A different approach to multiplicity-edited heteronuclear single quantum correlation spectroscopy.

A new experiment for recording multiplicity-edited HSQC spectra is presented. In standard multiplicity-edited HSQC experiments, the amplitude of CH2 signals is negative compared to those of CH and CH3 groups. We propose to reverse the sign of (13)C frequencies of CH2 groups in t1 as criteria for editing. Basically, a modified [BIRD](r,x) element (Bilinear Rotation Pulses and Delays) is inserted in a standard HSQC pulse sequence with States-TPPI frequency detection in t1 for this purpose. The modified BIRD element was designed in such a way as to pass or stop the evolution of the heteronuclear (1)JHC coupling. This is achieved by adding a 180° proton RF pulse in each of the 1/2J periods. Depending on their position the evolution is switched on or off. Usually, the BIRD- element is applied on real and imaginary increments of a HSQC experiment to achieve the editing between multiplicities. Here, we restrict the application of the modified BIRD element to either real or imaginary increments of the HSQC. With this new scheme for editing, changing the frequency and/or amplitude of the CH2 signals becomes available. Reversing the chemical shift axis for CH2 signals simplifies overcrowded frequency regions and thus avoids accidental signal cancellation in conventional edited HSQC experiments. The practical implementation is demonstrated on the protein Lysozyme. Advantages and limitations of the idea are discussed.