Probing Hydrogen Bonding by Solid-State NMR. Steven P. Brown

Transcription

1 Probing ydrogen Bonding by Solid-State M Steven P. Brown

2 Solution-State M: Isotropic Interactions Fast isotropic tumbling of the molecules averages to zero all anisotropic broadening Chemical Shift Differentiation of Chemically or Crystallographically Distinct Sites J Coupling Identification of Through-Bond Connectivities ppm

3 Solid-State M: Anisotropic Interactions Dipolar Coupling Chemical Shift Anisotropy Quadrupolar Coupling Electronic Structure and Bonding Internuclear Proximities and Distances Motional Processes

4 The dipolar coupling: An anisotropic interaction k θ B 0 θ = 0 θ = 35 j θ = 54. θ = 90 D = D c 2 (3 cos2 θ ) D c γ j γ k r 3 powder

5 elative Magnitudes of Solid-State M Interactions Dipolar Couplings 3C- = 23 kz (directly bonded C pair) - = 20 kz (C 2 group) 3C- 3 C = 3 kz (directly bonded CC pair) Chemical Shift Anisotropy 3C = 9 kz (carbonyl group, at 500 Mz) Isotropic Chemical Shift ange = 20 ppm = 0 kz (at 500 Mz) 3C = 200 ppm = 25 kz (at 500 Mz) J Couplings 5- = 90 z (directly bonded pair) 3C- 3 C = 35 z (directly bonded aliphatic CC pair)

6 A spectrum of a typical organic solid 25 kz

7 Magic-Angle Spinning (MAS) B0 54. νr

8 Magic-Angle Spinning (MAS) static ν r = 0 B ν r increasing ν r

9 igh-esolution Solid-State M Magic-Angle Spinning 3 C MAS 5 kz B ν r MAS 5 kz MAS 30 kz L-alanine CAMPS ppm

10 Combined otation and Multiple-Pulse Spectroscopy + Physical otation in otation Spin Space B rf nutation frequency ν r rf offset 54. Magic-Angle Spinning The Lee-Goldburg Condition

11 Structure Determining on-covalent Interactions: ydrogen Bonding C C C Solid-state packing is controlled by inter/intramolecular interactions, notably hydrogen bonding

12 Probing Structure-Determining on-covalent Interactions Proton-Proton proximities: DQ spectroscopy Weak hydrogen bonds: chemical shift ydrogen-bond mediated J couplings

13 Double-Quantum Coherence An isolated spin I = /2 nucleus A through-space dipolar-coupled pair of spin I = /2 nuclei ω D The observable (SQ) spectrum m = + /2 m = /2 m = ± ω 0 Single- Quantum coherence M = + M = 0 M = ω 0 ω D /2 ω 0 + ω D /2 SQ, DQ SQ (Also applies to a throughbond J-coupled spin pair) Double-Quantum (DQ) ( m = ±2) coherences cannot be directly observed in an M experiment, but they can be indirectly probed by a 2D experiment ω 0 A single resonance at the Larmor frequency Excitation of DQC Evolution of DQC (t ) Conversion to SQC Acquisition of FID (t 2 )

14 A Two-Dimensional Double-Quantum Spectrum To a first approximation, the signal intensity is proportional to the dipolar coupling squared (double-quantum coherences must be both excited and reconverted), i.e., the signal intensity is inversely proportional to the internuclear distance to the sixth power. Therefore, a DQ peak is only observed if there is a close proximity of the involved protons. B A A B B A A B ω A ω B single-quantum dimension ω A + ω A ω A + ω B ω B + ω B double-quantum dimension

15 igh-esolution Identification of - Proximities DQ CAMPS 2.5 kz MAS 3 + C C C C C C 2 C 3 DQ MAS 30 kz MAS (500 Mz) Proton Double-Quantum Frequency (ppm) Proton Double-Quantum Frequency (ppm) Proton Single-Quantum Frequency (ppm) Proton Single-Quantum Frequency (ppm)

