scholarly journals Band inversion amplifies31P-31P nuclear overhauser effects: Relaxation mechanism and dynamic behavior of ATP in the human brain by31P MRS at 7 T

2016 ◽  
Vol 77 (4) ◽  
pp. 1409-1418 ◽  
Author(s):  
Jimin Ren ◽  
A. Dean Sherry ◽  
Craig R. Malloy
Keyword(s):  
Human Brain ◽  
Dynamic Behavior ◽  
Relaxation Mechanism ◽  
Band Inversion ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

Positive and negative intramolecular nuclear Overhauser effects in an all-proton system

1968 ◽  
Vol 46 (21) ◽  
pp. 3421-3423 ◽  
Author(s):  
R. A. Bell ◽  
J. K. Saunders
Keyword(s):  
Relaxation Mechanism ◽  
Qualitative Explanation ◽  
Negative Effects ◽  
Dipole Relaxation ◽  
Positive Effects ◽  
Overhauser Effect ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

The Overhauser effects recorded for the alkaloid ochotensimine (1) show positive effects (area increases) for adjacent protons but negative effects (area decreases) for two protons separated by an intervening proton. A qualitative explanation based on the dominance of a dipole–dipole relaxation mechanism is advanced. The Overhauser effect between geminal protons on an sp2-carbon has been measured.

scholarly journals NMR solution conformation of heparin-derived tetrasaccharide

1996 ◽  
Vol 318 (1) ◽  
pp. 93-102 ◽  
Author(s):  
Dmitri MIKHAILOV ◽  
Kevin H. MAYO ◽  
Ioncho R. VLAHOV ◽  
Toshihiko TOIDA ◽  
Azra PERVIN ◽  
...  
Keyword(s):  
Chair Conformation ◽  
Coupling Constants ◽  
Solution Conformation ◽  
1H And 13C Nmr ◽  
Small Deviations ◽  
J Coupling Constants ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects ◽  
Dynamics Simulations ◽  
Ring Conformations

The solution conformation of the homogeneous, heparin-derived tetrasaccharide ΔUA2S(1 → 4)-α-d-GlcNpS6S(1 → 4)-α-l-IdoAp2S(1 → 4)-α-d-GlcNpS6S (residues A, B, C and D respectively, where IdoA is iduronic acid) has been investigated by using 1H- and 13C-NMR. Ring conformations have been defined by J-coupling constants and inter-proton nuclear Overhauser effects (NOEs), and the orientation of one ring with respect to the other has been defined by inter-ring NOEs. NOE-based conformational modelling has been done by using the iterative relaxation matrix approach (IRMA), restrained molecular dynamics simulations and energy minimization to refine structures and to distinguish between minor structural differences and equilibria between various ring forms. Both glucosamine residues B and D are in the 4C1 chair conformation. The 6-O-sulphate group is oriented in the gauche–trans configuration in the D ring, whereas in the B ring the gauche–gauche rotomer predominates. Uronate (A) and iduronate (C) residues are mostly represented by 1H2 and 2S0 twisted boat forms, respectively, with small deviations in expected coupling constants and NOEs suggesting minor contributions from other A and C ring conformations.

Structure assignment of some 3,4′-diquinolinyl sulfides studied by Nuclear Overhauser Effects, X-ray analysis and reactions with sodium methoxide

2010 ◽  
Vol 109 (10) ◽  
pp. 509-514 ◽  
Author(s):  
Stanislaw Boryczka ◽  
Andrzej Maślankiewicz ◽  
Miroslaw Wyszomirski ◽  
Teresa Borowiak ◽  
Maciej Kubicki
Keyword(s):  
Sodium Methoxide ◽  
X Ray ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects ◽  
Structure Assignment

scholarly journals Comparison of Methods for Bulk Automated Simulation of Glycosidic Bond Conformations

2020 ◽  
Vol 21 (20) ◽  
pp. 7626
Author(s):  
Victor Stroylov ◽  
Maria Panova ◽  
Philip Toukach
Keyword(s):  
Density Functional ◽  
Structural Features ◽  
Functional Theory ◽  
Conformational Ensembles ◽  
Explicit Solvent ◽  
Empirical Force Field ◽  
Automated Simulation ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects ◽  
Accuracy Speed

Six empirical force fields were tested for applicability to calculations for automated carbohydrate database filling. They were probed on eleven disaccharide molecules containing representative structural features from widespread classes of carbohydrates. The accuracy of each method was queried by predictions of nuclear Overhauser effects (NOEs) from conformational ensembles obtained from 50 to 100 ns molecular dynamics (MD) trajectories and their comparison to the published experimental data. Using various ranking schemes, it was concluded that explicit solvent MM3 MD yielded non-inferior NOE accuracy with newer GLYCAM-06, and ultimately PBE0-D3/def2-TZVP (Triple-Zeta Valence Polarized) Density Functional Theory (DFT) simulations. For seven of eleven molecules, at least one empirical force field with explicit solvent outperformed DFT in NOE prediction. The aggregate of characteristics (accuracy, speed, and compatibility) made MM3 dynamics with explicit solvent at 300 K the most favorable method for bulk generation of disaccharide conformation maps for massive database filling.

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