Heating and temperature gradients of lipid bilayer samples induced by RF irradiation in MAS solid‐state NMR experiments

Abstract

The MAS solid-state NMR has been a powerful technique for studying membrane proteins within the native-like lipid bilayer environment. In general, RF irradiation in MAS NMR experiments can heat and potentially destroy expensive membrane protein samples. However, under practical MAS NMR experimental conditions, detailed characterization of RF heating effect of lipid bilayer samples is still lacking. Herein, using H chemical shift of water for temperature calibration, we systematically study the dependence of RF heating on hydration levels and salt concentrations of three lipids in MAS NMR experiments. Under practical H decoupling conditions used in biological MAS NMR experiments, three lipids show different dependence of RF heating on hydration levels as well as salt concentrations, which are closely associated with the properties of lipids. The maximum temperature elevation of about 10 °C is similar for the three lipids containing 200% hydration, which is much lower than that in static solid-state NMR experiments. The RF heating due to salt is observed to be less than that due to hydration, with a maximum temperature elevation of less than 4 °C in the hydrated samples containing 120 mmol l of salt. Upon RF irradiation, the temperature gradient across the sample is observed to be greatly increased up to 20 °C, as demonstrated by the remarkable broadening of H signal of water. Based on detailed characterization of RF heating effect, we demonstrate that RF heating and temperature gradient can be significantly reduced by decreasing the hydration levels of lipid bilayer samples from 200% to 30%. Copyright © 2016 John Wiley& Sons, Ltd.

TmDOTP : An NMR- based Thermometer for Magic Angle Spinning NMR Experiments

“…The water chemical shift is known to be sensitive to temperature and has been employed as an internal thermometer in several studies 12,18,23 . We compared the temperature dependence of the chemical shift of the H 6 proton in TmDOTP versus the water proton in the same sample (Figure 3).…”

“…The absorption of RF energy is maximized when ωτ = 1, where ω represents the frequency of oscillating field and τ is the characteristic relaxation time of the molecule 14,15 . RF heating is of particular concern in SSNMR experiments on biological samples due to the resistive losses from the high concentration of ions in typical biological buffers and the dipolar losses from the presence of mobile permanent dipoles such as in hydrated lipids 12,15–18 . Since the heating mechanism is difficult to completely avoid for such samples, it is critical to monitor the temperature changes and heating gradient in order to control the sample temperature during SSNMR experiments.…”

Lipid-nanodiscs formed by paramagnetic polymers for fast NMR data acquisition

“…Most of the recent SMA research applied to structural biology has involved investigating several different polymer formulations. The simple variation of molecular weights and styrene to maleic anhydride ratios leads to various commercially available polymers 102,103 . For membrane proteins investigations, small-molecular weight SMAs are used.…”

“…Clearly, more evidence is needed to clearly state whether the use of RAFT-produced copolymers is more advantageous. Among the advantages of using synthetic polymers is the possibility of customization 96,103,147,148 . For example, the maleic anhydride units of SMAnh copolymers react with primary amines via a nucleophilic ring-opening reaction 149 , allowing the modification of the hydrophilic moiety (Figures 13a-b).…”