvement on restrictred Hartree–Fock (RHF) theory in the sense that the RHF instability problems are absent in DFT. Also, there is a steady improvement in the quality of the calculated spin–spin Couplings in the sequence LDA, BLYP, and B3LYP. For the first-row molecules investigated by us, the hybrid...
-
rovibrationally averaged magnetizability rotational g factor and indirect spin spin Coupling of the hydrogen fluoride molecule
Journal of Chemical Physics, 1999Co-Authors: Perolof Astrand, Kenneth Ruud, Kurt V. Mikkelsen, Trygve HelgakerAbstract:The magnetizability tensor, the rotational g factor, and the indirect Nuclear spin–spin Coupling constant of the hydrogen fluoride molecule have been calculated using large multiconfigurational self-consistent field wave functions and large basis sets. For a critical comparison with experiment, rovibrational corrections have also been calculated. For the magnetizability tensor and the spin–spin Coupling constant, we present results with higher precision than available experimental data; for the rotational g factor, our results are in good agreement with experiment.
-
an ab initio Nuclear magnetic resonance spectrum of vinyllithium
Principles and Practice of Constraint Programming, 1994Co-Authors: Kenneth Ruud, Trygve Helgaker, Poul Jorgensen, Keld L BakAbstract:We present a complete ab initio Nuclear magnetic resonance spectrum. All parameters in the spin Hamiltonian have been determined from a single restricted active space (RAS) multiconfigurational self-consistent field (MCSCF) wavefunction. All contributions to the indirect Nuclear Spin-Spin Coupling constants have been determined. The Nuclear shieldings have been calculated using London atomic orbitals. We show that a modest sized RAS MCSCF wavefunction is capable of predicting the qualitative, and to some extent also the quantitative, features of the proton spectrum of vinyllithium. Simulated spectra are presented both for 60 and 200 MHz NMR instruments.
Radek Marek - One of the best experts on this subject based on the ideXlab platform.
-
Platinum-Modified Adenines: Unprecedented Protonation Behavior Revealed by NMR Spectroscopy and Relativistic Density-Functional Theory Calculations
2016Co-Authors: Jan Vícha, Gabriel Demo, Radek MarekAbstract:Two novel PtIV complexes of aromatic cytokinins with possible antitumor properties were prepared by reaction of selected aminopurines with K2PtCl6. The structures of both complexes, 9-[6-(benzylamino)purine] pentachloroplatinate (IV) and 9-[6-(furfurylamino)purine] pentachloroplatinate (IV), were characterized in detail by using two-dimensional NMR spectroscopy (1H, 13C, 15N, and 195Pt) in solution and CP/MAS NMR techniques in the solid state. We report for the first time the X-ray structure of a nucleobase adenine derivative coordinated to PtIV via the N9 atom. The protonation equilibria for the complexes in solution were characterized by using NMR spectroscopy (isotropic chemical shifts and indirect Nuclear spin–spin Coupling constants) and the structural conclusions drawn from the NMR analysis are supported by relativistic density-functional theory (DFT) calculations. Because of the presence of the Pt atom, hybrid GGA functionals and scalar-relativistic and spin–orbit corrections were employed for both the DFT calculations of the molecular structure and particularly for the NMR chemical shifts. In particular, the populations of the N7-protonated and neutral forms of the complexes in solution were characterized by correlating the experimental and the DFT-calculated NMR chemical shifts. In contrast to the chemical exchange process involving the N7–H group, the hydrogen atom at N3 was determined to be unexpectedly rigid, probably because of the presence of the stabilizing intramolecular interaction N3–H···Cl. The described methodology combining the NMR spectroscopy and relativistic DFT calculations can be employed for characterizing the tautomeric and protonation equilibria in a large family of transition-metal-modified purine bases
-
platinum modified adenines unprecedented protonation behavior revealed by nmr spectroscopy and relativistic density functional theory calculations
Inorganic Chemistry, 2012Co-Authors: Jan Vicha, Gabriel Demo, Radek MarekAbstract:Two novel PtIV complexes of aromatic cytokinins with possible antitumor properties were prepared by reaction of selected aminopurines with K2PtCl6. The structures of both complexes, 9-[6-(benzylamino)purine] pentachloroplatinate (IV) and 9-[6-(furfurylamino)purine] pentachloroplatinate (IV), were characterized in detail by using two-dimensional NMR spectroscopy (1H, 13C, 15N, and 195Pt) in solution and CP/MAS NMR techniques in the solid state. We report for the first time the X-ray structure of a nucleobase adenine derivative coordinated to PtIV via the N9 atom. The protonation equilibria for the complexes in solution were characterized by using NMR spectroscopy (isotropic chemical shifts and indirect Nuclear spin–spin Coupling constants) and the structural conclusions drawn from the NMR analysis are supported by relativistic density-functional theory (DFT) calculations. Because of the presence of the Pt atom, hybrid GGA functionals and scalar-relativistic and spin–orbit corrections were employed for both...
