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Preface xv
Preface to 'Introduction to Modern Vibrational Spectroscopy' (1994) xix
I Modern Vibrational Spectroscopy and Micro-spectroscopy: Theory, Instrumentation and Biomedical Applications 1
I. 1 Historical Perspective of Vibrational Spectroscopy 1
I. 2 Vibrational Spectroscopy within Molecular Spectroscopy 2
References 4
1 Molecular Vibrational Motion 5
1.1 The concept of normal modes of vibration 6
1.2 The separation of vibrational, translational, and rotational coordinates 6
1.3 Classical vibrations in mass-weighted Cartesian displacement coordinates 7
1.4 Quantum mechanical description of molecular vibrations 13
1.4.1 Transition from classical to quantum mechanical description 13
1.4.2 Diatomic molecules: harmonic oscillator 14
1.4.3 Diatomic molecules: anharmonicity 19
1.4.4 Polyatomic molecules 20
1.5 Time-dependent description and the transition moment 22
1.5.1 Time-dependent perturbation of stationary states by electromagnetic radiation 22
1.5.2 The vibrational transition moment for absorption: harmonic diatomic molecules 25
1.5.3 The vibrational transition moment for absorption: anharmonic diatomic molecules 27
1.5.4 The vibrational transition moment for absorption: polyatomic molecules 30
1.5.5 Isotopic effects: diatomic molecules 31
1.6 Basic infrared and Raman spectroscopies 32
1.6.1 Infrared absorption spectroscopy 32
1.6.2 Raman (scattering) spectroscopy 35
1.7 Concluding remarks 38
References 38
2 Symmetry Properties of Molecular Vibrations 39
2.1 Symmetry operations and symmetry groups 40
2.2 Group representations 44
2.3 Symmetry representations of molecular vibrations 50
2.4 Symmetry-based selection rules for absorption processes 54
2.5 Selection rules for Raman scattering 56
2.6 Discussion of selected small molecules 57
2.6.1 Tetrahedral molecules: carbon tetrachloride, CCl4 , and methane, CH4 57
2.6.2 Chloroform and methyl chloride 64
2.6.3 Dichloromethane (methylene chloride), CH2 Cl2 67
2.6.4 Dichloromethane-d1 (methylene chloride-d1), CHDCl2 68
References 69
3 Infrared Spectroscopy 71
3.1 General aspects of IR spectroscopy 71
3.2 Instrumentation 73
3.2.1 Sources of infrared radiation: black body sources 73
3.2.2 Sources of infrared radiation: quantum-cascade lasers, nonlinear devices 75
3.2.3 Transfer optics 76
3.2.4 Color sorting devices: monochromators 76
3.2.5 Color encoding devices: interferometers 79
3.2.6 Detectors 82
3.2.7 Read-out devices 84
3.3 Methods in interferometric IR spectroscopy 84
3.3.1 General instrumentation 84
3.3.2 Optical resolution 86
3.3.3 Zero filling and fourier smoothing 86
3.3.4 Phase correction 88
3.3.5 Apodization 91
3.4 Sampling strategies 92
3.4.1 Transmission measurement 92
3.4.2 Specular reflection 94
3.4.3 Diffuse reflection 95
3.4.4 Attenuated total reflection 97
3.4.5 Infrared reflection absorption spectroscopy (IRRAS) 99
3.4.6 Fourier transform photoacoustic spectroscopy (FT-PAS) 100
3.4.7 Planar array infrared spectroscopy (PA-IRS) 101
3.4.8 Two-dimensional FTIR 101
3.4.9 Infrared microspectroscopy 102
References 102
4 Raman Spectroscopy 103
4.1 General aspects of Raman spectroscopy 104
4.2 Polarizability 105
4.3 Polarization of Raman scattering 107
4.4 Dependence of depolarization ratios on scattering geometry 111
4.5 A comparison between Raman and fluorescence spectroscopy 114
4.6 Instrumentation for Raman spectroscopy 116
4.6.1 Sources 116
4.6.2 Dispersive Raman instrumentation and multichannel detectors 116
4.6.3 Interferometric Raman instrumentation 121
4.6.4 Raman microspectroscopy 122
References 122
5 A Deeper Look at Details in Vibrational Spectroscopy 123
5.1 Fermi resonance 124
5.2 Transition dipole coupling (TDC) 128
5.3 Group frequencies 129
5.4 Rot-vibrational spectroscopy 130
5.4.1 Classical rotational energy 130
5.4.2 Quantum mechanics of rotational spectroscopy 132
5.4.3 Rot-vibrational transitions 137
