NMR Basic Principles and Progress - Böcker

1. Lyotropic Liquid Crystals The class of compounds known as thermotropic liquid crystals has been widely utilized in basic research and industry during recent years. The properties of these materials are such that on heating from the solid to the isotropic liquid state, phase transitions occur with the formation of one or more intermediate anisotropic liquids. The unique and sometimes startling properties of these liquid crystals are the properties of pure compounds. However, there exists a second class of substances known as lyotropic liquid crystals which obtain their anisotropic properties from the mixing of two or more components. One of the components is amphiphilic, containing a polar head group (generally ionic or zwitterionic) attached to one or more long-chain hydrocarbons; the second component is usually water. Lyotropic liquid crystals occur abundantly in nature, particularly in all living systems. As a consequence, a bright future seems assured for studies on such systems. Even now, many of the properties of these systems are poorly understood. It is the purpose of this review to consolidate the results obtained from nuclear magnetic resonance studies of such systems and to provide a coherent picture of the field. Probably the most familiar example of a lyotropic liquid crystal is soap in water. A common soap is sodium dodecylsulphate where an ionic group (sulphate) is attached to a hydrocarbon chain containing twelve carbons.

RF Probeheads 1. J. Link, Faellanden, Switzerland The Design of Resonator Probes with Homogeneous Radiofrequency Fields 2. M. Schnall, Philadelphia, PA/USA Probes Tuned to Multiple Frequencies for In-Vivo NMR RF Pulses 3. P.C.M. van Zijl, Rockville, MD/USA; C.T.W. Moonen, Bethesda, MD/USA Solvent Suppression Strategies for In Vivo Magnetic Resonance Spectroscopy 4. M. Garwood, K. Ugurbil, Minneapolis, MN/USA B1 Insensitive Adiabatic RF Pulses 5. P.G. Morris, Nottingham, UK Frequency Selective Excitation Using Phase-Compensated RF Pulses in One andTwo Dimensions 6. S. Mueller, Basel, Switzerland RF Pulses for MultipleFrequency Excitation: Theory and Application Spectrum Analysis 7. R. de Beer, D. van Ormondt, Delft, The Nethelands Analysis of NMR Data Using Time Domain Fitting Procedures 8. E.B. Cady, London, UK Determination of Absolute Concentrations of Metabolites from NMR Spectra

In recent years several improvements have been made in the manufacturing of resistive, superconducting and hybrid mag­ nets. Condensed matter physicists are nowadays doing ex­ periments in steady magnetic fields of up to 30 Tesla. But the field homogenity {/B}, required in a volume of the order of a 3 few cm is usually several orders of magnitude less severe than the one which is needed for high resolution NMR. Over the last 30 years, with each generation of new high resolution NMR spectrometers, from 100 MHz up to 600 MHz, taking advan­ tage of the increase in sensitivity and resolution, new areas of research have been opened in chemistry, physical chemistry and biochemistry. The generation of the 20 Tesla supercon­ ducting magnets is coming. Thus one may seriously start to consider high resolution NMR at 1 GHz. The purpose of this volume is to examine some of the advantages which can be obtained at such high frequencies and some of the problems we shall be facing. An important aspect of NMR at high field which is not presented in this volume concerns the design of the magnet. The building of a superconducting magnet, producing a field 10 3 higher than 20 T, with a field homogeneity IlB/B 10- , in a cm volume still remains today in 1990 a major challenge. Grenoble, France J. B. Robert Guest-Editor Professor J. B. Robert Service National des Champs Intenses B. P.

