2011-12-predavanje 1-nmr
TRANSCRIPT
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The Nobel Prize in Chemistry 2002
"for the development of methods for identification and structure
analyses of biological macromolecules"
"for their development of soft desorption
ionisation methods for mass spectrometric
analyses of biological macromolecules"
"for his
development of
nuclear magnetic
resonance
spectroscopy for
determining the
three-dimensional
structure of
biological
macromolecules in
solution"
John B. Fenn Koichi Tanaka Kurt Wüthrich
1/4 of the prize
1/4 of the prize
1/2 of the prize
USA Japan Switzerland
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IsotopeNatural %
AbundanceSpin (I)
Magnetic
Moment (μ)*
Magnetogyric
Ratio (γ)†
1H 99.9844 1/2 2.7927 26.753
2H 0.0156 1 0.8574 4,107
11B 81.17 3/2 2.6880 --
13C 1.108 1/2 0.7022 6,728
17O 0.037 5/2 -1.8930 -3,628
19F 100.0 1/2 2.6273 25,179
29Si 4.700 1/2 -0.5555 -5,319
31P 100.0 1/2 1.1305 10,840
* μ in units of nuclear magnetons = 5.05078•10-27 JT-1
† γ in units of 107rad T-1 sec-1
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Jedro z magnetnim momentom obravnavamo kot paličast magnet,
na katerega zunanje magnetno polje B0 izvaja navor M
M = B0
ki poskuša magnetni moment zasukati tako, da bi kazal v smeri
polja B0.
Posledica je precesija magnetnega momenta okrog smeri
zunanjega magnetnega polja B0
B0
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Precesija vrtavke
0 = M
Kombinacija klasične mehanike in kvantne mehanike
M = 0
0 = . B0 LARMORJEVA FREKVENCA PRECESIJE
0
0 = B0
2
M = B0 = . p B0
hip
vrtilna količina
kotna hitrost precesije
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Energija magnetnega momenta v zunanjem magnetnem
polju B0 je kvantizirana
E = - I B0 cos = -h2
m: -I, -I+1, ......, I-1, I magnetno kvantno število
E = + B0 cos h2
12
E= - B0 cos h2
12
E
E = B0h2
B0
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N (m = -1/2)
N (m = +1/2)= e – E/kT = e - h Bo
2πkT
Boltzmannova porazdelitev
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B0
B
Resonančni pogoj: frekvenca šibkega magnetnega polja B mora biti
enaka Larmorjevi frekvenci precesije.
E = B0h2
h . =
frekvenca polja B
B02 =
1H
13C
1H
13C
= = 26.753
6.728 = 3.975
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(Gauss) 1T(esla) = 10000 G
E = B0h . = h2
LOCK
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Shema NMR spektrometra
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‘’quenching’’
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NMR spektrometer
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Relaksacija
• T1 longitudinalni relaksacijski čas
‘’spin – lattice’’ relaksacijski čas
• T2 transverzalni relaksacijski čas
‘’spin – spin’’ relaksacijski čas
NMR tomografija (NMR imaging) = slikanje z magnetno resonanco
relaksacija (T1. T2)
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hip
-protoni (jedra 1H vode v telesu)
- T1 točka na rač. sliki
relaksacija (T1. T2)
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Reflecting the fundamental importance and applicability of MRI in the medical field, Paul Lauterbur and Sir Peter Mansfield of the University of Illinois,
Urbana-Champaign and University of Nottingham were awarded the 2003 Nobel Prize in Medicine or Physiology for their "discoveries concerning magnetic
resonance imaging". The Nobel Prize committee acknowledged Lauterbur's insight of using magnetic field gradients to introduce spatial localization, a discovery
that allowed rapid acquisition of 2D images. Sir Peter Mansfield was credited with introducing the mathematical formalism and developing techniques for
efficient gradient utilization and fast imaging.
The 2003 Nobel Prize in Medicine award was vigorously protested by Raymond Vahan Damadian, who claimed that he was the inventor of MRI, and that Paul
Lauterbur and Sir Peter Mansfield had merely refined the technology.
