Nuclear Magnetic Resonance in Modern Technology

Transcription

1 Nuclear Magnetic Resonance in Modern Technology

2 NATO ASI Series Advanced Science Institutes Series A Series presenting the results of activities sponsored by the NA TO Science Committee, which aims at the dissemination of advanced scientific and technological knowledge, with a view to strengthening links between scientific communities. The Series is published by an international board of publishers in conjunction with the NATO Scientific Affairs Division A Life Sciences B Physics C Mathematical and Physical Sciences D Behavioural and Social Sciences E Applied Sciences F Computer and Systems Sciences G Ecological Sciences H Cell Biology I Global Environmental Change Plenum Publishing Corporation London and New York Kluwer Academic Publishers Dordrecht, Boston and London Springer-Verlag Berlin, Heidelberg, New York, London, Paris and Tokyo NATO-PCO-DATA BASE The electronic index to the NATO ASI Series provides full bibliographical references (with keywords and/or abstracts) to more than contributions from international scientists published in all sections of the NATO ASI Series. Access to the NATO-PCO-DATA BASE is possible in two ways: - via online FILE 128 (NATO-PCO-DATA BASE) hosted by ESRIN, Via Galileo Galilei, Frascati, Italy. - via CD-ROM "NATO-PCO-DATA BASE" with user-friendly retrieval software in English, French and German ( WTV GmbH and DATAWARE Technologies Inc. 1989). The CD-ROM can be ordered through any member of the Board of Publishers or through NATO-PCO, Overijse, Belgium. Series C: Mathematical and Physical Sciences - Vol. 447

3 Nuclear Magnetic Resonance in Modern Technology edited by Gary E. Maciel Department of Chemistry, Colorado State University, Fort COllins, Colorado, U.S.A. Springer-Science+Business Media, B.V.

4 Proceedings of the NATO Advanced Study Institute on Nuclear Magnetic Resonance in Modern Technology Sarigerme Park (Dalaman), Turkey August 16 - September 4, 1992 A C.I.P. Catalogue record for this book is available from the Library of Congress. ISBN ISBN (ebook) DOI / Printed on acid-free paper AII Rights Reserved 1994 Springer Science+Business Media Dordrecht Originally published by Kluwer Academic Publishers in 1994 Softcover reprint of the hardcover 1st edition 1994 No part of the material protected by this copyright notice may be reproduced or utilized in any torm or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without written permission trom the copyright owner.

5 TABLE OF CONTENTS Preface vii Introduction G. E. Maciel ix Chapter 1. Introduction to NMR and Modern Technology E.W. Randall 1 Chapter 2. Foundations and Strategies of Multidimensional NMR R. Freeman 23 Chapter 3. Applications of High-Resolution NMR to Soluble Polymers A. Zambelli, A. Proto and L. Oliva 57 Chapter 4. High Resolution NMR: Applications to Biological Systems L.W. Jelinski 73 Chapter 5. Line Broadening in Solids R. Dupffie 87 Chapter 6. Basic Cross Polarization Magic Angle Spinning C.S. Yannoni 105 Chapter 7. NMR Studies of Solid Polymers and Resins: An Introduction G.R. Hatfield 127 Chapter 8. NMR Characterization of Solid Fossil Fuels. Coal and Oil Shale G.E. Maciel and O. Erbatur 165 Chapter 9. NMR in Industrial Process Control and Quality Control G.E. Maciel 225 Chapter 10. Solid State NMR Investigation of Zeolites and Related Materials C.A. Fyfe and G.T. Kokotailo 277

6 VI Chapter 11. NMR Study of Glasses ad Ceramics R. Dupree 339 Chapter 12. Averaging Effects in NMR J.S. Waugh 359 Chapter 13. NMR in the Study of Surfaces; 1 H CRAMPS and 29Si CP-MAS Studies of Silica G.E. Maciel 401 Chapter 14. Cross-Polarization Processes Involving Less Common Pairs of Nuclei C.A. Fyfe, K.T. Mueller and K.C. Wong-Moon 447 Chapter 15. NMR of Polymer Composites and Blends W.S. Vee man 483 Chapter 16. Applications of NMR Spectroscopy to Surfaces and Catalysts: Acidic Sites and Adsorbed Species H. Pfeifer 499 Chapter 17. Introduction to DOR NMR A. Samoson 525 Chapter 18. NMR Imaging: Introduction and Survey L.W. Jelinski 547 Chapter 19. High Resolution NMR Imaging of Solids W.S. Veeman 563 Index 593

