by Dieter Freude and Jörg Kärger, Institut für Experimentelle Physik der Universität Leipzig

1. MAS PFG NMR, Magic-Angle Spinning Pulsed Field Gradient Nuclear Magnetic Resonance,a New Tool for Diffusometry of Interface Materials • by Dieter Freude and Jörg Kärger, Institut für Experimentelle Physik der Universität Leipzig rotor with sample in the rf coil zr B0 = 9  21 T rot  10 kHz θ gradient coils forpulsed field gradients, maximum 1 T / m

2. B z B B B z z z 0 0 0 0 y y y y 5 1 4 2 M M x x 3 3 1 2 5 4 x x Introduction to pulsed field gradient NMR Spin recovery by Hahn echo without diffusion of nuclei: p p /2 r.f. pulse t gradient pulse t gmax = 25 T / m d free induction Hahn echo y magnetization t D D

3. p/2 p p/2 p/2 p/2 p p/2 rf pulses free induction decay t t t t g gradient pulses d d tecd  PFG NMR, signal decay by diffusion of the nuclei Pulsed field gradient NMR diffusion measurements base on NMR pulse sequences generating a spin echo, like the Hahn echo (two pulses) or the stimulated spin echo (three pulses). At right, the 13-intervall sequence for alternating gradients consisting of 7 rf pulses, 4 gradient pulses of duration , intensity g, observation time  and 2 eddy current quench pulses is described. The self-diffusion coefficient D of molecules in bulk phases, in confined geometries and in biologic materials is obtained from the amplitude S of the free induction decay in dependence on the field gradient intensity g by the equation

4. High-resolution solid-state MAS NMR Fast rotation (1-60 kHz) of the sample about an axis oriented at 54.7° (magic-angle) with respect to the static magnetic field removes all broadening effects with an angular dependency of zr B0 rot θ Chemical shift anisotropy,internuclear dipolar interactions,first-order quadrupole interactions, and inhomogeneities of the magnetic susceptibility are averaged out. It results an enhancement in spectral resolution by line narrowing for solids and for soft matter. The transverse relaxation time is prolonged.

5. zr B0 MAS PFG NMR for NMR diffusometry Application of MAS technique in addition to PFG improves drastically the spectral resolution. This allows the study of multi-component diffusion in confined geometry or soft matter. θm CH (iso) 3 CH (n - but) 3 = 0.4 ppm δ Δ but) CH (n - 2 ωr = 0 kHz CH (iso) gradient ωr = 1 kHz * * * * * * strength 4 2 0 -2 d / ppm δ = 0.02 ppm ωr = 10 kHz 1.0 2.0 d / ppm 2.0 1.5 1.0 0.5 d / ppm FAU Na-X , n-butane + isobutane Δδ

6. CH3 (n-butane) 10-9 CH3 (isobutane) 10-10 CH2 (n-butane) D / m2s-1 10-11 isobutane CH (isobutane) mixtures n-butane 10-12 0.0 0.2 0.4 0.6 0.8 1.0 n-butane molecules per intersection d/ ppm 1.0 2.0 gradient strength The self-diffusion coefficient of n-butane, isobutane, and mixtures of both adsorbed in silicalite-1 were measured. It was shown that the diffusion coefficient of n-butane mixed with isobutane in silicalite-1 decreases with increasing amount of isobutane. Mixture diffusion in zeolite silicalite-1 The figure presents a discontinuity at 0.6 n-butane molecule per channel intersection due to the blocking effect of isobutane molecules in interchannel sites. M. Fernandéz, J. Kärger, D. Freude, A. Pampel, J. M. van Baten, R. Krishna, Mixture diffusion in zeolites studied by MAS PFG NMR and molecular simulation, Microporous and Mesoporous Materials 105 (2007) 124-131.

7. octane CH2 CH3 acetone CH3 gradient strength 2.8 2.4 2.0 1.6 1.2 0.8 0.4 (ppm) 1 0 S / 0,1 S nonane C 9 octane C 8 heptane C 7 hexane C 6 0,01 0,00 0,05 0,10 0,15 0,20 0,25 2 2 -2 g / T m MAS PFG NMR studies of the self-diffusion of acetone-alkane mixtures in nanoporous glass The self-diffusion coefficients of mixtures of acetone with several alkanes were studied by MAS PFG NMR. Glasses with different nanopore sizes of 4 and 10 nm and a pore surface modified with trimethylsilyl groups were loaded with acetone –alkane mixtures (1:10). Stack plot of the 1H MAS PFG NMR spectra at 10 kHz of the 1:10 acetone and octane mixture absorbed in 4-nm-glass as function of increasing pulsed gradient strength for a diffusion time D = 600 ms. Semi-logarithmic plot of the decay of the acetone CH3 signal in binary mixtures with alkane in 4-nm-glass at 298 K. The diffusion time isD = 600 ms and the gradient pulse length is d = 2 ms.

8. -11 1,4x10 D % ( = 600 ms) D % ( = 800 ms) D % ( = 1200 ms) -11 1,2x10 -1 s 2 / m -11 D 1,0x10 -12 8,0x10 6 7 8 9 10 Carbon number of alkane solvent Zigzag effect of the self-diffusion of acetonein 4-nm-nanoporous glass Diffusion coefficient of acetone in mixture within 4-nm-glass in dependence on the number of carbons in the alkane solvent. The measurements were carried out with diffusion timeD= 600 ms, D = 800 ms and D = 1200 ms and the gradient pulse length d= 2 ms. The self-diffusion coefficients of acetone shows a zigzag effect depending on odd or even numbers of carbon atoms of the alkane solvent in the small pores (4 nm), but not in the larger pores (10 nm). M. Fernandez, A. Pampel, R. Takahashi, S. Sato, D. Freude, J. Kärger, Revealing complex formation in acetone-nalkane mixtures by MAS PFG NMR diffusion measurement in nanoporous hosts, Phys. Chem. Chem. Phys. 10 (2008) 4165.

