Probing the Structure and Dynamics of Hydrogen Bonds and Aromatic Pi-Pi Interactions by Solid-State NMR. Steven P. Brown

Transcription

1 Probing the Structure and Dynamics of ydrogen Bonds and Aromatic Pi-Pi Interactions by Solid-State MR Steven P. Brown Department of Physics University of Warwick

2 Solution-State MR Chemical Shift Differentiation of Chemically or Crystallographically Distinct Sites J Coupling Identification of Through-Bond Connectivities ppm

3 Solid-State MR: Anisotropic Interactions The resonance frequency of a given nucleus within a particular crystallite depends on the orientation of the crystallite For a powdered sample, anisotropic broadening is observed

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

5 Relative Magnitudes of Solid-State MR Interactions Dipolar Couplings 13C- 1 = 23 kz (directly bonded C pair) 1-1 = 20 kz (C 2 group) 13C- 13 C = 3 kz (directly bonded CC pair) Chemical Shift Anisotropy 13C = 9 kz (carbonyl group, at 500 Mz) Isotropic Chemical Shift Range 1 = 20 ppm = 10 kz (at 500 Mz) 13C = 200 ppm = 25 kz (at 500 Mz) J Couplings 15-1 = 90 z (directly bonded pair) 13C- 13 C = 35 z (directly bonded aliphatic CC pair)

6 igh-resolution Solid-State MR Magic-Angle Spinning 13 C MAS 5 kz B ν r MAS 5 kz MAS 30 kz L-alanine CRAMPS ppm

7 Double-Quantum Coherence An isolated spin I = 1/2 nucleus A through-space dipolar-coupled pair of spin I = 1/2 nuclei ω D The observable (SQ) spectrum m = + 1/2 m = 1/2 m = ±1 ω 0 Single- Quantum coherence M = + 1 M = 0 M = 1 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 MR 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 1 ) Conversion to SQC Acquisition of FID (t 2 )

8 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

9 Recovering the 13 C- 13 C J Coupling L-alanine MAS (30 kz) 1 decoupling (TPPM) 13 C 13 C J coupling is observed CO 1 1 dipolar coupling 13 C 13 C dipolar coupling ppm 1 13 C 13 C 1 13 C 1 13 C 13 C J coupling C C CSA 13 C 1 J coupling 13 C 1 dipolar coupling ppm 13 C Chemical Shift / ppm

10 The Solid-State IADEQUATE Experiment Fyfe et al, JACS 112, 3264 (1990) Lesage et al, JACS 119, 7867 (1997) ζ ε ε' δ δ' γ β α CO 1 : CP TPPM CO C ζ C δ C ε C Cε' C γ δ' C α C β X, e.g. 13 C p = CP τ Only homonuclear J couplings are active during 2τ τ t 1 t 2 double quantum frequency (ppm) single quantum frequency (ppm) 40 Double-Quantum Coherence is created for J-coupled nuclei through-bond connectivites are traced out

11 ydrogen-bond Mediated J-Couplings: Solution-State MR of Biomacromolecules Watson-Crick Base Pairs The Secondary Structure of Proteins 13 C O 13 C' O 13 C' residue i 13 C residue j 3h J C' = 0-1 z 2h J = 7-10 z 1h J = 2-4 z Dingley & Grzesiek JACS 120, 8293 (1998) Cordier and Grzesiek, JACS 121, 1601 (1999) Cornilescu et al, JACS 121, 2949 (1999) The hydrogen-bond mediated J couplings depend on the hydrogen-bonding distances and geometries, and are also correlated with the 1 chemical shifts.

