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.

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 μs
• Initial duration of the second pulse: 0
• Final duration of the second pulse: 4 μs
• Pulse duration increment: 0.25 μs
• Number of the second-pulse duration increment: 17
• Third-pulse duration: 9 μs
• 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

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

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.

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:

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.