X filter
DESCRIPTION
The X-filter element ( 96JB492-8 , 97JACS6711 ) plays an important role in multidimensional NMR experiments specifically designed to study biomolecular complexes, where one of the components, for instance the protein, is usually 13C and/or 15N-labeled and the another, the ligand, is at natural abundance. The X-filter is based in the evolution of J(XH) for 1H-13C systems whereas 1H-12C remains unaltered during an spin echo period. Thus, at the end of this period, 1H-12C is on the y axis whereas 1H-13C is on the x axis. A 90 proton pulse applied from x or y axis rotates only one of these two magnetizations to the z axis, whereas the other component remains in the transverse plane.

The use of this block can be improved using:

  • Pulsed field gradients around the 180(X) pulse ( 96JB492-8 , 97JACS6711 )
  • a gradient-based z-filter scheme to remove undesired transverse magnetization ( 96JB492-8 , 97JACS6711 )

  • adiabatic pulses for improved X-inversion ( 97JMR36-127 )
  • or the use of a doble-tuned scheme ( 96JB492-8 , 97JACS6711 )

    • This block can be easily inserted in conventional 2D 1H experiments (NOESY, TOCSY ...) replacing the original preparation (w1-filtering/editing) or detection (w2-filtering/editing) schemes. Examples have been reported for:

  • For instance, replacing the initial 90º 1H pulse by a X-filter in a NOESY experiment results in a 2D w1-X-filtered NOESY experiment
  • 2D w1,w2-X-filtered NOESY experiment
  • 2D w1-X-filtered COSY experiment
  • 2D w1-X-filtered TOCSY experiment
  • 2D w2-X-filtered TOCSY experiment
  • w2-X-filtered 3D HSQC-NOESY experiment
  • w1-X-filtered 3D NOESY-HSQC experiment
    • REQUIREMENTS
    Easy implementation on AVANCE spectrometers.
    EXPERIMENTAL DETAILS
     The interpulse delay is optimized to 1/(4*1JCH) .
    SYNTAX
    The most standard way to implement a refocused X filter in a pulse program is:
    ...
    p1 ph1
    d4
    (p2 ph2):f1 (p4 ph3):f2
    d4
    p1 ph4
    ...
    in which:
     

    RELATED TOPICS

    See Isotope filters.

    A series of widely used 3D and 4D experiments can result of this approach:

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