Enhancement of Solution NMR and MRI with Laser-Polarized Xenon

Abstract

ly. The oxygen fugacity (/02) of the experiments was not buffered externally. However, /02 calculations based on biotite-sanidine-magnetite-H20-02 equilibrium [D. R. Wones, Kozan Chishitsu 31, 191 (1981)] yield /02 values 1.5 to 2 log units above the nickel-nickel oxide buffer. This is consistent with the estimated f02 conditions of natural epidote-bearing magmas {6, 16). Quenched experimental charges were sectioned longitudinally, polished, and examined with reflected-light microscopy and backscattered electron imaging. Rim widths were measured with an optical microscope equipped with a graduated ocular lens; the rim widths reported are the average of 20 to 30 measurements. Rim width data are as follows: experiment Ep-10, t = 51.17 hours, rim width = 2.74 ± 0.9 fjim; experiment Ep-12, t = 141.20 hours, rim width = 4.95 ± 0.8 fjtm; and experiment Ep-11, t = 378.78 hours, rim width = 8.18 £ 1.3 fjtm. 9. D. C. Rubie and A.

250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMR

“…At present we are observing enhancements of ~40 in the 1 H polarization at 250 GHz/380 MHz, a number that is probably limited by the penetration of the microwaves into the sample [35] and the 1 H concentration. Subsequently, this enhanced polarization is transferred to 13 C or 15 N for observation. Detection is via the low-γ spin since this avoids the residual 1 H signal that is present in essentially all solid state probes.…”

“…Figure 5 is an illustration of one of the initial 2D 15 N-13 C spectra obtained with the pulse sequence illustrated in Figure 3. Because the 15 N Schiff base signal is well separated from the remainder of the 15 N signals in the spectrum of the protein, it is possible to selectively excite this resonance with a Gaussian pulse as it illustrated in Figure 3 and to subsequently transfer that magnetization to 13 C's in the retinal and lysine sidechain. Thus, following 1 H-15 N crosspolarization, magnetization is labeled with the 15 N chemical shift and then transferred to the 13 C spins using band-selective 15 N-13 C cross polarization.…”

“…Initially we reported [58] the 1D 15 N spectrum of the bR 555 / bR 568 mixture such as is shown in Figure 6 (left) and assigned the Schiff base line at 172 and 165 ppm to bR 555 and bR 568 respectively, based on their ~60:40 intensity ratio and the disappearance of the downfield signal on light adaptation. However, the 2D 15 N- 13 C spectrum that can be acquired with DNP ( Figure 6, right) clearly reveals a more complicated mixture, with two cross peaks in a ~2:1 intensity ratio associated with the bR 555 component. Our current interpretation of these results is that at 90 K we are quenching protein conformational equilibria that lead to dynamically averaged spectra and single lines in 1D and room temperature spectra of bR 555 .…”

“…Today, CP is an integral part of high resolution magic angle spinning (MAS) experiments in solids [6] and multiple INEPT transfers are present in essentially every biological solution NMR experiment [7]. In these approaches, the sensitivity is enhanced by a factor of (γ I /γ S ) or about 4 for I= 1 H and S= 13 C and 10 when S= 15 N. Another, and in fact the original, example of a polarization transfer experiment was proposed by Overhauser [8] and involved transfer of conduction electron polarization to nuclear spins in metals. Carver and Slichter [9,10] verified Overhauser's hypothesis that such transfers and signal enhancements were possible with low field (3.03 mT) experiments performed on samples of Li metal and other materials with mobile electrons.…”

“…Extension of electron-nuclear and other high polarization transfer experiments involving noble gases, para-hydrogen, semiconductors, or photosynthetic reaction centers [11][12][13][14][15][16][17][18][19][20][21][22][23] to contemporary solid state and solution experiments is very appealing, since it could significantly enhance the sensitivity in a variety of NMR experiments. In particular, the theoretical enhancement for electron-nuclear polarization transfers is approximately ~(γ e /γ I ), where now the ratio is ~660, because of the large magnetic moment of the electron relative to the 1 H, making the gains in sensitivity large.…”