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

这项计划的延长旨在建立在本计划第一阶段测量的含有自旋标记脂质的脂质双层的OE-DNP实验与导致这些实验结果的潜在分子运动之间的定量联系。虽然报道的DNP和CW-EPR实验为自旋标记物周围局部环境的性质和动力学提供了有价值的线索，但从脂类和水分子的运动角度解释这些实验是困难的。为了提供这样的解释，我们将使用嵌入自旋标记的脂类对几种脂类-双层系统进行原子分子动力学(MD)模拟。MD轨迹将接受两种类型的定量分析，以便与已报道的实验进行直接比较。首先，来自模拟的自旋标记物的动力学将被用于计算多频率的CW-EPR谱。其次，从电子自旋指向质子自旋的矢量的动力学将被用来计算自旋之间偶极相互作用的谱密度函数，由此得到OE-DNP耦合因子。计算和实验之间的最终一致将阐明高场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的不一致将揭示MD模拟中潜在的缺陷。此外，我们希望将我们关于脂双层的1H Over-Hauser DNP实验扩展到DOPC脂类。这将允许探索自旋标记脂与以前研究的DMPC脂之间的长度失配是否可能是实验观察到的DNP效率的低位置依赖性的原因，因为它导致了结构无序或改变了内部水分子的可及性和动力学。

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.