Hello,

You indeed need to use the "Unalias peak" dialog.  So you click on a peak 
in the window and bring that dialog up via the right mouse (Peak --> 
Unalias peak) or you select the peak e.g. in the Selected Peaks dialog 
and then click on the Unalias button.

Once that dialog is up you see that there is a "Num. Aliasing" column 
which is in green and the values default to 0.  In your case, assuming I 
am getting my conventions correct, that should probably be -1 in the 13C 
dimension.  (So +1 means the real ppm value goes down and -1 means it goes 
up.)

Once you have unaliased one like this you can do others more easily 
(assuming they have the same "Num. Aliasing" of course).  You select all 
the peaks and then with the cursor over the one that has already been 
unaliased, do right mouse Peak --> Unaliasing propagate.  (It seems to be 
a bit fussy but I got it to work.)

Wayne

On Thu, 19 Apr 2012, Aswani Kumar wrote:

> Hello Analysis Users,
>
> I am using HCcH-COSY along with HNCACB, CBCAcoNH, CCcoNH and 1H,15N-HSQC-TOCSY and HCCcoNH-TOCSY to assign the side chain protons and carbons. The HCch-COSY spectrum was acquired with a smaller 13C spectral width of 26 ppm. The spectrum extends  from  26ppm to 52ppm, and is centered at 39ppm. The peaks for resonances with carbon chemical shifts outside this spectral range are now aliased into the spectrum. The carbon chemical shits of aliased peaks are accordingly modified in the spectrum.
>
> I start from  an assigned peak in CBCAcoNH or CCcoNH and navigate to appropriate 1H-13C in the HCcH-COSY window and look for the desired peaks. Once I identify the peaks, I assign them using the assignment pop-up.
>
> The problem/question here is as follows:
> Everything works fine for peaks which are not folded in the 13C dimension in the HCcH-COSY spectrum. However for the peaks, which are folded in the 13C dimension, the assignment pop-up suggests right choices for the proton dimensions, but naturally it does not suggest anything appropriate for the carbon dimension. This is understandable as the chemical shift is modified due to aliasing in this spectrum. For eg., a peak with carbon chemical shift  of 55ppm now appears at 29ppm.
>
> Is there a way to let Analysis know that a few peaks in a given spectrum are aliased in a given dimension so that it can suggest appropriate assignments? There is an option "Aliased possible" in the assignment pop-up. But I am not sure how it works (where do we need to mention the spectral width?)!
>
> I have just found out from the help page of spectra, that we need to enter appropriate values for "Minimum Aliased Frequency" and "Maximum Aliased Frequency" in the menu M::Experiments::Spectra::Referencing. However this seems to try and un-alias all the peaks and make multiple copies of the peaks. Is there a way to specifically un-alias only the truly aliased peaks? How do the functions viz., "Unalias peak " and  "Unaliasing propagate" in the right click menu for a peak in a window work?
>
> I am using Analysis Version 2.1.5 on openSUSE 11.4 (x86_64).
>
> Many thanks in advance,
>
> Aswani Kumar. K
>
> K.Aswani Kumar, PhD Student,
> Molecular Biophysics Unit,
> Indian Institute of Science,
> Bangalore-560012, India.
> Phone: 09945633467  (mobile)
>       080-22932839 (lab)
>