For almost a quarter of a century the words "nuclear magnetic reso­ nance" were synonymous with proton I,leasurements. During this period the literature abounded with a seemingly infinite variety of 1H NHR studies concerned primarily with carbon chemistry. Occasionally a "novel" nucleus was studied and, even in those early days, the poten- 13 14 31 19 tial offered by C, N, P and F was clearly recognized. Despite the allure, the technical difficulties involved in measuring some of these nuclei were far from trivial. Small magnetic moments and low natural abundance in combination with spin-spin coupling from other nuclei, mostly protons, resulted in a signal-to-noise problem whose severity effectively excluded the study of metal complexes with unfa­ vorable solubility characteristics. The first important breakthrough came with the advent of broad band 1H-decoupling. For example, the featureless broad 31p resonance associated with the commonly used ligand triphenyl phosphine is converted to a sharp, more readily ob­ served singlet when wide-band decoupling is employed (see Fig. 1). Despite this improvement investigation of more interesting molecules, such as catalytically active complexes was forced to await the devel­ opment of Fourier Transform methods since only with relatively rapid signal averaging methods could sufficient signal-to-noise ratios be achieved.

1. D. Freude, J. Haase, Leipzig, FRG Quadrupole Effects in Solid-State Nuclear Magnetic Resonance 2. N.J. Clayden, Middlesborough, UK Solid State NMR of Synthetic Polymers 3. A. Bunn, Middlesborough, UK Solution NMR of Synthetic Polymers

1. G. Engelhardt, H. Koller, Stuttgart, FRG: 29Si NMR of Inorganic Solids 2. H. Pfeifer, Leizpig, FRG: NMR of Solid Surfaces 3. A. Sebald, Bayreuth, FRG: MAS and CP/MAS NMR of Less Common Spin-1/2 Nuclei 4. C. J{ger, Mainz, FRG: Satellite Transition Spectroscopy of Quadrupolar Nuclei 5. D. Brinkmann, M. Mali, Z}rich, CH: NMR-NQR Studies of High-Temperature Superconductors

After the proton and carbon, nitrogen is, with oxygen, the most impor­ tant atom in organic and especially bioorganic molecules. However, the development of nitrogen spectroscopy is indeed very recent. This is due to the fact that nitrogen-14, which is the naturally abundant iso­ tope, suffers, for structural studies, from the disadvantages inherent in nuclei with a quadrupolar moment (Table 1.1). Actually, indirect 15N measurements were reported in the early days of double resonance spectroscopy and the first direct detection of 15N resonance signals at the natural abundance level was realized in 1964 (R 17) at 4.33 MHz 1 (~ 1T) using a 15 mm o.d. cell in the field sweep mode (~ 0.16 min- ). Signal-to-noise ratios only of 3-4 were obtained for neat liquids and this low sensitivity of the 15N resonance still remains the main dis­ advantage for 15 spectroscopy (Table 1.1). However, nitrogen-15 has, N probably more than any other nucleus, benefited from the advances of NMR technology, i.e. Fourier transformation, multinuclear facilities, wide-bore super conducting solenoids, and, with the new generation of spectrometers, 15N-NMR is entering the field of routine investigation. Nevertheless, in spite of these spectacular improvements, obtaining 15N spectra of diluted species or large biochemical molecules is often not very easy and a good knowledge of the relaxation properties pecu­ liar to 15N may be necessary in order to adjust the pulse sequences and the decoupler duty cycle correctly (Section 2).

In NMR, it is well-known that the chemical shift conveys structural informa­ tion, e. g. a carbonyl carbon will have a resonance frequency appreciably dif­ ferent from a methyl carbon, etc. The relation between structure and chemical shift is mostly established by empirical rules on the basis of prior experience. It is only quite recently that the advent of both comparatively cheap comput­ ing power and novel quantum chemistry approaches have provided feasible routes to calculate the chemical shift at the ab initio level for molecules of reasonable size. This raises the question whether application of these novel theoretical concepts offers a means of obtaining new structural information for the complex chain molecules one deals with in polymer science. Solid state 13C-NMR spectra of glassy amorphous polymers display broad, partially structured resonance regions that reflect the underlying disorder of the polymer chains. The chemical shift responds to the variation of the ge­ ometry of the chain, and the broad resonance regions can be explained by an inhomogeneous superposition of various chain geometries (and thus chem­ ical shifts). In this review, we present a novel approach to combine polymer chain statistical models, quantum chemistry and solid state NMR to pro­ vide quantitative information about the local chain geometry in amorphous polymers. The statistical model yields the relative occurrence of the various geometries, and quantum chemistry (together with a force field geometry op­ timization) establishes the link between geometry and chemical shift.

