Applied NMR spectroscopy for chemists and life scientists

Content: Preface XV     1 Introduction to NMR Spectroscopy 1     1.1 Our First 1D Spectrum 1     1.2 Some Nomenclature: Chemical Shifts, LineWidths, and Scalar Couplings 2     1.3 Interpretation of Spectra: A Simple Example 5     1.4 Two-Dimensional NMR Spectroscopy: An Introduction 9     Part One Basics of Solution NMR 11     2 Basics of 1DNMR Spectroscopy 13     2.1 The Principles of NMR Spectroscopy 13     2.2 The Chemical Shift 16     2.3 Scalar Couplings 17     2.4 Relaxation and the Nuclear Overhauser Effect 20     2.5 Practical Aspects 23     2.5.1 Sample Preparation 23     2.5.2 Referencing 25     2.5.3 Sensitivity and Accumulation of Spectra 27     2.5.4 Temperature Calibration 29     2.6 Problems 30     Further Reading 31     3 1H NMR 33     3.1 General Aspects 33     3.2 Chemical Shifts 34     3.2.1 Influence of Electronegativity of Substituents 35     3.2.2 Anisotropy Effects 35     3.2.3 Other Factors Affecting Chemical Shifts: Solvent, Temperature, pH, and Hydrogen Bonding 37     3.2.4 Shift Reagents 37     3.3 Spin Systems, Symmetry, and Chemical or Magnetic Equivalence 39     3.3.1 Homotopic, Enantiotopic, and Diastereotopic Protons 42     3.3.2 Determination of Enantiomeric Purity 43     3.4 Scalar Coupling 44     3.4.1 First-Order Spectra 45     3.4.2 Higher-Order Spectra and Chemical Shift Separation 47     3.4.3 Higher-Order Spectra and Magnetic Equivalence 49     3.5 1H   1H Coupling Constants 50     3.5.1 Geminal Couplings 50     3.5.2 Vicinal Couplings 50     3.5.3 Long-Range Couplings 52     3.5.4 1HCouplings to Other Nuclei 52     3.6 Problems 54     Further Reading 55     4 NMRof13C and Heteronuclei 57     4.1 Properties of Heteronuclei 57     4.2 Indirect Detection of Spin-1/2 Nuclei 59     4.3 13C NMR Spectroscopy 59     4.3.1 The 13C Chemical Shift 60     4.3.2 X,13C Scalar Couplings 64     4.3.3 Longitudinal Relaxation of 13C Nuclei 68     4.3.4 Recording 13C NMR Spectra 68     4.4 NMR of Other Main Group Elements 70     4.4.1 Main Group Nuclei with I D 1/2 71     4.4.2 Main Group Nuclei with I >
 1/2 75     4.5 NMR Experiments with Transition Metal Nuclei 78     4.5.1 Technical Aspects of Inverse Experiments with I D 1/2 Metal Nuclei 79     4.5.2 Experiments with Spin I >
 1/2 Transition Metal Nuclei 81     4.6 Problems 82     Further Reading 84     Part Two Theory of NMR Spectroscopy 85     5 Nuclear Magnetism     A Microscopic View 87     5.1 The Origin of Magnetism 87     5.2 Spin     An Intrinsic Property of Many Particles 88     5.3 Experimental Evidence for the Quantization of the Dipole Moment: The Stern   Gerlach Experiment 93     5.4 The Nuclear Spin and Its Magnetic Dipole Moment 94     5.5 Nuclear Dipole Moments in a Homogeneous Magnetic Field: The Zeeman Effect 96     5.5.1 Spin Precession 98     5.6 Problems 103     6 Magnetization     A Macroscopic View 105     6.1 The Macroscopic Magnetization 105     6.2 Magnetization at Thermal Equilibrium 106     6.3 Transverse Magnetization and Coherences 108     6.4 Time Evolution of Magnetization 109     6.4.1 The Bloch Equations 110     6.4.2 Longitudinal and Transverse Relaxation 112     6.5 The Rotating Frame of Reference 115     6.6 RF Pulses 117     6.6.1 Decomposition of the RF Field 118     6.6.2 Magnetic Fields in the Rotating Frame 119     6.6.3 The Bloch Equations in the Rotating Frame 120     6.6.4 Rotation of On-Resonant and Off-Resonant Magnetization under the Influence of Pulses 121     6.7 Problems 122     7 Chemical Shift and Scalar and Dipolar Couplings 125     7.1 Chemical Shielding 125     7.1.1 The Contributions to Shielding 127     7.1.2 The Chemical Shifts of Paramagnetic Compounds 131     7.1.3 The Shielding Tensor 132     7.2 The Spin   Spin Coupling 133     7.2.1 Scalar Coupling 134     7.2.2 