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

本项目的延长旨在在本项目第一阶段测量的含有自旋标记脂质的脂质双分子层的OE-DNP实验与产生这些实验结果的潜在分子运动之间建立定量联系。虽然报道的DNP和w- epr实验提供了关于自旋标签周围局部环境的性质和动力学的有价值的提示，但根据脂质和水分子的运动来解释实验是困难的。为了提供这样的解释，我们将对嵌入自旋标记脂质的几种脂质双层系统进行原子分子动力学（MD）模拟。MD轨迹将进行两种类型的定量分析，以便与报告的实验进行直接比较。首先，从模拟中得到的自旋标签的动力学将用于计算多频cw-EPR谱。其次，从电子自旋指向质子自旋的矢量动力学将用于计算自旋之间偶极相互作用的谱密度函数，从中得到OE-DNP耦合因子。计算和实验之间的最终一致将揭示高场OE-DNP增强所依赖的分子因素。另一方面，实验和计算之间可能存在的分歧将揭示MD模拟中潜在的缺陷。此外，我们希望将脂质双分子层的1H Over-hauser DNP实验扩展到DOPC脂质。这将允许探索自旋标记脂质与先前研究的DMPC脂质之间的长度不匹配是否可以通过引起结构紊乱或改变内部水分子的可及性和动力学来负责实验观察到的DNP效率的低位置依赖性。

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.