Conformational Analysis with Carbon−Carbon Coupling Constants. A Density Functional and Molecular Mechanics Study

1997 ◽  
Vol 62 (11) ◽  
pp. 3702-3704 ◽  
Author(s):  
Martin Stahl ◽  
Ulrich Schopfer ◽  
Gernot Frenking ◽  
Reinhard W. Hoffmann
Keyword(s):  
Conformational Analysis ◽  
Molecular Mechanics ◽  
Density Functional ◽  
Coupling Constants

Prediction of spin-spin coupling constants in solution based on combined density functional theory/molecular mechanics

2009 ◽  
Vol 130 (13) ◽  
pp. 134508 ◽  
Author(s):  
Andreas Møgelhøj ◽  
Kestutis Aidas ◽  
Kurt V. Mikkelsen ◽  
Stephan P. A. Sauer ◽  
Jacob Kongsted
Keyword(s):  
Density Functional Theory ◽  
Molecular Mechanics ◽  
Density Functional ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Functional Theory ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Conformational analysis and complete assignment of the proton and carbon NMR spectra of ouabain and ouabagenin

1990 ◽  
Vol 68 (8) ◽  
pp. 1263-1270 ◽  
Author(s):  
Deane D. McIntyre ◽  
Markus W. Germann ◽  
Hans J. Vogel
Keyword(s):  
Conformational Analysis ◽  
Molecular Mechanics ◽  
Nmr Spectra ◽  
Coupling Constants ◽  
X Ray Diffraction ◽  
Proton Proton ◽  
Proton Coupling ◽  
Nmr Techniques ◽  
Phase Sensitive ◽  
C Nmr

The 1H and 13C NMR spectra of the cardenolide ouabain and its aglycon ouabagenin have been completely assigned by two-dimensional NMR techniques, including phase-sensitive COSY and carbon–proton correlation (HETCOR, HMQC, and COLOC) spectra. The major conformer of these two compounds in solution is all-chair as determined from proton–proton coupling constants and is similar to that in the crystal lattice as previously determined by X-ray diffraction. The conformations of the A and D rings of ouabain in water are somewhat different than in DMSO/CDCl3 (2:1). At lower temperatures (−20 °C) signals from two conformers in slow exchange were readily observed in the 13C spectra, with an approximate ratio of 1:7. Molecular mechanics and dynamics calculations indicate that the conformational process responsible for this involves a chair/twist-boat interconversion of the A ring, with the all-chair conformer highly preferred. Keywords: ouabain, conformational analysis, 2-D NMR, molecular mechanics, molecular dynamics.

Density Functional Restricted–Unrestricted/Molecular Mechanics Theory for Hyperfine Coupling Constants of Molecules in Solution

2011 ◽  
Vol 7 (10) ◽  
pp. 3261-3271 ◽  
Author(s):  
Zilvinas Rinkevicius ◽  
N. Arul Murugan ◽  
Jacob Kongsted ◽  
Bogdan Frecuş ◽  
Arnfinn Hykkerud Steindal ◽  
...  
Keyword(s):  
Molecular Mechanics ◽  
Density Functional ◽  
Hyperfine Coupling ◽  
Coupling Constants ◽  
Hyperfine Coupling Constants

Assessing the Calculation of Exchange Coupling Constants and Spin Crossover Gaps Using the Approximate Projection Model to Improve Density Function Calculations

2019 ◽  
Author(s):  
Xianghai Sheng ◽  
Lee Thompson ◽  
Hrant Hratchian
Keyword(s):  
Density Functional Theory ◽  
Exchange Coupling ◽  
Density Functional ◽  
Spin Crossover ◽  
Coupling Constants ◽  
Spin Projection ◽  
Coupling Constant ◽  
Projection Model ◽  
Functional Theory

This work evaluates the quality of exchange coupling constant and spin crossover gap calculations using density functional theory corrected by the Approximate Projection model. Results show that improvements using the Approximate Projection model range from modest to significant. This study demonstrates that, at least for the class of systems examined here, spin-projection generally improves the quality of density functional theory calculations of J-coupling constants and spin crossover gaps. Furthermore, it is shown that spin-projection can be important for both geometry optimization and energy evaluations. The Approximate Project model provides an affordable and practical approach for effectively correcting spin-contamination errors in molecular exchange coupling constant and spin crossover gap calculations.

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