Simulation of z-filtered MQMAS
NMR for a spin I = 5/2.
Contributor: R. Hajjar




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Z-filtered MQMAS

AIM: We provide Mathematica-5 notebooks and SIMPSON1.1.1 Tcl scripts to optimize the echo and antiecho amplitudes for z-filtered MQMAS NMR experiment applied to half-integer quadrupole spin.

J.-P. Amoureux and coworkers [Z filtering in MQ MAS NMR, J. Magn. Reson. A 123, 116-118 (1996)] present the z-filter approach which allows the symmetrization of both echo and antiecho transfer pathways, generating a 2D pure absorption MQMAS spectrum.

Z-filter MQMAS sequence and coherence transfer pathways

Fig. 1: Z-filtered MQMAS pulse sequence and coherence transfer pathways for 3Q echo and -3Q antiecho of a spin I = 5/2 system.
0Q -> 3Q -> 0Q -> -1Q is the 3Q echo transfer pathway.
0Q -> -3Q -> 0Q -> -1Q is the -3Q antiecho transfer pathway.
The echo amplitude and the antiecho amplitude have the same sign.

Method: We simulate the echo and the antiecho amplitudes of a spin I = 5/2 with increasing second-pulse duration in a powder rotating at the magic angle, using Mathematica-5 notebooks and SIMPSON1.1.1 Tcl scripts.

The parameters for these simulations are:

  • Nucleus: 27Al
  • Spin: 5/2
  • 27Al Larmor frequency: 208.61889974 MHz
  • Proton Larmor frequency: 800 MHz
  • Only 3Q and -3Q coherences belonging to the second diagonal of the density matrix are taken into account for the simulation
  • Amplitude of the strong radio-frequency pulse: 90 kHz
  • Amplitude of the weak radio-frequency pulse: 9.3 kHz
  • First-pulse duration: 4 s
  • Initial duration of the second pulse: 0
  • Final duration of the second pulse: 4 s
  • Pulse duration increment: 0.25 s
  • Number of the second-pulse duration increment: 17
  • Third-pulse duration: 9 s
  • Rotor spinning speed: 5 kHz
  • Quadrupole interaction: first and second orders
  • Quadrupole coupling constant: 5 MHz
  • Asymmetry parameter: -1 for notebook and 1 for Tcl script
  • Crystal file: rep100_simp for notebook and rep100.cry for Tcl script
  • Number of summation steps of the Euler angle γ of the rotor: 10

(A) Mathematica-5 notebook

(1) Preliminary

Optimization
with
Notebook
strong pulse p1 zfilter_P1.nb (pdf)
strong pulse p2 zfilter_P2.nb (pdf)
soft pulse p3 zfilter_P3.nb (pdf)
  1. Download Mathematica-5 notebook zfilter_P2.nb, that for MAS NMR utilities QUADRUPOLE_1_0.nb (the corresponding PDF file), and the crystal file rep100_simp.
  2. Save these three files into the software Mathematica-5 folder. Forbidden the Operating System of your computer to include extra file extension to rep100_simp by providing the file name with double quotes such as "rep100_simp".
  3. Open QUADRUPOLE_1_0.nb file with Mathematica-5.
  4. Press "Ctrl-A" to select the notebook, then press "Shift-enter" to start the notebook. (Some warning messages appear but they have no consequences on the results.) A new file called QUADRUPOLE is created in Mathematica-5 folder.

(2) Simulation

  1. Open zfilter_P2.nb file with Mathematica-5.
  2. Press "Ctrl-A" to select the notebook, then press "Shift-enter" to start simulation. (Some warning messages precede the simulation.) At the end a data file called zfilter_P2 is created in Mathematica-5 folder. MS Excel can open this data file for graphic representation.

(B) SIMPSON1.1.1 Tcl script

(1) Preliminary

Optimization with SIMPSON1.1.1
strong pulse p1 zfilter_p1.in
strong pulse p2 zfilter_p2.in
soft pulse p3 zfilter_p3.in

Download and save zfilter_p2.in file into the software SIMPSON1.1.1 folder.

(2) Simulation

  1. Run zfilter_p2.in in a DOS window.
  2. The simulated signal amplitudes are saved in the file called zfilter_p2.fid in SIMPSON1.1.1 folder. MS Excel also can open this data file for graphic representation.

(C) Result

Figure 2 represents the simulated data. Notebook and Tcl script provide the same curve.

Aluminum z-filtered 3Q-echo and -3Q antiecho amplitudes

Fig. 2: 27Al z-filtered 3Q echo and -3Q antiecho amplitudes versus the second-pulse duration.

We also provide notebooks and SIMPSON1.1.1 Tcl scripts where all the coherences belonging to the same MQ coherence transfer pathway are considered:

Optimization
with
Notebook SIMPSON
1.1.1
strong pulse p1 zfilter_P1S.nb,
(pdf)
zfilter_p1S.in
strong pulse p2 zfilter_P2S.nb,
(pdf)
zfilter_p2S.in
soft pulse p3 zfilter_P3S.nb,
(pdf)
zfilter_p3S.in

These files allow us to compare simulated data with those obtained with SPAM MQMAS approach.

Nicolas Malicki and coworkers [Multiplex MQMAS NMR of quadrupolar nuclei, Solid State Nucl. Magn. Reson. 28, 13-21 (2005)] present the Multiplex z-filter approach which reduces the experimental time considerably.

 

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[Contact me] - Last updated December 16, 2012
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