EasySpin forum

I collected an EPR spectrum of photolyzed struvite in the presence of DMPO in water. I expect it to mainly generate reactive oxygen species. I then simulated EPR spectra for several DMPO adducts and oxidation products using the literature hyperfine splitting values from Buettner's 1987 Free Radical Biology and Medicine paper. I also considered ammonia and phosphate radicals since these could come from struvite. (I had to shift the g-value 0.002 units away from its literature value due to our instrument, as I mentioned in a previous post.) I overlaid the simulated spectra with my experimental spectrum in Origin and found that many of my peaks could be assigned, but there were several which did not correspond to any of the DMPO adducts or oxidation products I considered. Does anyone have any idea as to what these unassigned features might be, or know of a reference that might be able to help? I am attaching my experimental spectrum to this post.
Here is my code. I converted the x-axis to g-values at the end since that is what my instrument reports:
%DMPO-OH simulation
clear,clc,clf
Sys.S=1/2;
Sys.Nucs='14N,1H';
Sys.g=2.00829;
Sys.A=[42 42];
Sys.lwpp=0.1;
Exp.mwFreq=9.851525;
Exp.Range=[345 355];
[B1,spc1]=garlic(Sys,Exp);
%%
%DMPO-OOH simulation
Sys.S=1/2;
Sys.Nucs='14N,1H,1H';
Sys.g=2.00829;
Sys.A=[40.1 32.8 3.52];
Sys.lwpp=0.1;
Exp.mwFreq=9.851525;
Exp.Range=[345 355];
[B2,spc2]=garlic(Sys,Exp);
%%
%DMPOX simulation
Sys.S=1/2;
Sys.Nucs='14N,1H,1H';
Sys.A=[19.9 11.8 11.8];
Sys.g=2.00829;
Sys.lwpp=0.1;
Exp.mwFreq=9.851525;
Exp.Range=[345 355];
[B3,spc3]=garlic(Sys,Exp);
%%
%3-DMPO-yl simulation
Sys.S=1/2;
Sys.Nucs='14N,1H';
Sys.A=[46.2 62.8];
Sys.g=2.00829;
Sys.lwpp=0.1;
Exp.mwFreq=9.851525;
Exp.Range=[345 355];
[B4,spc4]=garlic(Sys,Exp);
%%
%DMPO dimer simulation
Sys.S=1/2;
Sys.Nucs='14N,1H';
Sys.A=[39.8 44.5];
Sys.g=2.00829;
Sys.lwpp=0.1;
Exp.mwFreq=9.851525;
Exp.Range=[345 355];
[B5,spc5]=garlic(Sys,Exp);
%%
%Simulating the degradation product of DMPO and O2-
Sys.S=1/2;
Sys.Nucs='14N,1H'
Sys.A=[42.9 61.6];
Sys.g=2.00829;
Sys.lwpp=0.1;
Exp.mwFreq=9.851525;
Exp.Range=[345 355];
[B6,spc6]=garlic(Sys,Exp);
%%
%DMPO-NH3 simulation
Sys.S=1/2;
Sys.Nucs='14N,1H,14N';
Sys.A=[39.2 52.5 8.76];
Sys.g=2.00829;
Sys.lwpp=0.1;
Exp.mwFreq=9.851525;
Exp.Range=[345 355];
[B7,spc7]=garlic(Sys,Exp);
%%
%DMPO-PO2(OH)2 simulation
Sys.S=1/2;
Sys.Nucs='14N,1H,1H,31P';
Sys.A=[40.9 34.8 3.08 1.4];
Sys.g=2.00829;
Sys.lwpp=0.1;
Exp.mwFreq=9.851525;
Exp.Range=[345 355];
[B8,spc8]=garlic(Sys,Exp);
%%
%Simulating the sum of multiple DMPO products
total=spc1+spc2+spc3+spc4+spc5+spc6+spc7+spc8;
G=B110;
gnumerator=planck9.8515251e9ones(1,1024);
gdenominator=bmagn1e-4G;
g=gnumerator./gdenominator;
plot(g,total)

You posted the parameter file. Where is the .spc file ?
I am curious about your experimental spectrum

I apologize for posting the incorrect file type. Here is the .spc file

You summed up several EPR spectral simulations and I am not sure if it is realistic.
Your total spectrum does not resemble the experimental data (see attachment)
Here is my simulation and a comparison to experimental data (it is not quite right but close).
If you can refine my simulation code and may be correct it, you could obtain something quite right (see my code below).

%%
clear, clc, clf
[data_one, data_two,exp_parameters]= eprload ('500_uM_struvite_photolyzed.spc');

plot(data_one/10, data_two/max(data_two)); % checking experimental data
%

Sys.S=1/2;
Sys.Nucs='14N,1H,1H,1H';% this is not necessarily true but you could think more about this

Sys.n = [1 1 2 2];% arbitrary for now but think from this perspective
Sys.g=2.0127; % randomly shifted the spectrum, so...

Sys.A=[41.5 21.96 11.7 10.26];% literature values my not necessarily describe your sample especially in a random system like adducts, so I started with these values
Sys.lwpp=0.099;
Exp.mwFreq=9.8415;
Exp.Range=[345 355];
Exp.nPoints= 512;
Vary.A = [10 10 10 10];
Vary.g= [0.05];

Vary.lwpp = 0.05;
[B2,spc2]=garlic(Sys,Exp);

plot(data_one/10, spc2/max(spc2))

esfit(@garlic,data_two,Sys,Vary,Exp) % not outputting simulation yet
return

Thank you for taking the time to write this code. I am confused as to how you came up with the parameters for the g-value and the hyperfine splittings. I'm guessing the two sets of two equivalent hydrogen nuclei come from the other positions on the ring? I was hoping to identify specific reactive oxygen species, but it sounds like my spectrum might be too complex for that.

Dear all,

I am currently working with a sulphur derived compound (oxone: KHSO5 · 0.5KHSO4 · 0.5K2SO4) that is estimated to generate hydroxyl, superoxide and sulfate radicals. I tried the BMPO trap and I don't get any signal, so I believe there are no hydroxyl or superoxide radical production in this system (or low concentration).
With DMPO, I got a signal with eight lines, as you can see in the attached files. However, I am having difficulties in simulating this spectrum. I tried to simulate estimating having a sulfate radical but the spectrum obtained does not correspond to the experimental one. I also tried mixtures with carbon radicals and with hydroxyl radicals but always without success. In literature I have not seen anything similar. Does anyone have any ideas to help?
Thank you very much and best regards,
Tania

This is the cumulative result of the two spin systems. Sys1：DMPO-H ； Sys2：DMPO-R (R = Saturated alkyl)