Protocol: Wpmlgxmx1d1  Sequence: wpmlgxmx1d1.c  Apptype: solidseq1d

Description:

Wpmlg1dxmx is Wpmlg1d with a Z rotation supercycle.
It uses shapes in loop. CAUTIONS: shapes in loop require VNMRJ3.1 or 
higher. For older versions use wpmlgxmx1d.

Quadrature, windowed PMLG (wPMLG) for multiple-pulse acquisition. This 
sequence uses a composite preparation pulse involving a quadrature 
phase-shifted 90 and a 54.7-degree pulse along Y to place the 
magnetization perpendicular to the multiple-pulse axis of precession 
(sqrt(2/3), 0 sqrt(1/3)),  wPMLG has a cycle time of tauXwpmlg = 
2.0*(4.0*pwX90)*sqrt(2/3)) + B where pwX90 is the 90-degree pulse and B 
is the window time. The pulse time is fixed, and changing tauXwpmlg 
changes the window time B.  Wpmlgxmx1d is used with moderate spinning 
speeds of 8 to 14 kHz. 

Additional Software

reset_wpmlgxmx1d1 - This macro uses the calibrated values of pwH90 and aH90 
to calculate the intial parameters for the wpmlgX waveform and sets up 
2D parameters. 
   
Setup:

Load a calibrated data set and select the protocol Wpmlgxmx1d.  For a new 
calibration set the observe nucleus to protons and calibrate pw90X with 
a sample of Benzene doped with Chromium AcAc using Onepul, Xx and Xmx.  
An alternative sample is "RTV" silicon rubber spinning at about 2.5 
kHz. 

An alternate calibration is to set the proton pulse width pwH90 using 
Tancpx, a sample of Glycine and 13C observe. After calibration set the 
nucleus to proton and set tpwr, aX90 and pwX90 (of protons) equal to 
the calibrated values of dpwr, aH90 and pwH90 of Tancpx.  Set the 
sequence to Onepul and turn off the decoupler.  Observe a proton 
wideline spectrum with a 200 kHz spectral width and gain < 10. A good 
spin rate for this measurement is 10 kHz.  

Load the proton data set obtained with Onepul of either calibration and 
select Wpmlgxmx1d. 

The macro reset_wpmlg1d1 is run from the Wpmlgxmx1d1 protocol.  This 
macro performs the following 4 steps. 

1. Set aXprep1 = aH90.  Set pw1Xprep1 = pwX90, pw2Xprep1 = 
pwX90*54.7/90.0.
2. Set aXwpmlg = aX90.  Set pwXwpmlg = sqrt(2/3)*4.0*pwX90. The value 
of pwXwpmlg is rounded to a 12.5 ns grid and the value of aXwpmlg is 
adjusted to reflect the change. 
3. Set tauXwpmlg = (6/5)*2.0*pwXwpmlg, allowing a window of 1/6 of a 
cycle or a minimum of 4.0 us. 
4. Set sw = 1.0/tauXwpmlg. 

Set qXwpmlg = -5.  qXwpmlg = 5 is incorrect.   qXwpmlg can be reset to 
a larger value to provide PMLGN.  The maximum value of qXwpmlg is 
determined by pwXwpmlg/qXwpmlg >= 50 ns and large values will generate 
an acquisition error. 

To optimize the sample window. Set r1Xwpmlg = 0.5 us, r2Xwpmlg = 0.5uus 
and r3Xwpmlg = 1.0uus.  Set rof3 = r3Xwpmlg on the Receiver page 
(important!!). Set npaXwpmlg = 10 for a 1.0 us reciever on-time.  It 
may be necessary to increase tauXwpmlg to allow more time for 
acquisition.  An error will be generated on acquisition if tauXwpmlg is 
too small to.   Noise and spikes in the spectrum from ring-down in the 
window are also evidence that tauXwpmlg must be increased. 

Set scalesw = sqrt(3) for an approximate default scale factor. 

Obtain a spectrum of the glycine (spin rate 10.0 kHz) or doped benzene 
with a minimum of 4 scans.  The quadrature phase cycle must be used to 
avoid artifacts.  See the discussion below to optimize the spectrum. 

Referencing and Scaling Wpmlg2d:

Fine-adjust the scale factor with two lines of known ppm.  A good test 
sample is n.a. glycine where the two methylene lines are 1.0 ppm apart.  
To set the F2 scale factor put a cursor on each methylene line and set 
scalesw = (ppm2- ppm1)*sfrq/delta.  To set the F1 scale factor put a 
cursor on each methylene line and set scalesw1 = (ppm2-
ppm1)*sfrq/delta.  To reference F2 of the scaled 2D spectrum put a 
cursor on the line of interest and type rl(ppm*sfrq/scalesw).  To 
reference F1 of the scaled 2D spectrum put a cursor on the line of 
interest and type rl1(ppm*sfrq/scalesw1). 

