Pulse with gradient coherence selection

Figure 3 presents an example of such a situation. The 2Q-HoMQC spectrum of apo-cytochrome c was acquired in 93% H2O at 480 ixM concentration on a Varian Unity/INOVA 600 MHz NMR instrument overnight, using a pulse sequence with gradient coherence selection and weak gradient spin-echo during excitation delays and the evolution period [29], respectively (I.P., not published). The spectral windows were 8 kHz both in F2 and F. ... 

Figure 13 Timing diagram for the clean HMBC experiment with an initial second-order and terminal adiabatic low-pass 7-filter.42,43 The recommended delays for the filters are the same than for a third-order low-pass J filter. <5 and 8 are gradient delays, where 8 — <5 + accounts for the delay of the first point in the 13C dimension. The integral over each gradient pulse G, is H/2yc times the integral over gradient G2 in order to achieve coherence selection. The recommended phase cycle is c/)n = x, x, x, x 3 — 4(x), 4(y), 4( x), 4(—y) with the receiver phase c/)REC = x, x.

The 15N,1H shift correlation maps are most conveniently recorded with a sensitivity-enhanced HSQC sequence with incorporated water flip-back pulses for reduced saturation transfer and pulsed-field gradients for coherence selection. The pulse sequence of the experiment is shown in Fig. 14.4 A. 

Fig. 4. Modified X/Y IMPEACH-MBC pulse sequence used for 19F/15N shift correlation according to Ref. 27. The notation of 90° and 180° pulses is as before. The (d/2 — 180°(Y) — d/2) element represents a variable delay that is incremented concurrently with the decrementation of the accordion delay vd. Pulse phases are x, unless specified x = — x 2 = x, — x 3 = x, x, — x, — x = , — x, — x, x. The bipolar gradients Gs flanking the 180°(Y) pulse can be set to arbitrary power levels, and the relative strengths of the coherence selection gradients G and G2 are determined by G2/G1 =2 Yy/Tx-...

Coherence Pathway Selection with Pulsed Field Gradients... 

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