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NMR Basic Principle

NMR Basic Principle. 2009. 7. 30. 노 정 래 군산대학교. Magnetization in the magnetic field Magnetization under RF pulse Detection of Magnetization Digitization of FID Fourier Transformation Experiment Setup Chemical shift & Spin coupling constant. Energy E = h u h is Planck constant

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NMR Basic Principle

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  1. NMR BasicPrinciple 2009. 7. 30 노 정 래 군산대학교

  2. Magnetization in the magnetic field • Magnetization under RF pulse • Detection of Magnetization • Digitization of FID • Fourier Transformation • Experiment Setup • Chemical shift & Spin coupling constant

  3. Energy E = hu h is Planck constant u frequency - spin, I - Positive charge - Magnetogyric ratio, g nucleus Magnetic moment, m

  4. If magnetic field, Bo is applied to the direction of Z, E = - mz Bo = g Iz Bo I = 1 I = 1/2 Z Iz = +1 Iz = +1/2 Iz = 0 Iz = -1/2 Iz = -1/2

  5. Magnetic moments in the magnetic field, Bo (one-spin system) w0: Larmor Frequency I=1/2 w0=gBo Bo m E = gBoh / 2p

  6. Magnetic moments in the magnetic field, Bo Mz = Mo Bo ≡ Mz Mx,y ≡

  7. The behavior of magnetic moments in the magnetic field, Bo Bo In the Magnetic field, Bo Mo w0=gBo - Magnetization, Mo Mo = Nh2g2Bo / 4pkT - Precession of Mo at frequency, wo about the axis of Bo Equilibrium

  8. w0=gBo u0 = gBo/2p gH = 2.675  108 T-1 rad s-1 w0=gBo

  9. Magnetization under RF pulse First NMR Spectra on Water 1H NMR spectra of water Bloch, F.; Hansen, W. W.; Packard, M. The nuclear induction experiment. Physical Review (1946), 70 474-85.

  10. Coherence Bo x x y y x x y y partially correlated spins (Mx,y) coherence

  11. RF Energy + coherence Spin inversion Relaxation Equilibrium Non equilibrium

  12. rotating frame (회전좌표계) z Bo z Bo Mo Mo w 0 w 0 w y y | w - w 0| x x w 0

  13. z z Bo- w/g Bo =0 Mo Mo  w 0- w w = w 0 w  w 0 y y x x Off-resonance On-resonance

  14. RF wave (에너지) 2B1sin(wtp+ a) B1 (w) x x 2B1 B1 (w)

  15. Magnetization in the RF field (phase a=0) 2B1cos(wtp+ a) On-resonance z z w1=gB1 Bo = 0 q Mo q=w1tp w = w 0 y y My B1 x B1 x phase = x effect of B1 at w = w 0 (on-resonance) B1 (wo)

  16. Magnetization in the RF field (phase a=0) Off-resonance z weff = gBeff Bo - w/g Mo Mo q Bo- w/g w  w 0  w 0- w Beff My B1 y B1 x effect of B1 at w  w 0 (off-resonance)

  17. RF pulse description B1 pulse B1 Beff >> Bo – w/g tp 2B1cos(wt+ a) w w  Dw w +

  18. z 90x Mo y z x Mo z 180x,y y y x z x Mo Mo y x 90y

  19. 90x 180y t t Spin-echo 4 1 2 3 5 z z z Mo y y y ( w 0- w) t Mo Mo x x x 3 2 1 z z 1 Mo ( w 0- w) t Mo y y x x 5 4

  20. Relaxation Non equilibrium Equilibrium( Mx,y= 0, Mz = M0) 1. Longitudinal (spin-lattice) relaxation : Recovery to Mo Mo t > 5 T1 2. Transverse (spin-spin) relaxation : recovery to Mx,y=0 Mx,y 0 t

  21. Magnetization for one spin system 1. w = w 0 (on-resonace) 90x Signal detection 2. wo - w= 50 Hz w w RF FID (free induction decay) w o P PSD w o 3. wo - w= 100 Hz Coil (induction current)

  22. Summary z 90x z Mo w o y (Off-resonace) w > wo w x y x

  23. Fourier Transformation (FT) real imaginary real imaginary w w D(w) A(w)

  24. Fourier Transformation (FT) Real part 1. w = w 0 Reference frequency Offset frequency w 2. w - w0 = 50 Hz w 0 -w 0 3. w - w0 = 100 Hz w 0 -w 0

  25. FT real imaginary W w W -W 0 RF f W -W 0 y w o • = wo-w • wo > w PSD P x W W -W 0 W -W 0 + + W Quadrature Detection W -W 0

  26. Scan 1 (nt) Scan 2 Pulse width (pw) Pulse power (tpwr) Relaxation delay (d1) Acquisition time (at) Offset frequency (tof) Spectral width (sw)

  27. Digitization of FID PSD ADC = Analog to Digital Converter

  28. Digitization of FID Nyquist frequency 주파수 f인 주기 함수를 data point로 나타내기 위한 최소 주파수, 2f 따라서 한 주기 당 적어도 data point를 적어도 2개 이상 얻어야 한다.