References 141
6 Special Raman Methods: Resonance, Surface-Enhanced, and Nonlinear Raman Techniques 143
6.1 Resonance Raman spectroscopy 144
6.2 Surface-enhanced Raman scattering (SERS) 146
6.3 Nonlinear Raman effects 149
6.3.1 Spontaneous (incoherent) nonlinear Raman effects 149
6.3.2 Coherent nonlinear effects 152
6.4 Continuous wave and pulsed lasers 159
6.4.1 Einstein coefficients and population inversion 160
6.4.2 Operation of a gas laser 162
6.4.3 Principles of pulsed lasers 163
6.4.4 Operation of pulsed lasers 163
6.5 Epilogue 164
References 164
7 Time-Resolved Methods in Vibrational Spectroscopy 167
7.1 General remarks 167
7.2 Time-resolved FT infrared (TR-FTIR) spectroscopy 168
7.2.1 Experimental aspects 168
7.2.2 Applications of TR-FTIR spectroscopy 169
7.3 Time-resolved Raman and resonance Raman (TRRR) spectroscopy 171
7.3.1 Instrumental aspects 171
7.3.2 Applications of TRRR 173
7.3.3 Heme group dynamic studies 173
7.3.4 Rhodopsin studies 174
References 175
8 Vibrational Optical Activity 177
8.1 Introduction to optical activity and chirality 177
8.2 Infrared vibrational circular dichroism (VCD) 179
8.2.1 Basic theory 179
8.2.2 Exciton theory of optical activity 180
8.3 Observation of VCD 181
8.4 Applications of VCD 185
8.4.1 VCD of biological molecules 185
8.4.2 Small molecule VCD 185
8.5 Raman optical activity 186
8.6 Observation of ROA 188
8.7 Applications of ROA 189
8.7.1 ROA of biological molecules 189
8.7.2 Small molecules ROA 190
References 190
9 Computation of Vibrational Frequencies and Intensities 193
9.1 Historical approaches to the computation of vibrational frequencies 193
9.2 Vibrational energy calculations 194
9.2.1 Classical approaches: the Wilson GF matrix method 194
9.2.2 Early computer-based vibrational analysis 197
9.3 Ab initio quantum-mechanical normal coordinate computations 197
9.4 Vibrational intensity calculations 198
9.4.1 Fixed partial charge method for infrared intensities 198
9.4.2 Quantum mechanical infrared and Raman intensities: localized molecular orbitals 200
9.4.3 The finite perturbation method 200
References 202
II Biophysical and Medical Applications of Vibrational Spectroscopy and Microspectroscopy 203
10 Biophysical Applications of Vibrational Spectroscopy 205
10.1 Introduction 205
10.2 Vibrations of the peptide linkage and of peptide models 206
10.2.1 Amino acids and the peptide linkage 206
10.2.2 The vibrational modes of the peptide linkage 206
10.3 Conformational studies of peptides and polyamino acids 210
10.4 Protein spectroscopy: IR, VCD, Raman, resonance Raman, and ROA spectra of proteins 215
10.5 Nucleic acids 219
10.5.1 Structure and function of nucleic acids 219
10.5.2 Phosphodiester vibrations 222
10.5.3 Ribose vibrations 222
10.5.4 Base vibrations 222
10.6 Conformational studies on DNA and DNA models using IR, Raman, and VCD spectroscopies 223
10.7 Lipids and phospholipids 227
10.8 Epilogue 231
References 231
11 Vibrational Microspectroscopy (MSP) 235
11.1 General remarks 235
11.2 General aspects of microscopy 236
11.3 Raman microspectroscopy (RA-MSP) 239
11.3.1 Dispersive (single point) systems 240
11.3.2 Micro-Raman imaging systems 241
11.4 CARS and FSRS microscopy 242
11.5 Tip-enhanced Raman spectroscopy (TERS) 243
11.6 Infrared microspectroscopy (IR-MSP) 243
11.6.1 Fourier-transform infrared imaging systems 244
11.6.2 QCL-based systems 246
11.7 Sampling strategies for infrared microspectroscopy 247
11.7.1 Transmission measurement 247
11.7.2 Transflection measurement 247
11.7.3 Attenuated total reflection (ATR) 248
11.8 Infrared near-field microscopy 249
References 249
12 Data Preprocessing and Data Processing in Microspectral Analysis 251
12.1 General remarks 251
12.2 Data preprocessing 252
12.2.1 Cosmic ray filtering (Raman data sets only) 253
12.2.2 Linear wavenumber interpolation (Raman data sets only) 253
12.2.3 Conversion from transmittance to absorbance units (some infrared data sets) 253
