Interferogram and real-time acquisition methods

Transcription

1 Interferogram and real-time acquisition methods Peter Kiraly NMR Methodology Group, School of Chemistry, University of Manchester Workshop on Pure Shift NMR 2 th Sep 207

2 Outline Why are we interested in decoupling? Basic concepts in pure shift NMR Active and passive spins Active spin refocusing elements: BS / Zangger-Sterk / PSYCE / BIRD The interferogram acquisition method Theory and pulse sequences Illustrative examples The real-time acquisition method Theory and pulse sequences Illustrative examples Summary 2

3 Suppressing multiplet structure heteronuclear decoupling C proton coupled 3 C-{ } proton decoupled Partial 3 C NMR spectrum of estradiol in DMSO-d 6 with (bottom) and without (top) proton decoupling 3

4 Suppressing multiplet structure homonuclear decoupling NMR of glucose in D 2 O pure shift conventional Partial NMR spectrum of glucose in D 2 O 4

5 The concepts of spin decoupling 3 C eteronuclear decoupling WALTZ / GARP / adiabatic bi-level time / s omonuclear decoupling? pure shift time / s. time management 2. selectivity problem 5

6 Active and passive spins in pure shift NMR pure shift conventional 50 mm quinine in dmso-d 6 6

7 ASR - Active Spin Refocusing - elements Magn. Reson. Chem. 35, 9 (997) J. Magn. Reson. 24, 486 (997) Angew. Chem. Int. Ed. 53, 6990 (204) Chem. Phys. Lett. 93, 504 (982) BS Zangger-Sterk PSYCE BIRD frequency selective RSNOB pulse frequency selective RSNOB pulse Small flip angle CIRP pulses G z G z 3 C/ 5 N all work by differentially manipulating active and passive subpopulations of protons 7

8 ASR - Active Spin Refocusing - elements Magn. Reson. Chem. 35, 9 (997) J. Magn. Reson. 24, 486 (997) Angew. Chem. Int. Ed. 53, 6990 (204) Chem. Phys. Lett. 93, 504 (982) BS Zangger-Sterk PSYCE BIRD multiple frequency RSNOB pulse multiple frequency RSNOB pulse Small flip angle CIRP pulses G z G z 3 C/ 5 N all work by differentially manipulating active and passive subpopulations of protons 8

9 Double spin echo experiment with an ASR element excitation 90 pulse broadband 80 pulse active spin refocusing 80 pulse 4τ chunk acquisition chemical shift is refocused at the beginning of acquisition, but J-evolution is negligible during the first few data points (period 4τ ) delivering a small chunk of the desired pure shift FID homonuclear coupling (J) is refocused 2τ later 9

10 Interferogram pure shift experiment 2D acquisition pure shift FID analogous to 2D NMR 0 / sw 0 / sw J-refocus G z G z 0.5 / sw 0.5 / sw J-refocus J << δ allows data acquisition in chunks of duration /sw G z t /2 J-refocus t /2 0

11 The interferogram pure shift pulse sequence excitation 90 pulse drop points delay broadband 80 pulse active spin refocusing 80 pulse chunk acquisition Chemical shift is refocused = [integer] / sw later than the beginning of acquisition J is refocused at the midpoint of each chunk (4τ ) Incremented delay allows recording all chunks of pure shift FID (during t δ evolves, but J is refocused) Phase cycle and/or PFG pairs can enforce CTP selection

12 The triple spin echo analogue with an ASR element drop points delay excitation 90 pulse broadband 80 pulse active spin refocusing 80 pulse broadband 80 pulse chunk acquisition Frequency-swept broadband pulses can be implemented Useful to deal with strong coupling artefacts e.g. in TSE-PSYCE Duration of the chunk is not limited by duration of gradient pulses, but more relaxation loss 2

13 Resolution in interferogram pure shift experiments line-width at half height 3.8 z number of chunks 6 duration of the complete interferogram (pure shift acquisition time) 0.3 s 2.2 z s.5 z 64.2 s Interferogram band-selective pure shift spectra of an AX spin system calculated in Matlab/Spinach. (20 ms chunk duration; J AX = 0 z) 3

