Double-quantum NMR spectroscopy of 31P species submitted to very large CSAs

We introduce an original pulse sequence, BR2(2)(1) (tau pi tau), which is a block super-cycled R2(2)(1) sequence employing as basic element a pi pulse sandwiched by 'window' intervals. This homonuclear dipolar recoupling method allows the efficient excitation of double-quantum coherences between spin-1/2 nuclei submitted to very large chemical shift anisotropy. We demonstrate that this technique can be employed in double-quantum <-> single-quantum P-31 homonuclear correlation experiment at high magnetic field ( B-0 >= 14 T) and high MAS frequencies (nu(R) >= 30 kHz). The performances of BR2(2)(1) (tau pi tau) are compared to those of the double-quantum recoupling methods, such as BABA and bracketed fp-RFDR, which were already employed at fast MAS rates. The BR2(2)(1) (tau pi tau) sequence displays a higher robustness to CSA and offset than the other existing techniques. (C) 2009 Elsevier Inc. All rights reserved.