12.2.4 Normalization 253
12.2.5 Noise reduction 254
12.2.6 Conversion of spectra to second derivatives 256
12.3 Reduction of confounding spectral effects 257
12.3.1 Reduction of water vapor contributions in cellular pixel spectra 258
12.3.2 Mie and resonance Mie scattering 258
12.3.3 Correction of dispersive band shapes 260
12.3.4 Standing wave effect 262
12.4 Unsupervised multivariate methods of data segmentation 263
12.4.1 Factor methods 264
12.4.2 Data segmentation by clustering methods 269
12.5 Supervised multivariate methods 272
12.5.1 Discussion of sensitivity, specificity, and accuracy 272
12.5.2 Soft independent modeling of class analogy (SIMCA) 273
12.5.3 Artificial neural networks (ANNs) 274
12.5.4 Support vector machines (SVMs) 275
12.5.5 Random forests (RFs) 276
12.5.6 Cross-validation 277
12.6 Summary of data processing for microspectral analysis 278
12.7 Two-dimensional correlation methods in infrared spectroscopy (2D-IR) 278
References 280
13 Infrared Microspectroscopy of Cells and Tissue in Medical Diagnostics 283
13.1 Introduction 283
13.2 Spectral histopathology (SHP) 284
13.2.1 Review of classical histopathology 284
13.2.2 Spectral methods in histopathology 285
13.2.3 Infrared absorption spectroscopy of cells and tissue: introductory comments 285
13.3 Methodology for SHP 287
13.3.1 General approach 287
13.3.2 Sequence of steps in classical histopathology 288
13.3.3 Sequence of steps for spectral histopathology 288
13.4 Applications of SHP for the classification of primary tumors 294
13.4.1 Cervical tissue and cervical cancer 294
13.4.2 Lung cancer 298
13.4.3 Prostate cancer 303
13.4.4 Breast cancer 304
13.5 Application of SHP toward the detection and classification of metastatic tumors 304
13.5.1 Detection of colon cancer metastases in lymph nodes 304
13.5.2 Detection of breast cancer metastases in lymph nodes 306
13.5.3 Detection and classification of brain metastases 307
13.6 Future prospects of SHP 309
13.7 Infrared spectral cytopathology (SCP) 310
13.7.1 Classical cytopathology 311
13.7.2 Spectral cytopathology 314
13.7.3 Methods for SCP 314
13.8 SCP results 316
13.8.1 Early results of SCP 316
13.8.2 Fixation studies 317
13.8.3 Spectral cytopathology of cervical mucosa 320
13.8.4 Spectral cytopathology of the oral mucosa 323
13.8.5 Spectral cytopathology of esophageal cells 326
13.9 SCP of cultured cells 328
13.9.1 Early SCP efforts and general results 328
13.9.2 SCP of cultured cells to study the effects of the cell cycle and of drugs on cells 328
13.10 Infrared spectroscopy of cells in aqueous media 331
13.11 Future potential of SCP 333
References 333
14 Raman Microspectroscopy of Cells and Tissue in Medical Diagnostics 339
14.1 Introduction 339
14.2 Experimental Consideration for Raman Microspectroscopy 341
14.3 High-Resolution Raman Spectral Cytopathology 343
14.3.1 Subcellular organization 343
14.3.2 Subcellular transport phenomena 345
14.4 Low-Resolution Raman SCP of Cultured Cells In Vitro 349
14.5 Raman SCP in Solution 352
14.5.1 Optical tweezing of cells in aqueous media 352
14.5.2 Cells trapped in microfluidic chips 353
14.5.3 Resonance Raman spectroscopy of erythrocytes 353
14.6 Raman Spectral Histopathology (Ra SHP) 354
14.7 In Vivo Raman SHP 356
14.8 Deep Tissue Raman SHP 357
14.8.1 Hard tissue diagnostics 357
14.8.2 Deep tissue imaging of breast tissue and lymph nodes 358
References 359
15 Summary and Epilogue 363
Appendix A The Particle in a Box: A Demonstration of Quantum Mechanical Principles for a Simple, One-Dimensional, One-Electron Model System 365
A. 1 Definition of the Model System 365
A. 2 Solution of the Particle-in-a-Box Differential Equation 367
A. 3 Orthonormality of the Particle-in-a-Box Wavefunctions 370
A. 4 Dipole-Allowed Transitions for the Particle in a Box 370
A. 5 Real-World PiBs 371
Appendix B A summary of the Solution of the Harmonic Oscillator (Hermite) Differential Equation 373
