2D Infrared Correlation Spectroscopy Research Articles

A thermal oxidative degradation study of triallyl isocyanurate crosslinking moiety in fluorinated rubber by two-dimensional infrared correlation spectroscopy

Thermal degradation of crosslinking moiety in fluorinated rubbers was studied with a new method using spatial-dependent infrared (IR) microscopy and two-dimensional (2D) IR correlation spectroscopy. Upon heating the fluorinated rubber, initially the amount of crosslinker decreased followed by generating another chemical species with carbonyl substituent with IR absorption at around 1730 cm–1, implying generation of carboxylic acids forming intermolecular hydrogen bonding. Furthermore, projection 2D IR correlation analysis revealed that another chemical species with IR absorption at around 1755 cm–1 generates, indicating that further degradation progresses upon heating and intermolecular hydrogen bonding were broken. As a result, the multi-step degradation process of the crosslinker in the fluorinated rubber could be detected by combination of spatial-dependent IR microscopy and projection 2D IR correlation spectroscopy.

Synthesis and characterization of a new catalyst for RhB degradation constructed by [SiMo12O40]4− anionic cluster

Abstract A Keggin-type polyoxomolybdate [H 2 biim]{Ni(biim) 3 (SiMo 12 O 40 )} [biim = 1 H ,1′ H -[2,2′]biimidazolyl] has been synthesized under hydrothermal condition and characterized by XRD, temperature-dependent IR, TG, temperature-induced and magnetism-induced 2D infrared correlation spectroscopy (2D-IR COS) and UV–vis DRS in order to explore the relationship between structure and properties. Temperature-induced 2D-IR COS spectroscopy indicates that the terminal Mo O μ / ν bonds are more sensitive than the bridging Mo O t bands to temperature variation, which is in agreement with the conclusion of temperature-dependent IR. Magnetism-dependent 2D-IR COS spectroscopy reveals the stretching vibration of the Mo O t occurs prior to the stretching vibration of the Mo O μ / ν , which is due to the coordination environment and the valence of the Si atom. The stability of compound 1 is investigated via TG and temperature-dependent IR. In RhB degradation, compound 1 shows good photocatalytic abilities.

Investigation of selective molecular interactions using two-dimensional Fourier transform IR spectroscopy

A novel method of studying molecular interactions is introduced. It is a method based on the framework of a two-dimensional (2D) infrared (IR) correlation spectroscopy technique with a new data pretreatment strategy. In this method, an additional external perturbation stimulates the system to cause some selective changes in the state, order, and surroundings of system constituents. The overall response of the stimulated system to the applied external perturbation leads to distinctive changes in the measured spectrum, and a series of perturbation-induced dynamic spectra are collected in a systematic manner. Such a set of dynamic spectra are then transformed into a set of 2D correlation spectra by cross-correlation analysis. Temperature was chosen as an external perturbation, and the molecular interaction between 4-aminopyridine (Apy) and methacrylic acid (MAA) was investigated by 2D IR correlation spectroscopy. Synchronous cross peaks exist between the stretching vibration of the C-O group of MAA at 1,298 and 1,202 cm(-1) and the C=N group of Apy at 1,531 cm(-1), and between the carbonyl group of MAA at 1,705 cm(-1) and the amino group of Apy at 3,382 and 3,212 cm(-1). The synchronous cross peaks are from orientation of MAA and Apy vibrations generated at the same time; the synchronization of microstructure movements in the molecules indicates that there exists strong interactions between MAA and Apy. According to 2D correlation rules, static electricity and hydrogen-bonding interactions exist between Apy and MAA. Such results were further verified by (1)H-NMR spectroscopy. The successful application demonstrates that 2D IR correlation spectroscopy may be a convenient and effective method in the study of molecular interactions.

Analysis of the CO2 and NH3 Reaction in an Aqueous Solution by 2D IR COS: Formation of Bicarbonate and Carbamate

The two-dimensional (2D) infrared correlation spectra obtained from the reaction time- and concentration-dependent IR spectra elucidates the reaction of CO2 and NH3 in an aqueous solution for CO2 absorption. In the synchronous 2D correlation spectra, the interrelation of the proton with carbamate and bicarbonate indicates that the pH level affected the formation reactions of the two products. Furthermore, the interrelation of carbamate with bicarbonate confirmed the conversion of carbamate into bicarbonate with the release of protons (or the decrease of the pH). From the experimental results including the asynchronous 2D correlation spectra, the reaction of the CO2 and aqueous ammonia proceeded through the following steps: formation of carbamate, formation of bicarbonate, release of protons, and conversion of carbamate into bicarbonate. The analysis of the formation of carbamate and bicarbonate by 2D infrared correlation spectroscopy provides useful information on the reaction mechanism of CO2 and NH3 in aqueous solutions.

