Heteronuclear correlated spectroscopy

Heteronuclear correlation spectroscopy (HETCOR) Shift-correlation spectroscopy in which the chemical shifts of different types of nuclei (e.g., H and C) are correlated through their mutual spin-coupling effects. These correlations may be over one bond or over several bonds. 

For compounds that contain a limited number of fluorine atoms, heteronuclear correlation spectroscopy experiments such as F H HETCOR and 2H-19F heteronuclear Overhauser enhancement spectroscopy (HOESY) can provide considerable assistance distinguishing structural isomers and diastereomers as well as for conformational analysis. HOESY experiments have been frequently used for conformational analysis of biomolecules containing fluorine labels.18... 

When combining isotope filtering/editing with coherence transfer steps to multidimensional experiments, then further size restrictions apply. For example, isotope edited / filtered H TOCSY or COSY experiments are generally limited to systems of <10 kDa, because of their sensitivity to T2 relaxation. In larger systems, heteronuclear correlation spectroscopy can be used for the correspondingly labeled component, while structural information about both the labeled and unlabeled moiety can be extracted from isotope edi-ted/filtered NOESY spectra, respectively. 

Rochet and Lancelin50 reported revised 1H and 13C NMR assignments of the polyene antibiotic Filipin m (83). This macrolide which was isolated from Streptomyces filipinensis was reinvestigated in DMSO-dg solution using homonuclear and heteronuclear correlation spectroscopy. In addition to several corrections to previous 1H NMR... 

The structures of the compounds were elucidated by a combination of NMR techniques (lH-, 13C-, and 13C-DEPT NMR) and chemical transformation, enzymatic degradation, and as well as mass spectrometry, which gives information on the saccharide sequence. A more recent approach consists of an extensive use of high-resolution 2D NMR techniques, such as homonuclear and heteronuclear correlated spectroscopy (DQF-COSY, HOHAHA, HSQC, HMBC) and NOE spectroscopy (NOESY, ROESY), which now play the most important role in the structural elucidation of intact glycosides. These techniques are very sensitive and non destructive and allow easy recovery of the intact compounds for subsequent biological testing. 

Indirect Detection of Insensitive Nuclei and Heteronuclear Correlation Spectroscopies in Solution... 

Heteronuclear correlation spectroscopy is not restricted to the spin pair H- C. H-X correlations are also used for structure elucidation, e.g. for... 

The number of sugar residues and constituent monosaccharides are determined by a combination of COSY (two-dimensional homonuclear correlation spectroscopy), HOHAHA (2D homonuclear Hartman-Hann spectroscopy) and HETCOR (direct heteronuclear correlation spectroscopy)... 

In this review, we shall introduce some basic concepts about sohd-state NMR of half-integer quadrupolar nuclei and discuss the most useful and promising methods presently available to study them. These include older methods, such as Double Rotation (DOR) and Dynamic Angle Spinning (DAS), and novel techniques including MQMAS, Quadrupolar Phase Adjusted Spinning Sidebands QPASS, SateUite Transition (ST) MAS and Inverse-STMAS NMR, and Fast Amplitude Modulation (FAM). We also discuss several techniques based on dipolar interactions between quadrupolar and spin-1/2 nuclei, such as Cross-Polarization (CP) MQMAS, MQ Heteronuclear Correlation Spectroscopy... 

Heteronuclear correlation spectroscopy Non-classical CP model - see text and Eq. (1)... 

In order to remove unwanted organic peaks in the proton spectra, one has to resort to 2D H- P heteronuclear correlation spectroscopy (HETCOR). When performed via CP, HETCOR sees only protons capable of pro-... 

HSQC (heteronuclear correlation spectroscopy)—a two-dimensional NMR experiment commonly used to show the correlation of the chemical shifts of N or spins with their bound proton resonances. 

WiUker, W., Leibfritz, D., Kerssebaum, R., and Bermel, W. (1992) Gradient selection in inverse heteronuclear correlation spectroscopy. Magn. Reson. Chem. 31, 287-292. 

The INEPT sequence was the first non-specific polarization transfer experiment and subsequently the INEPT unit has becomes an important part of heteronuclear correlation spectroscopy as in the IH HSQC experiment. The INEPT sequence creates... 

This section focuses on the coupling evolution that occurs during the pulse sequences of heteronuclear correlation experiments. Because polarization transfer is a requirement of intensity optimized heteronuclear correlation spectroscopy this section also acts as a short introduction to coherence transfer by polarization transfer. A coherence transfer from a sensitive nucleus, e.g. in most experiments, to a nucleus contributes a gain of signal intensity. To obtain the required antiphase coherence for the transfer step the coherence must evolve exclusively by heteronuclear coupling during a free precession periods. This can only be assumed in theoretical spin systems. In real samples three aspects make this ideal approach more difficult ... 

Comparative sensitivity gain by coherence transfer in heteronuclear correlation spectroscopy [5.3]. 

In the early days of heteronuclear correlation spectroscopy, a gradient free version of the double low-pass filter was proposed [5.212, 5.213], but the necessity to suppress unwanted coherences, particularly in INADEQUATE experiments, has forced the design of a gradient version [5.214]. The application of this filter is not just restricted to INADEQUATE experiments it has also become the element of choice in ACCORD-HMBC and ACCORD-CIGAR-HMBC experiments to reduce residual one-bond correlations. These experiments are very sensitive to the suppression of one-bond... 

---