7 PREFACE This volume represents the primary lectures of the NATO Advanced Study Institute (ASI) on "Nuclear Magnetic Resonance in Modern Technology," which was held at Sarigerme Park (near the Dalaman Airport) on the southern Aegean shore of Turkey from August 23 to September 4, As indicated in the title, this ASI was aimed at examining, displaying, and perhaps influencing, the role of nuclear magnetic resonance (NMR) in modern technological activity. The lectures summarized in this volume and the numerous short contributed talks and posters were primarily aimed at the question, "What is NMR doing in support of modern technology?" During the main discussion periods and the numerous small scheduled meetings of specific interest groups this same topic was also addressed, along with questions like, "What could or should NMR be doing in support of modern technology?" With this kind of subject orientation, the organizers attempted to include a large participation at the ASI from scientists and engineers from diverse private industries in which NMR does, or perhaps should, play a substantial role in supporting or optimizing technology. Perhaps because of a combination of worldwide industrial contractions and residual corporate nervousness regarding the then recent Gulf War (which caused a one-year postponement of this ASI), the participation from private industry was numerically disappointing. We hope that this book will serve to bring the role of NMR in modern industry to the attention of numerous industrial scientists and engineers who were unable to attend the AS!. vii

8 viii For the success of the ASI, we are grateful to many people. This certainly includes the lecturers for providing excellent lectures, notes and ultimately chapters, the students and other participants for the stimulation that they provided, and Dr. Oktay Erbatur and Dr. Gaye Erbatur and their assistants, who handled all of the local arrangements in Turkey. The AS! arrangements and the site were outstanding, and the Turkish hospitality was superb. Of course, we are grateful to NATO for the basic grant that made possible the AS! on "Nuclear Magnetic Resonance in Modern Technology." We also thank the U.S. National Science Foundation for travel grants to graduate students, the U.S. Naval Research European Office for co-sponsoring this AS! with a substantial grant, and the following private companies (listed in alphabetical order), whose financial contributions substantially enhanced the quality of the ASI in all respects: BP International, Doty SCientific, DSM Research, IBM, Nabisco Brands, Otsuka Chemagnetics, Unilever, Union Carbide, and W. R. Grace. I also wish to thank Cheryl Tyler, Barbara Wilson and Vicky Pan for their help in preparing the final manuscript. Gary E. Maciel, Fort Collins, Colorado, USA

9 INTRODUCTION GARY E. MACIEL Department of Chemistry Colorado State University Fort Collins, CO USA This book covers a variety of very fundamental topics in chemistry and physics, in most cases with the aim of preparing the reader to understand technological applications of NMR that are described in this volume or elsewhere. With a publication date that comes at approximately the fiftieth anniversary of the discovery of NMR,' this book is timely, in the sense of providing an excellent view of the substantial role that this maturing, yet dynamic phenomenon/technique is having in modern technology. The level of most of the coverage in this volume is approximately that which would be appropriate for a graduate chemistry student with an elementary introduction in the following basic principles of NMR: 1. The NMR spectrum (Fig. 1 B) of a sample is its frequency response, due to nuclear spin transitions (Fig. 1 A), induced by a radiofrequency (rf) radiation field (B 1 ) in the presence of a static magnetic field (8 0 ).2 In "high resolution" experiments the spectrum is typically dominated by the chemical shift, a measure of the shielding (0) of a nucleus from the unadulterated effect of the applied static field Bappl due to the local field generated by circulations of electrons induced by Bappl(Bo = BapPI(l- 0) ); and by "indirect" (J) coupling between nuclei in a molecule, reflecting the interaction between spins mediated (communicated) by the bonding electrons involved with the coupled nuclei. 3 ix

10 x A hu yh ~E =-2 B = hu 1t 0 B J ~ J J ( )( ) G(m), 1 I ~ f-ro Ib roa roc 0 COo 0 Figure 1. The NMR spectrum as a frequency response for transitions of a spin-1/2 system in a magnetic field, Bo' A) Energy levels and transitions, where Bo is the field experienced by the spins as a result of a large static applied field, B appl ' B) Frequency response NMR spectrum, showing three different chemical environments with chemical shifts 0a' 0b' 0c (corresponding to shieldings O"a' O"b and o"c' respectively, and resonance frequencies (J)~ (J)~ and (J)~), and J coupling between the spins of environments band' c with a pattern that is characteristic of protons in a ~C H C -CH% moiety.

11 2. In modern Fourier transform (FT) NMR experiments,4 as first demonstrated by Ernst and Anderson,5 the frequency-response spectrum G(m) is obtained by Fourier transformation of the timeresponse get) of the voltage induced in the rf coil by the transverse (x-y) magnetization following a pulse of rf energy at or near the resonance frequency (Figure 2). Xl A z x, \, ~~----~' y rf coil B get) G(m) t-+- Fourier) transform Figure 2. The basis of Fourier transform (FT) NMR. A) The effect of a 90 pulse of rf energy on the magnetization vector Mo' showing the decay of transverse (x-y) magnetization (with a time constant T 2) and re-establishment of longitudinal (z) magnetization (with a time constant T 1 ). 8) Fourier transformation of the time-response (oscillatory decay), get), due to the x component of magnetization, generating the frequency response spectrum, G(m). This figure shows the simple case of one chemical shift and no J couplings.

