Pure-shift , HSQC

Figure 3 Pulse schemes to obtain pure shift HSQC spectra. (A) HSQC-RESET experiment which uses a pseudo-3D BIRD-based ZS acquisition scheme (B) PS-HSQC experiment using real-time homodecoupling by the combination of a hard 180°( H)-BIRD element during data acquisition (C) sensitivity-improved PS-HSQC (D) HOBS-HSQC experiment using real-time homodecoupling during detection achieved by applying a pair of hard/band-selective 180° pulses (represented as solid and shaded shapes). In (B-D), the homodecoupling element is applied at the middle of 2t=AQ//i periods, where AQ is the acquisition time and n is the number of concatenated loops. See original publications for a more detailed description.

Figure 4 Selected areas corresponding to the (A) conventional HSQC and (B) pure-shift HSQC spectra of strychnine (1). One-dimensional traces are shown for selected CH and CH2 spin systems. Data were acquired, processed, and displayed with the same conditions to allow a quantitative comparison.

Figure 6 (A) Expanded areas comparing some cross-peaks in SA-and SAPS-HSQC spectra of the racemic compound (3)// -PA (Pirkle Alcohol) mixture acquired with a reduced spectral width of 2.5 ppm. (B) Experimental line widths and relative sensitivities obtained in conventional HSQC, pure shift HSQC (PS-HSQC) and pure shift sensitivity-improved HSQC (PS-HSQCsi) experiments. Qne-dimensional traces correspond to the H12/C12 cross-peak. Adapted from Ref. [72].

Y. Liu, M.D. Green, R. Marques, T. Pereira, R. Helmy, R.T. Williamson, W. Bermel, G.E. Martin, Using pure shift HSQC to characterize microgram samples... 

M. Perez-TrajiUo, L. Castanar, E. Monteagudo, L.T. Kuhn, P. Nolis, A. Virgih, R.T. Williamson, T. Parella, Simultaneous and C NMR enantiodifierentiation from highly-resolved pure shift HSQC spectra, Chem. Commun. 50 (2014) 10214-10217. 

High-Resolved HSQC Using Pure Shift NMR... 

SAPS-HSQC Spectral Aliasing and Pure-Shift NMR HSQC Methods for Measuring S(CH)... 

Keywords NMR, HSQC, HSQMBC, Proton-carbon coupling constants, Pure Shift NMR, Pulse sequence development... 

The aim of this article is to compile all new HSQC-related NMR experiments published in the last years that have been specifically designed and applied to small molecules at natural abundance (Scheme 1). Special focus will be made on novel HSQC schemes including concepts such as fast NMR and pure shift NMR. In addition, reference to improved J-compensated HSQC sequences will be made, discussing the effects of the intensity and phase signal modulation dependence with respect to J(CH) and/or J(HH) which are generated during INEPT periods. A particular analysis will be also made on modem NMR methods designed for the quantitative measurement of J(CH) and/or D(CH) and, by... 

HIGH-RESOLVED HSQC USING PURE SHIFT NMR... 

SAPS-HSQC) [72] method has proved to be a fast and very efficient tool for the detection and accurate differentiation and quantification of very small A Ad values simultaneously for and (Fig. 6). The method combines the complementary features of the pure shift approach that enhances signal resolution in the alternate dimension with those related to spectral aliasing in the dimension. This approach has been successfully applied to enantiodifferentiation studies and it can found interest in the analysis of complex mixtures or the distinction of isomers with very similar NMR spectra. 

Enantiodifferentiation analysis through the SAPS-HSQC spectrum has been shown to be superior than the conventional ID the conventional or even the broadband homodecoupled ID ZS spectra. SAPS-HSQC data allow the detection of enantiodifferentiated signals even in the case that AAd( H) or AAd( C) is close to 0, whenever one of these two values is sufficiendy dispersed. In a previous work, ID pure shift H NMR already demonstrated its practical usefulness in enantiodifferentiation studies to distinct signals separated by more than... 

Pure shift versions of the FI-HSQC and Fl-ilNEPT experiments have not been published but they are easy to design and implement with the aim to achieve automated peak picking and automated extraction of J(CH) and J(HH) couphng constants. 

I. Timari, L. Kaltschnee, A. Kolmer, R.W. Adams, M. Nilsson, C.M. Thiele, G.A. Morris, K.E. Kover, Accurate determination of one-bond heteronuclear coupling constants with pure shift broadband proton-decoupled CLIP/CLAP-HSQC experiments, J. Magn. Reson. 239 (2014) 130—138. 

In contrast to the basic "C detected experiment, and as a consequence of the final H detection, the 2D spectra obtained with HMQC or HSQC have a projection onto the F2 axis which corresponds to the normal H spectrum and includes all chemical shifts and all Jfi, couplings. The latter may give rise to rather broad cross peaks for extensively coupled protons. The projection onto the Fl axis corresponds to a normal C spectrum but with the quaternary carbons missing. With HMQC, but not with HSQC, cross peaks are additionally split in Fl by "J couplings. The HMQC and the HSQC experiment are usually performed in phase-sensitive mode, which, after proper phasing in both dimensions, allow peaks to be displayed in pure absorption. 

NMR spectroscopy enables the direct analysis of crude extracts in solution or, using the magic angle spinning (MAS) technique, of intact tissues. Potentially NMR spectroscopy can detect any molecule containing one or more atoms with a non-zero nuclear magnetic moment such as H, C, N, TSf or P. The technique is non-destractive and non-invasive and allows the analysis of in vivo samples. In routine profiling only one-dimensional (ID) solution state H NMR spectra of extracts are acquired. In addition some two-dimensional (2D) NMR spectra are acquired ( H- H COSY, H- H TOCSY, H- C HSQC, HMBC are the most common experiments) from a few representative samples in order to determine H and chemical shifts of constituents in the extracts. These can then be compared with data from chemical shift libraries of pure compounds for identification. 

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