Couplings, heteronuclear measurement

ID [DC, IR] INEPT experiment for heteronuclear coupling constant measurement... 

In 2001, Meissner and Sprensen described methods for the measurement of Jhh anO "Jch couplings employing the broadband excitation approach (see Section 3.3.7) with the report of the broadband XLOC and broadband J-HMBC experiments, respectively. In a further extension of the idea of accordion optimization, Williamson ef reported the development of the J-IMPEACH-MBC pulse sequence. This approach is similar to the EXSIDE experiment previously described by Krishnamurthy and the J-resolved HMBC experiments of Furihata and Seto"- in its use of J-scaling to render small, long-range heteronuclear couplings conveniently measurable. Finally, Williamson e/ also described a new method, G-BIRDr-HSQMBC, that was reported in their survey of the available methods. 

Heteronuclear couplings were measured by quantitative J correlation spectroscopy. 

There has also been a recent upsurge in interest in measurements of heteronuclear coupling constants involving N or nuclei, and in one- and two-bond couplings. These measurements should provide additional valuable information about torsion angles and their distributions. 

Polarization transfer techniques like INEPT and DEPT have been used to enhance sensitivity in heteronuclear 2D /-resolved spectra. In combination with the semiselective sequence just described, INEPT has been used to suppress long-range Jen couplings and to measure the one-bond couplings (Fig. 5.15) (Rutar, 1984). Driven equilibrium pulses for fast restora-... 

Nolls, P., Parella, T. Spin-edited 2D HSQC-TOCSY experiments for the measurement of homonuclear and heteronuclear coupling constants application to carbohydrates and peptides. /. Magn. Reson. 2005, 176, 15-26. 

Rotational-echo double-resonance (REDOR)(75,79) is a new solid-state NMR technique which is sensitive to through-space carbon-nitrogen interactions between selectively 13C and 15N-enriched sites separated by up to 5A (20-22). The parameter directly measured in a REDOR experiment is the heteronuclear dipolar coupling constant DCN, which is in itself proportional to the inverse third power of the intemuclear distance, rCN. It is this dependence on (icn)3 which accounts both for REDOR s ability to accurately measure short distances and its insensitivity to longer-range interactions. As a technique which can probe, in detail, intermolecular interactions over a distance range of 5A, REDOR is well suited to studying the distribution of small selectively-labeled molecules in polymer delivery systems. 

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