ACERT Highlights: Recent Highlights

National Institute of General Medical Sciences
	National Biomedical Resource for Advanced ESR Spectroscopy

Recent Highlights

Theory and Least Squares Fitting of CW ESR Saturation Spectra Using the MOMD Model

CW saturation experiments are widely used in ESR studies of relaxation processes in proteins and lipids. We develop the theory of saturation in ESR spectra in terms of its close relation with that of 2D-ELDOR. Our treatment of saturation is then based on the microscopic order macroscopic disorder (MOMD) model and can be used to fit the full CW saturation spectrum, rather than fitting just the peak–peak amplitude as a function of microwave field B₁ as is commonly done. This requires fewer experiments to yield effects on T₁, as well as provides a more extensive dynamic structural picture, for example, for scanning experiments on different protein sites. The code is released as a publicly available software package in Python that can be used to fit CW saturation spectra from biological samples of interest.

Publication: Appl. Magn. Reson. (2021); PMCID in progress.

Figure: Fit to experimental 5PC-DMPC CW saturation spectra at 39° C. Static field B₀ = 3360 G (X band). The maximum value of B₁ determined for a small sample of PADS, as described by Goldman Bruno, and Freed (1973), was 0.97 Gauss. With the correction for the difference in resonator Q-values, this number for the 5PC-in-DMPC sample was estimated as 0.9 Gauss. We used 20 orientations per MOMD calculation. χ² residual for the simultaneous fits was 0.57.

Pranav Gupta, Boris Dzikovski, and Jack H. Freed. (ACERT)

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ACERT is supported by grant 1R24GM146107 from the National Institute of General Medical Sciences (NIGMS), part of the National Institutes of Health.

National Biomedical Resource for Advanced ESR Spectroscopy

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National Institute of
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