Definition of echo and antiecho signals in MQMAS NMR




Home and Applets > Pulse Program > XwinNMR 3.5 > Echo and Antiecho Definition

In 3QMAS NMR of a spin I = 5/2 system, an echo signal E(t1, t2) and an antiecho signal A(t1, t2) have the following expressions:

where t1 is the evolution period and t2 the acquisition period.

Echo and antiecho in z-filter MQMAS

Z-filter 3QMAS sequence and coherence transfer pathway for a spin I = 3/2

Fig. 1: Z-filter 3QMAS NMR pulse sequence and coherence transfer pathway.
The echo amplitude and the antiecho amplitude have the same sign.

The three-pulse z-filter MQMAS sequence generates echo and antiecho, which have the same amplitude with the same sign.

The detected signal is the contribution of E(t1, t2) and A(t1, t2):

S3(t1, t2) = H.E(t1, t2) + H.A(t1, t2)

The amplitude H is a complex number. The 2D Fourier transform of S3(t1, t2) generates phase-twisted 2D peak.

The standard solution to this problem is the application of States procedure to generate 2D pure absorption peak. It consists in acquiring two complementary signals:

The echo SE(t1, t2) and antiecho SA(t1, t2) signals are obtained from Sx(t1, t2) and Sy(t1, t2):

Echo and antiecho in two-pulse MQMAS

Amplitude-modulated two-pulse 3QMAS sequence and coherence transfer pathway

Fig. 1: Amplitude-modulated two-pulse 3QMAS NMR pulse sequence and coherence transfer pathway.
The echo amplitude and the antiecho amplitude have opposite signs.

The two-pulse MQMAS sequence generates echo and antiecho, which do not have the same amplitude but with opposite signs.

The detected signal is the contribution of E(t1, t2) and A(t1, t2):

S2(t1, t2) = H.E(t1, t2) - H.A(t1, t2)

For simplicity, they are supposed to have opposite amplitudes. The 2D Fourier transform of S2(t1, t2) generates phase-twisted 2D peak.

The States procedure consists in acquiring two complementary signals:

The echo SE(t1, t2) and antiecho SA(t1, t2) signals are obtained from Sx(t1, t2) and Sy(t1, t2):

Conclusion

For these two pulse sequences in 3QMAS NMR of a spin I = 5/2 system, the echo SE(t1, t2) and antiecho SA(t1, t2) signals are obtained with the same formulas:

These two formulas are a consequence of the +π/2 angles involved in Sy(t1, t2). This +π/2 angle is included in the pulse program by applying to the first pulse a phase change of +π/|2p| for Sy(t1, t2) acquisition.

Conversely, Sx(t1, t2) and Sy(t1, t2) can be expressed as:

In the States method, pure 2D absorption spectrum is the Fourier transform in the t1 domain of
Re[Sx(t1, ω2)] + i.Re[Sy(t1, ω2)]

(top)

[Contact me] - Last updated December 16, 2012
Solid-state NMR bibliography for
Aluminum-27
Antimony-121/123
Arsenic-75
Barium-135/137
Beryllium-9
Bismuth-209
Boron-11
Bromine-79/81
Calcium-43
Cesium-133
Chlorine-35/37
Chromium-53
Cobalt-59
Copper-63/65
Deuterium-2
Gallium-69/71
Germanium-73
Gold-197
Hafnium-177/179
Indium-113/115
Iodine-127
Iridium-191/193
Krypton-83
Lanthanum-139
Lithium-7
Magnesium-25
Manganese-55
Mercury-201
Molybdenum-95/97
Neon-21
Nickel-61
Niobium-93
Nitrogen-14
Osmium-189
Oxygen-17
Palladium-105
Potassium-39/41
Rhenium-185/187
Rubidium-85/87
Ruthenium-99/101
Scandium-45
Sodium-23
Strontium-87
Sulfur-33
Tantalum-181
Titanium-47/49
Vanadium-51
Xenon-131
Zinc-67
Zirconium-91



Copyright 2002- pascal-man.com. All rights reserved.