Faculty of Engineering and Natural Sciences, Sabancι University, Orhanlι-Tuzla, 34956 Istanbul, Turkey.
Phys Chem Chem Phys. 2014 Jan 21;16(3):1022-32. doi: 10.1039/c3cp53565g. Epub 2013 Nov 27.
The recently introduced methodology (Sezer, Phys. Chem. Chem. Phys., 2013, 15, 526) for calculating dynamic nuclear polarization (DNP) coupling factors through synergistic use of molecular dynamics (MD) simulations and the analytical model of diffusing hard spheres with spins at their centers (HSCS) is applied to several nitroxides in water. Computations with one TEMPONE and one TEMPOL in water agree with experiments at 0.35 T and 3.4 T, respectively. At 9.2 T the predicted coupling factors are larger by about 50% than the experimental numbers obtained with 1 M TEMPOL solution. MD simulations at this elevated concentration reveal nanoscopic TEMPOL clusters and qualitatively explain the lower experimental values. Comparing the dynamics from the MD simulations with those of the HSCS model, the assumption of centered spins is shown to be too limiting even for small molecules like TEMPOL and water. Using the available extension of the HSCS model to off-centered spins, the current procedure for analyzing hydration water dynamics from Overhauser DNP measurements on spin-labeled proteins is revisited.
最近引入的一种通过分子动力学（MD）模拟和带有自旋的扩散硬球（HSCS）分析模型协同使用来计算动态核极化（DNP）偶合因子的方法（Sezer，Phys. Chem. Chem. Phys.，2013，15，526），被应用于几种水中的氮氧自由基。在 0.35 T 和 3.4 T 下，用一个 TEMPONE 和一个 TEMPOL 在水中的计算与实验结果一致。在 9.2 T 下，预测的偶合因子比用 1 M TEMPOL 溶液获得的实验值大约 50%。在这个高浓度下的 MD 模拟揭示了纳米级 TEMPOL 簇，并定性地解释了较低的实验值。通过将 MD 模拟的动力学与 HSCS 模型的动力学进行比较，即使对于 TEMPOL 和水这样的小分子，自旋中心的假设也被证明过于局限。利用 HSCS 模型对非中心自旋的扩展，重新审视了基于自旋标记蛋白的 Overhauser DNP 测量分析水合动力学的当前方法。