Quadrupolar Coupling 140     7.2.3 Dipolar Coupling 141     7.3 Problems 144     Further Reading 145     8 A Formal Description of NMR Experiments: The Product Operator Formalism 147     8.1 Description of Events by Product Operators 148     8.2 Classification of Spin Terms Used in the POF 149     8.3 Coherence Transfer Steps 151     8.4 An Example Calculation for a Simple 1D Experiment 152     Further Reading 153     9 A Brief Introduction into the Quantum-Mechanical Concepts of NMR 155     9.1 Wave Functions, Operators, and Probabilities 155     9.1.1 Eigenstates and Superposition States 156     9.1.2 Observables of Quantum-Mechanical Systems and Their Measured Quantities 157     9.2 Mathematical Tools in the Quantum Description of NMR 158     9.2.1 Vector Spaces, Bra   s, Ket   s, and Matrices 158     9.2.2 Dirac   s Bra   Ket Notation 159     9.2.3 Matrix Representation of State Vectors 160     9.2.4 Rotations between State Vectors can be Accomplished with Tensors 161     9.2.5 Projection Operators 162     9.2.6 Operators in the Bra   Ket Notation 163     9.2.7 Matrix Representations of Operators 165     9.3 The Spin Space of Single Noninteracting Spins 166     9.3.1 Expectation Values of the Spin-Components 168     9.4 Hamiltonian and Time Evolution 169     9.5 Free Precession 169     9.6 Representation of Spin Ensembles     The Density Matrix Formalism 171     9.6.1 Density Matrix at Thermal Equilibrium 173     9.6.2 Time Evolution of the Density Operator 173     9.7 Spin Systems 175     9.7.1 Scalar Coupling 176     Part Three Technical Aspects of NMR 179     10 The Components of an NMR Spectrometer 181     10.1 The Magnet 181     10.1.1 Field Homogeneity 182     10.1.2 Safety Notes 183     10.2 Shim System and Shimming 184     10.2.1 The Shims 184     10.2.2 Manual Shimming 185     10.2.3 Automatic Shimming 186     10.2.4 Using Shim Files 187     10.2.5 Sample Spinning 187     10.3 The Electronics 187     10.3.1 The RF Section 188     10.3.2 The Receiver Section 189     10.3.3 Other Electronics 189     10.4 The Probehead 189     10.4.1 Tuning and Matching 190     10.4.2 Inner and Outer Coils 191     10.4.3 Cryogenically Cooled Probes 191     10.5 The Lock System 192     10.5.1 The 2H Lock 192     10.5.2 Activating the Lock 193     10.5.3 Lock Parameters 194     10.6 Problems 194     Further Reading 194     11 Acquisition and Processing 195     11.1 The Time Domain Signal 197     11.2 Fourier Transform 199     11.2.1 Fourier Transform of Damped Oscillations 199     11.2.2 Intensity, Integral, and Line Width 200     11.2.3 Phases of Signals 201     11.2.4 Truncation 202     11.2.5 Handling Multiple Frequencies 202     11.2.6 Discrete Fourier Transform 203     11.2.7 Sampling Rate and Aliasing 204     11.2.8 How Fourier Transformation Works 205     11.3 Technical Details of Data Acquisition 209     11.3.1 Detection of the FID 209     11.3.2 Simultaneous and Sequential Sampling 210     11.3.3 Digitizer Resolution 213     11.3.4 Receiver Gain 214     11.3.5 Analog and Digital Filters 215     11.3.6 Spectral Resolution 216     11.4 Data Processing 217     11.4.1 Digital Resolution and Zero Filling 217     11.4.2 Linear Prediction 219     11.4.3 Pretreatment of the FID: Window Multiplication 220     11.4.4 Phase Correction 227     11.4.5 Magnitude Mode and Power Spectra 229     11.4.6 Baseline Correction 230     11.5 Problems 231     Further Reading 232     12 Experimental Techniques 233     12.1 RF Pulses 233     12.1.1 General Considerations 234     12.1.2 Hard Pulses 235     12.1.3 Soft Pulses 236     12.1.4 Band-Selective RF Pulses 237     12.1.5 Adiabatic RF Pulses 238     12.1.6 Composite Pulses 240     12.1.7 Technical Considerations 241     12.1.8 Sources and Consequences of Pulse Imperfections 243     12.1.9 RF Pulse Calibration 244     12.1.10 