Detection of C',Calpha correlations in proteins using a new time- and sensitivity-optimal experiment.

Sensitivity- and time-optimal experiment, called COCAINE (CO-CA In- and aNtiphase spectra with sensitivity Enhancement), is proposed to correlate chemical shifts of (13)C' and (13)C(alpha) spins in proteins. A comparison of the sensitivity and duration of the experiment with the corresponding theoretical unitary bounds shows that the COCAINE experiment achieves maximum possible transfer efficiency in the shortest possible time, and in this sense the sequence is optimal. Compared to the standard HSQC, the COCAINE experiment delivers a 2.7-fold gain in sensitivity. This newly proposed experiment can be used for assignment of backbone resonances in large deuterated proteins effectively bridging (13)C' and (13)C(alpha) resonances in adjacent amino acids. Due to the spin-state selection employed, the COCAINE experiment can also be used for efficient measurements of one-bond couplings (e.g. scalar and residual dipolar couplings) in any two-spin system (e.g. the N/H in the backbone of protein).