Hexagonal ice in pure water and biological NMR samples

Area of Science:

• Biophysical Chemistry
• Spectroscopy
• Materials Science

Background:

• Ice is a crucial component in protein Nuclear Magnetic Resonance (NMR) spectroscopy at subfreezing temperatures.
• Spectroscopic observation of ice in this context has been limited.
• Understanding ice's behavior is vital for interpreting NMR data from frozen protein samples.

Purpose of the Study:

• To spectroscopically characterize ice in protein samples used for NMR.
• To investigate the temperature-dependent behavior of ice from 100 to 273 K.
• To understand how experimental techniques like magic-angle spinning (MAS) and radiofrequency (rf) multiple-pulse sequences affect ice spectra.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy.
• Variable temperature studies (100–273 K).
• Analysis of spectroscopic data in relation to ice properties and experimental parameters.

Main Results:

• Ice in protein samples exhibits spectroscopic behavior consistent with pure water ice.
• The temperature range studied (100–273 K) reveals characteristic ice spectral features.
• Magic-angle spinning (MAS) and rf multiple-pulse sequences significantly interfere with spectra due to interactions with Bjerrum-defect motion.

Conclusions:

• Ice can be spectroscopically observed and characterized in protein NMR samples.
• The observed ice properties align with those of pure water ice.
• Experimental conditions, particularly MAS and rf pulse sequences, critically impact ice spectra through interactions with protonic defects.