Insensitive Nuclei Enhanced by Polarization Transfer
Encyclopedia
Insensitive Nuclei Enhanced by Polarization Transfer (INEPT) is a signal enhancement method used in NMR spectroscopy
which involves the transfer of nuclear spin
polarization from spins with large Boltzmann population
differences to nuclear spins of interest with low Boltzmann population differences. INEPT uses J-coupling
for the polarization transfer in contrast to the Nuclear Overhauser Effect
(NOE) which arises from dipolar cross-relaxation.
The signal enhancement has two sources:
As a result, INEPT can enhance the NMR signal by a factor larger than K, while the NOE can increase the signal by a factor of at most 1+K/2. Note that a negative value of K may result in a reduction in signal intensity; historically INEPT was proposed a method to enhance the signal from the limited number of nuclei with negative magnetogyric ratio e.g. 15N or 29Si.
NMR spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is a research technique that exploits the magnetic properties of certain atomic nuclei to determine physical and chemical properties of atoms or the molecules in which they are contained...
which involves the transfer of nuclear spin
Spin (physics)
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...
polarization from spins with large Boltzmann population
Boltzmann distribution
In chemistry, physics, and mathematics, the Boltzmann distribution is a certain distribution function or probability measure for the distribution of the states of a system. It underpins the concept of the canonical ensemble, providing its underlying distribution...
differences to nuclear spins of interest with low Boltzmann population differences. INEPT uses J-coupling
J-coupling
J-coupling is the coupling between two nuclear spins due to the influence of bonding electrons on the magnetic field running between the two nuclei. J-coupling contains information about dihedral angles, which can be estimated using the Karplus equation...
for the polarization transfer in contrast to the Nuclear Overhauser Effect
Nuclear Overhauser effect
The Nuclear Overhauser Effect is the transfer of nuclear spin polarization from one nuclear spin population to another via cross-relaxation. It is a common phenomenon observed by nuclear magnetic resonance spectroscopy. The theoretical basis for the NOE was described and experimentally verified...
(NOE) which arises from dipolar cross-relaxation.
The signal enhancement has two sources:
- The spin population effect increases the signal by a factor of K = ratio of magnetogyric ratioMagnetogyric ratioIn physics, the gyromagnetic ratio of a particle or system is the ratio of its magnetic dipole moment to its angular momentum, and it is often denoted by the symbol γ, gamma...
s of the nuclei. - Nuclei with higher magnetogyric ratio generally relax more quickly. Since the rate at which the INEPT transfer can be repeated is limited by the relaxation of these spins (rather than the low sensitivity spins), then the experiment can be repeated more frequently, increasing the signal-to-noise ratio.
As a result, INEPT can enhance the NMR signal by a factor larger than K, while the NOE can increase the signal by a factor of at most 1+K/2. Note that a negative value of K may result in a reduction in signal intensity; historically INEPT was proposed a method to enhance the signal from the limited number of nuclei with negative magnetogyric ratio e.g. 15N or 29Si.