Evaluating spin diffusion in MAS-NOESY spectra of phospholipid multibilayers

Area of Science:

• Biophysics
• Structural Biology
• Nuclear Magnetic Resonance Spectroscopy

Background:

• Biological semisolids, like phospholipid dispersions, are crucial for cellular function.
• High-resolution 1H NMR spectra and NOESY are powerful techniques for studying molecular structures and interactions.
• Understanding proton-proton distances in lipids is key to elucidating membrane structure and dynamics.

Purpose of the Study:

• To investigate the origin of an anomalous NOESY crosspeak between lipid headgroup and acyl chain methyl groups.
• To explore spin communication mechanisms in phospholipid bilayers using advanced NMR techniques.
• To test structural models for phospholipid arrangements based on NMR data.

Main Methods:

• Utilized magic-angle spinning (MAS) for high-resolution 1H NMR spectroscopy.
• Employed two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY) to determine proton-proton distances.
• Studied selectively deuterated dimyristoylphosphatidylcholines (DMPC) in aqueous dispersions.

Main Results:

• Observed an anomalous NOESY crosspeak between methyl groups of the headgroup and acyl chains.
• Spin-relaxation and line-narrowing data argued against efficient spin diffusion.
• MAS-NOESY results did not support interdigitated or chain-bendback structural models.

Conclusions:

• Proposed a mechanism for spin communication within a conventional lipid bilayer structure.
• Mechanism involves through-space interactions between adjacent molecules followed by spin diffusion along acyl chains.
• The findings provide new insights into molecular interactions within phospholipid membranes.