Multiple-quantum correlation spectra

Multiple-quantum correlation spectra provide information about through-bond connectivities as all COSY type experiments do. In addition, direct topology information is also available from the same spectrum through remote and combination peaks [5]. Correlation peaks between spins with small chemical shift difference can be examined, too, since there are no diagonal peaks. In this sense, a correlation of MQ coherences with those... 

Nuclear Overhauser effect (NOE) difference measurements were used to assign structure 79 for the product of reaction of diphenylnitrile imine with 5-ethylsulfonyl-2-methyl(27/)pyridazinone. Thus in the H NMR spectrum the ot/, o-protons of the arylhydrazino moiety (which were identified by two-dimensional heteronuclear multiple quantum correlation (2-D HMQC) spectroscopy) were shown in differential NOE (DNOE) experiment to be significantly enhanced on irradiation of pyridazine hydrogen H-7, proving their steric proximity <2000JST13>. 

The structural assignment of both 29 and 30 was accomplished through extensive two-dimensional (2-D) NMR heteronuclear multiple quantum correlation (HMQC) and heteronuclear multiple bond correlation (HMBC) spectroscopic studies <2004T8189>. In the HMBC spectrum of 29, the proton at 8.64p.p.m. shows a strong correlation Jq-h with the carbonyl carbon (C-10) at 180.9 ppm and the proton at 8.82p.p.m. with the carbonyl carbon (C-5) at 181.7 ppm. The HMBC spectrum of 30 shows a significant strong correlation Vq h of the C-5 carbonyl carbon with the H-6 proton at 8.52 ppm and the H-4 proton at 8.52p.p.m. 

The structural assignment of the trithiepines 44-46 has been performed using H, 13C, heteronuclear multiple bond correlation (HMQC), heteronuclear multiple quantum correlation (HMBC), and variable-temperature NMR spectroscopic data. The 60MHz H NMR spectrum of trithiepine 44 exhibits a broad singlet at 3.05 ppm in CDC13, whereas a narrow ABCD multiplet was observed for all of the protons in a 300 MHz spectrum. The two 13C NMR signals at... 

HMQC (heteronuclear multiple quantum correlation) is a variant of the HSQC spectrum that gives essentially the same results with a slightly different strategy (Fig. B. 14). Instead of converting antiphase SQC into antiphase 13C SQC, a single 90° pulse on 13C alone converts it into multiple quantum coherence (DQC and ZQC). DQC (I+S+) is selected... 

The Si NMR spectrum of pentaorganosilicate 25 was recorded at —50°C to minimize signal broadening <2004AGE3440>. H NMR, NMR, heteronuclear multiple quantum correlation (HMQC), and heteronuclear multiple bond correlation (HMBC) spectroscopic measurements were also performed. The observed 7c2,si value of 86 Hz was similar to that of a typical Si(sp )-C(sp ) bond, while the /c 2, si value of 30 Hz was much smaller than that of a Si(sp )-C(sp ) bond (64-70 Hz). 

The two-dimensional, heteronuclear multiple quantum correlation (HMQC) and heteronuclear multiple bond correlation (HMBC) spectra were taken with standard Bruker pulse programs. The HMQC and HMBC spectra are given in Figures 8 and 9 (9). The chemical shifts and spectral assignments are provided in Table 2 (9,10). The effect of Al3+ on the carbon spectrum of lomefloxacin is shown in Figure 10 (9). 

Figure 8. Heteronuclear multiple quantum correlation (HMQC) spectrum of Lomefloxacin mesylate.

A H(detected)- C shift correlation spectrum (conmion acronym HMQC, for heteronuclear multiple quantum coherence, but sometimes also called COSY) is a rapid way to assign peaks from protonated carbons, once the hydrogen peaks are identified. With changes in pulse timings, this can also become the HMBC (l eteronuclear multiple bond coimectivity) experiment, where the correlations are made via the... 

The heteronuclear multiple-quantum coherence (HMQC) spectrum, H-NMR chemical shift assignments, and C-NMR data of podophyllo-toxin are shown. Determine the chemical shifts of various carbons and connected protons. The HMQC spectra provide information about the one-bond correlations of protons and attached carbons. These spectra are fairly straightforward to interpret The correlations are made by noting the position of each crossf)eak and identifying the corresponding 8h and 8c values. Based on this technique, interpret the following spectrum. 

C-NMR, COSY, HMQC (heteronuclear multiple quantum coherence), and HMBC (heteronuclear multiple bond correlation).48 Furthermore, the structure of trimer was confirmed by X-ray crystallography.48 The incorporation of 13C into the indole 3a position proved valuable in these structural determinations and in documenting the ene-imine intermediate. For example, the presence of a trimer was readily determined from its 13C-NMR spectrum (Fig. 7.7). 

Several of the spectra in this workbook were obtained using techniques such as proton-detected C-H shift correlation and multiple-quantum-filtered phase-sensitive COSY which were not covered in detail in our main text because they have come into general use since it was written. This is a measure of the rate at which practical NMR is progressing but presents no problem in the interpretation of the spectra. Various field strengths and modes of presentation, ranging from continuous-wave traces to phase-sensitive two-dimensional contour plots, were used for the spectra. In part, this reflects the history of individual problems, but it is also intentional. It is important to be able to extract the essential message of a spectrum independently of the way it is presented. 

Figure 13(b) shows a JH—15N HSQC spectrum acquired from 0.5 mmol l-1 sample of a 41-residue peptide toxin from the spider Agelena orientalis. The toxin was produced recombinantly and uniformly labeled with 15N. This HSQC spectrum was collected in 30 min, compared with the 12 h required to acquire a natural abundance spectrum from an unlabeled sample of equivalent concentration (see Figure 11). The HSQC, together with the related heteronuclear multiple quantum coherence (HMQC)54 experiment, forms the cornerstone of a wide range of 2D, 3D, and 4D experiments that are designed to facilitate sequence-specific resonance assignment and determination of protein structure. Note that the HSQC technique is the technique of choice for correlation of H and 15N shifts due to generally narrower linewidths in the 15N dimension.55,56 Furthermore, because these and most of the other heteronuclear experiments described below are designed to observe amide protons, the sample must be in H20 (rather than D20). Consequently, a means of suppressing the H20 resonance is required (for details see Section 9.09.2.6).

During a period of evolution in which multiple-quantum states are present, the magnetization acquires a modulation due to the nutation frequency of the MQCs. Thus, signals which are due to single sites during other evolution periods will have the same spectral frequency in a multiple-quantum domain as those signals which had passed through the same MQC. This can therefore easily be read in a multi-dimensional spectrum as a correlation between these nuclear sites. In addition, a multiple-quantum domain as part of a multi-dimensional spectrum removes the auto-correlation peaks on... 

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