Two-Dimensional Correlation Spectroscopy: Applications in Vibrational and Optical 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 ĦSaĦsic 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