Heteronuclear Correlation Experiments II

Heteronuclear correlation experiments with IR detection in the direct acquisition period t2 are often called inverse detected experiments. The term inverse is also used to describe probeheads that are constructed with the coil as the inner coil and the rf coil for the heteronuclear frequency as the outer coil. The outer coil has a lower sensitivity because of the lower fill factor. This term may also be used to distinguish between two classes of experiments. The HETCOR and COLOC experiments belong to the class of direct detection experiments with take advantage of the coherence transfer from the sensitive nucleus to the relatively insensitive heteronucleus. This type of experiment is illustrated by the first entry in Table 5.22. However experiments in this category are no longer popular and have been superseded by inverse detected experiments, shown in the second entry in Table 5.22. In a comparison of the different types of experiments the IH detected heteronuclear correlation experiments have three distinct advantages over the detected experiment  

Homonuclear IH, coupling can evolve with the first IH excitation pulse. NMR-active heteronuclei are often only the minor component in the isotope mixture of an element. Consequently the IH coherences from several isotopomers, which do not contain the NMR-active isotope, contribute to the IR detected signal and these often strong signals must be suppressed. 

Correlation of IR and signals by scalar 1J(1R, coupling, IR detection, intensity enhancement by polarization transfer 

RMQC [5.185, 5.186, 5.187], BIRD-RMQC [5.188], relayed RMQC [5.189], DEPT-RMQC [5.68], gs-RMQC [5.190, 5.191, 5.192], TANGO-SL-RMQC, RMQC-TOCSY [5.193] 

In Check it 5.7.LI the basic structure of the ID RMQC experiment is introduced. The limits of IR coherence suppression of l C isotopomers, the so-called coherence, by phase cycling is shown and the use of the BIRD-d7 filter element as one solution to this problem is illustrated. 

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The interactions between histidine and metal species play essential roles in a wide range of important biological processes including enzymes catalysis and signal transduction. Zhou et al. have employed solid-state NMR techniques to determine the interaction between histidine and Zn(ii) from pH 3.5 to 14. 2D homo- and heteronuclear correlation NMR experiments were utilized to extract the and N chemical... 

TTie most used heteronuclear X,Y correlation technique for the characterization of lithium organyls seems to be ID- and 2D- li, C HMQC experiments which rely on V(C,Ii) couplings and allow the detection of directly connected Li, C spin pairs. TTie two-dimensional version is particularly useful for the characterization of compounds containing several distinguishable different Li sites and allowed to prove for the first time the existence of a dilithiated carbon atom carrying two different lithium atoms. ... 

The most common two-dimensional NMR experiment is COSY (pronounced cozy ), which is an abbreviation for correlated. spectroscopy. This experiment exploits internuclear coupling to establish relationships among peaks in the spectrum an example will be discussed in Sec. II.H.4. In homo-nuclear COSY, the pulse sequence is essentially the same as that depicted in Fig. 16 the heteronuclear version utilizes a somewhat more complex scheme. The whimsically named INADEQUATE (mcredible atural-abun-dance do xb e-quantam transfer experiment) reveals a molecule s carbon skeleton. Similarly, /zeteronuclear wultiple-ftond correlation (HMBC) estab-... 

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