| Abstract
| - A number of groups have utilized molecular dynamics (MD) to calculate slow-motional electron paramagneticresonance (EPR) spectra of spin labels attached to biomolecules. Nearly all such calculations have been basedon some variant of the trajectory method introduced by Robinson, Slutsky and Auteri (J. Chem. Phys. 1992,96, 2609−2616). Here we present an alternative approach that is specifically adapted to the diffusion operator-based stochastic Liouville equation (SLE) formalism that is also widely used to calculate slow-motional EPRline shapes. Specifically, the method utilizes MD trajectories to derive diffusion parameters such as the rotationaldiffusion tensor, diffusion tilt angles, and expansion coefficients of the orienting potential, which are thenused as direct inputs to the SLE line shape program. This approach leads to a considerable improvement incomputational efficiency over trajectory-based methods, particularly for high frequency, high field EPR. Italso provides a basis for deconvoluting the effects of local spin label motion and overall motion of the labeledmolecule or domain: once the local motion has been characterized by this approach, the label diffusionparameters may be used in conjunction with line shape analysis at lower EPR frequencies to characterizeglobal motions. The method is validated by comparison of the MD predicted line shapes to experimentalhigh frequency (250 GHz) EPR spectra.
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