NOE without Spin Diffusion
Measurement of Nuclear Overhauser Enhancement is a crucial point in the accurate structural determination of molecules in solution by NMR. Such measurements, particularly over long distances, are often compromised by the effects of multi-step magnetization transfer, usually referred as spin diffusion. Several modifications of the basic NOESY pulse scheme have been proposed to remove such undesired spin diffusion effects:
  • MINSY experiment ( 88JMR150-78 )
  • QUIET-BIRD-NOESY experiment ( 96JACS3531 and 99JMR289-140 ) that inserts a BIRD sandwich in the center of the mixing time of a NOESY sequence
  • QUIET-NOESY experiment ( 94JACS362 , 96JB169 , 96JMRB40-111 , and 99JMR330-138 ) in which a doubly-selective inversion pulse is inserted in the middle of the mixing time in a NOESY pulse scheme.
  • Use of synchronous nutation ( 93JCP1721 , 92JACS10679 ) where two selected spins are simultaneous irradiated with two rf fields, so that cross-relaxation occurs only between the two selected spins while spin diffusion is suppressed. Modified schemes (MYSIN experiment) have been also proposed ( 94JCP7273 , 96JMRB288-110 , 96JMRA223-120 )
  • BD-NOESY ( 93JMRB232-102 and 94METH106 ) and CBD-NOESY ( 91JMR651-92 , 92JACS1523 , 95JACS5610 ) experiments.
  • Incorporation of two semiselective inversion pulses into the mixing time of a DPFGE-NOE pulse scheme ( 99JMR504-140 )
  • Isotope-Assisted NOESY experiment in which a Double-INEPT edited building block is placed at the middle of the mixing time ( 97JB317 ) in order to selectively invert CH/CH3 or CH2 protons.
    •  Recently, several of such methods have been compared and analyzed in detail ( 99JMR354-139 ).