Optimizing the Spectrum: 

All multiple-pulse spectra are strongly affected by phase transient of 
the probe. The effect of phase transient is to shift the frequency of 
the entire spectrum and increase the individual linewidths.  In an 
optimized setup, a Benzene (or RTV) line should be on resonance with 
both the sequences Onepul and Wpmlgxmx1d. Likewise a good spectrum of 
glycine obtained with tof = 0.0 and proper referencing with setref 
should be centerd around 5 ppm and have the minimum linewidths.  

A spectrum that is strongly affected by phase transient will be shifted 
to lower frequencies and it will be necessary to set a lower frequency 
offset to get the best linewidths.  A common practice in the presence 
of phase transient is to shift the carrier to about -5 ppm and obtain 
the entire spectrum at higher frequencies. Good spectra can be obtained 
this way and historically a low frequency carrier was needed anyway for 
non-quadrature experiments. 

Phase transient can be minimized through the adjustment of the cable 
length between the preamplifier and the probe.  A small further 
adjustment can be made by moving the center of the tuning dip off of 
the carrier frequency. The manual file tunerp has the procedures for 
minimization of phase transient. 

Spectra obtained with Wpmlgxmx1d also can show a strong center glitch or 
"pedestal". The pedestal is a real signal that results from spins that 
have been spin-locked along the axis of precession of wPMLG.  Spins 
from the sample end up in pedestal if the preparation pulse pw2Xprep1 
is adjusted incorrectly. Also, proton background spins from the module 
end up along the precession axis because they have a low flip-angle and 
are not refocused by wPMLG. Vespel modules have a strong proton signal 
that may be larger than the signal of the sample so pedestal removal 
involvesan exact subtraction of two large numbers. Kel-f modules have 
fewer protons but have a 19F background.  Also, spectra that are not 
obtainedwith a multiple of 4 scans will have a pedestal. 

The pedestal can be removed completely, even in the presence of high 
background, by adjustment of pw2Xprep1, if the pulses are close to 
resonance and phase transient has been minimized. Array pw2Xprep1 over 
several microseconds around the 54.7-degree pulse. If one would rather 
not make the effort to remove the pedestal move the carrier and 
pedestal to lower a frequency where it is out of the spectrum. 

wPMLG spectra are best obtained with a medium spinning frequency, in 
the range 8.0 to 14.0 kHz. At faster speeds the rotor cycle interferes 
with the multiple pulse cycle and lowers the performance.  At slower 
speeds spinning does not contribute to averaging. 

Referencing and Scaling Wpmlg2d:

Fine-adjust the scale factor with two lines of known ppm.  A good test 
sample is n.a. glycine where the two methylene lines are 1.0 ppm apart.  
To set the scale factor put a cursor on each methylene line and set 
scalesw = (ppm2- ppm1)*sfrq/delta.  To reference F2 of the scaled 2D 
spectrum put a cursor on the line of interest and type 
rl(ppm*sfrq/scalesw).  

Parameter Groups: 

prepX:  Module:  no
Sequence:  br24q.c
Description:  Implements a variable length pulse to provide quadrature
              detection about a tilted precession axis. Typically
              followed by a windowed multiple-pulse acquisition.
Parameters:  Sequence Page
       aXprep - the amplitude of the obs pulses.
       pwXprep - 90-degree flip on the obs channel.
       phXprep - small-angle phase offset of the pulse. The phase must
              be reset to zero after the pulse.

scaleX: (processing)  Module:  no 
Sequence:  br24.c    
Description:  Shows the F2 scale factor, scalesw, for evolution of the 
              obs nuclei under a multiple-pulse waveform. 
Parameters:  Sequence Page
       scalesw - the F2 scale factor. Typically scalesw is the inverse 
              of the mutiple-pulse scale factor.       

wpmlg1X:  Module:  yes
Sequence:  wpmlg1d1.c  
Description:  Implements windowed PMLG homonuclear decoupling with 
              acquisition in the window using shapes in loop
Parameters:  Sequence Page
       aXwpmlg - amplitude of PMLG on obs.
       pwXwpmlg - 360-degree flip on obs, off resonance (the length of 
              each of the two PMLG pulses).  
       qXwpmlg - number of phase steps that make up pwXpmlg. A negative 
              value implements descending phases in the first pulse.
       r1Xwpmlg - pre-pulse delay (similar to rof1). 
       r2Xwpmlg - post_pulse delay (similar to rd or rof2).
       r3Xwpmlg - T/R-to-rcvron delay (must equal rof3 or 2.0 us if 
              rof3 is not defined. 
       tauXwpmlg - time for one PMLG cycle including the window.
       npaXwpmlg - number of 100 ns ticks in the detection window.
       chXwpmlg = 'obs' must be set (not shown).
       ofXwpmlg - offset value in Hz
Implementation:  WMPA wpmlg = getwpmlgxmx1("wpmlgX");
Underscore function: _wpmlg1(wpmlg,phXwpmlg);  phXwpmlg is the overall 
              phase table. 