16 DQ CAMPS π θ θ θ 2 θ 2 2 acq PST-C edumb- 22 DUMB- PST-C p = t t 2 n PST C ohwy et al, J. Chem. Phys. 998, 08, 2686 DUMB Sakellariou et al, Chem. Phys. Lett. 2000, 39, 253 edumb- 22 Elena et al, Chem. Phys. Lett. 2004, 398, 532 windowed DUMB- Lesage et al, J. Magn. eson. 2003, 63, 05 DQ CAMPS Brown et al, J. Am. Chem. Soc 2004, 26, 323

17 Pseudo-polymorphism in Pharmaceuticals ydrogen bonded ydrogen bonded 0 anhydrate 0 monohydrate 4 4 DQ ppm DQ 20. ppm SQ ppm DQ 8.0 ppm SQ ppm DQ CAMPS M: Brown et al, J. Am. Chem. Soc 2004, 26, Mz, MAS 2.5 kz, 30 mg sample, experimental time 05 mins DQ CAMPS M spectra of anhydrous and hydrous drug samples reveal different - contacts Different hydrogen-bonding in the two pseudo-polymorphs changes the chemical shift of the hydrogen-bonded proton

18 Pseudo-polymorphic Form of the API in Stressed Tablets * * * 0 4 anhydrate DQ ppm DQ ppm DQ 20. ppm Pure Anhydrate SQ ppm DQ 20. ppm Stressed Tablet 0 monohydrate SQ ppm Crushed tablet stressed at 40 C, 5% humidity for week DQ CAMPS M confirms no change in pseudo-polymorphic form DQ ppm DQ 8.0 ppm Pure ydrate SQ ppm

19 Probing Structure-Determining on-covalent Interactions Proton-Proton proximities: DQ spectroscopy Weak hydrogen bonds: chemical shift ydrogen-bond mediated J couplings

20 Weak ydrogen Bonding C I spectroscopy: C stretching frequency of,3,5-trichlorobenzene lowered by 35 cm upon adding pyridine, due to C-... weak hydrogen bonding Single-Crystal Diffraction: Statistical Analysis of crystal structures in databases, e.g., probing C-... contacts in small molecules, and more recently proteins Solution-State M: Downfield shift of C ε - proton chemical shift of ~0.6 to 0.8 ppm for the catalytic histidine in a serine protease h3j CαC couplings of 0.2 to 0.3 z across Cα-α...=C hydrogen bonds in protein β-sheet Is a C... close proximity indicative of a bonding interaction, or simply a chance consequence of a packing arrangement that is determined by other interactions?

21 Weak ydrogen-bonding: Uracil t 2 π/2 Excitation t econversion 2.84 Å τ /2 τ /2 τ /2 τ / Å 2 n n X- X- Conventional - ydrogen bond 3.2 Å Å bond distance bond angle C Weak C- ydrogen bond p = DQ ppm Planes within crystal structure - MAS 40 kz Samoson.8 mm probe (600 Mz) SQ ppm

22 Probing intermolecular weak C... hydrogen-bonding by first-principles calculations DQ ppm intermolecular effects on chemical shifts: hydrogen bonding aromatic ring currents 2.84 Å SQ ppm 2.83 Å Å Å C- C- Experimental esults Atom 4 δ ppm First principles chemical shift calculations (CASTEP) Isolated ptimised Full Isolated Isolated Molecule Difference Crystal Structure Plane Molecule relaxed Plane - molecule δ ppm δ ppm δ ppm δ ppm δ ppm Uldry et al, JACS 30, 945, 2008

23 Probing Structure-Determining on-covalent Interactions Proton-Proton proximities: DQ spectroscopy Weak hydrogen bonds: chemical shift ydrogen-bond mediated J couplings

24 ydrogen-bond Mediated J-Couplings: Solution-State M of Biomacromolecules Watson-Crick Base Pairs The Secondary Structure of Proteins 3 C C' 3 C' residue i 3 C residue j 3h J C' = 0- z 2h J = -0 z h J = 2-4 z Dingley & Grzesiek JACS 20, 8293 (998) Cordier and Grzesiek, JACS 2, 60 (999) Cornilescu et al, JACS 2, 2949 (999) The hydrogen-bond mediated J couplings depend on the hydrogen-bonding distances and geometries, and are also correlated with the chemical shifts.