Solid-State NMR is a branch of Nuclear Magnetic Resonance which is presently experiencing a phase of strongly increasing popularity. The most striking evidence is the large number of contributions from Solid-State Resonance atNMR meetings, approaching that ofliquid­ state resonance. Important progress can be observed in three areas: Methodological developments, applications to inorganic matter, and applications to organic matter. These developments are intented to be captured in three volumes in this series, each of them being devoted to more or less one of these areas. The present volume on Solid-State NMR III is devoted mainly to organic matter. The recent developments of deuteron NMR and their applications are reviewed in the first chapter. Crosspolarization, MAS, and dynamic angle spinning are being explored for enhancement of information and sensitivity. In addition to the analysis of classical relaxation times and modern 2D spectra, detailed dynamic information becomes accessible from investigations of the relaxation time anisotropies. The second chapter examines cross-polarization in static and rotating solids under conditions of spin diffusion and thermal motion. The underlying dipole-dipole interaction is further exploited by the techniques described in the third chapter for studies of polymer-polymer miscibility. Short­ range techniques are discriminated from long-range techniques based on spin diffusion. The use ofthese techniques is illustrated by a case study ofPMMAJPVF blends. The last chapter addresses novel z methods and applications of two-dimensional exchange NMR for investigations of relative molecular orientations, polymer morphology, molecular dynamics, and macroscopic molecular order.

Nuclear magnetic resonance spectroscopy, which has evolved only within the last 20 years, has become one of the very important tools in chemistry and physics. The literature on its theory and application has grown immensely and a comprehensive and adequate treatment of all branches by one author, or even by several, becomes increasingly difficult. This series is planned to present articles written by experts working in various fields of nuclear magnetic resonance spectroscopy, and will contain review articles as well as progress reports and original work. Its main aim, however, is to fill a gap, existing in literature, by publishing articles written by specialists, which take the reader from the introductory stage to the latest development in the field. The editors are grateful to the authors for the time and effort spent in writing the articles, and for their invaluable cooperation. The papers presented here are condensed versions of the main contributions to the 7th Colloquium on Nuclear Magnetic Resonance Spectroscopy, which was made possible by the generous support of the Freunde der Aachener Hoch­ schule (FAHO). The RWTH is indebted to the FAHO and to all the participants who contributed to the success of the Colloquium.

Nuclear magnetic resonance spectroscopy, which has evolved only within the last 20 years, has become one of the very important tools in chemistry and physics. The literature on its theory and application has grown immensely and a comprehensive and adequate treatment of all branches by one author, or even by several, becomes increasingly difficult. This series is planned to present articles written by experts working in various fields of nuclear magnetic resonance spectroscopy, and will contain review articles as well as progress reports and original work. Its main aim, however, is to fill a gap, existing in literature, by publishing articles written by specialists, which take the reader from the introductory stage to the latest development in the field. The editors are grateful to the authors for the time and effort spent in writing the articles, and for their invaluable cooperation. The Editors Contents o. Kanert and M. Mehring Static Quadrupole Effects in Disordered Cubic Solids 1 F. Noack Nuclear Magnetic Relaxation Spectroscopy 83 Static Quadrupole Effects in Disordered Cubic Solids O. KANERT and M. MEHRING Physikalisches Institut der Universitat MUnster, BRD Contents I. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 II. Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Zero Field Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. High Field Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Transformation of the Electric Field Gradient Tensor . . . . . . . . . . 7 III. The Influence of the Quadrupole Perturbation on the NMR Signal . 8 1. General Theory . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 a) The Free Induction Decay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 b) The Wide-Line Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 c) The Spin Echo Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . :. .