Appendix C Character Tables for Chemically Important Symmetry Groups 377
C. 1 The nonaxial groups 377
C. 2 The Cn groups 377
C. 3 The Dn groups 379
C. 4 The Cnv groups 379
C. 5 The Dnh groups 382
C. 6 The Dnd groups 384
C. 7 The Sn groups 385
C. 8 The cubic groups 386
C. 9 The groups C8, and D8h for linear molecules 387
C. 10 The icosahedral groups 388
Appendix D Introduction to Fourier Series, the Fourier Transform, and the Fast Fourier Transform Algorithm 389
D. 1 Data Domains 389
D. 2 Fourier Series 390
D. 3 Fourier Transform 392
D. 4 Discrete and Fast Fourier Transform Algorithms 393
References 395
Appendix E List of Common Vibrational Group Frequencies (cm-1) 397
Appendix F Infrared and Raman Spectra of Selected Cellular Components 399
Index 405
The subject of this monograph, vibrational spectroscopy, derives its name from the fact that atoms in molecules undergo continuous vibrational motion about their equilibrium position, and that these vibrational motions can be probed via one of two major techniques: infrared (IR) absorption spectroscopy and Raman scattering, and several variants of these two major categories. IR spectroscopy experienced a boon in the years of World War II, when the US military was involved in an effort to produce and characterize synthetic rubber. Vibrational spectroscopy, for which industrial application guides were published as early as 1944 [1], turned out to be a fast and accurate way to identify different synthetic products. The rapid growth of the field of vibrational spectroscopy can be gauged by the fact that by the mid-1940s, the field was firmly established as a scientific endeavor, and the volume "Molecular Spectra and Molecular Structure" by Herzberg (one volume of a trilogy of incredibly advanced treatises on molecular spectroscopy [2]) reported infrared and Raman results on hundreds of small molecules. Similarly, the earliest efforts to use infrared spectroscopy as a means to distinguish normal and diseased tissue - the subject of Part II of this book - were reported by Blout and Mellors [3] and by Woernley [4] by the late 1940s and early 1950s. In the 1960s, the petroleum industry added another industrial use for these spectroscopic techniques when it was realized that hydrocarbons of different chain lengths and degrees of saturation produced distinct infrared spectral patterns, and for the first time, computational methods to understand, reproduce, and predict spectral patterns were introduced [5]. By then, commercial scanning infrared spectrometers were commercially available.
The 1970 produced another boon when commercial Fourier transform (FT) infrared spectrometers became commercially available, and gas lasers replaced the mercury arc lamp as excitation source for Raman spectroscopy. Before lasers, Raman spectroscopy was a somewhat esoteric technique, since large sample volumes and a lot of time were required to collect Raman data with the prevailing Hg arc excitation sources. Yet, after the introduction of laser sources, Raman spectra could be acquired rapidly and as easily as infrared spectra. After the introduction and wide acceptance of interferometry, infrared spectroscopy became the method of choice for many routine and quality control applications. During the ensuing decade, the field of vibrational spectroscopy blossomed at a phenomenal rate, and it is safe to state that no other spectroscopy grew at such a pace than vibrational spectroscopy, perhaps with the exception of nuclear magnetic resonance techniques. Other spectroscopic methods, such as ultraviolet/visible (UV/vis), microwave, or electron paramagnetic resonance (EPR) spectroscopy certainly profited from theoretical and technical advances; however, in vibrational spectroscopy, the sensitivity of the measurements increased by orders of magnitude while the time requirements for data acquisition dropped similarly.