9. Studies of free and confined liquid crystals The chemical structure of 5CB (a). 1H MAS NMR spectra of 5CB confined in Bioran glasses with a pore diameter of 200 nm above (b) and below (c) the isotropization temperature Tc. isotrop nematic crystalline Tc = 308,5 K T = 297,2 K E. E. Romanova, F. Grinberg, A. Pampel, J. Kärger, D. Freude, Diffusion studies in confined nematic liquid crystals by MAS PFG NMR, J. Magn. Reson. 196 (2009) 110-114. Temperature dependence of the 1H MAWS NMR linewidth fwhm for bulk 5CB () and for 5CB confined in Bioran glasses with a pore diameter of 30 nm () and 200 nm (). Empty symbols correspond to the isotropic phase and full symbols correspond to the nematic / crystalline phase.

10. T / K 294 334 319 299 1 1 S / S0 D / 10 -10m2 s-1 • T = 334 K, 200-nm-Bioran T = 299 K, 200-nm-Bioran T = 334 K, 30-nm-Bioran D for T = 334 K D for T = 299 K isotropic phase nematic phase T = 299 K, 30-nm-Bioran 0.1 - 11 2 - 1 - 11 2 - 1 bulk phase 0.1 5.5 ´ 10 m s 2.9 ´ 10 m s - 11 2 - 1 - 11 2 - 1 11010 21010 31010 41010 51010 200 - nm - Bioran 0 4.8 ´ 10 m s 2.0 ´ 10 m s 3.0 3.1 3.2 3.3 3.4 - 11 2 - 1 - 11 2 - 1 30 - nm - Bioran 4.2 ´ 10 m s 2.7 ´ 10 m s k / sm-2 T -1 103 / K-1 Diffusion of free and confined liquid crystals 1H MAS PFG NMR spin echo attenuation Temperature dependence of the diffusion coefficient D of bulk 5CB () and of 5CB confined in Bioran glasses with pore diameter of 30 nm () and 200 nm ().The diffusivities were measured at 10 kHz rotation frequency, except three values for Bioran-200-nm, which were measured at 5 kHz () and without rotation (). Empty symbols correspond to the isotropic phase and full symbols correspond to the crystalline phase. It is found that the confinement of the liquid crystal 5CB in porous glasses with mean pore diameters of 30 and 200 nm does not notably change its self-diffusion behavior in comparison with the bulk state.

11. Jörg Kärger and Dieter Freude acknowledge contributions from Dr. Moisés Fernández Dr. Farida Grinberg Dr. André Pampel Dr. Ekaterina Romanova For request of reprints of the presentation and the three publications send E-mail to freude@uni-leipzig.de.

12. Diffusion Fundamentals III Basic Principles of Theory, Experiment and ApplicationAugust 23rd - 26th, 2009Athens, Greece In the biennial series of meetings devoted to the basic principles of diffusion theory, experiment and application, researchers from the interdisciplinary fields of diffusion are invited to exchange the most recent results of research, which are of general interest to the whole community. All presentations are scheduled to address a broad, interdisciplinary audience avoiding parallel sessions. Contributions will be presented at the web-site diffusion-fundamentals.org, especially in the Diffusion Fundamentals Online Journal.

13. References • Refererences to the first combined application of PFG NMR with MAS are: • H. C. Gaede, K. Gawrisch, Multi-dimensional pulsed field gradient magic angle spinning NMR experiments on membranes,Magnetic Resonance in Chemistry 42 (2004) 115-122. • P. Rousselot-Pailley, D. Maux, J. M. Wieruszeski, J. L. Aubagnac, J. Martinez, G. Lippens, Impurity detection in solid-phase organic chemistry: Scope and limits of HR MAS NMR,Tetrahedron 56 (2000) 5163-5167. • H. Schröder, High resolution magic angle spinning NMR for analyzing small molecules attached to solid support,J. Comb. Chem. 6 (2003) 741-753. • S. Viel, F. Ziarelli, S. Caldarelli, Enhanced diffusion-edited NMR spectroscopy of mixtures using chromatographic stationary phases,Proceedings of the National Academy of Sciences of the United States of America 100 (2003) 9696-9698. • A. Pampel, M. Fernandez, D. Freude, J. Kärger, New options for measuring molecular diffusion in zeolites by MAS PFG NMR,Chem. Phys. Lett. 407 (2005) 53-57. • A. Pampel, F. Engelke, P. Galvosas, C. Krause, F. Stallmach, D. Michel, J. Kärger, Selective multi-component diffusion measurement in zeolites by pulsed field gradient NMR,Microporous Mesoporous Mater. 90 (2006) 271-277. • Refrences to the three studies summarized in the present contribution are: • M. Fernandez, J. Kärger, D. Freude, A. Pampel, J. M. van Baten, R. Krishna, Mixture diffusion in zeolites studied by MAS PFG NMR and molecular simulation, Microporous and Mesoporous Materials 105 (2007) 124-131. • M. Fernandez, A. Pampel, R. Takahashi, S. Sato, D. Freude, J. Kärger, Revealing complex formation in acetone-nalkane mixtures by MAS PFG NMR diffusion measurement in nanoporous hosts, Phys. Chem. Chem. Phys. 10 (2008) 4165-4171. • E. E. Romanova, F. Grinberg, A. Pampel, J. Kärger, D. Freude, Diffusion studies in confined nematic liquid crystals by MAS PFG NMR, J. Magn. Reson. 196 (2009) 110-114.