iNMR news #99

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GB, author of iNMR

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Jun 21, 2014, 4:57:14 PM6/21/14
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COVARIANCE NMR

The new versions 5.3.7 (for Mac) and 2.3.7 (for Windows), both available since June 20, add Covariance NMR to the processing toolbox. This technique creates a symmetric square matrix, starting from any 2-D matrix. The result can look completely different from the starting spectrum, though the information contained is necessarily the same. An example is hsqc-tocy (a kind of hetero-correlation experiment). After normal processing, it has two different axes: a 1-H axis and a 13-C axes. Starting from here you can apply two different kinds of Covariance. The so-called Direct Covariance creates a symmetric H-H matrix. The so-called Indirect Covariance creates a symmetric C-C matrix. Both are homo-correlation plots.

A more detailed description is available here:

http://nmr-analysis.blogspot.it/2008/10/introduction-to-covariance-nmr.html

This link leads to the pioneer of the method:

https://research.chemistry.ohio-state.edu/bruschweiler/web-servers/370-2/

From my point of view there is no difference between direct and indirect Covariance, because they start from the notion that a given axis belongs to a given dimension. This notion is absent in NMR, where transpositions occur too frequently, either invoked by the processing engine or by the user (whenever you click Shift-T). For this reason, the distinction between direct and indirect covariance is unnecessary.

If the starting  vertical axis is a 1-H axis, after Covariance both axes will point to the 1-H nucleus. If you start from a 13-C vertical axis, you will get two 13-C axes. The trivial trick is to transpose the matrix, if necessary, before selecting the command Process > Covariance.
A Google search for "Covariance NMR" yields over 2000 results. At first examination, all those pages were written by a handful of teams. My impression is that Covariance is not so important in the NMR context. A better proof of my theory is that no user had ever asked for it until this week. Eventually somebody asked. Before the end of the week a new version of iNMR has been released.

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IMPORTING A TEXT FILE

A page of our web site has been partially rewritten. It explains how you can import any kind of 1-D or 2-D table into iNMR via a textual file.

http://www.inmr.net/articles/ASCIIimport.html

The number of different styles that are accepted by iNMR has now increased to four. In practice you can use iNMR to display not just NMR data, but any kind of numerical data. All you have to do is to save your numerical values in a suitable text format.

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IMPORTANT NOTE FOR WINDOWS USERS: Please update your copy of iNMR. Version 2.3.7 contains a couple of important improvements, not described here, that you will certainly enjoy.

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