Pulsed triple electron resonance (TRIER) for dipolar correlation spectroscopy.

Area of Science:

• Molecular Biophysics
• Magnetic Resonance Spectroscopy
• Biophysical Chemistry

Background:

• Double electron-electron resonance (DEER) is crucial for nanometer-scale distance determination in molecules.
• Analyzing molecules with multiple paramagnetic centers presents challenges for traditional DEER experiments.
• Distinguishing between different molecular conformations using DEER can be ambiguous.

Purpose of the Study:

• Introduce a novel pulse sequence, triple electron resonance experiment (TRIER), for correlating dipolar frequencies.
• Extend the capabilities of electron spin resonance spectroscopy for complex molecular systems.
• Provide a method to resolve ambiguities in distance measurements arising from molecular conformations.

Main Methods:

• Utilize linear chirp pulses with smoothed edges for a refocused observer echo.
• Employ two hyperbolic secant pulses with distinct excitation windows to target specific spin subsets.
• Record a two-dimensional dipolar modulation pattern by varying pump pulse positions.
• Apply a two-dimensional Fourier transform to correlate dipolar frequencies within a molecule.

Main Results:

• Successfully developed and demonstrated the TRIER pulse sequence.
• Generated a 2D correlation plot of dipolar frequencies within molecules containing more than two paramagnetic centers.
• Showcased TRIER's potential to correlate distances derived from DEER measurements.

Conclusions:

• TRIER offers a powerful new tool for analyzing complex spin systems in molecules.
• This technique can potentially resolve conformational ambiguities that challenge standard DEER analysis.
• TRIER provides complementary information to DEER, enhancing structural insights at the nanoscale.