NMR Shift Reagents
Rare Earth Products, Inc. offers a comprehensive listing of NMR Shift Reagents.
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NMR ( nuclear magnetic resonance ) shift reagents
Paramagnetic shift reagents have the ability to induce chemical
shifts and thus simplify complex NMR spectra. The most efficient
shift reagents are complexes of paramagnetic lanthanide ions
such as europium(III) for down field shifts and
praseodymium(III) for upfield shifts.
Over the past several decades, nuclear magnetic resonance
spectroscopy has become one of the most important analytical
methods of structure elucidation of organic, bioorganic and
organometallic compounds. For example, the chemical shifts and
coupling patterns provide invaluable information for the
determination of stereochemistry. Organic molecules contain
mainly carbon and hydrogen, and thus most of the structural
information is gained from proton and carbon NMR data. However,
the proton NMR signals are not spread over a wide range (0 to 15
ppm) and therefore proton NMR spectra of complex organic and
biological molecules consist of featureless clusters that are
very difficult to assign. It has been known that paramagnetic
transition metal ions perturb the proton NMR spectra of the
ligands that coordinate them. Based on this observation, a wide
range of paramagnetic shift reagents have been prepared that
have the ability to induce chemical shifts and thus simplify
complex proton NMR spectra. Theoretical studies revealed that
the induced shifts are the consequence of contact and dipolar
(pseudo-contact) interactions between the paramagnetic ion and
the organic molecule. The requirements for an effective shift
reagent include optimal sifting power with minimal line
broadening effect and an ability to bind to a large variety of
organic molecules. The most efficient shift reagents are
complexes of paramagnetic lanthanide ions such as europium (III)
for down field shifts and praseodymium(III) for upfield shifts.
The most commonly used ligands include dipivaloyl methane (DPM),
2,2,6,6-tetramethyl-3,5-heptanedione (THD), and
1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione (FOD).
Signal overlap is a major problem for determining three
dimensonal protein structures. Paramagnetic lanthanide(III)
salts and DTPA complexes have been used to resolve overlaps in
the NMR spectra of certain proteins.
