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fixing weight contributions to equal 1

Posted: Tue Apr 19, 2022 1:17 pm
by katiemdunleavy

I am fitting nitroxide spectra of an intrinsically disordered protein using a two component chili script. As I titrate on a binding partner, I'm monitoring the percent contribution of the second, slower component as being the percent of bound protein. When I use the script (below), I'm not getting the weight distribution to add up to 1, but rather a value less than one in most cases. Is there a way to account for this in my script? Or would this indicate I'm missing a third component?

Script:
[B,spc] = eprload(['file']);
b = B/10;
plot(b,spc);

Exp.mwFreq = 9.408;
Exp.Range = [min(b), max(b)];
Exp.nPoints = numel(spc);

Sys1.g = [2.012 2.001 2.003];
Sys1.Nucs = '14N';
Sys1.A = [20 28 95];
Sys1.lwpp = [0.12];

Sys2.g = [2.009 2.005 2.0025];
Sys2.Nucs = '14N';
Sys2.A = [19 19 96];
Sys2.lwpp = [0.3];

Sys1.logtcorr = -9;
Sys2.logtcorr = -8;

Sys1.weight = 0.3;
Sys2.weight = 0.7;

Vary1.g = [0.01 0.01 0.01];
Vary2.g = [0.01 0.01 0.01];
Vary1.weight = 0.3;
Vary2.weight = 0.3;
Vary1.A = [5 5 10];
Vary2.A = [5 5 10];
Vary1.logtcorr = 0.5;
Vary2.logtcorr = 0.5;
Vary1.lwpp = 0.1;
Vary2.lwpp = 0.1;

esfit(@chili,spc,{Sys1, Sys2},{Vary1,Vary2},Exp);

download/file.php?mode=view&id=509


Re: fixing weight contributions to equal 1

Posted: Thu Jun 09, 2022 3:22 am
by Stefan Stoll

EasySpin does not normalize the sum of weights. They are just (absolute) linear combination coefficients that are used to compute the total spectrum from the simulated component spectra.

To analyze titration data, you can normalize the sum of the weights to 1 after finishing the fit. This should give you the relative populations of the various species.