Selective spin inversion in solution by magic field cross polarization

Abstract A pulsed element is proposed allowing the selective inversion of a single 1H nucleus, without regard to the presence of other degenerate 1H nuclei, provided that it is coupled to a heteronuclear spin with adequate chemical shift resolution in a 2D heteronuclear correlation spectrum. The approach is based on selective cross polarization, in which matched weak RF fields of specific amplitude are applied on resonance to the targeted 1H-X spin pair. It is shown theoretically that when the RF field amplitudes are set to specific values (ie. at a magic field), transfer of coherence can be fruitfully achieved transverse to the applied RF fields in addition to the normal longitudinal transfers. This enables the construction of a pulsed element which has the characteristics of a BIRDr,X element (Uhrin, et al, 1993), yet with 2D frequency selectivity. Demonstration of the pulsed element is made in the context of selective spin inversion, by which all 1H spins are inverted except the targeted 1H spin.