MQD--multiplex-quadrature detection in multi-dimensional NMR.
Bottom Line: With multiplex-quadrature detection (MQD) the tasks of coherence selection and quadrature separation in N-dimensional heteronuclear NMR experiments are merged.The minimum number of transients per indirect data point, which have to be combined to give pure-phase spectra, is thus decreased by a factor (3/4)(N-1).This reduction is achieved without adjustable parameters.
Affiliation: Institute of Organic Chemistry, Johannes Kepler University Linz, Altenberger Str. 69, 4040 Linz, Austria.Show MeSH
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Mentions: Instead of shortening experiments at unchanged resolutions one can take the advantage of the saved time to achieve resolution enhancement. Therefore, we compare results of an MQD to a States-TPPI HNCO experiment obtained in the same amount of time. In the standard experiment 27 complex points were acquired in the carbon dimension, while in the MQD experiment 48 complex points could be recorded in the same time. In Figure 4 we show a representative region of the proton–nitrogen plane at the 13CO chemical shift (179.9 ppm) of residue L104. An intense cross-peak connects this C to the 1H15N pair of Q105. Six cross-peaks, four of them with similarly high amplitudes, appear in the States-TPPI HNCO due to similar CO shifts. Only the four bigger peaks appear in the same plane of the MQD HNCO experiment, and significant amplitude differences reduce assignment ambiguities substantially. This comparison corroborates the advantage of using the time saved by the multiplex approach to accommodate more evolution-time increments, thereby increasing the resolution in the indirect dimensions.
Affiliation: Institute of Organic Chemistry, Johannes Kepler University Linz, Altenberger Str. 69, 4040 Linz, Austria.