Separation of intra- and intermolecular NOEs through simultaneous editing and J-compensated filtering: A 4D quadrature-free constant-time J-resolved approach

The NMR methods used to characterize molecular interactions through NOEs re ly on isotope editing/ filtering strategies designed to select for/against C-13(N-15)-bound proton spins. The filter efficiency depends critically on the optimal compensation for variations in J(CH) scalar coupling constants, which is effectively obtained by the currently available second- and third -order isotope filters but at the cost of losing all intramolecular NOEs. H ere a new filtering/ediling strategy based on quadrature-free constant-time J-spectroscopy is presented that achieves J(CH)-compensation and the simul taneous measurement of inter- and intramolecular NOEs between C-13-bound H- 1 spins. The J-resolved frequency dimension is incorporated in a semiconsta nt-time NOESY-HSQC experiment resulting in a 4D spectrum in which signals a rising from protons bound to C-13 (or N-15) separated from those originatin g from proton bound to C-12 (or N-14) nuclei. The filter performance does n ot depend on double tuning of delays or on empirical correlations. In addit ion, the filter efficiency is not limited by upper bounds Bn the JCH values . The large J-bandwidth and the substantial timesaving make the pulse seque nce here outlined a valuable tool for investigating noncovalent molecular a ssemblies by NMR, especially in the context of fast structural elucidations required for the development of structural genomics.