Transmitter Pulse Calibration 245     12.1.11 Decoupler Pulse Calibration (13C and 15N) 246     12.2 Pulsed Field Gradients 247     12.2.1 Field Gradients 247     12.2.2 Using Gradient Pulses 248     12.2.3 Technical Aspects 250     12.3 Phase Cycling 251     12.3.1 The Meaning of Phase Cycling 251     12.4 Decoupling 255     12.4.1 How Decoupling Works 255     12.4.2 Composite Pulse Decoupling 256     12.5 Isotropic Mixing 257     12.6 Solvent Suppression 257     12.6.1 Presaturation 258     12.6.2 Water Suppression through Gradient-Tailored Excitation 259     12.6.3 Excitation Sculpting 260     12.6.4 WET 260     12.6.5 One-Dimensional NOESY with Presaturation 260     12.6.6 Other Methods 261     12.7 Basic 1D Experiments 262     12.8 Measuring Relaxation Times 262     12.8.1 Measuring T1 Relaxation     The Inversion-Recovery Experiment 262     12.8.2 Measuring T2 Relaxation     The Spin Echo 263     12.9 The INEPT Experiment 266     12.10 The DEPT Experiment 268     12.11 Problems 270     13 The Art of Pulse Experiments 271     13.1 Introduction 271     13.2 Our Toolbox: Pulses, Delays, and Pulsed Field Gradients 272     13.3 The Excitation Block 273     13.3.1 A Simple 90y Pulse Experiment 273     13.3.2 The Effects of 180y Pulses 273     13.3.3 Handling of Solvent Signals 274     13.3.4 A Polarization Transfer Sequence 275     13.4 The Mixing Period 277     13.5 Simple Homonuclear 2D Sequences 278     13.6 Heteronuclear 2D Correlation Experiments 279     13.7 Experiments for Measuring Relaxation Times 281     13.8 Triple-Resonance NMR Experiments 283     13.9 Experimental Details 284     13.9.1 Selecting the Proper Coherence Pathway: Phase Cycles 284     13.9.2 Pulsed Field Gradients 286     13.9.3 N-Dimensional NMR and Sensitivity Enhancement Schemes 288     13.10 Problems 289     Further Reading 289     Part Four Important Phenomena and Methods in Modern NMR 291     14 Relaxation 293     14.1 Introduction 293     14.2 Relaxation: The Macroscopic Picture 293     14.3 The Microscopic Picture: Relaxation Mechanisms 294     14.3.1 Dipole   Dipole Relaxation 295     14.3.2 Chemical Shift Anisotropy 297     14.3.3 Scalar Relaxation 298     14.3.4 Quadrupolar Relaxation 298     14.3.5 Spin   Spin Rotation Relaxation 299     14.3.6 Paramagnetic Relaxation 299     14.4 Relaxation and Motion 299     14.4.1 A Mathematical Description of Motion: The Spectral Density Function 300     14.4.2 NMR Transitions That Can Be Used for Relaxation 302     14.4.3 The Mechanisms of T1 and T2 Relaxation 303     14.4.4 Transition Probabilities 304     14.4.5 Measuring Relaxation Rates 306     14.5 Measuring 15N Relaxation to Determine Protein Dynamics 306     14.5.1 The Lipari   Szabo Formalism 307     14.6 Measurement of Relaxation Dispersion 310     14.7 Problems 313     15 The Nuclear Overhauser Effect 315     15.1 Introduction 315     15.1.1 Steady-State and Transient NOEs 318     15.2 The Formal Description of the NOE: The Solomon Equations 318     15.2.1 Different Regimes and the Sign of the NOE: Extreme Narrowing and Spin Diffusion 320     15.2.2 The Steady-State NOE 321     15.2.3 The Transient NOE 324     15.2.4 The Kinetics of the NOE 324     15.2.5 The 2D NOESY Experiment 325     15.2.6 The Rotating-Frame NOE 327     15.2.7 The Heteronuclear NOE and the HOESY Experiment 329     15.3 Applications of the NOE in Stereochemical Analysis 330     15.4 Practical Tips for Measuring NOEs 332     15.5 Problems 333     Further Reading 334     16 Chemical and Conformational Exchange 335     16.1 Two-Site Exchange 335     16.1.1 Fast Exchange 338     16.1.2 Slow Exchange 340     16.1.3 Intermediate Exchange 340     16.1.4 Examples 342     16.2 Experimental Determination of the Rate Constants 344     16.3 Determination of the Activation Energy by Variable-Temperature NMR Experiments 346     