Author: Johannes Leisen

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.

The design of the NMR experiment does not lend itself for measurements at exactly determined temperatures. During experiments the NMR tube sits in an rf-coil and the proximity of any parts made out of metal – including a thermocouple – will interfere with the experiment. Therefore, the thermocouple used to measure and regulate the temperature of an air-stream surrounding the sample is sited at a distance from the sample. In addition it also does not help that it is virtually impossible to achieve a homogenous Temperature distribution along the NMR tube, which will lead to convections.

The only type of thermometer, which can be used to directly measure temperatures during the conduct of magnetic resonance experiments are fluoroptic thermometers. These thermometers detect the color change of specific dyes with temperature. Fluoroptic thermometers have been used in MRI studies, however for an NMR experiment one would have to deal with the signal from the thermometer (i.e. the dye and its solvent).

A direct way to directly measure the temperature in the NMR tube is through the temperature-dependent chemical shift of some solvents. For instance the chemical shift difference between the two peaks of methanol is temperature dependent and it can be used to calibrate the actual temperature in the NMR tube with respect to the temperature measured by the thermocouple.

If things are bad in solution they are worse for solid-state MAS experiments. Here the temperature is regulated for the stator, which is the ceramic housing surrounding the spinning MAS rotor. In between the spinning rotor and the temperature-regulated stator is a stream of ambient air, the bearing. This air stream is used to float the rotor within the stator. Again, it is possible to regulate the temperature of the sample within the MAS rotor through the chemical shift of a reference sample. In this case it is lead-nitrate, where the temperature dependence of 207Pb-NMR chemical shift is well characterized.

Rey, our 700 MHz instrument has a dual configuration. It can be used as solution NMR instrument with a cryoprobe or it can be used as a solid-state NMR instrument. Changing the cryoprobe to conduct solid-state NMR experiments involves the following:

Pushing the “warm-up” button. This will start the automatic warm up procedure, which will take several hours. After this a lot of cables and hoses need to be disassembled. Pulling out the heavy cryoprobe takes two persons. One has to take great care to only hold the probe at its base to avoid damage. The cryoprobe has to be safely tucked away. Then the solid-state MAS probe can be installed, which involves deactivating the sample-changer, hooking tubes for the MAS pneumatic and connecting a bunch of cables. Once this is done a few calibration have to be performed or at least checked: the shim, the magic angle, power levels. A few glitches are to be expected – on Monday it took us ~4 hours to get the instrument ready, this is not counting the time it took the probe to warm up.

Reinstalling the cryoprobe is a similar effort. It is even worse – some of the connectors are really finnicky. They are difficult to reach and difficult to see for someone who wears glasses with bifocal lenses.

Frequent removal of the cryoprobe also puts wear on the system. Please let us know well in advance if you want to conduct solid-state NMR experiments on our 700 MHz instrument.