HMQC pulse sequence

In practice, any available HMBC pulse sequence could be used to record fast-HMBC spectra.88 As HMBC are recorded without broadband heteronuclear decoupling, the duty cycle is no longer an issue with FAST-HMBC schemes, as it is using the standard SOFAST-HMQC or FAST-HMQC pulse sequences. 

Fig. 21 HMQC pulse sequences for (a) 14N-13C and (b) 14N- H correlations under rotor-synchronized MAS. In (b), dipolar recoupling is usually applied during time intervals Texc and Trec. (c) Coherence transfer pathways for the observation of SQ (solid lines) and DQ (dashed lines) in the 14N dimension...

Fig. 10.14. Gradient-enhanced HMQC pulse sequence described in 1991 by Hurd and John derived from the earlier non-gradient experiment of Bax and Subramanian. For 1H-13C heteronuclear shift correlation, the gradient ratio, G1 G2 G3 should be 2 2 1 or a comparable ratio. The pulses sequence creates heteronuclear multiple quantum of orders zero and two with the application of the 90° 13C pulse. The multiple quantum coherence evolves during the first half of ti. The 180° proton pulse midway through the evolution period decouples proton chemical shift evolution and interchanges the zero and double quantum coherence terms. Antiphase proton magnetization is created by the second 90° 13C pulse that is refocused during the interval A prior to detection and the application of broadband X-decoupling.

The HSQC experiment is based on single rather than multiple quantum coherence during the evolution time, t. The contemporary multiplicity-edited gradient HSQC pulse sequence is shown in Fig. 10.15. Relative to the much simpler HMQC pulse sequence, the HSQC... 

ID spectra measured by the HMQC pulse sequence in which the evolution period was replaced by a fixed short delay (without the refocusing pulse) and recorded without 29Si... 

Figure 9 Gradient-accelerated ID HMQC pulse sequence...

The basic HMQC pulse sequence (Figure 13) is the shortest, simplest HMQC experiment and gives the best sensitivity, ft is used both to determine the chemical shifts of an insensitive nuclide (spin S) coupled to a nuclide of higher sensitivity (spin I) and to correlate the coupled pairs of I and S spins. The experiment is not phase sensitive hence lineshapes are not Lorentzian and coupling constants cannot... 

Figure 15 HMQC pulse sequence incorporating a BIRD filter to suppress magnetization from molecules containing NMR silent S nuclei...

Since its introduction, several other coherence transfer pathways have been employed. The described FSLG-HETCOR and recently proposed MAS-J-HMQC pulse sequence uses heteronuclear dipolar couplings, while the REPT-HMQC employs the rotational-echo double resonance (REDOR) recoupling pulse sequence. 

Figure 3 Selective HMQC pulse sequence employing a time reversed q-SNEEZE pulse for de-excitation of X nuclei qs is a q-SNEEZE pulse and re is a RE-BURP pulse...

Figure 8 The /-BIRD HMQC pulse sequence. The delay T is tuned to minimize the appearance of the parent proton resonance and the delay A is set to 0.5//hx sel = selective pulse Dec. = decoupling...

Figure 11 The HMQC pulse sequence incorporating a binomial J filter...

Figure 14 The BIS HMQC pulse sequence. The first 90° proton pulse in the standard HMQC experiment is substituted by a doubly selective 90° pulse. Dec. = decoupling, bisel = doubly selective pulse...

The BIS HMQC pulse sequence may give relatively intensive residual parent lines resulting from imj>erfections of the 180° pulse. These can be removed using the post-acquisition solvent suppression techniques. 

Figure 16 Determination of geminal Si- Si coupling in HSi(OSiMe3)3 using proton detected, selective, 2D H- Si correlated HMQC pulse sequence employing SNOB pulses [17]. V( Si, Si)= +2.4Hz was obtained from F,. The spectrum was recorded at 500 MHz ( H) frequency on a Varian Unity Plus spectrometer 64 experiments of 16 scans H)=1.2Hz, J( Si, H) = 291.5Hz...

VARIANTS OF THE H-" Sn HMQC PULSE SEQUENCE 5.7.1 Low-pass Filter HMQC versus HMBC... 

Figure 10 Folding in the Fj dimension of the 2D H- Sn HM( spectrum which may reduce the total experiment time without coarse digitization in F,. It should be noted that for the basic HMQC pulse sequence presented above this folding occurs from the opposite spectrum edge...

Fig. 28 a /-HMQC pulse sequence and coherence transfer pathways, b Experimental MAS /-HMQC P A1 spectrum, c Simulated MAS /-HMQC P A1 spectrum of microporous aluminophosphateVPl-S.See [70] for details. Reprinted with permission from [72],Massiot D et al. (2003) J Mag Reson 164 160-164. Copyright (2003) Elsevier Science... 

In addition to some practical considerations which will be discussed in Section 2.3, the cases of spin systems with several magnetically equivalent Y nuclei need some further consideration. In principle, both DEPT and HMQC pulse sequences are in their standard forms designed to detect magnetization of spin systems with a single indirectly detected ""Y nucleus, which is perfectly suited for inverse observation of rare nuclei such as C or N. However, metal complexes may contain heteronuclei with high natural abundance such... 

Fig. 18. P"C H)( Fe) HMQC spectrum of the complex [(Cp)(PPh3)(COCH3)]Fe obtained with the bi-selective HMQC pulse sequence of Fig. 11(c) using a binomial excitation pulse. Reproduced, with permission, from ret 112. Copyright 19%, John Wiley Sons.

Mandal, P. K., and Majumdar, A. (2004) A comprehensive discussion of HSQC and HMQC pulse sequences. Concepts Mag. Reson. Part A 20A(1), 1-23. 

Coherence level scheme of a ID l C, IH HMQC pulse sequence using the p scale. 

Pulse programs are written independently of a particular spin system or spectrometer configuration such as magnetic field strength or transmitter pulse power so that, for instance, the same HMQC pulse sequence can be used for a 13C/19F or a i N/lR... 

The relay HMQC pulse sequence with BIRD-d7 element. 

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