POLARIZATION TRANSFER DYNAMICS IN DNP EXPERIMENTS

DNP 实验中的偏振传递动力学

• 批准号: 6355122
• 负责人: VOLKER R WEIS
• 金额: $ 1.71万
• 依托单位: MASSACHUSETTS INSTITUTE OF TECHNOLOGY
• 依托单位国家: 美国
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-05-01 至 2001-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6355122
• 关键词: bioengineering /biomedical engineering; bioimaging /biomedical imaging; biological products; biomedical resource; magnetic resonance imaging; nuclear magnetic resonance spectroscopy; nucleic acids; proteins; spectrometry

Currently, the best polarization mechanism for DNP at 5 Tesla is the thermal mixing effect using 4-amino TEMPO free radical as polarizing agent. 'H-signal enhancements of up to F-=300-400 have been observed after microwave irradiation for 120 seconds. The experiment has to be carried out at low temperatures (T=12-20 K) in order to have sufficiently long nuclear relaxation times. However, at the same time the build up kinetic of the nuclear polarization is rather slow. The time constant was found to be aboutr=230 s at these temperatures. Clearly, it is desirable to have faster transfer mechanisms allowing for better sensitivity. We have studied the thennal mixing transfer kinetics for different TEMPO derivates in order to get a better understanding of the transfer mechanism. We found that thermal mixing with 4hydroxy TEMPO as polarizing agent allows a much faster polarizing rate (,r=41 s) with a comparable signal enhancement to 4-amino TEMPO. Experiments can, therefore, be performed at a higher repetition rate allowing for better S/N per unit time. We also started to perform experiments using other transfer pathways than those used with the currently available polarization mechanisms. Cross polarization under matched Hartmann-Hahn conditions should allow a polarization transfer on the timescale of several gs, the inverse of the hyperfine coupling strength. This type of experiment requires fast phase switching and strong fields on both the EPR and NMR channel and became possible with the newly developed high Q double resonance resonator (see subproject 'An Electron Nuclear Double Resonance Resonatorfor DNP and ENDOR at 5 Tesla').

目前，DNP在5特斯拉下的最佳极化机制是 使用4-氨基克里思自由基作为 极化剂 H信号增强高达F-=300-400， 在微波照射120秒后观察到。 的 实验必须在低温（T=12-20 K）下进行， 为了有足够长的核弛豫时间。 但 同时，核极化的建立动力学是 相当慢。 在这些温度下，时间常数约为r =230 s。 温度 显然，希望具有更快的传输速度， 使其具有更好的灵敏度。 我们研究了 不同克里思衍生物的热混合传递动力学 以便更好地了解转移机制。 我们 发现用4羟基克里思作为极化剂的热混合 允许更快的偏振速率（r=41 s）， 4-氨基克里思信号增强。 因此，实验可以 以更高的重复率执行，从而实现更好的每单位信噪比 时间 我们也开始进行实验，使用其他转移 与目前可用的极化相比， 机制等 匹配Hartmann-Hahn条件下的交叉极化 应该允许在几个GS的时间尺度上的偏振转移， 超精细耦合强度的倒数。 这种类型的 实验需要快速的相位切换和强磁场， EPR和NMR通道，并成为可能与新开发的高 Q双共振谐振器（见子项目“电子核 DNP和ENDOR的双共振共振器，5特斯拉）。