Nuclear magnetic resonance spectroscopy, which has evolved only within the last 20 years, has become one of the very important tools in chemistry and physics. The literature on its theory and application has grown immensely and a comprehensive and adequate treatment of all branches by one author, or even by several, becomes increasingly difficult. This series is planned to present articles written by experts working in various fields of nuclear magnetic resonance spectroscopy, and will contain review articles as well as progress reports and original work. Its main aim, however, is to fill a gap, existing in literature, by publishing articles written by specialists, which take the reader from the introductory stage to the latest development in the field. The editors are grateful to the authors for the time and effort spent in writing the articles, and for their invaluable cooperation. The Editors Analysis of NMR Spectra A Guide for Chemists R. A. HOFFMAN t S. FORSEN Division of Physical Chemistry, Chemical Center, Lund Institute of Technology, Lund, Sweden B. GESTBLOM Institute of Physics, University of Uppsala, Sweden Contents I. Principles of NMR Spectroscopy 4 1. 1. The Magnetic Resonance Phenomenon 4 a) Nuclear Moments. . . . . . . . 4 b) Magnetic Spin States and Energy Levels 5 c) The Magnetic Resonance Condition. 7 d) The Larmor Precession. . 7 e) Experimental Aspects . . . . 8 1. 2. Chemical Shifts . . . . . . . . 9 a) The Screening Constant 11. . . 9 b) Chemical Shift Scales (11 and r) 10 1. 3. Spin Coupling Constants 12 1. 4. Intensities. . . . . . . .

Nuclear magnetic resonance spectroscopy, which has evolved only within the last 20 years, has become one of the very important tools in chemistry and physics. The literature on its theory and application has grown immensely and a comprehensive and adequate treatment ofall branches by one author, or even by several, becomes increasingly difficult. by experts workinginvarious This seriesis planned to present articles written fields of nuclear magnetic resonance spectroscopy, and will contain review articles as well as progress reports and original work. Its main aim, however, is to fill a gap, existing in literature, by publishing articles written by specialists, which take the reader from the introductory stage to the latest development in the field. The editors are grateful to the authors for the time and effort spent in writing the articles, and for their invaluable cooperation. The Editors Computer Assistance in the Analysis of High-Resolution NMR Spectra P. DIEHL and H. KELLERHALS Departmentof Physics, University ofBasle, Switzerland E. LUSTIG Food and Drug Administration, Washington, D.C., U.S.A.

Nuclear magnetic resonance spectroscopy, which has evolved only within the last 20 years, has become one of the very important tools in chemistry and physics. The literature on its theory and application has grown immensely and a comprehensive and adequate treatment of all branches by one author, or even by several, becomes increasingly difficult. This series is planned to present articles written by experts working in various fields of nuclear magnetic resonance spectroscopy, and will contain review articles as well as progress reports and original work. Its main aim, however, is to fill a gap, existing in literature, by publishing articles written by specialists, which take the reader from the introductory stage to the latest development in the field. The editors are grateful to the authors for the time and effort spent in writing the articles, and for their invaluable cooperation. The Editors Contents c. W. Hilbers and C. MacLean NMR of Molecules Oriented in Electric Fields.

