Portal de Periódicos da CAPES

Rapid Quantitation of Parameters from Inhomogeneously Broadened EPR Spectra

1993; Academic Press; Volume: 103; Issue: 1 Linguagem: Inglês

10.1006/jmra.1993.1125

1096-0864

Howard J. Halpern, Miroslav Perić, Cong Yu, Barney L. Bales,

Photochemistry and Electron Transfer Studies

Spectral parameters from inhomogeneously broadened organic-free-radical EPR spectra, using nearly all the information in the spectrum, were extracted rapidly and accurately using an approximation of the spectral shape by the sum of a Lorentzian and a Gaussian function of equal linewidths. This approximate shape was fitted to the spectrum by a nonlinear least-squares fitting algorithm. Line position and overall spectral width were extracted directly, whereas component Lorentzian and Gaussian widths were extracted with further analysis of the fit parameters. We investigated the accuracy with which the sum function can be fitted to the more familiar Lorentzian/Gaussian convolution (Voigt) representation of EPR spectra for both a singlet and a closely spaced (overlapping) doublet spectrum. The strategy was applied, first, to synthetic spectra involving noise added to the Voigt doublet and, second, to spectral data from a nitroxide manifold consisting of a closely spaced doublet. This parametric extraction strategy increased the accuracy of the line-splitting measurement by an order of magnitude compared with other methods. It allowed deconvolution of the component Lorentzian linewidth that is consistent with previous direct measurements. It may allow the probing of subtle physical variations which have heretofore been difficult, if not impossible, to measure.