Thursday, July 01, 2010

Universal Hole

Earlier in this week I cited a paper by Kobzar and Luy. It contains the statement:
The coupling extraction procedure is not yet implemented in any available software.

that confirms and enforces what I have always being saying:
Any NMR program contains some hole and by the time it's filled another hole appears.

What they have found is a kind of super-hole that is common to every program. My first thought would normally be: "If nobody cares, why should I?", but this time I was intrigued by a figure just above the cited statement. That figure resembles a picture of mine I published here a few months ago. Despite the apparent similarity, however, the two methods have little in common.
Driven by curiosity, I looked on the web for anything more recent on the same subject and found this page that describes the very same "long range J" procedure. Does it mean that somebody has already filled the hole?
I have contacted the PR man at nucleomatica and he explained that the procedure is not commercial yet. It is a very simple data manipulation, there is no secret about it, but neither there is demand for it by the market. In conclusion, there is no hurry to make it available (to a distracted public).
Finally he gave me this picture, which is a world-exclusive of my blog:
Believe it or not, what you see is the same multiplet shown into the JMR figure (page 133, fig. 3d). Same molecule, same kind of experiment, another sample, another instrument.
The two experimental multiplets in black differ for the absence (top) or presence (bottom) of an anti-phase coupling. Both traces come from 2-D experiments and the resolution can never be enough to directly measure the size of the coupling.
The green circle hilights a slider. When you move the slider, the program adds an artificial coupling to the upper trace. The result is shown in red. When the red multiplet is like the black multiplet at the bottom we have succesfully simulated the missing coupling AND NOW WE KNOW HOW LARGE IT IS. That's what it's all about.
If you remember, I have gone much further with my unbeatable simulator, because it is able to extract all the couplings with a single experiments.
The strenght of my method is, alas, also its drawback: even when you are interested into a single J value, you are forced to measure them all. It can be very hard in cases like this.
Despite the external similarities the two methods are very different inside, serve two different purposes and can live side by side very well into the same program.


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