HIGH FIELD/HIGH FREQUENCY ESR FOR STUDYING DNP IN BIOMEMBRANES

该子项目是利用资源的许多研究子项目之一 由NIH/NCRR资助的中心拨款提供。子项目的主要支持 而子项目的主要调查员可能是由其他来源提供的， 包括其他NIH来源。 为子项目列出的总成本可能 表示子项目使用的中心基础设施的估计数量， 而不是由NCRR赠款提供给子项目或子项目工作人员的直接资金。 动态核极化（DNP），这是众所周知的，因为早期的磁共振，现在正在成为一个强大的工具，以提高灵敏度和分辨率的NMR和MRI技术在结构生物学和医学。从未成对电子自旋到耦合核自旋（质子、15 N、13 C）的极化转移导致NMR信号增强。对于固态NMR，这种增强可以高达三个数量级。然而，目前对DNP的理论理解是不完整的，ACERT凭借我们的高场ESR技术和ESR弛豫方面的专业知识，能够更好地理解这一现象。 核磁共振实验常用磁场中DNP效应的观测（3  20特斯拉）需要在相应的高场/高频ESR范围下微波辐照样品：  600千兆赫。 ACERT具有在宽频率范围内进行ESR实验的独特能力。 McDermott教授（哥伦比亚大学）对DNP的兴趣主要集中在具有连接基团的膜蛋白上。最近发现具有相对短的自旋间距（d 10）的氮氧双自由基是非常有效的极化剂。此外，已经表明刚性双自由基是比具有柔性系链的双自由基更强大的极化剂。然而，关于双自由基以及它们如何为DNP工作还有很多不太清楚的地方。特别是，多自由基增强DNP弛豫的确切机制仍然不清楚。 详细研究现有的和未来的DNP极化剂在高频下的ESR弛豫将为DNP现象提供有价值的见解。为了从嵌入膜的疏水核中的顺磁核获得DNP增强的NMR信号，核应该是极化剂可接近的。 ESR波谱，特别是高场ESR波谱，可以很容易地确定膜中可能的极化剂的深度位置，并预测各种跨膜蛋白片段的可及性。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Dynamic Nuclear Polarization (DNP), which has been well-known since the early years of magnetic resonance, is now becoming a powerful tool to improve the sensitivity and resolution for NMR and MRI techniques in structural biology and medicine. Transfer of polarization from unpaired electron spins to coupled nuclear spins (protons, 15N, 13C) results in an enhancement of the NMR signal. This enhancement could be as high as three orders of magnitude for solid state NMR. However, the current theoretical understanding for DNP is incomplete and ACERT, with our High Field ESR technology and expertise in ESR relaxation, is in a good position to better understand this phenomenon. Observation of DNP effects in magnetic fields routinely used for NMR experiments (3  20 Tesla) requires microwave irradiation of the sample at the corresponding High Field/High Frequency ESR range: 90  600 GHz. ACERT has a unique capability to carry out ESR experiments at a wide range of frequencies. Prof. McDermott's (Columbia University) interest in DNP is focused on membrane proteins with attached radicals. It has been recently found that nitroxide biradicals with relatively short interspin distances (d 10¿) are very efficient polarizing agents. Moreover, it has been shown that rigid biradicals are even more powerful polarizing agents than biradicals with flexible tethers. However, there is much that is not well understood about the biradicals and how they work for DNP. In particular, the exact mechanism of DNP relaxation enhancement by multiradicals is still unclear. A detailed study of ESR relaxation for existing and perspective DNP polarizing agents at high frequencies will provide valuable insights into the DNP phenomenon. To obtain DNP enhanced NMR signals from paramagnetic nuclei embedded into the hydrophobic core of the membrane, the nuclei should be accessible for the polarizing agent. ESR spectroscopy, and High Field ESR spectroscopy in particular, can easily determine the depth location of possible polarizing agents in the membrane and predict the accessibility of various transmembrane protein fragments.