Features topics in 2D optical and vibrational spectroscopy (IR, Raman, UV, Visible). This work is particularly useful for the analysis of large molecules such as polymers, as these often cannot be analyzed by normal spectroscopy.

Preface xi Acknowledgements xiii 1 Introduction 1 1.1 Two-dimensional Spectroscopy 1 1.2 Overview of the Field 3 1.3 Generalized Two-dimensional Correlation 6 1.3.1 Types of Spectroscopic Probes 7 1.3.2 External Perturbations 7 1.4 Heterospectral Correlation 9 1.5 Universal Applicability 10 2 Principle of Two-dimensional Correlation Spectroscopy 15 2.1 Two-dimensional Correlation Spectroscopy 15 2.1.1 General Scheme 15 2.1.2 Type of External Perturbations 16 2.2 Generalized Two-dimensional Correlation 17 2.2.1 Dynamic Spectrum 17 2.2.2 Two-dimensional Correlation Concept 18 2.2.3 Generalized Two-dimensional Correlation Function 19 2.2.4 Heterospectral Correlation 20 2.3 Properties of 2D Correlation Spectra 20 2.3.1 Synchronous 2D Correlation Spectrum 20 2.3.2 Asynchronous 2D Correlation Spectrum 22 2.3.3 Special Cases and Exceptions 24 2.4 Analytical Expressions for Certain 2D Spectra 24 2.4.1 Comparison of Linear Functions 24 2.4.2 2D Spectra Based on Sinusoidal Signals 26 2.4.3 Exponentially Decaying Intensities 28 2.4.4 Distributed Lorentzian Peaks 29 2.4.5 Signals with more Complex Waveforms 30 2.5 Cross-correlation Analysis and 2D Spectroscopy 31 2.5.1 Cross-correlation Function and Cross Spectrum 31 2.5.2 Cross-correlation Function and Synchronous Spectrum 32 2.5.3 Hilbert Transform 33 2.5.4 Orthogonal Correlation Function and Asynchronous Spectrum 34 2.5.5 Disrelation Spectrum 35 3 Practical Computation of Two-dimensional Correlation Spectra 39 3.1 Computation of 2D Spectra from Discrete Data 39 3.1.1 Synchronous Spectrum 39 3.1.2 Asynchronous Spectrum 40 3.2 Unevenly Spaced Data 41 3.3 Disrelation Spectrum 43 3.4 Computational Efficiency 43 4 Generalized Two-dimensional Correlation Spectroscopy in Practice 47 4.1 Practical Example 47 4.1.1 Solvent Evaporation Study 47 4.1.2 2D Spectra Generated from Experimental Data 48 4.1.3 Sequential Order Analysis by Cross Peak Signs 50 4.2 Pretreatment of Data 52 4.2.1 Noise Reduction Methods 52 4.2.2 Baseline Correction Methods 53 4.2.3 Other Pretreatment Methods 54 4.3 Features Arising from Factors other than Band Intensity Changes 56 4.3.1 Effect of Band Position Shift and Line Shape Change 56 4.3.2 Simulation Studies 57 4.3.3 2D Spectral Features from Band Shift and Line Broadening 59 5 Further Expansion of Generalized Two-dimensional Correlation Spectroscopy – Sample–Sample Correlation and Hybrid Correlation 65 5.1 Sample–Sample Correlation Spectroscopy 65 5.1.1 Correlation in another Dimension 65 5.1.2 Matrix Algebra Outlook of 2D Correlation 66 5.1.3 Sample–Sample Correlation Spectra 67 5.1.4 Application of Sample–Sample Correlation 69 5.2 Hybrid 2D Correlation Spectroscopy 72 5.2.1 Multiple Perturbations 72 5.2.2 Correlation between Data Matrices 72 5.2.3 Case Studies 73 5.3 Additional Remarks 74 6 Additional Developments in Two-dimensional Correlation Spectroscopy – Statistical Treatments, Global Phase Maps, and Chemometrics 77 6.1 Classical Statistical Treatments and 2D Spectroscopy 77 6.1.1 Variance, Covariance, and Correlation Coefficient 77 6.1.2 Interpretation of 2D Disrelation Spectrum 78 6.1.3 Coherence and Correlation Phase Angle 79 6.1.4 Correlation Enhancement 80 6.2 Global 2D Phase Maps 81 6.2.1 Further Discussion on Global Phase 81 6.2.2 Phase Map with a Blinding Filter 82 6.2.3 Simulation Study 83 6.3 Chemometrics and 2D Correlation Spectroscopy 86 6.3.1 Comparison between Chemometrics and 2D Correlation 86 6.3.2 Factor Analysis 87 6.3.3 Principal Component Analysis (PCA) 87 6.3.4 Number of Principal Factors 88 6.3.5 PCA-reconstructed Spectra 89 6.3.6 Eigenvalue Manipulating Transformation (EMT) 91 7 Other Types of Two-dimensional Spectroscopy 95 7.1 Nonlinear Optical 2D Spectroscopy 96 7.1.1 Ultrafast Laser Pulses 96 7.1.2 Comparison with Generalized 2D Correlation Spectroscopy 97 7.1.3 Overlap Between Generalized 2D Correlation and Nonlinear Spectroscopy 98 7.2 Statistical 2D Correlation Spectroscopy 99 7.2.1 Statistical 2D Correlation by Barton II et al. 99 7.2.2 Statistical 2D Correlation by Šašic and Ozaki 102 7.2.3 Other Statistical 2D Spectra 109 7.2.4 Link to Chemometrics 109 7.3 Other Developments in 2D Correlation Spectroscopy 110 7.3.1 Moving-window Correlation 110 7.3.2 Model-based 2D Correlation Spectroscopy 110 8 Dynamic Two-dimensional Correlation Spectroscopy Based on Periodic Perturbations 115 8.1 Dynamic 2D IR Spectroscopy 115 8.1.1 Sinusoidal Signals 115 8.1.2 Small-amplitude Perturbation and Linear Response 116 8.1.3 Dynamic IR Linear Dichroism (DIRLD) 117 8.1.4 2D Correlation Analysis of Dynamic IR Dichroism 119 8.2 Dynamic 2D IR Dichroism Spectra of Polymers 121 8.2.1 Polystyrene/Polyethylene Blend 122 8.2.2 Polystyrene 127 8.2.3 Poly(methyl methacrylate) 129 8.2.4 Human Skin Stratum Corneum 133 8.2.5 Human Hair Keratin 134 8.2.6 Toluene and Dioctylphthalate in a Polystyrene Matrix 137 8.2.7 Polystyrene/Poly(vinyl methyl ether) Blend 141 8.2.8 Linear Low Density Polyethylene 144 8.2.9 Poly(hydroxyalkanoates) 148 8.2.10 Block Copolymers 150 8.2.11 Summary 152 8.3 Repetitive Perturbations Beyond DIRLD 153 8.3.1 Time-resolved Small Angle X-ray Scattering (SAXS) 153 8.3.2 Depth-profiling Photoacoustic Spectroscopy 158 8.3.3 Dynamic Fluorescence Spectroscopy 165 8.3.4 Summary 166 9 Applications of Two-dimensional Correlation Spectroscopy to Basic Molecules 169 9.1 2D IR Study of the Dissociation of Hydrogen-bonded N-Methylacetamide 170 9.2 2D NIR Sample–Sample Correlation Study of Phase Transitions of Oleic Acid 174 9.3 2D NIR Correlation Spectroscopy Study of Water 176 9.4 2D Fluorescence Study of Polynuclear Aromatic Hydrocarbons 179 10 Generalized Two-dimensional Correlation Studies of Polymers and Liquid Crystals 187 10.1 Temperature and Pressure Effects on Polyethylene 187 10.2 Reorientation of Nematic Liquid Crystals by an Electric Field 195 10.3 Temperature-dependent 2D NIR of Amorphous Polyamide 199 10.4 Composition-based 2D Raman Study of EVA Copolymers 203 10.5 Polarization Angle-dependent 2D IR Study of Ferroelectric Liquid Crystals 209 11 Two-dimensional Correlation Spectroscopy and Chemical Reactions 217 11.1 2D ATR/IR Study of Bis(hydroxyethyl terephthalate) Oligomerization 217 11.2 Hydrogen–Deuterium Exchange of Human Serum Albumin 222 12 Protein Research by Two-dimensional Correlation Spectroscopy 231 12.1 Adsorption and Concentration-dependent 2D ATR/IR Study of β-Lactoglobulin 232 12.2 pH-dependent 2D ATR/IR Study of Human Serum Albumin 236 12.2.1 N Isomeric Form of HSA 237 12.2.2 N–F Transition Region of HSA 239 12.3 Aggregation of Lipid-bound Cytochrome c 241 13 Applications of Two-dimensional Correlation Spectroscopy to Biological and Biomedical Sciences 245 13.1 2D NIR Study of Milk 246 13.2 2D IR Study of Synthetic and Biological Apatites 251 13.3 Identification and Quality Control