HMBC Processing

gHMBC42a is acquired as a phase-sensitive spectrum in F1 but a Magnitude spectrum in F2. The apodization should be a cosine like function (cosine, cosine-squared) in F1 but a sine like function in F2

1) In most cases, default gHMBC processing will be fine in MestrReNova, but potentially you can improve it with adjusting Zero Filling , Linear Prediction , and Apodization , Phase Correction .

2) Zero-Filling. There is normally no need to zero-fill in F2 but if you acquired less than 2K points, zero-filling to 2K might help resolution some. in F1, you want to zero-fill to at least 1K, and probably 2K. This should lead to some resolution improvement.

3) Linear Prediction. There is no need to linear predict in F2. In F1, predicting 2 to 4 times the actual data points acquired will likely improve resolution. The software may default to predicting to the end of the zero-fill, but that might be too many. It is suggested to limit to the linear predicted points.

4) Apodization. The optimum apodization function in F1 is most often a cosine-squared function which yields moderately sharp resonances with minimal truncation artifacts. You can observe the shape of the function by turning on Full View under View Menu and then selecting Fid Preview at the bottom of the Apodization Menu. For a Cosine Squared function in both dimensions, either choose Sine Square 90° or Sine Square II -100.0% 100%. These 2 should be equivalent. For a sharper resonance, you could switch to a Cosine of Cosine II with the same 90° or -100.0% 100%. Alternatively, change the % values of the Cosine Square II and observe the change of the apodization function and result in the data.
In F2, the optimum apodization function is most often a sine-squared function in both dimensions which yields moderately sharp resonances with minimal truncation artifacts. You can observe the shape of the function by turning on Full View under View Menu and t hen selecting Fid Preview at the bottom of the Apodization Menu. For a Sine Squared function in both dimensions, either choose Sine Square 0° or Sine Square II 0.0% 50%. These 2 should be equivalent. For a sharper resonance, you could switch to a Sine Bell of Sine Bell II with the same 0° or 0.0% 50%. Alternatively, change the % values of the Sine Square II and observe the change of the apodization function and result in the data. You might observe some improvement by choosing an apodization in between Sine and Cosine, so a 30° shifted sine function or sine squared function.

5) Other options. The reduce t1 noise option under Processing menu can reduce the t1 noise across the spectrum. The t1 noise is noise across the spectrum in the t1 (F1) dimension off of intense peaks.

6) Display options. One option that can appear to improve resolution or signal is to adjust contours. Under the Edit Menu then Properties, there are options to change the Display including traces on the spectrum. One option that can improve the look of the plot is to increase the number of contours displayed, and decrease the spacing between contours. On the option 2D, just above Traces there are choices for Positive/Negative Contours, Scaling and Line Width. Increasing the number of contours can help, but drawing speed will slow as you increase that. More useful is setting the Scaling to ~1.3- the optimum value depends upon number of contours and the signal. Typically a number in the 1.1 to 1.5 range is best. The Line Width can also improve darkness on the screen.