INEPT ( Insensitive Nuclei Enhanced Polarization Transfer )

«Enhancement of Nuclear Magnetic Resonance Signals by Polarization Transfer» Gareth A. Morris, Ray Freeman, JACS 101:3, 1979

Emine Can Biomolecular structure and dynamics in solution, 2012

The sensitivity of NMR Signal

SNR

• Nuclear Magnetic Moment

• Nuclear Larmour Frequency

• Boltzman Polarization

• Noise in the coil

ɣ

ω

ω

∝

∝

∝

∝

∝

√ω  

ɣ ω2 ω1/2= |ɣ|5/2 B03/2

INEPT: Transfer of the polarization from strongly magnetic proton spinsto weakly magnetic nuclei (15N, 29Si...) by using J-couplings between the spins.

Sensitivity Enhancement

Pulse sequence for INEPT

τ=1/4J

a b c e f

d

Iz+Sz

a e f

Pulse sequence for INEPT

τ=1/4J

a b c e f

d

Iz+Sz

a e f

a

Iy+Sz

Pulse sequence for INEPT

τ=1/4J

a b c e f

d

Iz+Sz

a e f

b

Iy+Sz

ᵦα

Pulse sequence for INEPT

τ=1/4J

a b c e f

d

Iz+Sz

a e f

c

Iy+Sz

ᵦ α

Pulse sequence for INEPT

τ=1/4J

a b c e f

d

Iz+Sz

a e f

d

Iy+Sz

ᵦα

Pulse sequence for INEPT

τ=1/4J

a b c e f

d

Iz+Sz

a e f

= [Iycos(Πj2(1/4J))+2IxSzsin(Πj2(1/4J))]-Sz

= [Iycos(Π/2)+2IxSzsin(Π/2)]-Sz = 2IxSz-Sz

Iy+Sz [Iycos(πJ2τ)+2IxSzsin(πJ2τ)]-Sz

e

ᵦ

α

Pulse sequence for INEPT

τ=1/4J

a b c e f

d

Iz+Sz

a e f

= [Iycos(Πj2(1/4J))+2IxSzsin(Πj2(1/4J))]-Sz

= [Iycos(Π/2)+2IxSzsin(Π/2)]-Sz = 2IxSz-Sz

Iy+Sz [Iycos(πJ2τ)+2IxSzsin(πJ2τ)]-Sz

e

ᵦ

α

2IzSy+Sy

BI2IzSy + BSSy

transferred non-transferred

BI =10|BS|

Components of the INEPT Spectrumfor the case of 1H-15N system

* Spin Dynamics M.Levitt, p421

Results

Results

INEPT

NOE

Unenhanced

X 11B 13C 15N 29Si 57Fe 103Rh 109Ag 119Sn 183W

NOE 2.56 2.99 -3.94 -1.52 16.48 -16.89 -9.75 -0.41 13.02

INEPT 3.12 3.98 9.87 5.03 30.95 31.77 21.50 2.81 24.04

Enhancement factor:

• Enhancement factor• Repetition time• Nuclei with negative ɣ

Refocussed INEPT

Precess the anti-phase components into phase before aquisition. Decoupled spectrum+ Increased intensity with polarization transfer

2IxSz-Sz

-2IzSx-Sx

a b c e

a b e-Sy-2IzSx

transferrednon-transferred

BI =10|BS|

* Spin Dynamics M.Levitt, p422

Single 90 degree pulseProton decoupled

INEPT Refocussed INEPT

Results

Thanks!

emine.can[at]epfl.ch

References:1) G.A.Morris, R.Freeman, JACS, 101:3 19792) M. Levitt , ‘Spin Dynamics’ 20053) J.K.M.Sanders, B. Hunter ‘Modern NMR Spectroscopy’ 2nd Edition