12 xii 3. Following a 90 rf pulse (as depicted in Fig. 2), the z 0 component of the macroscopic magnetization returns exponentially to its thermodynamic equilibrium value Mo with a time constant T, (the so-called spin lattice relaxation time), while the transverse (xy) component of magnetization decays exponentially to zero, with a time constant T 2 (the transverse or spin-spin relaxation time) in the absence of inhomogeneous effects (such as a non-uniform magnetic field).4 4. A useful concept in NMR is the "rotating frame," a cartesian axis system (x', y', z') that rotates about its z axis (z'), which is colinear with B o ' at the oscillation frequency u of the rf field, B,(t) = 2iB 1 cos21tut (which can be viewed as two counter-rotating fields, B, and B~, one rotating clockwise and one counterclockwise about the z' axis). One of these rotating fields (B,) is chosen to define one axis of the rotating frame, as seen in Figure 3A. Figure A Z=Z B Z=Z, Bo y y _y)(p = 21tVt = rot x' -- -y x x Figure 3. The rotating frame (x', y', z') in relation to the static laboratory frame (x, y, z). A) One rotating component (B,) of B, (t) defining the x' axis of the rotating frame. B) Precession of a magnetization vector following a 90 pulse (ending at t = 0) for the 0 "on resonance" condition,-roo = ro = 21t u.

13 3B shows the precession, following a 90 pulse at t = 0, of a 0 magnetization vector with a resonance frequency roo exactly equal to xiii the rotating-frame frequency, roo = 21tV. 5. Following a 90 rf pulse (at or near resonance), if the rf field B 1 is phase-shifted by 90 instead of being shut off (Figure 3B), the 0 vector B 1 becomes colinear with the net magnetization vector M, with no torque exerted by B 1 on M (Figure 3C). In this so-called "spin-lock" condition, the transverse (xy) component of magnetization decays to zero exponentially with a time constant T 1 p that is referred to as the rotating-frame spin-lattice relaxation time (Figure 3D).4 A z' B z' c z' '" '" x' ~ ~ -pha;e shift x' M x' 8, ---",-,...,..,...--y' M Figure 4. A) At the end of a 90 0 pulse, the rf field B 1 is phase shifted by 90 0 B) The "spin-lock" condition. C) Exponential decay of the transverse component of M and B 1 in the spin-lock condition, with a characteristic time constant T 1 p. There are some sections of this book in which additional theoretical background is required. This is especially true in Chapters 12 and 17. However, most of the coverage has been built up from the kind of background represented by Figures 1, 2, 3 and 4.

14 xiv After Randall's general overview of the history of NMR in technological applications (Chapter 1), Freeman presents an introduction (Chapter 2) to multidimensional NMR, with applications to high-resolution experiments on liquid samples. This is followed by a chapter describing the application of high-resolution NMR techniques in the characterization of soluble polymers (Chapter 3), by Zambelli, Proto and Oliva, and by Jelinski's chapter on highresolution NMR applications to some biological systems (Chapter 4). The next two chapters in the book, by Dupree (Chapter 5) and Yannoni (Chapter 6), lay the fundamental groundwork on interactions and techniques for solid-state NMR applications. This is followed by Hatfield's chapter on the characterization of solid polymers (Chapter 7) and a chapter by Maciel and Erbatur on the characterization of solid fossil fuels, mainly coal (Chapter 8). A chapter by Maciel on NMR in industrial process control and quality control applications (Chapter 9) draws on both liquid-sample and solid-sample NMR characteristics and explores time-domain (mainly relaxation) strategies in some detail. Chapters by Fyfe and Kokotailo (Chapter 10) on NMR investigations of zeolite-type materials and by Dupree on NMR studies of ceramics and glasses (Chapter 11) complete the initial survey of solid-state NMR applications in industry. Waugh's chapter on averaging effects in NMR (Chapter 12) begins a series of chapters that are concerned primarily with more advanced topics in solid-state NMR. This series includes a chapter by Maciel on NMR studies of silica surfaces (Chapter 13), a chapter by Fyfe, Mueller and Wong-Moon on cross polarization among uncommon pairs of nuclei (Chapter 14), a chapter by Veeman on NMR

15 studies of polymer composites and blends (Chapter 15), a chapter by Pfeifer on NMR studies of surfaces, especially acidic catalytic surfaces (Chapter 16), and a chapter on double-rotation (DOR) experiments for quadrupolar nuclei (Chapter 17) by Samoson. The final two chapters of this volume are devoted to NMR imaging. Jelinski's chapter provides an introduction and overview of the subject (Chapter 18), and Veeman's chapter focuses on highresolution NMR imaging techniques for solids (Chapter 19). The array of primary lectures represented by these chapters provides an extensive overview of the basic principles and use of NMR in modern technological applications, especially for solid samples. At the ASI, these lectures were supplemented by some excellent contributed talks and posters, and stimulating discussions with an excellent group of students and participants. References 1. F. Bloch, W. W. Hansen and M. Packard, Phys. Rev., 70, 474 (1946). 2. J. A. Pople, W. G. Schneider and H. J. Bernstein, "High-resolution Nuclear Magnetic Resonance," McGraw Hill, New York, E. D. Becker, "High Resolution NMR: Theory and Chemical Applications," 2nd edition, Academic Press, New York, T. C. Farrar and E. W. Becker, "Pulse and Fourier Transform NMR. Introduction to Theory and Methods," Academic Press, New York, R. R. Ernst and W. A. Anderson, Rev. Sci. Instrum., 37, 93 (1966). xv