Development of Solid State NMR Methods and Technology

点击翻译按钮获取中文摘要

Progress in FY2008 was made in the following areas: (1) ULTRA-LOW-TEMPERATURE SOLID STATE NMR: Nearly all solid state NMR studies of interesting systems are limited by signal detection sensitivity. The sensitivity (i.e., signal-to-noise ratio) of solid state NMR measurements increases with decreasing sample temperature, approximately as 1/T1.5. Therefore, in principle, measurements at 30 K have thirty-fold higher sensitivity than measurements at room temperature, meaning that the time to complete a measurement can be reduced by a factor of 30 X 30 = 900 by operating at 30 K (since signal-to-noise is proportional to the square root of measurement time) if sample size is fixed. Alternatively, sample size requirements can be reduced by a factor of thirty. For these reasons, it is important to develop new solid state NMR technology for ultra-low-temperature measurements. In FY2008, we have succeeded in developing, testing, and applying a solid state NMR probe (which means the device that contains the sample and radiofrequency circuitry within the magnet of an NMR spectrometer) that operates at 25 K, with full capabilities for modern solid state NMR measurements. Capabilities include magic-angle spinning at 7 kHz and radio-frequency field strengths up to 140 kHz on the 1H channel, and greater than 50 kHz on the 13C channel, and liquid helium consumption less than 3 liters per hour. We have acquired experimental NMR data for several types of protein samples, including the helical protein HP35 in frozen solution, amyloid fibrils formed by residues 14-23 of the beta-amyloid peptide, and residues 1-40 of the HIV-1 Vpu transmembrane protein, in phospholipid bilayers. We have carried out two-dimensional 13C NMR measurements on these samples, as well as 13C-13C dipolar recoupling measurements on the amyloid sample. Other applications are now in progress.