The accordion-HMQC: heteronuclear correlations for a range of coupling constants

A method is presented for the simultaneous correlation of proton–heteronuclear fragments with varying coupling constants. This is achieved by incrementing the preparation delay, during the acquisition of a two-dimensional HMQC spectrum in accordion style. In addition to providing all correlations in a single spectrum, this approach also allows the extraction of proton–heteronuclear coupling constants from the indirect dimension. In addition, a theoretical analysis of the presented experiment is given which also allows for a better understanding of other accordion experiments, in particular the recently proposed ACCORD-HMBC. Results are shown for 15N-labeled urea, Cd-EDTA and the cadmium binding protein metallothionein.