Anomalous electron-spin state populations in the Electron Paramagnetic Re­ sonance (EPR) spectra of radicals formed during radio lysis experiments were observed in 1963 by FESSENDEN and SCHULER [170a]. This phenomenon did not receive much attention at the time. In 1967, BARGON, FISCHER, and JOHNSEN [5] and independently WARD and LAWLER [7,8] reported a similar phenomenon for Nuclear Magnetic Resonance (NMR) spectra taken during radical reactions: emission or enhanced absorption, or both. The earliest attempts to explain this new NMR phenomenon treated these effects in a way similar to that of Dynamic Nuclear Polarization (DNP) or the Overhauser effect. Although the polarization has a completely different origin, DNP gave its name to this effect: Chemically Induced Dynamic Nuclear Polariza­ tion (CIDNP). [The name Chemically Induced Dynamic Electron Polarization (CIDEP) was introduced later by analogy with CIDNP]. After the initial publica­ tions, all the new data demonstrated that the first theory could not be correct. In 1969, a new theory was proposed by CLOSS [18] and independently by KAPTEIN and OOSTERHOFF [23] and called the radical-pair theory. This mechanism was proposed to account for the observations of polarization in both NMR and EPR. The radical-pair theory is based on weak interactions in a pair of radicals: the strength of interaction between the electronic states of the radicals depends in particular on the nuclear-spin states.

The usefulness of solvent effect studies on NMR chemical shifts need not be elabo­ rated here; many applications of solvent effects continue to be published in great profusion. Quite a few intermolecular phenomenae may contribute to solvent shifts, but there is always the ubiquitous Van der Waals effect ow. Contrary to such other effects as neighbour anisotropy 0a, reaction field contribution 0E or complexation effects 0e, no major direct use has yet been found for the Van der Waals effect. So far the role of the Van der Waals effect has been that of a nasty, disturbing phenom­ enon, something to be eliminated at all costs. But it is precisely in this latter respect where almost all solvent effect studies fall short. Not only is Ow usually large (larger than 0a and 0E even in 1 H NMR and probably the dominating term with heavier nuclei), but it is strongly variable from one solute to another and even from one nu­ clear site to another in the same solute molecule. No referencing technique, however cleverly devised, will be capable of eliminating the Ow contribution from the other, presumedly more interesting contributions. It appeared quite recently that mathematical trickery by the name of "factor analysis" could achieve the sought-for separation of contribuants.

The increasing interest in NMR spectroscopy of what in some confer­ ences in this field is commonly termed "other nuclei" is unmistakable. Chemists and biologists who employ NMR spectroscopy to study their problems have, however, been somewhat reluctant to study nuclei with electric quadrupole moments. These nuclei frequently give rise to broad NMR signals, sometimes too broad to be detectable with ordinary high resolution NMR spectrometers. Spectrometers that could cope with broad NMR signals of low intensity, "wide-line" spectrometers, have been available since the mid 1950:s but it appears that most of these instruments ended up in physical laboratories where the research was primarily directed towards solid state problems. The study of quadrupolar nuclei can provide unique and very valuable information on a variety of physico-chemical and biological systems. For one thing the relaxation of quadrupolar nuclei is in many ways easier to interpret than the relaxation of non-quadrupolar nuclei, since the former is in many cases caused by purely intramolecular interactions modulated by the molecular motion. Studies of quadrupolar relaxation have therefore furnished important information about molec­ ular reorientation and association in liquids and have played - and will certainly play for many years - an important role in testing new theoretical models of molecular motion in liquids.

This set of essays was given as lectures at the 4th Waterloo International Summer School on Nuclear Magnetic Resonance held in June 1975 at the University of Water­ loo. The school was sponsored by the National Research Council of Canada and by the Canadian Association of Physicists. These Contributions are introductory and were not intended to be review papers. For valuable help, I would like to thank R. S. Hallsworth, D. W. Nicoll, and R. T. Thompson. M.M.Pintar Table of Contents A Guide to Relaxation Theory. By A. G. Redfield .................... 1 Thermodynamics of Spin Systems in Solids. An Elementary Introduction. By J. Jeener. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 . . . . . . . . . . . . Coherent Averaging and Double Resonance in Solids. By J. S. Waugh. . . . . .. . 23 Macroscopic Dipole Coherence Phenomena. By. E. L. Hahn . . . . . . . . . .. . . 31 . Nuclear Spins and Non Resonant Electromagnetic Phenomena. By G. J. Bene. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . 45 . . . . . . . . . Nuclear Spin Relaxation in Molecular Hydrogen. By F. R. McCourt. . . . . . .. . 55 Longitudinal Nuclear Spin Relaxation Time Measurements in Molecular Gases. By R. L. Armstrong . . . . . . . . . . . . . . . . . . . . . . . . .. . . . 71 . . . . . . . Spin-Lattice Relaxation in Nematic Liquid Crystals Via the Modulation of the Intramolecular Dipolar Interactions by Order Fluctuations. By R. Blinc . . .. 97 NMR Studies of Molecular Tunnelling. By S. Clough . . . . . . . . . . . . .. . . . 113 . . Effect of Molecular Tunnelling on NMR Absorption and Relaxation in Solids. By M. M. Pintar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . 125 . . . . . . . . . .

