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1 How to observe NMR? Excited Spin Bo Net Magnetization flipped to xy plane t FT Short and high power pulse irradiation at Fo MHz Continuum of Frequency Excite all Resonances at the same time υ F Time DomainFrequency Domain

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2 How to observe NMR? 1D NMR Experiment Precessing Spin Receiver at position x picked up a varying electromagnetic signal

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3 How to observe NMR? FT Free Induction Decay (FID) Time DomainFrequency Domain Intensity decreases with time. Why?

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4 Modern NMR Experiments Multi-pulses: 90 degree, 180 degree or shaped pulses Multi-channels : 1 H, 15 N, 13 C (one channel one freq) with gradient z Multi-dimensional: t1, t2, t3 (one dimension one t)

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5 What is Multi-pulsed NMR Experiments? t Short Pulse Excited Spin Bo Quantum States Bulk Magnetization (not quantized) Mz

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6 Spin Gymnastics! By varying the power, time length (angle) or phase (direction) of the pulse Bo Net Magnetization flipped to xy plane xy xy Mz -Mz 180y Mz My 90-x Models for the description of NMR experiments: 1. Quantum Model: Density Matrix Analysis, Product operator formalism, very powerful but difficult to use. 2. Vector Model: Classical formalism, too simple but easy to visualize. inverted

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7 Spin Gymnastics Use Right Hand Rule Phase of pulse (thumb position of your right hand) Starting M direction Interconversion rules between different M directions by applying 90 degree pulses Mz Mx 90y Mz 90z Mx 90x My 90y MzMxMy

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8 What is Multi-pulsed NMR Experiments? Magnetization can be transferred between nuclei through cross-talking by: 1.bonding: J coupling (H-H, H-C, H-N, etc…) 2.Close in space: dipolar coupling Therefore information related to the other nuclei (e.g. chemical shifts δ, bonding, J-couplings, distances d AB ) can be encoded in the NMR signals as well. C—HC—H N—HN—H d AB HBHB HAHA

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9 Mulit-Dimenstional NMR? Single pulse 1D NMR Experiment t1t1 1. Preparation: Recycle delay for relaxation 2. Applying pulse 3. Acquisition of FID Raw NMR data FID = F(t1) n1 points One dimension One t 2D NMR Experiment relaxation Raw NMR data FID = F(t1, t2) (n1 x n2 points) Exchange infoget FIDJ or δ coding in t

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10 1D2D3D Mulit-Dimenstional NMR? F(t1) FT F(t1,t2) FT F(t1,t2,t3) FT F(w1)F(w1,w2)F(w1,w2,w3)

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11 F(t1,t2) COSY: Correlation Spectroscopy F(w1,w2) δaδa δbδb H a J-coupled to H b FT(t2) Sine wave in t2 F(t1,w2) FT(t1) N2 points N1

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12 Homonuclear Experiment: Single channel, single resonance 2D NOESY (thru space d AB ) (NOE Spectroscopy) 2D ROESY (Rotating frame NOESY) (thru space d AB ) 2D COSY (directly J-coupled) TOCSY or HOHAHA (Total Correlation Spectroscopy) (directly or indirectly J-coupled)

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13 H,C-Hetero-COSY (directly H-C J-coupled) DEPT (Distortionless Enhancement via Polarization Transfer) HSQC (Heteronuclear Single Quantum Correlation) (directly H-C J-coupled) Heteronuclear Experiment: Double resonance (e.g H, C) HMQC (Heteronuclear Multi-Quantum Correlation) (directly H-C J-coupled) Inverse experiment: magnetization is transferred back to the more sensitive H Detecting C

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14 Heteronuclear Experiment: Triple resonance Triple resonance: H, C, N

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15 Why NMR? So informative, so many applications and so much FUN! 2nd advantage of pulsed FT NMR: allow multi-dimensional NMR

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