Author: Johannes Leisen

Our friends at Georgia State will organize the “Atlanta Magnetic Resonance Symposium”, which will take place in the Petit Science Center on the GSU campus.

This symposium is dear to us since it is the follow-up of the “workshop: Magnetic Resonance at Georgia Tech”, which took place many times and always featured great talks from students and post-docs along with fun and a year-end celebration of our accomplishments.

Idea of this Symposium is to present a great variety of applications to a broad audience so that the symposium is interesting for experts but also provides an entry into NMR and MRI for novices.

This year’s symposium will also have a poster session and I encourage everyone to register for the attendance and a poster at the link shown below.

Our laboratory has instruments from two Manufacturers: Varian and Bruker.

Our Varian instruments are both a early-mid  1990 vintage. Our Bruker spectrometers are of the AV3 and AV3-HD generation, which were produced from the ~2010 until ~2016. The company Varian was one of the pioneers in commercial NMR spectrometers. Unfortunately it sold off its NMR division to Agilent in 2010, which then decided to exit the NMR business in 2014.  Regrettably this ended a healthy competition with Bruker, a competition, which lead to important innovations in the field of NMR. However, in my opinion my opinion depsite the loss of a real competitor Bruker has continued the development of NMR technology. 

So what is the advantage of a modern Bruker 400 MHz NMR spectrometer over a Varian spectrometer, which is older than almost all of our graduate students? 

• The probe and electronics is more sensitive.  This will become relevant for nuclei other than ¹H.   However, the difference is really not that relevant when it comes to the “quick 1H spectrum”. 16 or 32 scans measures a decent 1H spectrum on both platforms provided that the sample is well prepared.

• The modern instrument comes with a great variety of experiments. Bruker instruments come with an extensive library of pulse sequences and associated parameter sets.  Out of those not all will run on a basic 400 MHz instrument.  But there is a whole set of 2D experiments, which run well on the Bruker experiment; for the Varian instrument it is not even worth trying to get these experiments to run.

•  The Bruker instrument (at least in our  AV3 version) can run nuclei other than 1H and 13C. In fact, we routinely run 19F and 31P experiments on our Bruker spectrometer. We have conducted NMR experiments of many other nuclei (29Si, 27Al, 11B, 109Ag to name just a few).

•  The Bruker instrument has a gradient probe. In addition to sending and receiving radio-frequency pulses the probe has also the option of sending pulsed magnetic field gradients. I.e. the usually very homogeneous magnetic field can be made inhomogeneous in a controlled manner. This opens the door for many new experiments such as the DOSY experiment, which correlates the diffusion coefficient for Brownian motion with the chemical shift of molecules. Gradients also help to eliminate the need for complex phase cycles, i.e. they remove unwanted magnetization components which are generated during 2D experiments, therefore leading to cleaner spectra, which can be recorded in a shorter acquisition time.

• The operation of the Bruker instrument is more automated. The command “atma” automatically tunes the probe, i.e. stepper motors automatically adjust the resonating circuit in the probe to be on-resonance with the desired measuring frequency. Then the command “topshim” starts an automated sequence leading to an automatic adjustment of the shim coils to achieve a homogenous magnetic field.  The automation of adjustments procedures facilitates the operation of the instrument; more important it makes the recording of spectra more reproducible and independent of the operator. The Varian Mercury spectrometer has a pre-tuned probe, where tuning of routine samples is not required. Shimming must be done manually, by adjusting shim currents and watching the intensity of the 2H signal (lock) on a clock-like display.

Does the Varian instrument have one advantage over the Bruker instrument?  Yes it does. A skilled operator can easily achieve a good shim in a shorter amount of time than Bruker’s Topshim software. So the simple 1H spectrum can be recorded quicker on the good old Varian instrument than on a modern Bruker instrument. And sometimes it is just cool to go vintage!  

The most common solvent for NMR experiments is deuterated chloroform, which is a carcinogen. So you do not want to transport your NMR tubes in your shirt pocket, your handbag or other places, where it can easily drop and break.

Pls use a secondary containment for transporting your prepared samples from your lab to the NMR lab. At minimum, you should place your sample in an Erlenmeyer Flask, which contains some absorbent medium. A good absorbent would be vermiculite. Chances are that you have plenty of that in your lab since this is used as protective layer for the shipping of chemicals. The best solution for the transport of NMR samples are “NMR tube carriers”, which are shatter and solvent resistant polymer tubes. You can purchase those from the major vendors of NMR tubes and a search in workday will point you to several vendors.