The revolutionary impetus of the NMR methods in organic chemistry has parallels in the field of boron chemistry. lIB NMR spectroscopy provided a basis for the elucida­ tion of structures and reactions of the boron hydrides. However, although many studies have been carried out with the higher boranes, carboranes, metalloboranes, etc. , and although certain patterns have emerged, the correlation between the observed chemical shift and the assigned structural unit is still not fully understood. Therefore, predictions in this area are still rather limited, and semiquantitative interpretations are not yet pos­ sible. Several years ago Eaton and Lipscomb sUpImarized the status in this field in their book "NMR Studies of Boron Hydrides and Related Compounds" and a plethora of new data has accumulated since then. The book also contained material on simple bo­ rane derivatives, but they were not discussed in any detail. On the other hand many systematic studies, both synthetic and spectroscopic, have been conducted on these simple boron materials in the last decade. Thus a large amount of NMR information is available, not only on lIB but also on 1 H, 1 3 C, and 14 N. However, this information is widely scattered in the literature, and often the data are not discussed at all. It see­ med appropriate, therefore, to collect these data and to present them in one volume.

Since the first successful NMR experiments in 1946 it was well appreciated that dynamic processes play an important role in the NMR spectroscopy of bulk matter [1]. Early theories on the dependence of the relaxation parameters Tl and T2 on the motions of nuclear spins were successful in explaining the dipolar broadening of the NMR signal in solids and the motional narrowing in liquids [2]. With the discovery of chemical shifts and spin-spin couplings another type of dynamical process affect­ ing the NMR line shape became apparent, the chemical exchange. As a consequence, dynamical NMR studies split into two groups differing not only in the dynamical topics but also in the method of investigation: physical studies of the motion of spins in liquids and solids by measurement of the relaxation times of single resonances and, on the other hand, chemical studies based on band shape analysis of NMR spectra recorded under steady state conditions. The two fields of research lost some of their basic differences with the development of the Fourier transform NMR method [3], which allows the measurement of relaxation times of different resonances at the same time, i. e. the study of differential motional behavior of different parts of mole­ cules, thus providing a new tool in conformational analyses. For example, informa­ tion can be obtained by this method on the relative importance of overall motions and internal motions [4].

The determination of the three-dimensional structure of a biological molecule is the starting point in the understanding of molecular mechanisms involved in its complex biochemical reactions. The molecular architecture of multimolecular systems such as membranes and chromosomes provides the key to the fascinating field of molecular biology. Stereochemical details of biological macromolecules and their interactions with pharmacological agents form the basis for drug design. Naturally, the study of the structure and function of biological molecules has aroused tremendous interest and investigations in this area are being carried out in a large number of laboratories. The techniques used for this purpose include both experimental methods (X-ray and neutron diffraction measurements, study of NMR, ESR, vibrational and electronic spectra, ORD, CD and dipole moment measurements, biochemical modifications etc. ) and the­ oretical methods (quantum mechanical and classical potential energy calculations, Monte­ Carlo simulations and molecular graphics). F or several years now, X-ray diffraction [1] has served as our only source of infor­ mation on the three-dimensional arrangements of atoms in biopolymers. Fiber-diffrac­ tion of DNA led to the proposal of the DNA double helix. Fibers of long~hain polymers show ordering in the direction of the fibre-axis but not in the transverse plane. Accurate estimates of the dimensions of helical structures can be made using techniques on the basis of which models of biopolymers can be constructed.

