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The ge-2D COSY-MQF experiment allows to obtain a 2D COSY-MQF spectrum with a single scan per t1 increment provided that the S/N ratio is adequate. The main advantage of such approach is the large reduction in the total acquisition time compared with a conventional phase-cycled 2D COSY-MQF experiment. Magnitude-mode or phase-sensitive data is obtained depending of the selected pulse sequence and acquisition/processing procedure.The COSY-MQF experiment permits to trace out through-bond proton-proton connectivities via the homonuclear JHH coupling constant.REQUIREMENTS
Easy implementation on any AVANCE spectrometer equipped with pulsed field gradients (PFGs).VERSIONS
The ge-2D COSY-MQF experiment is easily designed by incorporating a multiple-quantum filter (MQF), consisting of a 90°-PFG-90° block, as a mixing process. However, the incorporation of PFGs during the variable evolution period of the standard COSY-MQF experiment affords a magnitude-mode spectrum ( 90JMR422-87 , 91JMR637-94 , and 92MRC768 ). In principle, a 1:1:(n+1) gradient ratio was proposed to achieve proper n-filtering selection but recently it has been shown that a 4:3:10 gradient combination removes rapid-pulsing artifact characteristics in magnitude-mode COSY-DQF experiments ( 96JMRA110-120 ).EXPERIMENTAL DETAILSAlternatively, phase sensitive COSY-MQF spectra can be obtained using the echo-antiecho approach (The refocusing G3 gradient strength is inverted in alternates scans) ( 97JMR348-125 ) or avoiding the application of the defocusing PFG during the variable t1 period ( 91JMR637-94 ).
Gradient-selected E.COSY spectra can be obtained combining several COSY-MQF spectra ( 93JMRA348-102 ).
The incorporation of the WATERGATE scheme ( 94JMRB67-105 ), WET scheme ( 95JMRA295-117 ), RAWSCUBA scheme ( 95JMRB260-107 ), crafted selective pulses ( 92JMR200-98 ), or magic-angle gradients ( 95JMRA265-113 and 96JACS3253 ) in the ge-2D COSY-DQF experiment improves solvent suppression in aqueous samples allowing the clean detection of cross-peaks at the water frequency.
COSY-DQF experiment is usually recorded in routine and automation modes, and therefore can be run with minor changes from a predefined parameter set.SPECTRAList of available gradient-enhanced COSY pulse programs for AVANCE spectrometers.
In the phase sensitive version, a 1:2 gradient combination permit to select coherences evolving as DQC during the filter. A 1:3 gradient combination selects coherences evolving as TQC, and so on...
Tutorials: 2D homonuclear experiments Tutorials: 2D gradient-based homonuclear experiments Tutorials: 2D gradient-based homonuclear experiments in H2O
The spectrum resulting of the gradient-enhanced COSY-DQF version is a clean 2D map in which t1 noise has been efficiently reduced. As in the conventional COSY-DQF spectrum, cross-peaks correlate chemical shifts between J-coupled spins.RELATED TOPICS
Related experiments:2D homonuclear experiments 2D gradient-based homonuclear experiments