Quadrupolar coupling selective cross-polarization in solid state NMR

Abstract

A new strategy is presented for achieving selective heteronuclear polarization transfers from half-integer quadrupolar spins in magic-angle spinning (MAS) NMR. By combining cross-polarization with a recently introduced RAPT pulse sequence that selectively excites the signal of a half-integer quadrupolar nucleus based on its quadrupolar coupling constant magnitude, we demonstrate that hetero-nuclei in its close proximity may be selectively excited. Selective ²³Na → ¹H polarization transfers are demonstrated in Na₂MoO₄·2H₂O, Na₂HPO₄·2H₂O and a mixture of NaHCO₃ and Na₂HPO₄·2H₂O.