of Traditional Chinese Medicines 253 14 Application of Heterospectral Correlation Analysis 257 14.1 Correlation between different Spectral Measurements 257 14.2 SAXS/IR Dichroism Correlation Study of Block Copolymer 258 14.3 Raman/NIR Correlation Study of Partially Miscible Blends 260 14.4 ATR/IR–NIR Correlation Study of BIS(hydroxyethyl terephthalate) Oligomerization 262 14.5 XAS/Raman Correlation Study of Electrochemical Reaction of Lithium with CoO 264 15 Extension of Two-dimensional Correlation Analysis to Other Fields 271 15.1 Applications of 2D Correlation beyond Optical Spectroscopy 271 15.2 2D Correlation Gel Permeation Chromatography (GPC) 271 15.2.1 Time-resolved GPC Study of a Sol–Gel Polymerization Process 272 15.2.2 2D GPC Correlation Maps 274 15.2.3 Reaction Mechanisms Deduced from the 2D GPC Study 279 15.3 2D Mass Spectrometry 281 15.4 Other Unusual Applications of 2D Correlation Analysis 282 15.5 Return to 2D NMR Spectroscopy 283 15.5.1 2D Correlation in NMR 283 15.5.2 Generalized Correlation (GECO) NMR 284 15.5.3 2D Correlation in Diffusion-ordered NMR 284 15.6 Future Developments 288 Index 291

In the last decade or so, perturbation-based generalized two-dimensional (2D) correlation spectroscopy has become a powerful and versatile tool for the detailed analysis of various spectroscopic data. This seemingly straightforward idea of spreading the spectral information onto the second dimension, by applying the well-established classical correlation analysis methodology, has turned out to be very fertile ground for the development a new generation of modern spectral analysis techniques. In Chapter 1, some historical perspectives and an overview of the field of perturbation-based 2D correlation spectroscopy is provided. Chapter 2 covers the central theoretical background of the two-dimensional correlation method. Chapter 3 provides a rapid and simple computational method for obtaining 2D correlation spectra from experimentally obtained spectral data set, followed by the practical considerations to be taken into account for the 2D correlation analysis of real-world spectral data in Chapter 4. The next three chapters deal with more advanced topics. Chapter 5 introduces the concept of sample-sample correlation and hybrid correlation, and Chapter 6 explores the relationship between 2D correlation spectroscopy and classical statistical and chemometrical treatments of data. Chapter 7 examines other types of 2D spectroscopy, such as nonlinear optical 2D spectroscopy based on ultra fast laser pulses, 2D mapping of correlation coefficient, and newly emerging variant forms of 2D correlation analyses, such as moving-window correlation and model based correlation method. The remaining chapters of the book are devoted to specific application examples of 2D correlation spectroscopy illustrating how the technique can be utilized in various aspects of spectroscopic studies. These examples include: * Generalized Two-Dimensional Correlation Studies of Polymers and Liquid Crystals * Two-Dimensional Correlation Spectroscopy and Chemical Reactions * Protein Research by Two-Dimensional Correlation Spectroscopy * Applications of 2D Correlation Spectroscopy to Biological and Biomedical Sciences * Application of Hetero-spectral Correlation Analysis * Extension of Two-Dimensional Correlation Analysis to Other Field This book serves as an introductory text for newcomers to the field, as well as presents a survey of specific interest areas for the experienced practitioners.