12 Is it Possible to Observe ydrogen-bond Mediated J-Couplings in the Solid State? 3' 4' C ' 9 1' 4' 9 3' 1 solution (CDCl 3 ) (Claramunt et al Angew. Chem. 40, 420): 3' 4' 1' 1 J = 11.8 z 9 2h J = 8.6 z The homonuclear J couplings are not resolved in the 15 CP-MAS spectrum ppm 15 Chemical Shift / ppm (relative to nitromethane)

13 The Spin-Echo Experiment and Refocused Linewidths The spin-echo experiment CP τ τ +1 p = 0 1 All terms that appear as offsets (due to e.g. a chemical shift distribution or imperfect decoupling) are refocused (i.e., removed) Earl & Vanderart JACS 102, 3251 (1980) Cowans & Grutzner JMR A105, 10 (1993) Refocused linewidths as small as a few z are observed. Lesage, Bardet, & Emsley, JACS 121, (1999)

14 15 IADEQUATE Spectra CPMAS 3' 4' 9 1' 1 1 C 6 5 1D IADEQUATE Double-Quantum Frequency ppm Single-Quantum Frequency 200 ppm 15 Chemical Shift 2D IADEQUATE 9 1 1' ' Direct Detection of a Solid-State ydrogen Bond Brown et al, JACS 124, ' 4'

15 omonuclear J Spectroscopy The spin-echo experiment p = 0 1 CP τ τ intensity / a.u S(τ) = A exp( 2τ / T 2 ) τ Kubo & McDowell JCP 92, 7156 (1990) Wu & Wasylichen Organometallics 11, 3242 (1992) intensity / a.u S(τ) = A exp( 2τ / T 2 ) cos(2π J τ) For a series of rotor-synchronised τ values, measure the integrated intensity (after Fourier transformation) for a given resonance 0.5 (1/4J) (3/4J) (5/4J) Zero crossings at: 2π J τ = (2n-1) (π/2) τ

16 omonuclear J Spectroscopy: Measuring omonuclear J Couplings one J-coupled neighbour two J-coupled neighbours: fit to fit to A exp( 2τ / T 2 ) cos(2π J τ) A exp( 2τ / T 2 ) cos(2π J 1 τ) cos(2π J 2 τ) 1 C C 6 5 intensity / a.u ' 3' 4' intensity / a.u ' 3' 4' τ / ms T 2 = 248 ± 15 ms FWM = 1.3 z 1 J(9,1') = 11.9 ± 0.1 z τ / ms T 2 = 194 ± 15 ms FWM = 1.6 z 1 J(9,1') = 12.0 ± 0.1 z 2h J( ) = 7.2 ± 0.1 z

17 The Determination of J Couplings Triazole derivative in solution (CDCl 3 ): J = 11.8 z J = 8.6 z intensity / a.u J = 11.9 ± 0.1 z τ / ms 1 9 C 6 5 1' 3' 4' intensity / a.u J = 7.4 ± 0.1 z τ / ms 9 C 6 5 1' 3' 4' intensity / a.u J = 12.0 ± 0.1 z τ / ms 1 9 C 6 5 1' 3' 4' J = 7.2 ± 0.1 z Pyrrole derivative in solution (CDCl 3 ): J = 10.3 z J = 9.0 z intensity / a.u J = 10.3 ± 0.1 z τ / ms 1 9 C 6 5 1' intensity / a.u J = 8.1 ± 0.2 z τ / ms 1 9 C 6 5 1' intensity / a.u J = 10.2 ± 0.4 z τ / ms 1 9 C 6 5 1' J = 8.0 ± 0.3 z

18 1 MAS MR of an Alkyl-Substituted exabenzocoronene Derivative C 12 D 2 23 MAS at 35 kz A B C 23 D 2 C 12 C 12 D Mz (11.8 Tesla) solid phase (T = 60 C) 23 D 2 C 12 C 12 D 2 23 C 12 D 2 23 exabenzocoronene (BC) derivatives possess very high 1D charge carrier mobilities because of the overlap of the π orbitals due to the polyaromatic cores ppm liquidcrystalline phase (T = 110 C) In solution (CDCl 3 ), there is a single aromatic 1 resonance with a concentration-dependent chemical shift between 8.0 and 8.9 ppm

19 1 DQ MAS MR of an Alkyl-Substituted exabenzocoronene Derivative MAS at 35 kz 500 Mz (11.8 Tesla) solid phase (T = 60 C) A B C C 12 D D 2 C 12 C 12 D D 2 C 12 C 12 D 2 23 C 12 D 2 23 two types of pairs: C A C B double-quantum dimension A B and C C 20 in a ratio 2: ppm single-quantum dimension

