Jmodulation Experiment RDC
NMR Data Processing '> 'Jmod Measurement of RDCs'<o:p></o:p>
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Pulse Sequence (J H-N)
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The sequence is modified from the fast HSQC sequence (gNfhsqc) in Varian BioPack. For details see Tjandra N. et al, JACS (1996), 118, 6364-72
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A series of 2D experiments should be acquired with the J modulation delay (Delta) set to different values, preferably in an interleaved fashion. (Note that “Delta” is half the total modulation delay.) For example, in Vnmr, this can be realized by:
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array(‘Delta’,8,0.002,0.002)
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which sets Delta from 0.002 to 0.016, corresponding to J modulating delays from 4 to 32 msec. At least 3 modulation points are needed to extract the coupling constant, along with 15NT2 and a parameter related to pulse imperfection. It is recommended to take more than 3 points to get an estimation of experimental error. The maximum delay (32 msec in this case) should be bigger than 3/(2J) ( ~16 msec in case of JNH) to make sure the modulation curve crosses zero at least twice (Tjandra et al). Our simulation shows that the modulation interval should not be close to 1/J (~10ms for JNH), i.e. the stepsize for Delta should not be close to ~5 msec.