Time Shared

The concepts of pure-shift NMR and time-shared NMR are merged in a single experiment. A ¹³C/¹⁵N time-shared version of the real-time BIRD-based broadband homodecoupled HSQC experiment is described. This time-efficient approach affords simultaneously ¹H-¹³C and ¹H-¹⁵N pure-shift HSQC spectra in a single acquisition, while achieving substantial gains in both sensitivity and spectral resolution. We also present a related ¹³C/¹⁵N-F2-coupled homodecoupled version of the CLIP-HSQC experiment for the simultaneous measurement of ¹J_CH and ¹J_NH from the simplified doublets observed along the direct dimension. Finally, a novel J-resolved HSQC experiment has been designed for the simple and automated determination of both ¹J_CH/¹J_NH from a 2D J-resolved spectrum.

The presence of a highly abundant passive nucleus (Z = ¹⁹ F or ³¹P) allows the simultaneous determination of the magnitude and the sign of up to three different heteronuclear coupling constants from each individual cross‐peak observed in a 2D ¹H‐X selHSQMBC spectrum. Whereas J(HZ) and J(XZ) coupling constants are measured from E.COSY multiplet patterns, J(XH) is independently extracted from the complementary IPAP pattern generated along the detected F2 dimension. The incorporation of an extended TOCSY transfer allows the extraction of a complete set of all these heteronuclear coupling constants and their signs for an entire ¹H subspin system. ¹H‐X/¹H‐Y time‐shared versions are also proposed for the simultaneous measurement of five different couplings (J(XH), J(YH), J(XZ), J(YZ), and J(ZH)) for multiple signals in a single NMR experiment.

Details on the implementation of the simultaneous evolution of multiple frequencies into the same time period of a NMR pulse sequence are introduced. Time‐shared (TS) versions of the most useful inverse 2D NMR experiments (TS‐HMBC, TS‐HSQC, TS‐HSQC‐TOCSY, and TS‐HSQMBC) are presented and illustrated for simultaneous acquisition of ¹H/¹³C and ¹H/¹⁵N NMR spectra. The major benefits associated to the parallel acquisition of multiple spectra from a single NMR experiment are spectrometer time savings and the achievement of multiple and complementary information with improved sensitivity gains per time unit.

An improved approach to optimize the overall sensitivity and the resolution requirements in the indirect dimension of ¹³C/¹⁵N time‐shared (TS) NMR experiments is presented. A different data sampling acquisition procedure is applied for ¹³C and ¹⁵N in the indirect dimension, and a proper data recombination before conventional data processing allows a customized adjustment of spectral widths, number of scans and number of increments individually for ¹³C and ¹⁵N. The major benefit is an important improvement on the detection limits of the TS experiment that overcomes the lower sensitivity of ¹⁵N over ¹³C at natural abundance. We evaluate such enhancements from 2D TS‐HMBC experiments recorded on a nitrogen‐containing synthetic azole derivative of pharmaceutical interest.

A new one-shot NMR experiment (CN-HMBC) is proposed for the simultaneous acquisition of 2D ¹H,¹³C and ¹H,¹⁵N HMBC spectra. Important sensitivity enhancements (up to 41% simultaneously for both ¹³C and ¹⁵N) or time savings (about 50%) can be achieved when compared to the separate acquisition of individual HMBC spectra. The experiment is highly recommended for the complete structural analysis and simultaneous chemical shift assignments of protonated and nonprotonated ¹³C and ¹⁵N resonances in nitrogen-containing organic compounds.

Two novel HSQC-IPAP approaches are proposed to achieve α/β spin-state editing simultaneously for ¹³C and ¹⁵N in a single NMR experiment. The pulse schemes are based on a time-shared (TS) 2D ¹H,¹³C/¹H,¹⁵N-HSQC correlation experiment that combines concatenated echo elements for simultaneous J(CH) and J(NH) coupling constants evolution, TS evolution of ¹³C and ¹⁵N chemical shifts in the indirect dimension and heteronuclear α/β-spin-state selection by means of the IPAP principle. Heteronuclear α/β-editing for all CH _n (n = 1–3) and NH _n (1–2) multiplicities can be achieved in the detected F2 dimension of a single TS-HSQC-F2-IPAP experiment. On the other hand, an alternative TS-HSQC-F1-IPAP experiment is also proposed to achieve α/β-editing in the indirect F1 dimension. Experimental and simulated data is provided to evaluate these principles in terms of sensitivity and performance simultaneously on backbone and side-chain CH, CH₂, CH₃, NH, and NH₂ spin systems in uniformly ¹³C/¹⁵N-labeled proteins and in small natural-abundance peptides.

A new one-shot NMR experiment (CN-HMBC) is proposed for the simultaneous acquisition of 2D ¹H,¹³C and ¹H,¹⁵N HMBC spectra. Important sensitivity enhancements (up to 41% simultaneously for both ¹³C and ¹⁵N) or time savings (about 50%) can be achieved when compared to the separate acquisition of individual HMBC spectra. The experiment is highly recommended for the complete structural analysis and simultaneous chemical shift assignments of protonated and nonprotonated ¹³C and ¹⁵N resonances in nitrogen-containing organic compounds.