Broad-band excitation in indirectly detected (14)N overtone spectroscopy with composite pulses.

We show here that composite pulses allow broad-band excitation of nitrogen-14 overtone frequencies in proton detected D-HMQC experiments (referred to (1)H-{NOTDQ14} D-HMQC). Experimental verifications have been performed on glycine, L-histidine and N-acetyl-valine (NAV) samples. Composite pulses enable symmetric excitations of (14)N sites with large shift differences. Therefore, this approach is promising for recording high resolution (1)H-{NOTDQ14} D-HMQC spectra of most amino-acids, pharmaceutical samples and peptides.