250/500 GHZ GYROTRON BASED DNP/EPR SPECTROMETER

提出了基于回旋管的动态核极化/核磁共振（DNP/NMR）谱仪的操作。设想了两个系统。目前正在建造的第一台仪器将在9 T的磁场下工作（g = 2电子为250 GHz，1H NMR为380 MHz）。第二个仪器将是一个494千兆赫回旋管，将被集成到一个新的750兆赫核磁共振宽口径光谱仪将位于麻省理工学院。继续发展这些文书的理由有三个方面：1.利用5 T DNP/NMR回旋管光谱仪，我们证明了蛋白质T4溶菌酶的DNP增强魔角光谱（MAS）。在~55K时，我们在15/N光谱中实现了~50的增强。这种灵敏度的动态增加允许对分子量为10/5或更大的大分子进行结构/功能研究。分辨率和灵敏度将在更高的领域进一步提高。2. 在140 GHz处，g值色散使EPR谱的分辨率显著提高。这使我们能够记录一些顺磁性蛋白质的光谱 例如光系统I和II、核糖核苷酸还原酶、半乳糖氧化酶等。 其提供了从较低场光谱无法获得的重要生物化学问题的答案。我们预计在25 GHz下会得到类似的信息结果。3.阻碍DNP和脉冲EPR研究向更高频率扩展的关键因素是缺乏足够功率的微波源。我们最近克服了这个问题，成功地开发了一个250 GHz的连续波回旋管，可靠地运行在功率高达25瓦。因此，我们提出以下建议：DNP/NMR 380 MHz光谱仪：我们将完成380 MHz光谱仪的建造，并开始DNP和EPR研究。该光谱仪将使用125 mm孔径、9.0 T NMR磁体（带+/-1 T可扫B/0场）和DNP/MAS探头。准光传输线将被用来有效地耦合到样品的微波功率。将进行CW和脉冲EPR研究。DNP/NMR 750 MHz光谱仪：一旦DNP在380 MHz的可行性得到证明，我们将在麻省理工学院的新光谱仪上将这项技术扩展到750 MHz。这将需要一个500 GHz的谐波回旋振荡器的建设和集成到NMR光谱仪这个源。先进的回旋管技术：我们将研究250千兆赫陀螺放大器，它可以提供可调谐性（0.5 - 1.0%带宽）和先进的脉冲格式的EPR研究。我们还将把回旋管振荡器扩展到600 - 800 GHz。这种回旋管可以用于未来的0.9 - 1.2 GHz NMR光谱仪。

The operation of gyrotron-based dynamic nuclear polarization/nuclear magnetic resonance (DNP/NMR) spectrometers is proposed. Two systems are envisioned. The first instrument, now under construction, will operate at a magnetic field of 9 T (250 GHz for g=2 electrons and 380 MHz for 1H NMR). The second instrument will be a 494 GHz gyrotron that will be integrated into a new 750 MHz NMR wide-bore spectrometer to be located at MIT. The rationale for the continued development of these instruments is threefold: 1. Using a 5 T DNP/NMR gyrotron-based spectrometer, we have demonstrated DNP enhanced magic angle spectra (MAS) of the protein T4 lysozyme. At ~55k we have achieved enhancements of ~50 in 15/N spectra. This dynamic increase in sensitivity permits structure/function studies of macromolecules with molecular weights of 10/5 or greater. Resolution and sensitivity will be further improved at higher fields. 2. At 140 GHz the resolution of EPR spectra due to g value dispersion increases dramatically. This has permitted us to record a number of spectra of paramagnetic proteins for example, photosystem I and II, ribonucleotide reductase, galactose oxidase, etc. which provide answers to important biochemical problems not available from lower field spectra. We anticipate similar informative results at 25 GHz. 3. The critical factor that has impeded the extension of DNP and pulsed EPR research to higher frequencies has been the lack of microwave source with adequate power. We have recently overcome this problem with the successful development of a 250 GHz CW gyrotron that has operated reliably at powers up to 25 watts. We therefore propose the following: DNP/NMR 380 MHz Spectrometer: We will complete the construction of a 380 MHz spectrometer and begin DNP and EPR studies. This spectrometer will utilize a 125 mm bore, 9.0T NMR magnet with a +/- 1 T sweepable B/0 field, and DNP/MAS probes. A quasi-optical transmission line will be used to efficiently couple the microwave power into the sample. Both CW and pulsed EPR studies will be conducted. DNP/NMR 750 MHz Spectrometer: Once the viability of DNP at 380 MHz is demonstrated, we will extend this technique to 750 MHz on a new spectrometer at MIT. This will require the construction of a 500 GHz harmonic gyrotron oscillator and the integration of this source into the NMR spectrometer. Advanced Gyrotron Technology: We will investigate 250 GHz gyro- amplifiers, which could provide both tunability (0.5-1.0% bandwidth) and advanced pulse formats for EPR studies. We will also extend gyrotron oscillators to 600-800 GHz. Such gyrotrons could be used with future 0.9- 1.2 GHz NMR spectrometers.