Boy Scouts use the phrasing “out of abundance of caution” and since we want everybody to be safe we will introduce two new rules for the use of the NMR lab. Here is the first one:

Pls do not wear any ear-buds, in-ear headphones, headphones, airpods, or similar. While it might be fun and stimulating to listen to music while working in a laboratory you might also miss important things such as an accoustic fire alarm. In addition these devices contain magnets. So if you just come a bit too close to the magnet they might be sucked out of your ear, which might hurt you and cause big damage.

So Enjoy your Music, but not in the NMR lab.

This is also the place to thank Dr. Leslie Gelbaum for all he has done for the NMR at Georgia Tech and more importantly for all students, post-docs and scientists who have worked with him over the years.

Les is a true NMR pioneer in the sense that he has been using NMR instruments since they were commercially available. From 1994 until the spring of this year (2023) he was manager of our NMR center. He was instrumental in the initial setup of the Georgia Tech NMR lab (1994 in Boggs) in its move to the MoSE Building (2006) and our major upgrade in 2016. But there is one thing, where Les can rightfully be most proud of: he has taught more than 1000 (!!!) researchers how to use an NMR spectrometer.

Les and Hanno in 2016 during the installation of our 700 MHz magnet.

Our NMR magnets have a variety of vintages. Believe it or believe it not – out 300 MHz solid-state NMR magnet is more than 40 years old! Older magnets are unshielded, they have a much larger stray field and you should be much more careful about bringing any ferromagnetic materials close to them. The size of a magnet is not an indication of its stray field.

So make it a habit: when working with an NMR instrument empty empty your pockets and do not bring the following close to the magnet: your wallet (credit cards and coins), keys, cellphones, watches, penknives etc. If any of these items comes too close they might be destroyed and/or sucked into the magnet, which can cause a very expensive damage and serious injuries might happen as well.

Pls also watch what you are wearing in your hair. Our instruments are named after star-wars characters but the princess amidala hairdo, which required a lot of hairpins, is not a good idea!

My experience with jewelry is that it is usually safe as far as it is made of stainless steel, gold or silver is ok; jewelry form the dollar store often is not. I had to tell one user to back off very slowly from the magnet because their otherwise dangling earrings were now pointing towards the magnet.

In case of doubt: we do have a very strong permanent magnet, which can be used to test jewelry, watches, etc. for their safety.

P.S. Wireless earbuds have become very popular. Those contain ferromagnetic components. So for everybody’s safety, pls do not wear them in the NMR lab.

On March 11 2023 we had an open lab during the Georgia Tech Science and Engineering day. We had a continuous stream of visitors throughout the day. We feel that it was important and fun to share what we are doing with the broad public and it was especially nice to present to kids and teenagers.

GT Graduate Students Alicia Robang and Andrew Hill are explaining how NMR can be used to detect alterations in honey during the Science and engineering Day at Georgia Tech.

Theme of our open lab was “is my honey clean”. We demonstrated that it is easy to use NMR when it comes to the detection of honey alteration through the addition of sucrose-syrup. We tested high quality honey from local bee keepers together with low-cost super-market honey. The good news: we had a limited amount samples but the only fake honey, which we found, was the one, which we faked ourselves. We still recommend that you purchase honey from local beekeepers! A special thanks goes also to beekeeper Moreen Rebeira-Leisen, who supported our activities by telling our visitors all about bees and beekeeping.

NMR spectra can be used to detect if honey was alterated by the addition of sucorse-based syrup.

For 2023 Science Art Wonder has partnered us with Malik Blackman.

Malik’s pictures is entirely hand drawn and it depicts the process of recording an NMR spectrum: push button -> Fid -> spectrum. The scientist’s head is above all of that.

I have recently come across a really good collection of NMR exercises. If you need to practice your skills in interpreting NMR spectra here is your place to go:

NMR exercises and their solutions

Thank you to Rainer Haessner for this great teaching tool!

Last weekend (11/18/2022) I attended the symposium honoring my PhD Advisor Prof. Hans Wolfgang Spiess on his 80th birthday. Like no other Prof. Spiess has developed and established solid-state NMR techniques for the characterization of a great variety of materials. The research was driven by the insight that the understanding of material properties requires insight into both molecular structure and dynamics, which both can be measured in detail using methods of NMR.

Chem. Rev. 2016, 116, 3, 1272–1308 is just one of many reviews explaining this approach.