Dynamic nuclear polarization at 700MHz/460GHz

• Published in: Journal of magnetic resonance (1997) Vol. 224; pp. 1 - 7
• Main Authors: Barnes, Alexander B., Markhasin, Evgeny, Daviso, Eugenio, Michaelis, Vladimir K., Nanni, Emilio A., Jawla, Sudheer K., Mena, Elijah L., DeRocher, Ronald, Thakkar, Ajay, Woskov, Paul P., Herzfeld, Judith, Temkin, Richard J., Griffin, Robert G.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.11.2012
• Subjects: Dynamic nuclear polarization; Instrumentation; Low temperatures; Magic angle spinning; Nuclear magnetic resonance; Sensitivity; TOTAPOL; Sensitivity; Magic angle spinning; Instrumentation; Dynamic nuclear polarization; Nuclear magnetic resonance; TOTAPOL; Low temperatures
• ISSN: 1090-7807; 1096-0856
• DOI: 10.1016/j.jmr.2012.08.002

[Display omitted] ► DNP at 700MHz/460GHz. ► Magic angle spinning enhancements of |40|. ► Instrumentation for 460GHz (λ=0.65mm) and low temperatures. We describe the design and implementation of the instrumentation required to perform DNP-NMR at higher field strengths than previously demonstrated, and report the first magic-angle spinning (MAS) DNP-NMR experiments performed at 1H/e− frequencies of 700MHz/460GHz. The extension of DNP-NMR to 16.4T has required the development of probe technology, cryogenics, gyrotrons, and microwave transmission lines. The probe contains a 460GHz microwave channel, with corrugated waveguide, tapers, and miter-bends that couple microwave power to the sample. Experimental efficiency is increased by a cryogenic exchange system for 3.2mm rotors within the 89mm bore. Sample temperatures ⩽85K, resulting in improved DNP enhancements, are achieved by a novel heat exchanger design, stainless steel and brass vacuum jacketed transfer lines, and a bronze probe dewar. In addition, the heat exchanger is preceded with a nitrogen drying and generation system in series with a pre-cooling refrigerator. This reduces liquid nitrogen usage from >700l per day to <200l per day and allows for continuous (>7days) cryogenic spinning without detrimental frost or ice formation. Initial enhancements, ε=−40, and a strong microwave power dependence suggests the possibility for considerable improvement. Finally, two-dimensional spectra of a model system demonstrate that the higher field provides excellent resolution, even in a glassy, cryoprotecting matrix.