University of Ottawa NMR Facility Web Site

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Thursday, December 22, 2011

13C NMR of a Delicious Christmas Treat

As my Santa Claus-like belly may indicate, I love holiday treats. The solid-state 13C NMR spectra below were collected from a special sample of a holiday treat prepared by my wife, Patty from her Great Grandma Jennings lab book. The sample was prepared from only four ingredients as follows:

To 227 g of softened butter, 65 g of fructose was added while stirring with a spatula. Slowly, 199 g of flour and 1.26 g of sodium chloride were stirred into the mixture until it became difficult to mix with a spatula. The mixture was kneaded gently until cracks in the surface began to appear after which it was rolled to a thickness of 38 mm and cut into round samples of approximately 51 mm in size. The samples were heated in an oven at 436 K - 450 K for approximately 600 seconds until gold in color.

The bottom trace is a 13C CPMAS spectrum and the top trace is a 13C MAS spectrum. Both spectra were acquired with high power 1H decoupling. This pair of spectra serves to illustrate the different types of information available from each of these techniques. The sample is a mixture of rigid and mobile components. The 13C CPMAS technique detects mainly the more rigid components as it relies on the dipolar coupling between protons and 13C for the cross polarization. The dipolar coupling is averaged to nearly zero for the mobile constituents and therefore they do not appear in the spectrum. The 13C CPMAS spectrum therefore, shows primarily all of the rigid constituents (mainly flour and sugar). The 13C MAS spectrum with high power 1H decoupling shows both rigid and mobile constituents. The resonances from the mobile constituents (mainly butter) have sharp lines while the broader lines from the rigid constituents show up at very low intensity as the sensitivity is not enhanced by cross polarization.

Now, you too have enjoyed Patty's delicious shortbread.

Wednesday, December 7, 2011

Enlightening NMR Videos on YouTube

The Journal of Magnetic Resonance (JMR) has been publishing important contributions from NMR spectroscopists since 1969. Some of these contributions have become "classic papers" and have been sited thousands of times. A play list of videos has been assembled on YouTube highlighting some of the most significant contributions in NMR spectroscopy over the last few decades. The research is described anecdotally (and in some cases very humbly) by the original authors in the videos. I think you will enjoy putting faces to the names of the authors of these highly cited papers.