In recent years the development of the NMR method has been closely linked to the creation of the theory of the NMR in solids and with the elaboration on their basic principles and methods of high resolution in solids. The aim of this volume is to explain simply and clearly the principles for the understanding of the NMR in solid polymers, to show what kind of information can be gained using NMR investigations of bulk polymers, and to demonstrate the ways of obtaining this information, their correctness and their place in comparison with other methods. The discussion is restricted to the most important and typical nuclei 1H, 13C, and (briefly) 2D, and, in connection with that, to the dipolar and quadrupolar interaction and to the chemical shift.

In recent years, there has been a major expansion of high pressure research providing unique information about systems of interest to a wide range of scientific disciplines. Since nuclear magnetic resonance has been applied to a wide spec­ trum of problems in chemistry, physics and biochemistry, it is not surprising to find that high pressure NMR techniques have also had many applications in these fields of science. Clearly, the high information content of NMR experiments combined with high pressure provides a powerful tool in modern chem­ istry. It is the aim of this monograph, in the series on NMR Basic Principles and Progress, to illustrate the wide range of prob­ lems which can be successfully studied by high pressure NMR. Indeed, the various contributions in this volume discuss studies of interest to physics, chemical physics, biochemistry, and chemical reaction kinetics. In many different ways, this monograph demonstrates the power of modern experimental and theoretical techniques to investigate very complex systems. The first contribution, by D. Brinkman, deals with NMR and NQR studies of superionic conductors and high-Tc supercon­ ductors at high pressure. Pressure effects on phase transitions, detection of new phases, and pressure effects on diffusion and spin-lattice relaxation, represent a few of the topics discussed in this contribution of particular interest to solid state physics.

In 1931 Vrey, Brickwedde, and Murphy discovered the hydrogen isotope deuterium. The isotopic enrichment was found to arise from the fact that the electrolysis oflight water is faster than of heavy water [1,2]. This success showed that although different isotopes of an element behave identically from a chemical standpoint the different isotopic masses nevertheless lead to both isotope effects on equilibrium as well as on rate constants of chemical reactions. Soon, ratios of equilibrium constants of isotopic reactions were called "equilibrium isotope effects" (EIE), ratios of isotopic rate constants "kinetic isotope effects" (KIE). Isotope effects have been found to be especially large for those elements which are directly involved in bond breaking and bond formation during the reaction studied [3]. Such effects are, therefore, referred to as "primary". Isotopic substitution in atomic sites which maintain all chemical bonds with their neighbors during the reaction of interest leads then only to smaller "secondary" isotope effects. Because of the unique mass relation between the different hydrogen isotopes hydrogen/deuterium isotope effects are particularly large and have attracted most attention. The largest contributions to these effects arise from changes in the vibrational frequencies of the reactants. The theory of equilibrium isotope effects has been founded by Vrey [4] and Bigeleisen [5,6] and has widely been accepted [3].

