DQFCOSY spectrum

The DQFCOSY spectrum of RpII in D O is shown in Figure 2. Each cross peak in this spectrum identifies a pair of coupled spins of the amino acid side chains. Since couplings are not propagated efficiently across amide bonds, all groups of coupled spins occur within individual amino acids. The chemical structure of an amino acid side chain is reflected in the characteristic coupling network and chemical shifts (13). Valine spin system (CH-CH-(CH3)2) explicitly shown in Figure 2 as an example. 

Figure 2. DQFCOSY spectrum of RpII in D2O. Cross peaks corresponding to a-P protons of various spin systems are labeled. The valine spin systems are shown explicitly.

FIGURE 8 DQFCOSY spectrum of an extended spin system. Methyl I correlates to methylene 2, which neighbors methine 3. Methine 3 correlates to methylene 4, which in turn neighbors hydroxyl proton 5. 

Figure 4 Part of the dqfCOSY spectrum of the ascaroside (11), a component of the Caenorhabditis elegans dauer pheromone. The fine structure of the four shown crosspeaks permits accurate determination and assignments of the geminal and all vicinal coupling constants of the two methylene protons (red).43...

Figure 6 The 75-1.64 ppm region of the 1H-NMR and the dqfCOSY spectrum of psylloborine A (12) (CeD6, 500 MHz). The vicinal coupling constants of the proton 1 - Heq (1.37 ppm) cannot be directly extracted, due to poor resolution in F2 and overlap with other crosspeaks, for example, of the proton 8 - Heq at 1.36 ppm. The E.COSY signals corresponding to the crosspeaks (1 - Hec/1 - Ha ) and (1 - Hea/1 - Ha ) are shown in Figure 7.

Figure 3. The 2D-DQFCOSY spectrum of the acrylonitrile/acrylic acid copolymer in DMSO-d ...

If, on the other hand, one has an isolated sample of limited mass and/or a limited amount of time, an alternative approach should be taken. Carbon resonances and their corresponding multiplicity should be detected indirectly to maximize sensitivity and minimize acquisition times. Therefore, instead of acquiring an APT plus an HSQC spectrum, the more time-efficient DEPT-HSQC can be used. COSY affords improved sensitivity over DQFCOSY at the cost of resolution along the diagonal. Similarly, ACCORD-HMBC can be replaced with the more sensitive HMBC. This approach is recommended for time-limited situations or for the nominal mass range of lOOpg-lOmg. 

HSQC) and Total Correlated spectroscopy (TOCSY) experiments. The methylene, methine and methyl (A/M and A/G) carbon resonances show both stereochemical (triad level) and compositional (dyad, triad, tetrad, pentad and hexad level) sensitivity. 2D Double Quantum Filtered Correlated Spectroscopy (DQFCOSY) experiment was used in A/B copolymers to assign the complex NMR spectrum to different compositional sequences. 

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