Chemical shift
From NMR Wiki
Chemical shift is usually a little change in the resonating frequency of the nucleus. It's a shift that for a given environment is proportional to the magnetic field. So usually we express it as the ratio of the frequency shift of a given nucleus, and the resonating frequency of this kind of nucleus. It's usually expressed in part per million. Chemical shift could also be caused by a structure change, so it could be used to map ligand or protein binding region.
Wikipedia article about chemical shift
Contents |
Factor that influence the chemical shift
Local factors
Aromatic rings or other Pi system
Dihedral angles
Electric field
Hydrogen bonding
Isotopes of neighborer atoms
Global factors
Solvent
pH
Pseudocontact : it's a long range interaction that is caused by a paramagnetic center
Temperature
Chemical Shift and Structure
Value of the chemical shift is affected by the arrangement of covalent bonds and molecular conformation.
The latter property can be exploited to determine the molecular conformation. For proteins algorithms implemented in software TALOS and NIH-XPLOR 13C chemical shifts are used to determine backbone dihedral angle restraints.
Chemical Shift Calculation
Their are several software that allow to predict chemical shift in protein, for instance :
- shiftx
- shifts
Chemical shift could also be computed with quantum mechanics calculation, or using tabulated values, depending on the local groups ( that's more used for the determination in small molecules, atoms connectivity )
