Figure 5.

Experimental ¹⁵N dipolar chemical shift correlation spectrum of the lyophylized and rehydrated RNA sample (zoomed plot) obtained at a spinning speed of 7000 Hz, with a data acquisition in the direct dimension of 10 ms, dipolar recoupling period of 20 ms, CP contact time of 175 µs, recycle time of 4.1 s, ω₁ spectral width of 3000 Hz and 32 t₁ increments with 512 transients per t₁ increment. The RF carrier was kept at 164.6 p.p.m.. The amino nitrogen lines are folded in the ω₁ dimension. Dipolar recoupling was effected by employing the [p5p7m4] phasing scheme with ‘cagauss’ adiabatic pulses (142 µs, 28.0 kHz γH₁, 50 kHz sweep width) (23,32) as implemented in the Varian Pbox pulse-shaping software. The assignments of the different resonances are indicated in the spectral projection given. Also illustrated are the normal and reverse GC Watson–Crick base-pairing schemes. The spectral diagonal is indicated by a dotted line.