Accurate measurement of small spin-spin couplings in partially aligned molecules using a novel J-mismatch compensated spin-state-selection filter.

The accurate measurement of small spin-spin coupling constants in macromolecules dissolved in a liquid crystalline phase is important in the context of molecular structure investigation by modern liquid state NMR. A new spin-state-selection filter, DIPSAP, is presented with significantly reduced sensitivity to J-mismatch of the filter delays compared to previously proposed pulse sequences. DIPSAP presents an attractive new approach for the accurate measurement of small spin-spin coupling constants in molecules dissolved in anisotropic solution. Application to the measurement of 15N-13C' and 1H(N)-13C' coupling constants in the peptide planes of 13C, 15N labeled proteins demonstrates the high accuracy obtained by a DIPSAP-based experiment. Copyright 2001 Academic Press.