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/核磁共振)谱仪的工作原理。设想了两个系统。第一台仪器正在建造中，将在9T的磁场下运行(g=2电子的磁场为250 GHz，1H核磁共振的磁场为380 MHz)。第二台仪器将是一台494 GHz回旋管，它将被集成到位于麻省理工学院的新的750 MHz核磁共振大口径光谱仪中。继续开发这些仪器的理由有三个：1.使用基于5T DNP/核磁共振回旋加速器的光谱仪，我们展示了蛋白质T4溶菌酶的DNP增强魔角光谱(MAS)。在~55K，我们在15/N谱中获得了~50的增强。这种灵敏度的动态增加使得对分子量为10/5或更大的大分子的结构/功能研究成为可能。在较高的场强下，分辨率和灵敏度将进一步提高。2.在140 GHz处，由于g值的色散，EPR谱的分辨率大大提高。这使得我们能够记录一些顺磁蛋白质的光谱，例如光系统I和II，核苷酸还原酶，半乳糖氧化酶等，这些光谱为重要的生化问题提供了答案，这些问题是低场光谱所不能解决的。我们预计在25 GHz时会有类似的信息性结果。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。我们最近成功地开发了250 GHz CW回旋管，在25瓦以下的功率下可靠地运行，从而克服了这个问题。因此，我们建议如下：DNP/NMR380 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毫米口径、9.0T核磁共振磁体和+/-1T可扫描B/0场，以及DNP/MAS探针。一条准光传输线将被用来有效地将微波功率耦合到样品中。将进行连续波和脉冲EPR研究。DNP/NMR750 MHz光谱仪：一旦证明DNP在380 MHz下的可行性，我们将在麻省理工学院的一台新光谱仪上将这项技术扩展到750 MHz。这将需要建造一个500 GHz的谐回旋管振荡器，并将该源集成到核磁共振光谱仪中。先进的回旋管技术：我们将研究250 GHz回旋放大器，它可以为EPR研究提供可调谐(0.5-1.0%带宽)和先进的脉冲格式。我们还将把回旋管振荡器扩展到600-800 GHz。这种回旋管可以与未来的0.9-1.2 GHz核磁共振光谱仪一起使用。

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.