HIGH FIELD/HIGH FREQUENCY ESR FOR STUDYING DNP IN BIOMEMBRANES

这个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。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 动态核极化(DNP)早在磁共振研究初期就为人们所熟知，现已成为提高核磁共振和核磁共振技术在结构生物学和医学中的灵敏度和分辨率的有力工具。从未配对的电子自旋到耦合的核自旋(质子，15N，13C)的极化转移导致核磁共振信号的增强。对于固态核磁共振，这种增强可能高达三个数量级。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，可以更好地理解这一现象。要观察核磁共振实验中常规使用的磁场中的DNP效应(320特斯拉)，需要在相应的高场/高频ESR范围内对样品进行微波辐射：90 600 GHz。ACERT具有在广泛频率范围内进行ESR实验的独特能力。麦克德莫特教授(哥伦比亚大学)对DNP的兴趣主要集中在带有连接基团的膜蛋白上。最近发现，具有较短自旋间距(d10？)的氮氧双自由基是非常有效的极化剂。此外，研究还表明，刚性双自由基比柔性系链双自由基具有更强的极化性。然而，关于两个激进分子以及他们如何为DNP工作，还有很多事情没有被很好地理解。特别是，多自由基增强DNP驰豫的确切机制仍不清楚。对现有的和有前景的DNP极化介质在高频下的ESR弛豫进行详细的研究，将为理解DNP现象提供有价值的见解。为了从嵌入到膜疏水核心中的顺磁性核获得DNP增强的核磁共振信号，核应该可以被极化剂访问。ESR波谱，特别是高场ESR波谱，可以很容易地确定可能的极化剂在膜中的深度位置，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.