Chemically amplified 19F–1H nuclear Overhauser effects

Uniform illumination of optically dense NMR samples

“…Almost 20 years ago, Berliner and colleagues [14] demonstrated the use of an optical fibre held inside the NMR tube by means of a coaxial capillary insert (Fig. 1D), an arrangement we have used extensively for photo-CIDNP studies of proteins [15][16][17][18]. In our experience, the end of the insert must be positioned at least 2 mm above the NMR coil to avoid undue lineshape distortion.…”

“…The amount of light reaching the NMR sample can be conveniently monitored via the 19 F photo-CIDNP enhancement of 4-fluorophenol sensitised by flavin mononucleotide (FMN). For light flashes between 1 and 100 ms, the photo-induced 19 F magnetisation is a direct measure of the local light intensity [18] allowing the use of NMR imaging techniques to reveal the spatial distribution of light within the sample tube.…”

Photo-CIDNP experiments with an optimized presaturation pulse train, gated continuous illumination, and a background-nulling pulse grid

“…The timing is chosen such [see below, Eqs. (10)- (12)] that the background of the nucleus with the shortest relaxation time crosses zero at the end of D 2 . Self-compensation occurs because the other nuclei, which relax more slowly, regain a smaller fraction of their equilibrium magnetization during the pre-pulse period D 1 , so their relaxation during the post-pulse period D 2 starts from a less negative value.…”

“…(11)), or their sum (Eq. (12)) is constrained by the details of the pulse sequence to be the independent variable, one has to choose…”

“…Fortunately, the whole arsenal of highresolution NMR can be employed to overcome this limitation. Both coherence transfer methods [5][6][7][8][9] and nuclear Overhauser effects [5][6][7][10][11][12] have been applied to systems polarized by CIDNP. In this work, we have additionally combined CIDNP with 1D-TOCSY.…”