Intermolecular Interaction-Induced Hierarchical Transformation in 1D Nanohybrids: Analysis of Conformational Changes by 2D Correlation Spectroscopy

We have examined both self-assembly and confinement effect in room-temperature ionic liquid (RTIL)-aluminum hydroxide hybrids (RAHs) to attain a fundamental understanding of special phenomena in nanoscale spaces as well as to design functional nanomaterials for practical applications. Phase-controlled one-dimensional (1D) RAHs were synthesized through a simple ionothermal process. The RAHs were hierarchically transformed in terms of the molecular structures, morphologies, and phases of the materials during the ionothermal process with respect to the concentration of RTIL. In addition to the hierarchical transformation, the RTIL/aluminum hydroxide nanohybrids revealed unexpected physical behaviors, including thermal transition variation of the RTIL in confined environments and a phase transition from nanosolid to nanoliquid affected by changes of the melting points. More importantly, intermolecular interaction induced-self-assembly and confinement effect of RTILs inside an integrated hybrid system, which have not been clearly explained to date, were analyzed by 2D infrared correlation spectroscopy (2D IR COS); dynamic behaviors of RTILs, i.e., sequentially spatial reorientation and kinetically conformational changes, were attributed to the interactions between RTILs and aluminum hydroxides. 2D IR COS offers a new way to interpret highly complex, veiled systems such as the formation mechanism of nanoparticles, biomineralization, self/supramolecular assembly, and nanoconfinement.

Initial Crystallization Mechanism of Isotactic Polystyrene from Different States

The isothermal crystallization processes of isotactic polystyrene at 160 degrees C from different initial states (quenched glassy state and melt state), i.e., cold- and melt-crystallization processes, have been investigated by infrared (IR) and generalized two-dimensional (2D) IR correlation spectroscopy. It has been found that not only the crystallization kinetics and crystallinity but also the sequential changes of the amorphous and crystalline sensitive bands are quite different for the cold- and melt-crystallization processes. This leads to the conclusion that the physical origins for spinodal decomposition prior to polymer crystallization may be different for different crystallization processes.

Structure Changes during the Induction Period of Cold Crystallization of Isotactic Polystyrene Investigated by Infrared and Two-Dimensional Infrared Correlation Spectroscopy

The structural changes during the induction period of isotactic polystyrene (iPS) cold crystallization were investigated by using infrared (IR) spectroscopy together with 2D correlation analysis. It was found that the ordered orientation of the phenyl ring, local conformation change, and structural formation of 31 helix chain of iPS already appear during the induction period. Moreover, careful interpretation of the asynchronous 2D IR spectra generated from the time-dependent spectra enabled us to delineate the structural evolution during the induction period of iPS cold crystallization: Prior to the crystallization of iPS, the amorphous phase changes first, and then the ordering of the phenyl rings of iPS takes place. After that, the polymer chains adjust their local conformations to form the short 31 helix structure. The present study has also demonstrated that the generalized 2D IR correlation spectroscopy is powerful in studying small spectral changes in the induction period of polymer crystallization.

Two-dimensional infrared correlation spectroscopy studies on secondary structures and hydrogen bondings of side chains of proteins

This review paper reports usefulness of two-dimensional (2D) correlation spectroscopy in analyzing infrared (IR) spectra of proteins in aqueous solutions. In the 2D approach, spectral peaks are spread over the second dimension, thereby simplifying the visualization of complex spectra consisting of many overlapped bands, and enhancing spectral resolution. 2D correlation spectroscopy has a powerful deconvolution ability for highly overlapped amide I, amide II, and amide III bands of proteins, enabling these bands to be assigned to various secondary structures. It also provides the specific order of the spectral intensity changes taking place during the measurement on the value of controlling variable affecting the spectra. Therefore, one can monitor the order of secondary structure variations in proteins by using 2D IR correlation spectroscopy. 2D correlation spectroscopy also provides new insight into the hydrogen bondings of side chains of proteins. In this review the principles and advantages of 2D correlation spectroscopy are outlined first and then three examples of the applications of 2D IR spectroscopy to protein research are presented.

Two-Dimensional Infrared Spectroscopy and Principle Component Analysis Studies of the Secondary Structure and Kinetics of Hydrogen−Deuterium Exchange of Human Serum Albumin

Infrared (IR) spectra were measured as a function of time after dissolving human serum albumin (HSA) into D2O to investigate the secondary structure and the kinetics of hydrogen−deuterium (H/D) exchange. Two-dimensional (2D) IR correlation spectroscopy and principal component analysis (PCA) were used to analyze the obtained spectra. Two-dimensional IR spectra in the amide I and amide II (and II‘) regions were generated from time-dependent spectral variations in different exposure time domains of HSA in the D2O solution. The synchronous and asynchronous spectra in each time domain provide a clear separation of amide bands due to the different secondary structures and the asynchronous spectra show the specific sequence of the secondary structure exposed to the H/D exchange. PCA was used to select the appropriate time domains for the calculation of 2D correlation spectra. It was found that the loadings plots of PCA are useful also to assist the band assignments in the amide I and II region and to investigate the mechanism of the H/D exchange. The present study demonstrates the potential of PCA-2D correlation analysis combined method in the efficient separation of component bands due to different secondary structures and in the study of the kinetics of H/D exchange reaction.