Time-Efficient NMR

Broadband Homodecoupled Time-Shared 1H-13C and 1H-15N HSQC Experiments

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.

Simultaneous acquisition of two 2D HSQC spectra with different 13C spectral widths

A time-efficient NMR strategy that involves the interleaved acquisition of two 2D HSQC spectra having different spectral widths in the indirect ¹³C dimension is presented. We show how the two equivalent coherence transfer pathways involved in sensitivity-enhanced HSQC experiments are managed selectively and detected separately in different FID periods within the same scan. The feasibility of this new SADA-HSQC (Spectral Aliasing in Dually Acquired HSQC) technique is demonstrated by recording simultaneously two complementary datasets, conventional and highly-resolved spectral-aliased 2D HSQC spectra, in a single NMR experiment. Combining the information from both datasets, accurate chemical shift determination and excellent signal dispersion is achieved in a unique measurement using only few t₁ increments.

Multiple-FID Acquisition of Complementary HMBC Data

By combining the principles of time‐sharing evolution and multiple FID acquisition within the same scan, several fully complementary NMR spectra can be obtained in a single‐shot acquisition. Four different HMBC and HMBC‐relayed experiments (see spectra) can be carried out simultaneously for ¹³C and ¹⁵N at natural abundance, with a saving in measuring time of up to 75 %.

Simultaneous a/b-spin-state selection for 13C and 15N from a time-shared HSQC-IPAP experiment

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.

Time-sharing evolution and sensitivity enhancements in 2D HSQC-TOCSY and HSQMBC experiments

Modifications of time‐shared (TS) HSQC‐like experiments originally developed by Griesinger and co‐workers (Sattler M, Maurer M, Schleucher J, Griesinger C. J. Biomol. NMR 1995; 5: 97) are proposed to extract different types of information from a single NMR pulse scheme. It is shown that simultaneous acquisition of ¹H,¹³C and ¹H,¹⁵N HSQC‐TOCSY and HSQMBC experiments can afford experimental sensitivity enhancements of 20–40% with respect to the separate acquisition of individual ¹³C or ¹⁵N data. In addition, the incorporation of a number of independent editing elements can be easily used for different purposes, for instance, to assign unambiguously ¹H, ¹³C, and ¹⁵N chemical shifts, to differentiate directly from relayed cross‐peaks, or to measure simultaneously long‐range proton–carbon and proton–nitrogen coupling constants. The suggested methodologies can be applied to many different classes of nitrogen‐containing compounds and illustrative examples are provided for the peptide cyclosporine as a demonstration of the performance of such experiments.