14 Effect of duration of chunk (SW ) side-bands peak height <4 % 25 z pure shift peak height 94 % duration of chunk /SW (SW ) 40 ms (25 z) number of chunks (TD) 32 < % 50 z 99 % 20 ms (50 z) 64 <0.2 % 00 z 00 % 0 ms (00 z) 28 Interferogram band-selective pure shift spectra of an AX spin system calculated in Matlab/Spinach. (AQ =.3 s; J AX = 0 z) 4

15 Effect of RF phase instability (scan-to-scan) phase irreproducibility ±0 ± ±3 analogous to t -noise in 2D NMR interleaved 2D data acquisition is advisable for long experiments ±5 Interferogram band-selective pure shift spectra of an AX spin system calculated in Matlab/Spinach. (AQ =.3 s; J AX = 0 z; SW = 50 z) 5

16 Speeding things up interferogram approach real-time approach J. Magn. Reson. 24, 486 (997) Pure shift FID a set of experiments st experiment 2 nd experiment single experiment J. Magn. Reson. 28, 4 (202) 3 rd experiment 4 th experiment 6

17 Prototype pulse sequence of real-time pure shift NMR Chunks are collected from a single scan Resolution is worse compared to interferogram experiment, because of relaxation, diffusion/convection, and cumulative errors of pulse imperfection 7

18 Relaxation losses in real-time experiments SQC sequence elements [ ] acquisition J-refocus acquisition n τ r τ r line-width at half height Selected traces of real-time pure shift SQC BIRD. The total echo time (τ r ) of the J-refocusing element was incremented. Broadening here is due to proton T 2 relaxation. 8

19 Effect of BIRD timing error BIRD If τ = / (2 * J C ), then BIRD element refocuses the 3 C-attached protons. Selected traces of real-time pure shift SQC BIRD ( C = 90 z). The echo time (τ) of the BIRD element was varied (SQC sequence element was kept constant). Broadening here is due to BIRD timing error. 9

20 Effect of pulse imperfection in real-time pure shift SQC using BIRD Gradient pulses omitted, basic phase cycle, and no supercycle 2 nd carbon 80 pulse is omitted in BIRD G -4 varied chunk-to-chunk extended phase cycle (*2), and MLEV-6 supercycle extra signals next to the pure shift signal and F mirror images extra signals appear due to heteronuclear J-evolution during τ 2 clean 20

21 5 N SQC of L80C mutant N-PGK protein in water (90% 2 O / 0%D 2 O) 5 N SQC pure shift 5 N SQC N-terminal domain of PGK J. Biomol. NMR. 62, 43 (205) 2

22 0 mg amikacin in D 2 O pure shift 3 C SQC 3 C SQC 22

23 Mixture of glucose, trehalose, raffinose, and α-cyclodextrin 3 C SQC pure shift 3 C SQC 23

24 Interferogram vs real-time pure shift NMR experiment time conventional 0.5 min interferogram Zangger-Sterk real-time Zangger-Sterk 5 min 30 s 0.5 min 50 mm quinine in dmso-d 6 24

25 Summary Interferogram experiments Resolution enhancement requires extended experiment time There is a trade-off between experiment time and quality of spectrum Many kinds of active spin refocusing element are available System instability may affect very high resolution experiments Real-time acquisition Experiment times of parent and pure shift methods are practically identical Simultaneous sensitivity and resolution enhancement in real-time SQC using BIRD Resolution enhancement is limited by relaxation, diffusion/convection, and pulse imperfection Lock disturbance can be a problem in high resolution experiments 25

26 Acknowledgements Gareth Morris, Mathias Nilsson and the NMR Methodology Group Funding

27 A Pure Shift NMR Workshop.00 Gareth Morris Welcome, introduction and history.30 Peter Kiraly Interferogram and real-time acquisition methods 2.00 Laura Castañar Zangger-Sterk and band-selective methods 2.30 Mohammadali Foroozandeh PSYCE 3.00 Lunch and poster session 4.00 Ralph Adams Other pure shift and related methods 4.30 Mathias Nilsson Practical implementations 5.00 Adolfo Botana JEOL pure shift implementation 5.0 Vadim Zorin MestreNova pure shift implementation 5.20 Ēriks Kupče Bruker shaped pulse implementation 5.30 Question and answer session University of Manchester, 2 th September 207