How to fit an Heteronuclear Correlation spectrum

 Example :  31P/1H Heteronuclear Correlation  

By "hetero-nuclear correlation" we assume that the two dimensions (F1 & F2) of the spectrum have different characteristics.

Basic principles ...

  • in an heteronucelar correlation you can toggle between the two dimensions by transposing the 2D dataset (button in the left bar or in the bottom fit parameters, or [Menu,2D,TranposeRR].

  • be carefull that the saved parameters do not account for the transposition, your spectrum has to be in the same state when reloading the fit parameters.

  • only the parameters of the actual horizontal dimension (F2) can be modified in the fit parameters edition tools.

  • when dealing with quadrupoles, only the horizontal dimension can compute second order effects.

The basic different steps for initializing :

  1. create a fit of the F2 dimension or reload the fit of the corresponding 1D spectrum

  2. transpose and do the same in the second dimension (F1)

  3. switch to the 2D fitting mode (listbox in the left panel, enlarge the window if you don't see it).

  4. click the Crosspeaks box (left pannel) and switch to the heteromode. (The dialog box should display all possible cross peaks)

  5. click Init from 1D to create dummy intensity values

  6. zero the unexpected cross peaks

  7. return from dialog and click the compute button to update the graph. You should have a 2D fit supperimposed to the experimental spectrum.

Description of the procedure...

Step 1 : Fit of a 1D spectrum containing all the peaks that will be present in each of the dimensions of 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.

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).


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

  1. Call the "Cross Peaks dialog box" by clicking the button that appeared in the left panel.

  2. If the button at the top of the window is labeled "Auto" you will fit an homonuclear correlation, click it to switch to "Hetero" hetero-correlation mode.

  3. Click on "Init from 1D" to set default values or enter the values you want in the different cross peaks intensities

  4. 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 : Loading the second dimension parameters

description to come

Step 6 : Optimising the intensities of cross-peaks

  1. 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.

  2. Click the [Optimize] button to optimize the current solution (all boldface parameters will be adjusted as well as the non zero cross-peaks)

  3. Click on "Init from 1D" to set default values or enter the values you want in the different cross peaks intensities

  4. Click Ok to get back to the main window

Step 7 : 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.