Patricio Federico Provasi - One of the best experts on this subject based on the ideXlab platform.
-
the anomalous deuterium isotope effect in the nmr spectrum of methane an analysis in localized molecular orbitals
ChemPhysChem, 2008Co-Authors: Stephan P A Sauer, Patricio Federico ProvasiAbstract:Isotope effects on NMR indirect Nuclear spin–spin Coupling constants (SSCC) are less frequently studied than the corresponding effects on chemical shifts. Nevertheless, unusual effects have been observed for them and still lack a satisfying explanation. Raynes and co-workers measured the temperature dependence of the SSCC of the isotopomers of methane and found it puzzling that the reduced one-bond carbon–deuterium SSCC is larger than the carbon–proton Coupling constant for all mixed isotopomers. This implies that the secondary isotope effect [Eq. (1)] on the carbon–hydrogen SSCC
-
Interaction energies and NMR indirect Nuclear Spin-Spin Coupling constants in linear HCN and HNC complexes.
The Journal of Physical Chemistry A, 2005Co-Authors: Patricio Federico Provasi, Gustavo A. Aucar, Marina Sanchez, Ibon Alkorta, José Elguero, Stephan P A SauerAbstract:The cooperativity effects on both the electronic energy and NMR indirect Nuclear Spin-Spin Coupling constants J of the linear complexes (HCN) n and (HNC) n (n = 1-6) are discussed. The geometries of the complexes were optimized at the MP2 level by using the cc-pVTZ basis sets. The Spin-Spin Coupling constants were calculated at the level of the second-order polarization propagator approximation with use of the local dense basis set scheme based on the cc-pVTZ-J basis sets. We find strong correlations in the patterns of different properties such as interaction energy, hydrogen bond distances, and Spin-Spin Coupling constants for both series of compounds. The intramolecular Spin-Spin Couplings are with two exceptions dominated by the Fermi contact (FC) mechanism, while the FC term is the only nonvanishing contribution for the intermolecular Couplings. The latter do not follow the Dirac vector model and are important only between nearest neighbors.
-
the effect of lone pairs and electronegativity on the indirect Nuclear spin spin Coupling constants in ch2x x ch2 nh o s ab initio calculations using optimized contracted basis sets
Journal of Chemical Physics, 2001Co-Authors: Patricio Federico Provasi, Gustavo A. Aucar, Stephan P A SauerAbstract:The indirect Nuclear spin–spin Coupling constants of C2H4, CH2NH, CH2O, and CH2S were investigated by means of correlated ab initio calculations at the level of the second order polarization propagator approximation (SOPPA) and the second order polarization propagator approximation with coupled cluster singles and doubles amplitudes—SOPPA(CCSD) using large basis sets, which are optimized for the calculation of Coupling constants. It is found that at the self-consistent-field (SCF) level CH2NH and CH2S exhibit triplet instabilities whereas CH2CH2 and CH2O show triplet quasi-instabilities, which renders the SCF results meaningless. Our best results deviate between 0.3 and 2.7 Hz from the experimental values. We find that although the one-bond C–H and Y–H Couplings as well as the two- and three-bond H–H Couplings are dominated by the Fermi contact term, significant contributions of the orbital paramagnetic and sometimes even spin–dipolar terms are observed for the one-bond C–Y and two-bond C–H and Y–H coupli...
