Category Archives: Temperature Measurements

TmDOTP: An NMR-based thermometer for magic angle spinning NMR experiments

Knowing the actual sample temperature in a solid-state NMR experiment is crucial in many ways. Many different approaches exist from measuring the chemical shift difference in spectra of ethylene glycol (solution-state NMR spectroscopy) to measuring the peak position in lead nitrate or the T1 relaxation times of KBr (solid-state NMR spectroscopy). All of these methods have their pros and cons. This approach using TmDOTP, having a temperature coefficient of 1ppm/K and being inert to biopolymers is a valuable addition to the ssNMR toolbox.

Zhang, Dongyu, Boris Itin, and Ann E. McDermott. “TmDOTP: An NMR-Based Thermometer for Magic Angle Spinning NMR Experiments.” Journal of Magnetic Resonance 308 (November 1, 2019): 106574.

Solid state NMR is a powerful tool to probe membrane protein structure and dynamics in native lipid membranes. Sample heating during solid state NMR experiments can be caused by magic angle spinning and radio frequency irradiation such heating produces uncertainties in the sample temperature and temperature distribution, which can in turn lead to line broadening and sample deterioration. To measure sample temperatures in real time and to quantify thermal gradients and their dependence on radio frequency irradiation or spinning frequency, we use the chemical shift thermometer TmDOTP, a lanthanide complex. The H6 TmDOTP proton NMR peak has a large chemical shift (−176.3 ppm at 275 K) and it is well resolved from the protein and lipid proton spectrum. Compared to other NMR thermometers (e.g., the proton NMR signal of water), the proton spectrum of TmDOTP, particularly the H6 proton line, exhibits very high thermal sensitivity and resolution. In MAS studies of proteoliposomes we identify two populations of TmDOTP with differing temperatures and dependency on the radio frequency irradiation power. We interpret these populations as arising from the supernatant and the pellet, which is sedimented during sample spinning. In this study, we demonstrate that TmDOTP is an excellent internal standard for monitoring real-time temperatures of biopolymers without changing their properties or obscuring their spectra. Real time temperature calibration is expected to be important for the interpretation of dynamics and other properties of biopolymers.

Determination of sample temperature in unstable static fields by combining solid-state 79Br and 13C NMR

This is not an article about DNP-NMR spectroscopy, however, it deals with the measurements of temperatures in solid-state NMR experiments using KBR and referencing its chemical shift to 13C of adamantane in unstable magnetic fields.

Purusottam, R.N., G. Bodenhausen, and P. Tekely, Determination of sample temperature in unstable static fields by combining solid-state (79)Br and (13)C NMR. J Magn Reson, 2014. 246(0): p. 69-71.

Monitoring the isotropic chemical shifts to calibrate the sample temperature presupposes a perfect stability of the static magnetic field. It can be difficult to satisfy this requirement in solid-state NMR measurements. This paper describes a simple way to recover the accurate temperature dependence of the (79)Br resonance after subtracting changes of resonance frequency due to variations of the static field, monitored by the (13)C resonance.

Remote sensing of sample temperatures in nuclear magnetic resonance using photoluminescence of semiconductor quantum dots

This article is not exclusively about DNP-NMR spectroscopy, but describes an interesting approach of measuring cryogenic temperatures using a simple fiber optic-based setup. It is particularly useful for low-temperature MAS NMR experiments, including DNP-NMR spectroscopy.

Tycko, R., Remote sensing of sample temperatures in nuclear magnetic resonance using photoluminescence of semiconductor quantum dots. J Magn Reson, 2014. 244C(0): p. 64-67.

Knowledge of sample temperatures during nuclear magnetic resonance (NMR) measurements is important for acquisition of optimal NMR data and proper interpretation of the data. Sample temperatures can be difficult to measure accurately for a variety of reasons, especially because it is generally not possible to make direct contact to the NMR sample during the measurements. Here I show that sample temperatures during magic-angle spinning (MAS) NMR measurements can be determined from temperature-dependent photoluminescence signals of semiconductor quantum dots that are deposited in a thin film on the outer surface of the MAS rotor, using a simple optical fiber-based setup to excite and collect photoluminescence. The accuracy and precision of such temperature measurements can be better than +/-5K over a temperature range that extends from approximately 50K (-223 degrees C) to well above 310K (37 degrees C). Importantly, quantum dot photoluminescence can be monitored continuously while NMR measurements are in progress. While this technique is likely to be particularly valuable in low-temperature MAS NMR experiments, including experiments involving dynamic nuclear polarization, it may also be useful in high-temperature MAS NMR and other forms of magnetic resonance.

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