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Paramagnetna kontrastna sredstva
• kompleksi gadolinija (lantanid)
• skrajšujejo longitudinalne (T1) in – v manjši meri –
transverzalne (T2) relaksacijske čase protonov vode v tkivu
[Xe] 4f7 5d1 6s2
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Periodni sistem elementov
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gadopentetna kislina gadobenska kislina
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gadodiamid gadobutrol
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mangafodipir
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Merilne metode pri NMR spektroskopiji
CW (continuous wave NMR)
FT (Fourier transform NMR)
E = B0h . = h2
kratki radiofrekvenčni pulzi
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magnetizacijski vektor……………………….. vektorska vsota magnetnih momentov
relaksacija (T1. T2)
signal proste precesije
free induction decay (FID)
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Fourierova transformacija
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Fourierova transformacija
signal proste precesije
free induction decay (FID)
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• kemijski premik
• sklopitve
• integral
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Kemijski premik
= 10 - σ
σ = σdia + σpara + σ’ + σmedium
ppm (parts per million)
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300 MHz
10 ppm = 3000 Hz
resonančne frekvence
protonov
ν
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Kemijski premik
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1H-NMR spekterCH3COOH v CDCl3
13C-NMR spekterCH3COOH v CDCl3(širokopasovnaprotonska razklopitev)
h = B0h2
resonančni pogoj:
visok Bo
nizka
velik
majhen Bo
visoka
majhen
Bo
1H-NMR: obseg kem. premikov 1-10 ppm 13C-NMR: obseg kem. premikov 1-200 ppm
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- /
- /
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Kemijski premik
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Inkrementni sistem
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• kemijsko ekvivalentna jedra
• magnetno ekvivalentna jedra
simetrijska operacija
hitra intramolekularna gibljivost (rotacija)
kemijsko ekvivalentna, vendar
magnetno neekvivalentna protona
Kemijski premik - vplivi
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• vpliv porazdelitve elektronske gostote v vezi H-X
na kemijski premik
CH3-CH2-OH CH3-CH2-SH
3.71 2.44
Kemijski premik - vplivi
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Kemijski premik - vplivi
• intramolekularni
kemijski procesi
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TMS
510
TMS
510
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Kemijski premik - vplivi
• anizotropijski efekti
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H
• povečano zasenčenje nad in pod obročem
• zmanjšano zasenčenje ob obroču
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• kemijski premik
• sklopitve
• integral
Spin-spin sklopitveS singlet
d dublet
t triplet
q kvartet
...
m multiplet
• homonuklearna interakcija
• heteronuklearna interakcija
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Proton A, proton X I = 1/2
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J 1H-1H med -20 in +20 Hz13C-1H cca 250 Hz13C-13C cca 170 Hz
Velikost sklopitvene konstante (Hz)
neodvisna od zunanjega magn. polja Bo
1J sklopitvena konstanta preko 1 vezi1J sklopitvena konstanta preko 2 vezi
...itd
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razdalja med signaloma 8 Hz
7.0 ppm
dva singleta ali dublet ???
posnamemo spekter pri drugi frekvenci,
npr. 400 MHz
a) razdalja med signaloma v Hz ostane ista
b) razdalja med signaloma v Hz se spremeni
200 MHz protonski
NMR spekter
dublet
dva singleta
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XmAn
Multipliciteta za A = m 2Ix + 1
Multipliciteta za X = n 2IA + 1
Multipliciteta signalov
CH2CH3
AnXm
proton
A
proton
X
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rezidualni protoni
sklopitev rezidualnih protonov z devterijem
Multipliciteta za A = m 2Ix + 1
Multipliciteta za H = 2 x 2 x 1+ 1 = 5
spin
devterija
1H – NMR spekter
CHD2
jedro A jedro X
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sklopitev jeder 13C z devterijem
Multipliciteta za A = m 2Ix + 1
Multipliciteta za C = 3 x 2 x 1+ 1 = 7
spin
devterija
13C – NMR spekter
CHD3
jedro A jedro XMultipliciteta signalov CDCl3 ???
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Devterirana topila
Solvent B.P. °CResidual1H signal (δ)
Residual13
C signal (δ)
acetone-d6 55.5 2.05 ppm 206 & 29.8 ppm
acetonitrile-d3 80.7 1.95 ppm 118 & 1.3 ppm
benzene-d6 79.1 7.16 ppm 128 ppm
chloroform-d 60.9 7.27 ppm 26.4 ppm
cyclohexane-d12 78.0 1.38 ppm 26.4 ppm
dichloromethane-
d2
40.0 5.32 ppm 53.8 ppm
dimethylsulfoxide
-d6
190 2.50 ppm 39.5 ppm
nitromethane-d3 100 4.33 ppm 62.8 ppm
pyridine-d5 1147.19, 7.55 & 8.71
ppm
150, 135.5 &
123.5 ppm
tetrahydrofuran-d8 65.0 1.73 & 3.58 ppm 67.4 & 25.2 ppm
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CH3
N+
O-
O
1H-NMR Spekter 1-nitropropana v CDCl3
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Sklopitvene konstante
• velikost geminalne sklopitve raste z naraščajočim s-karakterjem hibridne orbitale
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• vicinalne sklopitve
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• sklopitve na daljavo (long-range sklopitve)
• sklopitve protonov v aromatskih obročih
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Temperaturne meritve
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Devterijska izmenjava
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Sklopitve z drugimi jedri
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13C NMR spektroskopija
Širokopasovna protonska razklopitev (Proton broad-band decoupling)
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DEPT metoda
net
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• moduliran spin-echo eksperiment