Strong coupling effects during X-pulse CPMG experiments recorded on heteronuclear ABX spin systems: artifacts and a simple solution.

Simulation and experiment have been used to establish that significant artifacts can be generated in X-pulse CPMG relaxation dispersion experiments recorded on heteronuclear ABX spin-systems, such as (13)C( i )-(13)C( j )-(1)H, where (13)C( i ) and (13)C( j ) are strongly coupled. A qualitative explanation of the origin of these artifacts is presented along with a simple method to significantly reduce them. An application to the measurement of (1)H CPMG relaxation dispersion profiles in an HIV-2 TAR RNA molecule where all ribose sugars are protonated at the 2' position, deuterated at all other sugar positions and (13)C labeled at all sugar carbons is presented to illustrate the problems that strong (13)C-(13)C coupling introduces and a simple solution is proposed.