Spin Echo Correlation SpectroscopY

Another 2D homonuclear shift-correlation experiment that provides the coupling information in a different format is known as SECSY (spin-echo correlation spectroscopy). It is of particular use when the coupled nuclei lie in a narrow chemical shift range and nuclei with large chemical shift differences are not coupled to one another. The experiment differs... 

SECSY (spin-echo correlated spectroscopy) is a modified form of the COSY experiment. The difference in the pulse sequence of the SECSY experiment is that the acquisition is delayed by time mixing pulse, while the mixing pulse in the SECSY sequence is placed in the middle of the period. The information content of the resulting SECSY spectrum is essentially the same as that in COSY, but the mode... 

Nagayama K, Wiithrich K, Ernst RR, Two-dimensional spin echo correlated spectroscopy (SECSY) for 1H NMR studies of biological macromolecules, Biochem. Biophys. Res. Commun., 90 395, 1979. 

The 2D ESR technique was developed by Freed and his co-workers (Freed, 2000 Gorcester et al., 1990 Freed and Mobius, 1992) by the analogy of the well-known NMR two-dimentional spectroscopy, correlation spectroscopy (COSY) and spin-echo correlation spectroscopy (SECSY) (Wiitrich, 1986 and references tsherein). 

The pulse methods rely on selective irradiation of a particular resonance line with a radio frequency (rf) and observation of the resulting effects in the rest of the spectrum. Among commonly employed methods are 2D correlated spectroscopy (COSY), 2D spin-echo correlated spectroscopy (SECSY), 2D nuclear Overhauser and exchange spectroscopy (NOESY), 2D J-resolved spectroscopy (2D-J), and relayed coherence-transfer spectroscopy (RELAYED-COSY) (Wutrich, 1986). 

Laurie was one of the first to apply two-dimensional (2D) NMR to carbohydrates. With students Subramaniam Sukumar and Michael Bernstein, and visiting scientist Gareth Morris, he demonstrated and extended the application of many of the directly observed 2D NMR techniques of the time. These included the homo- and hetero-nuclear 2D /-resolved techniques, delayed proton /-resolved NMR that allowed broad resonances to be suppressed, for example, those of dextran in the presence of methyl /Lxvlopyranoside. proton-proton chemical shift correlation spectroscopy (COSY), nuclear Overhauser enhancement spectroscopy (NOESY), proton-carbon chemical shift correlation (known later as HETCOR), and spin-echo correlated spectroscopy (SECSY). Trideuteriomethyl 2,3,4,6-tetrakis-<9-trideuterioacetyl-a-D-glucopyranoside served as a commonly used model compound for these studies. 

Despite the high cost of the equipment required and the time taken for sample preparation and spectra acquisition, MAS-HR NMR provides invaluable stmctural information about the species present in a reaction. Only a few milligrams of resin beads are required and they can be recovered as the technique is nondestructive. The complementarity of the technique with other analytical methods is clear MALDl-TOP cannot discriminate among compounds with the same MW and depends on the ionization properties of the resin-bound compound, while PTIR depends on the presence of selected functional groups in the molecule. MAS-HR NMR can be used independently from the nature of the performed reaction and the functional groups formed or lost during the SPS step. Additionally, two-dimensional MAS techniques such as 2D-COSY (correlated spectroscopy) and TOCSY (total correlated spectroscopy) (171) or 2D-SECSY (spin echo correlation spectroscopy) (181) can provide more detailed information that may be useful in specific cases. 

It would be advantageous if we could retain the enhanced resolution afforded by the projection of the 2D J-resolved data and also obtain spin system connectivities. MAS spin-echo correlated spectroscopy (SECSY) (44) allows both spin connectivities and enhanced resolution to be obtained. The... 

The "spin echo correlated spectroscopy" technique retains the basic two-pulse sequence, but delays acquisition of a free induction decay until the maximum of the Hahn echo 50 51... 

D-correlation experiments are almost invariably presented in a contour plot. Homonuclear correlation spectroscopy, in the form of COSY (proton correlation spectroscopy) (25, 28) or SECSY (2D-spin echo-correlated spectroscopy) (279) pulse sequences, is routinely employed in modern natural products structure determination (198, 328). 

SECSY, 2D spin-echo-correlated spectroscopy [80N2] ... 

SECSY (spin-echo correlated spectroscopy), have been applied to... 

K. Nagayama and K. Wuthrich, Systematic application of two-dimensional proton nuclear magnetic resonance techniques for studies of proteins. 1. Combined use of spin-echo correlated spectroscopy and J-resolved spectroscopy for the identification of complete spin systems of non-labile protons in amino acid residues, Eur. J. Biochem. 114, 365 (1981). 

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