Fig. 3.

The 2D ¹H/¹³C refocused INEPT-HETCOR NMR spectrum of [U-¹³C/¹⁵N]-L-isoleucine. The delays τ and τ′ were set equal to 150 μs, the MAS frequency was 60 kHz, and TPPM ¹H decoupling was applied during acquisition with a rf field strength of 210 kHz. The recycle delay was 5 s, the sweep width in the indirect dimension was 30 kHz and 16 scans were acquired for each of the 128 complex t₁ points