NMR%20SPECTROSCOPY - PowerPoint PPT Presentation

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NMR%20SPECTROSCOPY

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In a spectrum, each signal represent the resonance frequency ... The gyromagnetic ratio and the natural isotopic abundance. determine the NMR signal available ... – PowerPoint PPT presentation

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Title: NMR%20SPECTROSCOPY


1
NMR SPECTROSCOPY
  • JM Franconi

2
MR SPECTROCOPY
Principle of FT NMR spectroscopy
In a spectrum, each signal represent the
resonance frequency of a nucleus in a specific
environment
Bo is fixed a RF pulse irradiate a broad range
of frequency
RF
irradiation
sampling
FT
t
spectrum
f
FID
3
MR SPECTROCOPY Non selective RF pulse
In spectroscopy the RF pulse used is lt 100
microsecond
RF
sinc
rectangular
g.B1 gt 2pF
F frequency range
4
MR SPECTROCOPY RF pulse Magnetisation evolution
During RF pulse M rotate Around x direction with
an angle
Bo
z
Q g. t . B1
q
Mz
M
y
O
Mxy
x
5
MR SPECTROCOPY spectrum parameter chemical
shift
f
f1
f2
f3
f4
A same nucleus can have different resonance
frequency
6
MR SPECTROCOPY chemical shift phenomenon
Bo
Bo
Bo1
H2
Bo2
H1
O
C
Bo2
Bo1
7
MR SPECTROCOPY chemical shift measurement
u i
u ref
reference
f
paramagnetic low field high electronégativity
Diamagnetic High field Low electronégativity
8
MR SPECTROCOPY J coupling
J coupling is an interaction between close
nuclei This interaction is independant of Bo
field It does not exit on one isolated molecule
JAB
f
fA
fB
9
MR SPECTROCOPY J scalar coupling
H1
H1 is influenced by the 2 H2 sites Jcoupling is
transported by chemical bond
C
C
50(1/2)
H2
50(-1/2)
f1dBH2
f1
f1- dBH2
10
MR SPECTROCOPY J dipolar coupling
Coupling is also possible directly through space
r
H1
H2
1/r6
11
MR SPECTROCOPY J coupling
The Nuclei magneticaly equivalent have the same
chemical shift. They do not show any coupling
effect
Ha
C
fHa fHb fHc
C
Hb
Hc
12
MR SPECTROCOPY J coupling
Rules for multiplicity determination
A I nucleus coupled to n spin S give a signal
with 2.n.S 1 componants
The componants relative intensity are given by a
binomial Distribution.
13
MR SPECTROCOPY Signal area
NMR spectroscopy is a quantitative method
f
14
MR SPECTROCOPY spectrum quality
DR
Concept of digital resolution
AT N.DW
DW
t
f
At
R 1/AT
Digital resolution
FT
Frequency domain
Time domain
T2
TR1/pT2
t
f
True NMR resolution
CONDITION TR gt DR
15
MR SPECTROCOPY Sampling rules
Application of Nquist theorem
DW
f1
f2
f1
f2
f2
F1/Dw
2. F. Aq N
16
MR SPECTROCOPY Sensitivity
  • The gyromagnetic ratio and the natural isotopic
    abundance
  • determine the NMR signal available

- the nucleus sensitivity is proportional to Bo2
and g3
17
MR SPECTROCOPY concept of population and
coherence
Mz
Mz
MR signal
E2
RF
E2
E1
E1
Cohérencetransition
population
18
MR SPECTROCOPY Polarisation transfer (NOE)
C
1/2
-1/2-1/2
Transition C13
C
-1/21/2
1/2
Long distance
1/2
H
Transition H1
Niveau C13
1/2-1/2
-1/2
1/21/2
H
Niveau H1
2 independant level of energy
system of 4 levels of energy
NO COUPLING
COUPLING
19
MR SPECTROCOPY Polarisation transfer (NOE)
dH 4.dC
f
f
5
-dH-dC
dH-dC
C13 transition
-dHdC
H1 transition
dH-dC
-dH-dC
-3
-dHdC
dHdC
POLARISATION
H1 TRANSITION SATURATION
20
SEQUENCE
21
SEQUENCE
SPIN ECHO SEQUENCE
22
SEQUENCE
23
SEQUENCE
24
SEQUENCE
DEMI TOUR!
25
SEQUENCE
26
SEQUENCE
ECHO coherence recovery
27
SEQUENCE SPIN ECHO
28
SPIN ECHO SEQUENCE
180
90
TR
TE
RF
GS
GP
DAC on
GR
CONCEPT OF PULSE SEQUENCE
29
NMR SPECTROSCOPY APPLICATION
  • Chemical structure determination (protein, ADN,)
  • Quantitative measurement
  • (isotopic enhancement determination)
  • ?food and beverage quality control
  • Spectroscopy in vivo (metabolism caracterisation)
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