Alternate HMQC experiments for recording HN and HC-correlation spectra in proteins at high throughput

Alternate implementations of the SOFAST-HMQC experiment are described. In these alternate SOFAST-HMQC experiments (ALSOFAST-HMQC) excitation of the magnetization of interest is achieved by non-selective rf pulses while preserving the equilibrium polarization of passive spins. This alternate excitation scheme also allows the incorporation of a novel sensitivity enhancement protocol which has been most recently developed by Brutscher and coworkers and which permits simultaneous detection of both the x- and y-components of the indirectly detected t(1)-interferograms without the need to introduce additional rf pulses and delays. We show that the ALSOFAST HC-HMQC experiment, which implements an alternate means of frequency selection, enables the detection of methyl resonances with large secondary proton chemical shifts. This is achieved by selecting coherences of interest via a frequency selective carbon inversion pulse. Detailed comparisons between SOFAST- and the presented ALSOFAST-HMQC experiment reveals a considerable degree of mutual complementarity.