Double-quantum filter INADEQUATE

By allowing multiple-quantum coherence to process during the evolution period of a two-dimensional experiment, Drobny et al. were able to detect its effects indirectly. This idea subsequently blossomed into the new technique of filtration through double-quantum coherence. Multiple-quantum coherence of order n possesses an n-fold sensitivity to radiofrequency phase shifts, which permits separation from the normal single-quantum coherence. This concept inspired the popular new techniques of double-quantum filtered correlation spectroscopy (DQ-COSY) and the carbon-carbon backbone experiment (INADEQUATE), both designed to extract useful connectivity information from undesirable interfering signals. 

Today, a number of one- and two-dimensional NMR experiments are available for the detection of homonuclear Li, Li and Li, Li couplings. Aside from the COSY experiment, the double quantum filtered COSY (COSY-DQF), the TOCSY, and the ID and 2D INADEQUATE experiments [24] have been successfully employed. An attractive feature of all these experiments is their sensitivity for small scalar interactions which give rise to crosspeaks even if line splittings in the corresponding ID spectra are not resolved. This was first demonstrated with COSY experiments for a paramagnetic nickel complex [82] and for quadrupolar nuclei in the case of boron-11 [83]. 

During tu the frequencies that evolve are not the chemical shifts of the coupled nuclei as they are in a typical COSY. Instead, it is the sum of the chemical shifts of the coupled nuclei which evolve during tu and, because it is double quantum filtered, it is only the two-spin AB and AX systems that contribute significantly to the intensity in the INADEQUATE spectrum. Proper selection of the delays (t) in the pulse sequence allows us to select the larger one-bond couplings (UC( ) thus ensuring that we are only looking at directly bonded... 

The homonudear 2-D NMR experiments that use I-coupling indude the correlation spectroscopy (COSY, and variants induding gradient-selected COSY or gCOSY, double-quantum filtered COSY or DQF-COSY) experiment, the total correlation spectroscopy (TOCSY) experiment, and the incredible natural abimdance double quantum transfer experiment (INADEQUATE) [3]. 

Bourdonneau M and Ancian B (1998) Rapid-pulsing artifact-free double-quantum-filtered homonuclear spectroscopy. The 2D-INADEQUATE experiment revisited./ourwa/ of Magnetic Resonance 132 316-327. 

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