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Techniques & Tools Spectroscopy, Mass Spectrometry

What’s in the Surprise Gift Box?

Modern spectroscopic methods have a great importance in many areas of molecular sciences. Apart from structure determination they are used to analyze dynamic phenomena and interactions between molecules. In particular, NMR spectroscopy and mass spectrometry are key techniques in these analyses, perhaps because of their wide range of analytical applications. However, to gain a reliable description of structures and processes on a molecular level, data from different spectroscopic and spectrometric techniques have to be combined for interpretation.

Getting a sample of an unknown organic compound for structural analysis is like receiving a present in a gift box. The receiver of the gift is likely to be inquisitive, shaking the gift box lightly. Next, he or she might make some estimations about its content before unwrapping the present. A spectroscopist, however, does not really have the chance to unwrap the object in the gift box. Rather, a given spectroscopic method can be used to take a look inside the box. The analytical process at work here can be described as making a little hole into one side of the box and looking into it with a magnifying glass. The view into the hole provides a single two-dimensional image of the three-dimensional object within. Notably, it only allows a view from one spatial direction. An interpretation of the view can be made by the spectroscopist, resulting in a conclusion about the structure of the wrapped object.

Let’s assume the first spectroscopist, Nicolas M. Resonance, sees a ring-like object when he looks through his little hole in the gift box. In the interpretation, he will use all of his knowledge and experience about three-dimensional structures of circular looking objects. This will likely lead him to the conclusion that there is almost certainly a ball inside the box. The second spectroscopist, Mary Spectrometry, makes a second hole in the box from another spatial direction. She has a completely different view of the object and sees a rectangle. The rectangle does not have a perfect shape – its two shorter sides are slightly curved.  But in her opinion, this effect can be explained by inaccuracies in the measurements. She therefore concludes that there is certainly a cuboid in the box.

Presumably, M. Spectrometry and N. M. Resonance will strongly disagree about the shape of the object in the gift box. They turn to Ian Red, also a spectroscopist, to make another hole in the box from a third spatial direction. His impression is rather similar to those of M. Spectrometry. He also sees a rectangle with two slightly curved sides and also draws the conclusion that there is a cuboid in this box.

At this point, two of the three spectroscopists agree about the structure of the object, which is hidden in the gift box. They write a joint publication, not considering or mentioning the results of N. M. Resonance. The presented results and conclusions appear to be consistent, and are hence accepted for publication and quoted in future papers. However, the conclusion about the structure has a slight blemish: it is completely wrong!

Considering all results of the three analyses, including the slightly curved sides of the rectangles would lead to an entirely different and somehow surprising conclusion about the object’s structure. A cylinder explains all three two-dimensional views, which have been gained from the different spectroscopic methods. Therefore, a joint publication from N. M. R., M. S. and I. R., probably together with some other spectroscopists, presents a well-founded and reliable argument about the cylindrical structure in the gift box.

The moral of the story? Sometimes even two techniques are not enough to find the right answer; it makes much more sense to combine all the results from several different analytical methods – especially when there is any doubt.

Of course, though such an approach sounds logical and simple in theory, there are often many factors that block the way to finding the correct solution. And sometimes communication between researchers isn’t always as good as it should be. But if we spectroscopists work well together, there are very few difficulties we cannot overcome.

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About the Author
Lothar Brecker
Lothar Brecker

Studying Chemistry at TU Dortmund University Lothar Brecker got a comprehensive knowledge about molecular structures and reactions. He expended this view to static molecular formulas beeing a post doc at Graz University of Technology. There he used NMR spectroscopy as a window to the world of molecular movement and interaction. It was like watching TV on reaction mechanisms and enzyme transformations. The resulting virtual motion pictures, however, looked still like two dimensional images of the three dimensional reality. Actually working at University of Vienna he involves different analytical approaches to gain 3D virtual images of molecular interactions. Combining these results lead to detailed knowledge of spatial and chronological details in biocatalysed transformations.

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