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

Area of Science:

• Biophysical Chemistry
• Solid-State Nuclear Magnetic Resonance (NMR) Spectroscopy
• Membrane Protein Structural Biology

Background:

• Solid-state NMR is crucial for membrane protein analysis in native environments.
• Sample heating during NMR experiments introduces temperature uncertainties and sample degradation.
• Accurate temperature monitoring is vital for interpreting protein dynamics and structure.

Purpose of the Study:

• To introduce TmDOTP, a lanthanide complex, as a chemical shift thermometer for real-time temperature measurement in solid-state NMR.
• To quantify thermal gradients and their dependence on experimental parameters like radio frequency irradiation and spinning frequency.
• To validate TmDOTP as an internal standard for biopolymer temperature monitoring without spectral interference.

Main Methods:

• Utilized the H6 proton NMR peak of TmDOTP, a lanthanide complex, as a chemical shift thermometer.
• Measured real-time sample temperatures and thermal gradients during magic angle spinning (MAS) NMR experiments.
• Analyzed TmDOTP's thermal sensitivity and resolution compared to other NMR thermometers.

Main Results:

• TmDOTP demonstrated high thermal sensitivity and resolution, with its H6 proton peak well-resolved from protein and lipid signals.
• Identified two distinct TmDOTP populations with different temperatures and radio frequency power dependencies in MAS studies of proteoliposomes.
• Interpreted these populations as originating from the supernatant and pellet fractions of the sample.

Conclusions:

• TmDOTP serves as an effective internal standard for real-time temperature monitoring in biopolymer solid-state NMR.
• This method allows for precise quantification of thermal gradients, crucial for accurate interpretation of structural and dynamic data.
• Real-time temperature calibration using TmDOTP enhances the reliability of biopolymer property analysis in native lipid membranes.