Overhauser Dynamic Nuclear Polarization at high magnetic fields (9.4 T) on Lipid Bilayers

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The prolongation of this project aims to establish a quantitative link between the OE-DNP experi-ments with lipid bilayers containing spin-labeled lipids measured in the first period of this project, and the underlying molecular motions that give rise to these experimental results. While the re-ported DNP and cw-EPR experiments provide valuable hints about the nature and dynamics of the local environments surrounding the spin labels, interpreting the experiments in terms of the mo-tions of the lipids and the water molecules is difficult. To provide such an interpretation, we will perform atomistic molecular dynamics (MD) simulations of several lipid-bilayer systems with em-bedded spin-labeled lipids. The MD trajectories will be subjected to two types of quantitative anal-yses that will allow for direct comparison with the reported experiments. First, the dynamics of the spin labels from the simulations will be used to calculate multi-frequency cw-EPR spectra. Second, the dynamics of the vector pointing from an electron spin to a proton spin will be used to calculate the spectral density function of the dipolar interaction between the spins, from which an OE-DNP coupling factor will be obtained. An eventual agreement between the calculations and the experi-ments will shed light on the molecular factors on which the high-field OE-DNP enhancements rely. A possible disagreement between the experiments and the calculations, on the other hand, will illuminate latent deficiencies in the MD simulations. Additionally, we want to extend our 1H Over-hauser DNP experiments on lipid bilayers to DOPC lipids. This will allow exploring if the length mismatch between the spin-labeled lipids with the formerly studied DMPC lipids could be respon-sible for the experimental observed low position dependence of the DNP efficiency by causing structural disorder or changing the accessibility and dynamics of internal water molecules.