25 5 efocused IADEQUATE: Identification of Intermolecular ydrogen Bonding 5 C 2 dgc3 9 C Lesage et al: JACS 2, 098 (999) 5 double-quantum dimension [ppm] single-quantum dimension [ppm] Pham et al: JACS 2, 608 (2005) CP CP TPPM decoupling t τ τ τ τ TPPM decoupling theoretical description demonstrates that DQ correlation peaks are indeed indicative of a J coupling (if the two isotropic chemical shifts of the two nuclei are different and the MAS frequency is far from rotational resonance) Fayon et al: JCP 22, 9433 (2005) t 2

26 5 efocused IADEQUATE: Identification of Intermolecular ydrogen Bonding G-ribbon 5 double-quantum dimension[ppm] single-quantum dimension [ppm] C 9 5 double-quantum dimension[ppm] C dgc single-quantum dimension [ppm] G-quartet

27 ydrogen-bond Mediated J Couplings in Solid-State M linewidths (~50 z) in 5 CP MAS spectrum are significantly greater than the J couplings (< 0 z) ppm 5 C 2 9 C In a spin-echo experiment, all terms that appear as offsets (due to e.g. a chemical shift distribution) are refocused CP τ 2 T 2 T 2 * τ 2 {{ + p = 0 The spin-echo linewidth (corresponding to T 2 ) is usually much narrower than the MAS linewidth (corresponding to T 2 *)

28 The Quantitative Determination of J Couplings + The spin-echo experiment CP τ 2 T 2 ' T 2 * τ 2 {{ intensity / a.u S(τ) = A exp( τ / T 2 ') τ p = 0.0 Kubo & McDowell JCP 92, 56 (990) Wu & Wasylichen rganometallics, 3242 (992) intensity / a.u (/2J) (3/2J) (5/2J) S(τ) = A exp( τ / T 2 ') cos(π J τ) τ theoretical description demonstrates that a J coupling between a pair of nuclei can be accurately determined by a MAS spin-echo experiment even in the presence of stronger anisotropic interactions (i.e., CSA, dipolar couplings) Duma et al: ChemPhysChem 5,85 (2004)

29 ydrogen-bond Mediated J Couplings: Quantifying ydrogen-bond Strength 0.8 Molecule 2h J b,a = 6.2 ± 0.4 z 5 C S(τ) / normalized units Molecule 2h J a,b =.4 ± 0.4 z C ~ 5 chemical shift / ppm ~ τ / ms dgc3 X-ray single-crystal structure two molecules per asymmetric unit cell C a b 2.88 Å ~ 2.8 Å a b Pham et al: PCCP 9, 346 (200)

30 First Principles Calculation of J Couplings Density Functional Theory (DFT) calculations within CASTEP, using plane-wave basis sets (applicable to periodic crystals) and pseudopotentials 5 C 2 9 C experimental 2 J 9,3 = 4.3 ± 0.2 z calculated 2 J 9,3 = 4.2, 4.4 z ~ ~ experimental 2h J a,b =.4 ± 0.4 z experimental 2h J b,a = 6.2 ± 0.4 z a b 2.88 Å 2.8 Å b a calculated 2h J a,b =. z calculated 2h J b,a = 6.5 z ~

31 Probing Structure-Determining on-covalent Interactions Proton-Proton proximities: DQ spectroscopy Weak hydrogen bonds: chemical shift ydrogen-bond mediated J couplings

32 Solid-State M at 850 Mz: A World-leading UK Facility to deliver Advances in Materials Science, Chemistry, Biology, Earth Science and Physics expected to be operational Summer 2009 to be sited in the new Magnetic esonance Centre, University of Warwick

33 Acknowledgements Tran Pham, John Griffin, Amy Webber Dave Martin Bénédicte Elena, Anne Lesage, Lyndon Emsley Stefano Masiero & Giovanni Gottarelli Claudiu Filip Paul odgkinson Jonathan Yates Chris J. Pickard, Anne-Christine Uldry Sian Joyce Warwick, U.K. Astra Zeneca. U.K. Lyon, France Bologna, Italy Cluj, omania Durham, U.K. Cambridge, U.K. St Andrews, U.K. Cork, Ireland