Volume localized spin echo correlation spectroscopy with suppression of ‘diagonal’ peaks

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

“…Herein we present our results at X-and W-bands and report successful ODNP-enhanced homonuclear 19 F correlation experiments such as COSY, SECSY, and especially DISSECT. DISSECT (diagonal suppressed spin echo correlation spectroscopy) [11] is an experiment developed from our Lab for suppression of "diagonal" peaks in SECSY (that is, multiplets that are centered at F 1 = 0), and leads to in-phase cross-peaks in the direct dimension F 2 . In DISSECT, a third 908 pulse is applied at the end of the evolution period, that is, at the top of the coherence transfer echo that results from SECSY.…”

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].…”

“…This may be readily seen from the observable state of a two-spin-1/2 (AX) system resulting after the SECSY and DISSECT sequences, respectively; tracking the fate of longitudinal magnetization of spin A (I 1 ), we have [17]:…”

“…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.…”