Localization 1. C.S. Bosch, J.J.H. Ackerman, St. Louis, MO/USA SurfaceCoil Spectroscopy 2. P. Styles, Oxford, UK Rotating Frame Spectroscopyand Spectroscopic Imaging 3. P.A. Bottomley, Schenectady, NY/USA DepthResolved Surface Coil Spectroscopy (Dress) 4. R.J. Ordidge, J.A. Helpern, Detroit, MI/USA Image Guided Volume Selective Spectroscopy: A Comparison of Techniques for In-Vivo 31P NMR Spectroscopy of Human Brain 5. M. Decorps, D. Bourgeois, Grenoble, France Localized Spectroscopy Using Static Magnetic Field Gradients: Comparison of Techniques 6. J.A. den Hollander, P.R. Luyten, Ad J.H. Marien, Best, The Netherlands 1H NMR Spectroscopy and Spectroscopic Imaging of the Human Brain Spectral Editing and Kinetic Measurements 7. H.P. Hetherington, Birmingham, AL/USA Homo- and Heteronuclear Editing in Proton Spectroscopy 8. D. Freeman, R. Hurd, Fremont, CA/USA Metabolite Specific Methods Using Double Quantum Coherence Transfer Spectroscopy 9. B.A. Berkowitz, Research Triangle Park, NC/USA Two-Dimensional Correlated Spectroscopy In-Vivo 10. G. Navon, Tel Aviv, Israel; T. Kushnir, Tel Hashomer, Israel; N. Askenasy, O.Kaplan, Tel Aviv, Israel Two-Dimensional 31P-1H Correlation Spectroscopy in Intact Organs and Their Extracts 11. M. Rudin, A. Sauter, Basel, Switzerland Measurement of Reaction Rates In Vivo Using Magnetization Transfer Techniques

Isolated Cells and Perfused Organs 1. O. Kaplan, P.C.M. van Zijl, J.S. Cohen, Washington, DC/USA NMR Studies of Metabolism of Cells and Perfused Organs Individual Nuclei 2. S.R. Williams, London, UK In Vivo Proton Spectroscopy: Experimental Asoects and Potential 3. N. Beckmann, Basel, Switzerland In Vivo 13C Spectroscopy in Humans 4. M.J.W. Prior, R.J. Maxwell, J.R. Griffiths, London, UK Fluorine - 19F NMR Spectroscopy and Imaging In Vivo 5. J.S. Ingwall, Boston, MA/USA Measuring Cation Movements Across the Cell Wall Using NMR Spectroscopy: Sodium Movements in Striated Muscle 6. M. Rudin, A. Sauter, Basel, Switzerland In Vivo Phosphorus-31 NMR: Potential and Limitations

1. A.-R. Grimmer, Berlin, FRG; B. Bl}mich, Aachen, FRG: Introduction to Solid-State NMR 2. F. Laupretre, Paris, France: High-Resolution 13C NMRInvestigations of Local Dynamics in Bulk Polymers at Temperatures Below andAbove the Glass-Transition Temperature 3. D. Raftery, Philadelphia, PA;B.F. Chmelka, Santa Barbara, CA: Xenon NMR Spectroscopy 4. G. Fleischer, Leipzig, FRG; F. Fujara, Mainz, FRG: NMR as a Generalized Incoherent Scattering Experiment 5. P. Bl}mler, B. Bl}mich, Mainz, FRG: NMR Imaging of Solids

Solid-State NMR is a branch of Nuclear Magnetic Resonance which is presently experiencing a phase of strongly increasing popularity. The most striking evidence is the large number of contributions from Solid-State Resonance at NMR meetings, approaching that ofliquid­ state resonance. Important progress can be observed in the areas of methodological developments and applications to organic and inorganic matter. One volume devoted to more or less one of each of these areas has been published in the preceding three issues. This volume can be considered an addendum to this series. Selected methods and applications of Solid-State NMR are featured in three chapters. The first one treats the recoupling of dipolar interactions in solids, which are averaged by fast sample rotation. Following an introduction to effective Hamiltonians and Floquet theory, different types of experiment such as rotary resonance, dipolar chemical shift correlation spectroscopy, rotational resonance and multipulse recoupling are treated in the powerful Floquet formalism. In the second chapter, the different approaches to line narrowing of quadrupolar nuclei are reviewed in a. consistent formulation of double resonance (DaR) and dynamic angle spinning (DAS). Practical aspects of probe design are considered as well as advanced 2D experiments, sensitivity enhancement techniques, and spinning sideband manipulations. The use of such techniques dramatically increases the number of nuclei which can be probed in high resolution NMR spectroscopy. The final chapter describes new experimental approaches and results of structural studies of noncrystalline solids.