Sensitivity Enhancement and Fast NMR BCMB 8190

Transcription

1 Sensitivity Enhancement and Fast NMR BCMB 8190

2 References T. Maly, G.T. Debelouchina, V.S. Bajaj, K-N. Hu, C-G. Joo, M.L. Mak Jurkauskas, J.R. Sirigiri, P.C.A. van der Wel, J. Herzfeld, R.J. Temkin, and R.G. Griffin. (2008). Dynamic nuclear polarization at high magnetic fields. J. Chem. Phys. 128: B.M. Goodson. (2002) Advances in Magnetic Resonance: Nuclear Magnetic Resonance of Laser- Polarized Noble Gases in Molecules, Materials, and Organisms. J. Mag. Reson. 155: Title: Principles and Progress in Ultrafast Multidimensional Nuclear Magnetic Resonance M. Mishkovsky and L. Frydman. (2000) Principles and progress in multidimensional NMR. Ann. Rev. Phys. Chem. 60:

3 Sensitivity Enhancement: Where can you Get It? Better detection: cryo-probes, SQUIDS, mechanical oscillators Higher magnetic fields: 23.4T (1.0 GHz) Higher polarization: low temp, transfer from systems with higher γ, pumping For S=1/2 detection with a coil at low polarization: Signal = γ 3 B 02 h 2 / (16π 2 kt) P = γb 0 h/(4πkt)

4 Alkali Metal Spin Exchange From: B.M. Goodson (2002) J. Mag. Reson. 155: Depends on the use of circularly polarized light and the conservation of angular momentum

5 Experimental Set-up: Optical Pumping and Spin Exchange of Alkali Metal 1) 129 Xe (or 3 He) at low pressure (~ 8 atm) is enclosed in a cylindrical glass chamber in a low magnetic field (~ 10 G). Trace amounts of Rb added, heated to 200 C. 2) Circularly polarized laser light applied. λ = nm, 5s to 5p (D1) transition of Rb 3) Absorption of the laser light produces a high electronic polarization in the Rb atoms by means of optical pumping. Polarization transferred to 129 Xe by flip-flop term of Fermi-contact hyperfine interaction. Can reach 10% polarization enhancements of 10,000

6 Lung MRI using HP gases First report of a HP gas MR lung image was in 1994 of mouse lungs: Albert MS, Cates GD, Driehuys B, et al. Biological magnetic resonance imaging using laser-polarized 129 Xe. Nature. 1994;370: First human images were reported in 1996: Kauczor HU, Hofmann D, Kreitner KF, et al. Normal and abnormal pulmonary ventilation: visualization at hyperpolarized He-3 MR imaging. Radiology. 1996;201: MacFall JR, Charles HC, Black RD, et al. Human lung air spaces: potential for MR imaging with hyperpolarized He-3. Radiology. 1996;200:

7 Lungs Coronal HP 3 He image of normal healthy volunteer lungs showing homogeneous signal distribution throughout the pulmonary gas space Secondary branching of bronchi is visible as well as some pulmonary vasculature characterized as low-intensity structures Moller, H.E., et al., MRI of the lungs using hyperpolarized noble gases. Magn Reson Med, (6): p

8 Coronal HP 3 He lung images of patients with cystic fibrosis a) patient with mild disease and normal spirometry (FEV1 = 91% of predicted) shows few peripheral ventilation defects b) patient with severe cystic fibrosis (FEV1 41% of predicted) has extensive ventilation defects FEV1 forced expiratory volume in one second Moller, H.E., et al., MRI of the lungs using hyperpolarized noble gases. Magn Reson Med, (6): p

9 Coronal HP 3 He lung images of patients with asthma a) patient with mild disease and normal spirometry (FEV1 = 98% of predicted) shows few pleural-based peripheral ventilation defects b) patient with severe asthma (FEV1 36% of predicted) has large number of defects Moller, H.E., et al., MRI of the lungs using hyperpolarized noble gases. Magn Reson Med, (6): p

10 Enhancing Sensitivity for Metabolite Observation Dynamic Nuclear Polarization (DNP) Transfers large electron polarization to nucleus (γ e / γ p = 650) Usual detection is 15 N or 13 C (loss of 32 or 316 in S/N vs 1 H) Requires addition of a free radical and micro wave irradiation Samples are frozen prior to enhancement (2K) With low temp enhancements can be 1000 to 10,000 Data acquired with a single pulse train of small angle pulses Several mechanisms: The Overhauser Effect liquids and certain solids The solid effect requires hyperfine coupling The cross effect a three spin process (we1 = we2 +wn) Thermal mixing - combination of this with CE most probable Maly et al, (2009) J. Chem. Phys. 128:

11 Dynamic Nuclear Polarization (DNP) the Overhauser Mechanism Illustrated for a 15 N-electron pair Irradiate with micro waves Allow relaxation in which W 0 is most efficient αα 0 βα δ αβ Δ ββ Δ+δ αα Δ/2 αα Δ/2 }δ βα δ+δ/2 }δ βα δ }Δ/2 -δ αβ Δ/2 αβ Δ }δ ββ Δ/2+δ }δ ββ Δ/2+δ }Δ/2 -δ!

12 Polarization Instrumentation is Complex NMR Magnet Polarizer Transfer of polarized sample must be fast. Lasts only a few tens of seconds Courtesy of Oxford Instruments Ardenkaer-Larsen et al. PNAS 100:10158 (2003)

13 Direct 15 N observe of 50% Deuterated 15 N- Acetyl Phenylalanine Enhancement of 5000; 250 DNP, 200 temperature ~4000 µg 50 MHz Not enhanced 2376 scans ~40 µg 40 MHz DNP enhanced One scan Courtesy, Steve Reynolds, Oxford Instruments

14 =O Polarization Storage Limits Experiment Time Long relaxation times are desirable -N T 1 for N-D T 1 for C=O B 0 (Tesla) B 0 (Tesla) Singlet storage in proton pairs can also be explored: -N (αβ-βα)/ 2

15 DNP Enhanced 13 C-Pyruvate in Perfused Rat Heart M.E. Merritt et al (2008) ENC; M.E. Merritt et al (2007) PNAS 104:

16 DNP Enhanced 13 C-Acetate: IV Injection in a Mouse Magnus Karlsson, René Zandt, Pernille R. Jensen, Georg Hansson, Sven Månsson, Anna Gisselsson and Mathilde H. Lerche (2008) Experimental NMR Conference, Asilomar CA

17 Second Dimension Offers Improved Resolution of Metabolites HSQC of Glucose

18 2nd Dimension Normally Collected a Point at a Time t1 t1 FT ν1 ν2 ν2

19 Ultra-Fast HSQC 2D in 1s Mishkovsky and Frydman, ChemPhysChem, 9: (2008) Chirp Chirp Mix RF ω 1 ω 2 τ 1 τ 2 Gradients Δ Observe (echo-planar) Z t 1 t 1 t 1 t 1 t 1 t 1 t 1 t 1 For each chemical shift, ω 1 = zgγ + Ω; ω 2 = -zgγ + Ω ω 1 = c τ 1 ; ω 2 = c τ 2 ; τ 1 + τ 2 = 2Ω/c; Δ - τ 1 + τ 2 = n/ Ω Therefore each element in tube has unique chemical shift inversion spatial encoding t 2

20 1 Sec 2D HSQC Taken with Ultra-Fast Sequence DNP polarization enhanced M. Mishkovsky and L. Frydman. (2000) Ann. Rev. Phys. Chem. 60: