Chemical‐Shift‐Resolved ¹⁹F NMR Spectroscopy between 13.5 and 135 MHz: Overhauser–DNP‐Enhanced Diagonal Suppressed Correlation Spectroscopy

Abstract

Overhauser-DNP-enhanced homonuclear 2D (19)F correlation spectroscopy with diagonal suppression is presented for small molecules in the solution state at moderate fields. Multi-frequency, multi-radical studies demonstrate that these relatively low-field experiments may be operated with sensitivity rivalling that of standard 200-1000 MHz NMR spectroscopy. Structural information is accessible without a sensitivity penalty, and diagonal suppressed 2D NMR correlations emerge despite the general lack of multiplet resolution in the 1D ODNP spectra. This powerful general approach avoids the rather stiff excitation, detection, and other special requirements of high-field (19)F NMR spectroscopy.

A quasi-optical and corrugated waveguide microwave transmission system for simultaneous dynamic nuclear polarization NMR on two separate 14.1 T spectrometers

“…However, when high power, high-frequency microwave sources became available, Griffin and coworkers demonstrated polarization transfer mechanisms that scale more efficiently with B 0 , such as the cross effect and the Overhauser effect in insulating solids [9–11]. DNP via the Overhauser effect in liquids involves stochastic interactions between the electron spins of stable radicals and the nuclei of interest that are either dominated by dipolar [12–16] or scalar interactions [7,14,17], and can theoretically enable significant polarization enhancements even at field strengths of interest for solution-state analytical NMR spectroscopy.…”

Ultrahigh 19F Loaded Cu1.75S Nanoprobes for Simultaneous 19F Magnetic Resonance Imaging and Photothermal Therapy

“…1,2 19 F MRI is anticipated to be a promising alternative to conventional 1 H MRI because of its high sensitivity (0.83 relative to 1 H), 3–6 negligible background signals, 7 and cost-effectiveness, which allows direct detection of 19 F-labeled probes such as cells 6,8 and drug capsules 9 for unambiguous identification and quantification, unlike typical metal-based contrast agents. 10,11 In order to obtain highly sensitive 19 F MRI probes for their practical implications, it is important to increase the number of fluorine atoms in the MRI probes.…”

1H and 2H NMR: Diagonal suppressed total correlation spectroscopy in spin echo mode

“…Recently a diagonal suppressed homonuclear correlation experiment for scalar coupled spin systems, termed DIagonal Suppressed Spin Echo Correlation specTroscopy (DISSECT) [17][18][19][20] was reported for suppression of SECSY 'diagonal' peaks in each scan of a two scan procedure. In DISSECT, diagonal suppression is achieved by converting the diagonal terms into unobservable multiple quantum coherences or longitudinal magnetization by applying a third 90 • pulse at the time of the maximum of the spin echo, i.e., at the end of the second half of the evolution period in a standard SECSY sequence.…”

“…Cross peaks however arise from magnetization whose precession frequency has changed in magnitude between the two halves of the evolution period, and whose refocusing is therefore incomplete: in other words the corresponding magnetization is oriented at the end of the evolution time in a direction in the rotating frame that does depend on the duration of evolution, giving rise in general to two orthogonal components, one of them along a direction orthogonal to the preparation pulse phase. An additional RF pulse of suitable phase and flip angle therefore serves to distinguish magnetization leading to diagonal peaks from that leading to cross peaks, and hence allows suppression of the former [17][18][19][20].…”

“…It may be noted that despite the duplication of cross-peaks in a rectangular array, DISSECT has superior sensitivity in practice compared to other methods [9,10], because the latter spend half the experiment time collecting no cross peaks at all. Applications of DISSECT have included volume localized in vivo spectroscopy (MRS) [17], Overhauser Dynamic Nuclear Polarization (ODNP) [18], as well as ultrafast homonuclear correlation spectroscopy [19]. This limitation of the DISSECT strategy to short FID acquisition times arises principally from the fact that the final DISSECT 90 • pulse can itself give rise to further coherence transfer and therefore could relay magnetization in systems with more than two coupled spins.…”