Ohio Advanced EPR Laboratory at Miami University

A resource serving the pulsed and CW EPR needs of the greater Ohio area.

Double Electron-Electron Resonance

DEER, also known as PELDOR or Pulsed ELDOR, uses two separate microwave frequencies to examine the coupling between two electron spins in order to make a distance measurement, typically between two nitroxide spin labels.

DEER

In the experiment, a Hahn Echo sequence is used to produce an echo for the spins in resonance with the probe microwave frequency.  At a time τ2 after the first echo, a second π pulse is applied to form a refocused echo.  At a separate microwave frequency, the pump frequency, a π pulse is applied to invert the population of a separate set of spins.  This π pulse is then incremented in time and the intensity of the refocused echo is monitored.  The set of spins affected by the probe frequency experiences a different magnetic environment before and after the pump π pulse.  The change in the magnetic environment affects the ability of the magnetization to be called back with the second probe π pulse.  The net effect is a modulation in the intensity of the refocused echo with a periodicity that is a function of the strength of the coupling and therefore, the distance, between the two electron spins.

Time Domain DEER Data from a Doubly Nitroxide Spin-labeled Protein

Time Domain DEER Data from a Doubly Nitroxide Spin-labeled Protein

An FT of the time domain data gives a spectrum in the frequency domain, indicating the coupling between the two electron spins.

Frequency Domain DEER Data from a Doubly Nitroxide Spin-labeled Protein

Frequency Domain DEER Data from a Doubly Nitroxide Spin-labeled Protein

From the frequency domain data, a distrubution of electron-electron distances can be constructed indicating the distance between the two site directed spin labels.

Distance Domain DEER Data from a Doubly Nitroxide Spin-labeled Protein

Distance Domain DEER Data from a Doubly Nitroxide Spin-labeled Protein

Here at the Ohio Advanced EPR Laboratory, we have the fortunate capability of conducting DEER measurements at both X-Band and Q-Band.  The incredible signal to noise enhancement that is achieved at Q-band is evident from the figure below.  What would typically be a 12 hour experiment at X-band can be done in only a couple of hours at Q-band with better results.

Comparison of X-band and Q-Band DEER

Comparison of X-band and Q-Band DEER

 

Miami University

Department of Chemistry and Biochemistry

Ohio Advanced EPR Laboratory
701 East High Street
101 Hughes Laboratories
Oxford, OH 45056

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