Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Phys Chem Chem Phys. 2010 Jun 14;12(22):5861-7. doi: 10.1039/c003763j. Epub 2010 May 8.
This contribution addresses four potential misconceptions associated with high-resolution dynamic nuclear polarization/magic angle spinning (DNP/MAS) experiments. First, spectral resolution is not generally compromised at the cryogenic temperatures at which DNP experiments are performed. As we demonstrate at a modest field of 9 T (380 MHz (1)H), 1 ppm linewidths are observed in DNP/MAS spectra of a membrane protein in its native lipid bilayer, and <0.4 ppm linewidths are reported in a crystalline peptide at 85 K. Second, we address the concerns about paramagnetic broadening in DNP/MAS spectra of proteins by demonstrating that the exogenous radical polarizing agents utilized for DNP are distributed in the sample in such a manner as to avoid paramagnetic broadening and thus maintain full spectral resolution. Third, the enhanced polarization is not localized around the polarizing agent, but rather is effectively and uniformly dispersed throughout the sample, even in the case of membrane proteins. Fourth, the distribution of polarization from the electron spins mediated via spin diffusion between (1)H-(1)H strongly dipolar coupled spins is so rapid that shorter magnetization recovery periods between signal averaging transients can be utilized in DNP/MAS experiments than in typical experiments performed at ambient temperature.
这篇文章讨论了与高分辨率动态核极化/魔角旋转（DNP/MAS）实验相关的四个潜在误解。首先，在进行 DNP 实验的低温下，光谱分辨率通常不会受到影响。正如我们在 9T（380MHz(1)H）的适度场强下所证明的那样，在天然脂质双层中的膜蛋白的 DNP/MAS 光谱中观察到 1ppm 的线宽，而在 85K 的结晶肽中报告的线宽<0.4ppm。其次，我们通过证明用于 DNP 的外源自由基极化剂以避免顺磁展宽的方式分布在样品中，从而维持全谱分辨率，解决了 DNP/MAS 光谱中蛋白质的顺磁展宽问题。第三，增强的极化不是集中在极化剂周围，而是有效地、均匀地分散在整个样品中，即使是在膜蛋白的情况下也是如此。第四，通过(1)H-(1)H 强偶极耦合自旋之间的自旋扩散介导的电子自旋传递的极化分布非常迅速，因此可以在 DNP/MAS 实验中利用比在环境温度下进行的典型实验更短的磁化恢复周期。
