What is NMR spectroscopy and How Does it Work?

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Everything around us is made of matter, from living organisms to the air we breathe, and all of this matter is made up of atoms. When these atoms bind with one another, they form molecules. Understanding these molecules and their behavior is the key to understanding the physical world around us. By using a technology called nuclear magnetic resonance (NMR) spectroscopy, scientists are able to see these molecules and magnify even their smallest details, observing how they behave in all types of matter.

Nuclear magnetic resonance spectroscopy is an analytical chemistry technique. It was first demonstrated in 1946 by Felix Bloch and Edward Mills Purcell, who subsequently shared the Nobel prize for their accomplishments and research in this field. The first commercial spectrometers were created in the 1950s and quickly became an indispensable tool for research chemists. These early spectrometers were expensive, bulky, and had a large footprint compared to the tabletop NMR and benchtop spectrometers used today. The first commercial spectrometers were based on conventional electromagnets and permanent magnets. By the 1960s, superconducting magnets, such as those used in modern benchtop spectrometers, had been largely adopted as the standard by chemists.

There are a wide variety of NMR applications, and this technology particularly useful in the field of cancer research, where it's used for the development of smart delivery systems for cancer-treating drugs. NMR can also help scientists understand the molecular basis for photosynthesis in plants and algae, making it possible to determine which crop strains are best suited to thrive in different environments.

Another application in which NMR spectrography shows usefulness is in the development of next generation batteries. To that end, portable NMR benchtop spectrometers play a crucial role in establishing the molecular details of a battery's energy-storing capability.

How Does NMR Actually Work?

When molecules are placed in a strong magnetic field, the nuclei of some atoms will begin to behave like small magnets. If a broad spectrum of radio frequency waves are applied to the sample, the nuclei will being to resonate at their own specific frequencies. This is similar to the use of a tuning fork, where a guitar string will only resonate in response to a tone of the exact right frequency.

The resonant frequencies of the nuclei are then measured and converted into an NMR spectrum that displays all of the right frequencies as peaks on a graph. The height of each peak represents the number of nuclei that resonates at each specific frequency. This is known as the intensity of signal. The more resonating nuclei, the higher the intensity.

The value of each frequency, or tone, gives information about the surroundings of the atom in question; such as its neighboring atoms and their relative positions. When atoms are in close proximity to one another, they can even cause each other to resonate. By examining the cross-peaks, scientists can then determine the 3D structure of molecules and observe how they move.

The Bigger the Magnet, The Finer the Detail

Through the use of increasingly stronger magnets, scientists and researchers can study more complex molecules in even greater detail. In the long run, this will provide us with answers to many vital questions. How can doctors be sure that drugs are only active in particular areas of the body? How can we make batteries more energy efficient, and reduce our dependency on fossil fuels? How can we prepare and safeguard ourselves against the impending consequences of climate change?

To answer these questions and more, in 2016, 5 Dutch universities joined forces in a collaborative effort to install a new 22 Tesla Magnet in the NMR spectrometer at Utrecht University. That's a serious magnet compared to the ones found in benchtop spectrometers. For comparison, consider that a 100 Tesla magnet is equivalent to approximately 2 million times Earth's magnetic field. These mega magnets represent a huge step forward in the effort to find detailed answers to some of the most important questions facing our future.