More than ADEQUATE: doubling the sensitivity of ¹³CH-¹³CH correlations in double-quantum NMR experiments

We present modifications of the ADEQUATE experiment which more than double the sensitivity of carbon-carbon correlations of ¹³CH-¹³CH moieties. Additionally, these improvements can be applied without a sensitivity penalty to obtain spectra with a ¹³C chemical shift axis in the indirectly detected dimension, instead of a double-quantum frequency, allowing simpler interpretation of spectra. The modified experiments, which use refocussing of ¹J_CH couplings and ¹H decoupling during J_CC evolution intervals, were tested on several molecules, including a pentasaccharide (20 mg, 19 mM), where on average a 2.6-fold signal-to-noise improvement was achieved and the number of observable correlations increased. Doubling sensitivity results in a 4-fold reduction of the experimental time, allowing ADEQUATE spectra to be recorded overnight instead of over multiple days.