After the introduction of tunable, high power, and pulsed lasers, not only were faster and more sensitive techniques developed (for example, resonance Raman and time-resolved techniques), but also, entirely new spectroscopic methods were discovered, among them a number of "non-linear" Raman techniques (such as Hyper-Raman and Coherent Anti-Stokes Raman Scattering, CARS) in which the effect depends non-linearly on the laser field strength. Dramatic progress was also achieved in IR spectroscopy, due to the advent of infrared lasers and further refinements of interferometric methods.
Aside from small molecule applications of vibrational spectroscopy, the past three decades have seen an ever increasing use of vibrational spectroscopy in biophysical, biochemical, and biomedical studies. This field has enormously enhanced the ability to determine solution conformations of biological molecules, their interaction and even reaction pathways. All major classes of biological molecules, proteins, nucleic acids, and lipids, exhibit vibrational spectra that are enormously sensitive to structure and structural changes, and thousands of research papers have been published demonstrating the value of these methods for the understanding of biochemical processes.
With the advent of vibrational micro-spectroscopic instruments, that is, infrared or Raman spectrometers coupled to optical microscopes, cell biological and medical application of vibrational spectroscopy was practical since the spatial resolution in Raman and infrared absorption microscopy is sufficient to distinguish, by spectral features, parts of cells and tissue. These methods are poised to enter the medical diagnostic field as inherently reproducible and objective tools. This monograph will provide an introduction to many of these fields mentioned above.
Molecular spectroscopy is a branch of science in which the interactions of electromagnetic radiation and matter are studied. While the theory of these interactions itself is the subject of ongoing research, the aim and goal of the discussions here is the elucidation of information on molecular structure and dynamics, the environment of the sample molecules and their state of association, interactions with solvent, and many other topics.
Molecular (or atomic) spectroscopy is usually classified by the wavelength ranges (or energies) of the electromagnetic radiation (e.g., microwave or infrared spectroscopies) interacting with the molecular systems. These spectral ranges are summarized in Table I.1.
Table I.1 Table of photon energies and spectroscopic ranges
In Table 1.1, NMR and EPR stand for nuclear magnetic and electron paramagnetic resonance spectroscopy, respectively. In both these spectroscopic techniques, the transition energy of a proton or electron spin depends on the applied magnetic field strength. All techniques listed in Table 1.1 can be described by absorption processes (see below) although other descriptions, such as bulk magnetization in NMR, are possible as well.
The interaction of the radiation with molecules or atoms that was referred to above as an "absorption process" requires that the energy difference between two (molecular or atomic) "stationary states" exactly matches the energy of the photon:
where h denotes Planck's constant (h = 6.6 × 10-34Js) and ? the frequency of the photon, in s-1. As seen from Table 1.1, these photon energies are between 10-16 and 10-25 J/molecule or about 10-4 to 105 kJ/(mol photons). In an absorption process, one photon interacts with one atom or molecule to promote it into a state of higher excitation, and the photon is annihilated. The reverse process also occurs where an atomic or molecular system undergoes a transition from a more highly excited to a less highly excited state; in this process, a photon is created. However, this view of the interaction between light and matter is somewhat restrictive, since radiation interacts with matter even if its wavelength is far different than the specific wavelength at which a transition occurs. Thus, a classification of spectroscopy, which is more general than that given by the wavelength range alone, would be a resonance/off-resonance distinction. Many of the effects described and discussed in spectroscopy books are observed as resonance interactions where the incident light, indeed, possesses the exact energy of the molecular transition in question. IR and UV/vis absorption spectroscopy, microwave spectroscopy, or EPR are examples of such resonance interactions. However, interaction of light and matter occurs, in a more subtle way, even if the wavelength of light is different from that of a molecular transition. These off-resonance interactions between electromagnetic radiation and matter give rise to well-known phenomena such as the refractive index of dielectric materials, and the anomalous dispersion of the...
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