Heteronuclear 2D correlation spectroscopy with inverse detection

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Heteronuclear 2D correlation spectroscopy with
inverse detection
NMR 2003 NMR applications to Structural Chemistry
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Heteronuclear 2D correlation spectroscopy

• Basis
• Heteronuclear correlation 2D experiments
  establish connectivities between any pair of
  nuclei, in the majority of cases, between a
  proton and an heteronucleus (13C, 15N), which
  are connected by a scalar coupling.
• Applications
• Assignment of the observed resonances in the NMR
  spectra to the specific atoms in the molecule.
• Identification of the number of protons directly
  bonded to a given carbon atom.
• Transfer of established protons assignments onto
  the directly bonded heteronucleus or, on
  occasions, vice versa.

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• Heteronuclear 2D correlation spectroscopy with
  inverse detection
• Direct detection and inverse detection
• Sensitivity advantages of inverse detection
• 2D HSQC
• 2D HMQC
• Suppression of 1H bound to nuclides with I?1/2
  (1H-12C,1H-14N) in HMQC and HSQC
• Phase-cycling
• Pulsed field gradients gradient-enhanced HMQC
  and gradient-enhanced HSQC
• 2D HMBC

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Heteronuclear 2D correlation spectroscopy
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Heteronuclear 2D correlation spectroscopy
direct detection

• i) Proton excitation (I)
• ii) Frequency labeling of proton during the
  evolution time t1
• ii) Polarisation transfer of proton (I) to the
  heteronucleus (S)
• v) Heteronucleus S detection (during acquisition
  time t2)

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Heteronuclear 2D correlation spectroscopyinverse
detection

• i) Proton excitation (I)
• ii) Polarisation transfer of proton (I) to the
  heteronucleus (S)
• iii) Frequency labeling of the heteronucleus,
  during evolution time t1
• iv) Polarisation transfer of the heteronucleus to
  the proton
• v) Proton detection (during acquisition time t2)

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Heteronuclear 2D correlation spectroscopy
relative sensitivity
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Heteronuclear 2D correlation spectroscopy
Comparison HETCOR (direct detection)/HSQC
(inverse detection)
HSQC spectrum Santonine (20mg /0.7 ml CDCl3) Exp
time 1h 8 min, ns4
HETCOR spectrum Santonine (65mg /0.7 ml
CDCl3) Exp time 1h 15 min, ns32
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Heteronuclear 2D correlation spectroscopy with
inverse detection technical aspects

• Technical problems associated with the design of
  heteronuclear correlation experiments

• a) Suitable hardware
• The spectrometer, probe and control software must
  have two or more independent rf channels, so that
  one can pulse 1H and 13C (or 15N) and detect 1H
  magnetisation while performing 13C decoupling.
• The use of inverse probes allow a large
  improvement in sensitivity. The probe is designed
  with the 1H coil wound closest to the sample, for
  maximum detected 1H signal.

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Heteronuclear 2D correlation spectroscopy with
inverse detection technical aspects
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Heteronuclear 2D correlation spectroscopy with
inverse detection technical aspects
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Heteronuclear 2D correlation spectroscopy with
inverse detection technical aspects

• b) 13C decoupling
• 13C decoupling while sampling 1H magnetisation is
  a very demanding requirement, since the 13C
  spectral bandwith is much larger than the 1H
  bandwith.
• There are decoupling methods (GARP) that afford
  very effective 13C decoupling over wide
  bandwidths.
• c) Selective detection of 1H signals associated
  with protons in 13CHn fragments, while
  suppressing the 1H signals associated with
  protons in 12CHn fragments.
• This can be very difficult since the natural
  abundance of 13C is only 1.1, so one must
  suppress signals that may be 100 times more
  intense than the desired signals.