16.4 Problems 348     Further Reading 349     17 Two-Dimensional NMR Spectroscopy 351     17.1 Introduction 351     17.2 The Appearance of 2D Spectra 352     17.3 Two-Dimensional NMR Spectroscopy: How Does It Work? 354     17.4 Types of 2D NMR Experiments 357     17.4.1 The COSY Experiment 358     17.4.2 The TOCSY Experiment 359     17.4.3 The NOESY Experiment 362     17.4.4 HSQC and HMQC Experiments 364     17.4.5 The HMBC Experiment 365     17.4.6 The HSQC-TOCSY Experiment 366     17.4.7 The INADEQUATE Experiment 367     17.4.8 J-Resolved NMR Experiments 368     17.5 Three-Dimensional NMR Spectroscopy 370     17.6 Practical Aspects of Measuring 2D Spectra 370     17.6.1 Frequency Discrimination in the Indirect Dimension: Quadrature Detection 370     17.6.2 Folding in 2D Spectra 376     17.6.3 Resolution in the Two Frequency Domains 377     17.6.4 Sensitivity of 2D NMR Experiments 378     17.6.5 Setting Up 2D Experiments 379     17.6.6 Processing 2D Spectra 380     17.7 Problems 381     18 Solid-State NMR Experiments 383     18.1 Introduction 383     18.2 The Chemical Shift in the Solid State 384     18.3 Dipolar Couplings in the Solid State 386     18.4 Removing CSA and Dipolar Couplings: Magic-Angle Spinning 387     18.5 Reintroducing Dipolar Couplings under MAS Conditions 388     18.5.1 An Alternative to Rotor-Synchronized RF Pulses: Rotational Resonance 390     18.6 Polarization Transfer in the Solid State: Cross-Polarization 391     18.7 Technical Aspects of Solid-State NMR Experiments 393     18.8 Problems 394     Further Reading 394     19 Detection of Intermolecular Interactions 395     19.1 Introduction 395     19.2 Chemical Shift Perturbation 397     19.3 Methods Based on Changes in Transverse Relaxation (Ligand-Observe Methods) 398     19.4 Methods Based on Changes in Cross-Relaxation (NOEs) (Ligand-Observe or Target-Observe Methods) 400     19.5 Methods Based on Changes in Diffusion Rates (Ligand-Observe Methods) 403     19.6 Comparison of Methods 404     19.7 Problems 405     Further Reading 406     Part Five Structure Determination of Natural Products by NMR 407     20 Carbohydrates 419     20.1 The Chemical Nature of Carbohydrates 419     20.1.1 Conformations of Monosaccharides 422     20.2 NMR Spectroscopy of Carbohydrates 423     20.2.1 Chemical Shift Ranges 423     20.2.2 Systematic Identification by NMR Spectroscopy 424     20.2.3 Practical Tips: The Choice of Solvent 429     20.3 Quick Identification 430     20.4 A Worked Example: Sucrose 430     Further Reading 437     21 Steroids 439     21.1 Introduction 439     21.1.1 The Chemical Nature 440     21.1.2 Proton NMR Spectra of Steroids 441     21.1.3 Carbon Chemical Shifts 443     21.1.4 Assignment Strategies 444     21.1.5 Identification of the Stereochemistry 447     21.2 A Worked Example: Prednisone 449     Further Reading 456     22 Peptides and Proteins 457     22.1 Introduction 457     22.2 The Structure of Peptides and Proteins 458     22.3 NMR of Peptides and Proteins 461     22.3.1 1HNMR 461     22.3.2 13C NMR 464     22.3.3 15N NMR 467     22.4 Assignment of Peptide and Protein Resonances 469     22.4.1 Peptides 470     22.4.2 Proteins 473     22.5 A Worked Example: The Pentapeptide TP5 476     Further Reading 480     23 Nucleic Acids 481     23.1 Introduction 481     23.2 The Structure of DNA and RNA 482     23.3 NMR of DNA and RNA 486     23.3.1 1HNMR 486     23.3.2 13C NMR 489     23.3.3 15NNMR 490     23.3.4 31P NMR 490     23.4 Assignment of DNA and RNA Resonances 492     23.4.1 Unlabeled DNA/RNA 492     23.4.2 Labeled DNA/RNA 496     Further Reading 498     Appendix 499     A.1 The Magnetic H and B Fields 499     A.2 Magnetic Dipole Moment and Magnetization 500     A.3 Scalars, Vectors, and Tensors 501     A.3.1 Properties of Matrices 504     Solutions 507     Index 525