Heteronuclear correlations technique

The structures of the lamellarins, except for A and E, were established by a combination of H and C NMR analyses using heteronuclear correlation techniques. New procedures for differentiation of HMBC at two- and three-bond correlation <96TL363> in combination with ADEQUATE experiments <96JMR282> and with coi-refocused 1,1-ADEQUATE <96JMR295> experiments were developed for a comprehensive identification of Vch and Vch... 

Heteronuclear correlation techniques exhibit considerable variety, as pulses affecting only one nuclear species at a time allow the two spectra being correlated to be manipulated independently. 

The development and application of multidimensional solid state homo- and heteronuclear correlation (HETCOR) NMR techniques have lead to an increasingly important role in structure solution of zeolitic materials and have had many practical applications in the detailed structural characterization of completely siliceous zeolites[6,7] and AlPOs.[8-ll] However, HETCOR NMR is not readily applicable to aluminosilicates... 

Information about the surface and interface structures in hexadecylamine-capped CdSe NC of 2 nm size has been obtained by a variety of 1H, 13C, 113Cd, and 77Se NMR techniques [342]. The 77Se CP-MAS-NMR spectrum showed five partially resolved peaks from surface or near-surface Se environments. It was possible to obtain 2D heteronuclear correlation (HETCOR) spectra between 1H and the other three nuclei despite the inherent sensitivity limitations (the 77Se- 3I-I HETCOR experiment required 504 h ). The latter experiment indicated that the methylene protons of the hexadecylamine chain interact with the surface Se atoms via a tilt of the chain toward the surface. The surface Se atoms were not seen to interact with thiophenol present, and it was suggested that thiophenol binds to a selenium vacancy at the surface. 

While the early days of LC-NMR and LC-NMR-MS were plagued by the poor sensitivity of the NMR spectrometer, the recent probe design advances have provided a means to potentially overcome this hurdle. As reported in the literature, it is possible to get both ID and 2D homo-nuclear and heteronuclear correlation data on sub micrograms of materials in quite complex mixtures utilizing cryogenic flow-probes in tandem with SPE peak trappings [98]. While these technologies are still in their infancy, they have the potential to revolutionize LC-NMR as a structure elucidation technique. 

Krishnamurthy, V.V. et al., 27,37-HMBC a new long-range heteronuclear shift correlation technique capable of differentiating 2/CH from 3/CH correlations to protonated carbons, J. Magn. Reson., 146, 232, 2000. 

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. 

The cationic Jt-allyl complex is often isolable and has been the subject of considerable study. X-ray structures of the 7t-allyl complexes with chiral ligands have been a primary source of structural information from which the design and predictive model of chiral catalysts derive. Chiral-metal-olefin complexes, which constitute another important class of intermediates have also been isolated, albeit few in number [31]. These static studies have been complemented by a growing number of NMR studies taking advantage of modem heteronuclear correlation and NOE techniques, which offer opportunities to monitor solution structures of the catalytic species [32-34],... 

H and 13C NMR techniques have widely been used to determine the configuration of new dioxepins and dithiepins and to elucidate the constitution and conformation of new naturally occurring substances. For example, the configuration of oximes 14 was determined by H and 13C correlated spectra, correlation spectroscopy (COSY), nuclear Overhauser enhancement spectroscopy (NOESY), heteronuclear correlation (HETCOR) spectroscopy, and hetero-nuclear multiple bond correlation (E1MBC) spectroscopy <1998CCA557>. 

Heteronuclear correlation (HETCOR) spectroscopy is a standard two-dimensional NMR technique. The resolution of 31P 1H CPMAS spectra is generally not sufficient to unequivocally detect the HP042 ions and the apatitic OH- ions in bone or dentin samples.15 In this regard, the breakthrough came from the first application of 31P 1H HETCOR to HAp and bone samples,24 where the correlation peak at 0.2 and 3 ppm of the 1H and 31P dimensions, respectively, has been established as the spectral marker of apatitic OH- ions. To enhance the spectral resolution in the XH dimension, 1H homonuclear decoupling was employed during the fi... 

In the case of an unknown chemical, or where resonance overlap occurs, it may be necessary to call upon the full arsenal of NMR methods. To confirm a heteronuclear coupling, the normal H NMR spectrum is compared with 1H 19F and/or XH 31 P NMR spectra. After this, and, in particular, where a strong background is present, the various 2-D NMR spectra are recorded. Homonuclear chemical shift correlation experiments such as COSY and TOCSY (or some of their variants) provide information on coupled protons, even networks of protons (1), while the inverse detected heteronuclear correlation experiments such as HMQC and HMQC/TOCSY provide similar information but only for protons coupling to heteronuclei, for example, the pairs 1H-31P and - C. Although interpretation of these data provides abundant information on the molecular structure, the results obtained with other analytical or spectrometric techniques must be taken into account as well. The various methods of MS and gas chromatography/Fourier transform infrared (GC/FTIR) spectroscopy supply complementary information to fully resolve or confirm the structure. Unambiguous identification of an unknown chemical requires consistent results from all spectrometric techniques employed. 

In the early stage of development of NMR spectroscopy, the applicability of multi-dimensional approach was tested for condensed matter. Today, because of the excellent progress on this field, the "library" of different ND techniques used in SS NMR is pretty rich. On the basic level, these methods can be assigned to two groups homo- (HOMCOR) and heteronuclear correlations (HETCORs). Both correlations employ indirect (through-bond) or direct (through-space) coupling to correlate different spins. 

One of the common 2D SS NMR approaches employed for investigation of phosphoro-organic and bio-organic samples is based on high-resolution heteronuclear correlations (EIETCOR). In solution-state NMR, this technique is the basic method that allows assignment of proton and phosphorus to the molecular structure. In the solid state, the assignment is more complex because of the very... 

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... 

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. ... 

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