Visualization

Plotting Mass Spectra (PlotMS)

The PlotMS utility was developed to visualize the results of QCxMS calculations. The newest version can be found in the PlotMS repository.

The program analyzes the qcxms.res or qcxms_cid.res file and provides the results as m/z-values and abundances. Versions 6.0 and higher provide exact masses of the fragments.

To run the program, extract the PlotMS executable

> tar -xvzf PlotMS.v.X.X.tar.xz

Replace the X.X with the current version number. The program is designed to run on Linux operating systems.

Move the .mass_raw.agr file into the $HOME folder. Change into your working directory, in which you created the qcxms.res or qcxms_cid.res file and run plotms. This generates three files:

mass.agr -> XMGRACE file using the ~/.mass_raw.agr template file

results.jdx -> JCAMP-DX ( Joint Committee on Atomic and Molecular Physical data) file

results.csv -> CSV (comma seperated values) file for spreadsheet programs (e.g. Excel)

The spectra can be plotted as soon as the production run has started by using the getres script, which creates an tmpqcxms.res file. The file has to be deleted before getres is used a second time.

For comparison to experiment, a file including the intensity and m/z values can be copied into the folder of the .res file. The file can be read in using plotms -i <file>. Most recommended is using a .csv file format with the following specifications:

m/z <real>	,	intensity <real>
m/z <real>	,	intensity <real>
…..	,	…..

PlotMS will than plot the .agr file with direct comparison between computed and experimental results. A dot matching score is printed at the end of the program output.

For a comparison to experimental integer spectra from the NIST database (JCAMP-DX format), the file can be copied into the working directory as nist.dat.

Program flags and command-line options

There are some useful command-line options to manipulate your results.

-v, --verbose: print verbose options
-f, --file <file>: provide .res file for plotting the spectrum

-t <x> <y>: couting ions with charge x to y (give the value, e.g. “-t 1 2” for charge 1 to 2)

-w, --width <real>: broadening the charges by an standard distribution (given in decimal numbers between 0 and 1)
-s, --cascades <integer>: account only for only secondary and tertiary fragmentations (give the value, e.g. “-s 2” for secondary)
-m, --min <integer>: set minimum value for m/z, so rel. 100% value will be calculated for higher masses (x-axis)
-i, --mzmin <real>: set the minimum rel. intensity from which the signals are counted (y-axis)
-p, --noisotope: do not calculate the isotope pattern
-e, --exp <file>: use the following file as input for comparison to the calculated spectrum

Visualization of Trajectories

Trajectories are saved in the TMPQCXMS/TMP.XXX directories, where NUM is the first number of the specific trajectory track to be visualized. There are two programs that can easily display the trajectories, which are saved in the trj.NUM.xxx files. One is (g)molden, the other is VMD. Obtaining a video (.avi) of a given trajectory is possibly most easily done by loading the trajectory of choice into VMD (file type .xyz).

The msmovie and movie.tcl scripts for VMD generate a visualization using the dynamic bonds graphical representations setting. This allows for movie generation employing the VMD movie maker plug-in. Simply type msmovie X Y in the working directory to load the trajectory TMPQCXMS/TMP.X/trj.X.Y. For instance, msmovie 1 1 loads the first trajectory of the first folder. Some adjustments according to personal preferences for movie-making may have to be made in these scripts.