  29. 160ms Real part (COS) Imaginary part (SIN) Real + imaginary data points at simultaneous time (Varian) In Quadrature detection np: 총 data point sw: spectral width

  30. Sampling rate & alias(folding) Nyquist Theorem에위배

  31. 주파수가 1600Hz인 cos함수 주파수가 400Hz인 cos함수(alias 함수) Nyquist 주파수 :1000Hz Folding (aliased)

  32. Window function FT

  33. Window Functions S/N 61.8 72.0 30.6 122.0

  34. Experiment Setup probe

  35. Locking - 시간에 따른 자장의 변화를 보정 - NMR 용매로 사용하는 deuterium 핵을 이용 - acetone-d6, methanol-d4, chloroform-d, DMSO

  36. Shimming • NMR시료에 균일한 자장을 만드는 작업 • x,y방향은 spin, z 방향은 shim coil의 전류량으로 조절 • - shim은 NMR 시료 높이에 따라 의존 Shimming method • FID를 이용 • 한 spin핵에 대한 FID이 지수함수로 감소되도록 shim값을 변화 • 2. Lock level를 이용 • lock level이 최대가 되도록 shim값을 변화 • 3. Field gradient를 이용(Gradient shimming) • field map에 회귀분석적으로 shim값 조정 스펙트럼에서 최상의 해상도와 감도를 위해서는 shim조절이 필수

  37. 정상 Z2 감소 후 Z1재 조정 Z4감소 후 Z1,Z2 재 조정 Z3감소 후 Z1,Z2 재 조정 Z5감소 후 Z1,Z2 재 조정 X, Y, XZ, YZ XY, X2-Y2 Z3증가 Z4감소 후 Z1,Z2 재 조정

  38. Observer 90o pulse calibration 1. Spin 2. Temperature setting 3. Probe tune (dependence on solvent and temperature) 4. Lock & shim 5. Adjust reference frequency to the singlet line 6. Array pulse width tp qX 1H ( 13C ) > 5 T1 (1H ) BB q

  39. Decoupler90o pulse calibration with IS spin system(e.g. CH) 1. Decoupler 1H 90o calibration 90X 180X J 1/2J 1/2J S (13C) {1H} 13C qX I (1H) BB BB q =90o q DEPT, Hetcor, INADEQUATE, etc

  40. 2. Decoupler 13C 90o calibration J 90X 180X {13C} 1H 1/2J 1/2J I (1H) qX S (13C) 1H-12C q q =90o 1H-13C HMQC, HMBC, etc

  41. 1H spectrum of 13CH3I 1H-12C Observer decoupler on-resonance setting Temperature setting Tunning -minimize 1H-13C 1H-13C 151 Hz 15N-benzamide 90Hz

  42. Decoupler field strength(B2) calibration 13C 90X B2 S (13C) Jr I (1H) low-power CW mode B2 JCH 1H 90X I (1H)  S (13C) low-power CW mode wr w2

  43. Chemical shift & spin coupling constants Chemical Shift Shielding (Screening) factor, s 1H 1H < sa sb frequency na = g Bo(1-sa)/2p > nb = g Bo(1-sb)/2p CH2 CH3 HOCH2CH3 CDCl3 220 200 180 160 140 120 100 80 60 40 20 0 CH3 CH2 OH 10 9 8 7 6 5 4 3 2 1 0 ppm 125 600 500 400 300 200 100 MHz

  44. 1H and 13C Chemical shifts 1H (1.5~1.6) (1.15~1.16) (~0.75) 12 11 10 9 8 7 6 5 4 3 2 1 0 TMS ppm 13C (30~42) (22~35) (13~23) 220 200 180 160 140 120 100 80 60 40 20 0 TMS ppm

  45. some featured 13C chemical shifts alkane d= -2.3 + 9.1na + 9.4nb -2.5 ng 16.1 16.3 24.6 23.3 -2.3 6.5 alkene 133.4 141.8 127.2 73.5 115.9 111.3 212.6 170.4 123.5 24.2 19.9 alkyne arene 136.0 127.7 110.4 123.5 125.6 143.6 149.9 71.9 128.5 133.3 24.1 34.1 28.2 16.5 g-gauche effect

  46. Symmetry and Topicity ■ Homotopicity - indistinguishable atoms or groups by symmetry ■Enantiotopicity- atoms or groups having the mirror image in a molecule ■Diastereotopicity - atoms or groups not producing the mirror image

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