20 The Packing of the Aromatic Cores in exabenzocoronene A B C C B A The staggered arrangement of the aromatic cores leads to three different chemical shifts, because of the different ring current effects A B B A shielded (low ppm) erring-bone arrangement optimises pi-pi packing C C deshielded (high ppm)

21 DQ MAS Spinning-Sideband Patterns double-quantum D.τ exc double-quantum ppm single-quantum single-quantum ω/ω R

22 DQ MAS Spinning-Sideband Patterns 1 DQ MAS spinning-sideband patterns are very sensitive to the dipolar coupling solid phase MAS at 35 kz τ exc = 57 µs LC phase MAS at 10 kz τ exc = 200 µs ω/ω R fast rotation about columnar axis: reduction of dipolar coupling by 0.5 best-fit simulations: Solid phase: D = 15.0 ± 0.9 kz LC phase: D = 6.0 ± 0.5 kz LC order parameter S = 0.80 ± 0.08

23 1 (700 Mz) MR of a Molecular Tweezer DQ MAS spectrum 1 2 C C ppm MAS at 30 kz double-quantum dimension ppm ppm single-quantum dimension

24 1-13 C (700 Mz) Correlation Spectrum of a Molecular Tweezer One-bond (C-) correlations MAS at 30 kz C C chemical shift ppm ppm 1 chemical shift 13 C chemical shift

25 Ring Current Effects on the Guest View A Ab initio 1 chemical shift calculations GIAO-F/TZP//F/6-31G* View B C C vac- View View View vacuum full uum A B C sum calc. a b View C (Ochsenfeld et al, Solid State MR 22, 128, 2002) a b b b a a View A View B View C

26 Probing the Guest Dynamics C C Temperaturedependent changes in slices from 1 DQ MAS spectra T/K ppm -6 Upon heating, the two 1 guest aromatic resonances coalesce because of guest dynamics ppm 367 b a b a b ppm

27 1 (700 Mz) MR of Bilirubin O O C O O C 2 O responsible for jaundice in new-born babies insoluble in aqueous solution, because of strong intramolecular hydrogen bonding DQ MAS spectrum O 1 2 O C ppm 8 MAS at 30 kz O ppm ppm

28 1 (700 Mz) DQ MAS Spinning-Sideband Patterns for Bilirubin MAS at 30 kz O O C O O C 2 O τ exc 67 µs O C τ exc 100 µs Fitting to the experimental DQ MAS spinning-sideband patterns allows the accurate determination of τ exc 133 µs 186 ± 2 pm ω/ω R

29 Acknowledgements ans W. Spiess, Max-Planck-Institute for Polymer Research, Mainz, Germany ( ) Lyndon Emsley, Ecole ormale Superieure de Lyon, France ( ) ydrogen-bond Mediated J couplings: Rosa Claramunt, Marta Perez-Torralba, Dionisia Sanz (UED, Madrid, Spain) exabenzocoronenes: Klaus Muellen, Johann Diedrich Brand, Ingo Schnell (MPI-P, Mainz, Germany) Molecular Tweezers: Frank-Gerrit Klaerner, Torsten Schaller, Uta P. Seelbach (Essen, Germany) Christian Ochsenfeld, Felix Koziol (Tuebingen, Germany) Bilirubin: Xiao Xia Zhu (Montreal, Canada) Alexander von umboldt-stiftung (January December 1999) Marie Curie Fellowship (PMFCT ) (January September 2002) EPSRC Advanced Research Fellowship (October 2002-)

30 Papers ydrogen-bond Mediated J couplings: Brown et al, J. Am. Chem. Soc. 124, 1152 (2002) Brown et al, Chem. Comm (2002) exabenzocoronenes: Brown et al, J. Am. Chem. Soc. 121, 6712 (1999) Molecular Tweezers: Brown et al, Angew. Chem. Int. Ed. 40, 717 (2001) Ochsenfeld et al, Solid State MR 22, 128 (2002) Bilirubin: Brown et al, J. Am. Chem. Soc. 123, 4275 (2001) Review: Brown et al, Chem. Rev. 101, 4125 (2001)