How to Fit an Homonuclear Correlation experiment [Exchange]
Example :
1H 2D exchange spectrum fitted as an homonuclear correlation
By "homonuclear correlation" we assume that both
dimensions (F1 & F2) of the spectrum have the same characteristics. This will be
the case for the exchange experiments, no matter the recoupling mechanism, this
will not be the case for a Double Quantum/Single Quantum correlation (because
the two dimensions are not equivalent) nor for a LG/MAS correlation because the
lines do not have the same characteristics in both dimensions.
Step 1 : Fit of a 1D spectrum containing all
the peaks that will be present in the 2D spectrum.
This step is
not necessary but can simplify the process of fitting the 2D dataset.
If you need
you can learn more about fitting a 1D spectrum with
Gaussian/Lorentzian lines have
Step 2 : Switch to the 2D dataset.
Having the 1D
spectrum and fit loaded, just go the the [Menu/File/Open] and open the 2D
dataset (*.rr files for Bruker).
or
Load in the 2D dataset [Menu/File/Open] and open the 2D dataset (*.rr files for
Bruker) and load the 1D fit parameters [Menu/Decomposition/Load Other]
Step 3 : Switch the decomposition mode from 1D to
2D
In the lef
panel, change the fitting mode from "Fit 1D" to "Fit 2D" (if you do not see this
option, enlarge the dmfit window to make it appear).
Step 4 : Call the Cross Peaks dialog box and set
values
-
Call the
"Cross Peaks dialog box" by clicking the button that appeared in the left panel.
-
If the button
at the top of the window is labeled "Hetero" you will fit an heteronuclear
correlation, click it to switch to "Auto" Autocorrelation mode.
-
Click on "Init
from 1D" to set default values or enter the values you want in the different
cross peaks intensities
-
Click Ok to
get back to the main window
Remark : all no zero values for cross-peak
intensities will be optimised in the fitting process, future development should
allow fixing or freing all the individual lines. The display of the Cross-Peak
dialog is rather crowded, it can handle up to 50 lines and 2500 cross-peaks.
Step 5 : Optimising the intensities of cross-peaks
-
Same rules
apply for fitting 2D experiments and 1D experiment except that the 1D Amplitude
is not taken into account. All boldface paramters will be optimised. Be
carefull that this could lead to lengthy computations and minimise the number of
free parameters if you can.
-
Click
the [Optimize] button to
optimize the current solution (all boldface parameters will be adjusted
as well as the non zero cross-peaks)
-
Click on "Init
from 1D" to set default values or enter the values you want in the different
cross peaks intensities
-
Click Ok to
get back to the main window
Step 6 : Reporting and Saving
Fit parameters can be saved in machine readable binary
format [Menu/Decomposition/Save Fit] or [Menu/Decomposition/Save as Fit] and
thus retrieved later exactly in same state.
Parameters can be reported in human readable format by clicking
the [Report] button to report the current line
paramters in a dialog box from which you can Select/Copy and further Paste word
processing or SpreadSheet programs.
Tricks and techniques
If your dataset is symmetric as compared to the
diagonal of the spectrum, you can speed the computation by symmetrizing your
dataset [Menu/2D/Symetric] and treating only half of the off-diagonal crosspeaks
[Check the "symmetric autocorrelation" checkbox in the cross-peaks dialog].