Two-dimensional FT-IR Spectroscopy Research Articles

Host−Guest Interactions and Crystalline Structure Evolution in Clathrate Phases Formed by Syndiotactic Polystyrene and 1,2-Dichloroethane: A Two-Dimensional FTIR Spectroscopy Investigation

2D correlation spectroscopy has been used to investigate the behavior of a clathrate sample of syndiotactic polystyrene including 1,2-dichloroethane (DCE) in the crystalline phase. Isothermal desorption of DCE at 80 °C was selected as the perturbation process, with time as external variable, and it was shown that the response function of the system was an exponential decay. The resolution enhancement brought about by 2D analysis and the possibility to identify the temporal relationship among asynchronously correlated events allowed us to gather information on host−guest molecular interactions and on the development of the crystal structure, not readily available with more conventional approaches. It was shown that a characteristic peak of the guest molecules, i.e., the CH2 wagging mode of the trans conformer at 1235 cm-1, is significantly influenced by host−guest interactions taking place within the cavity of the s-PS clathrate. It was confirmed that the desorption of the guest molecules initially present in the amorphous phase of the sample takes place at a faster rate than the desorption of those included into the cavities of the crystalline phase. This effect, in turn, allowed us to discriminate between the peaks of DCE absorbed in the two phases. In terms of dynamic behavior, it was found that DCE peaks respond faster to the applied perturbation than the polymer peaks, and as for the polymer spectrum, the crystalline phase responds faster than the amorphous phase. The latter effect has been tentatively attributed to the occurrence of a mesomorphic phase.

Characterization of Uniaxially Aligned Chitin Film by 2D FT-IR Spectroscopy

Two-dimensional FT-IR spectroscopy (2D FT-IR) was applied to the investigations of crystalline chitin structure. From this study, new information about spectral bands which are not observed in conventional 1D FT-IR was obtained. In 2D spectra, three specific bands were differentiated at 3482, 3421, and 3380 cm(-1) in the OH region. They could be assigned as C(6)OH groups which are hydrogen-bonded to the next C(6)OH; C(3)OH groups hydrogen-bonded to O(5); and C(6)OH groups bifurcated hydrogen-bonded to C(6)OH as well as C=O, respectively. Two pairs of bands appeared in the amide region, indicating the two types of hydrogen-bonded states of C=O groups. This is in good agreement with the results in the OH region; half of the C(6)OH groups are hydrogen-bonded to C=O as well as the next C(6)OH. The results accurately confirmed the Blackwell model which was established by an X-ray diffraction study. The temperature-dependency of hydrogen-bonds was also revealed by 2D FT-IR. Interchain hydrogen-bonds [C(6)OH...O(6)] first respond to a temperature followed by intrachain [C(6)OH...O=C] and [C(3)OH...O(5)] with increasing temperature. Interchain hydrogen-bonds [NH...O=C] are relatively stable in the temperature range of 40-180 degrees C.

Light-Induced Two-Dimensional FT-IR Spectroscopy of BacterioRhodopsin

Two-dimensional Fourier transform infrared (2D FT-IR) spectroscopy was applied to study the slower states of the membrane protein bacterioRhodopsin (bR) photocycle, with bR adsorbed on a ZnSe attenuated total reflectance (ATR) crystal. The M and the N states of the bR photocycle could be discriminated, and 2D spectra revealed an N state absorption band at 1536 cm−1 that is normally covered by the broader and bigger 1527 cm−1 M state absorption band. 2D FT-IR absorbance changes are presented in a more convenient way for analysis than in traditional 2D FT-IR spectroscopy by using 2D-phase spectra and phase/amplitude calculations.

Two-Dimensional FT-IR Spectroscopy: A Powerful Method to Study the Secondary Structure of Proteins Using H-D Exchange

Two-dimensional infrared spectroscopy has been used for the first time to study the conformation of proteins by hydrogen–deuterium exchange. In order to generate the two-dimensional synchronous and asynchronous maps, hydrogen–deuterium exchange of the amide protons of proteins deposited on attenuated total reflection crystals has been used as an external perturbation. Owing to the fact that the amide protons associated with each conformation are not exchanged at the same rate, the different conformational contributions of the amide bands could be separated. The use of different sampling time domains turned out to be very helpful in order to separate more efficiently the fast kinetics from the slower ones. The results obtained on myoglobin show that this method is particularly useful to unravel the different components under the poorly resolved amide I, II, and II' bands of proteins. The analysis of the synchronous and asynchronous maps of myoglobin demonstrates that the amide I band of this protein is composed of at least four components that could be assigned to α-helical, intermolecular β-sheet, β-turn, and random coil conformations.

Dynamic two-dimensional infrared spectroscopy. Part II: Morphological assignments in melt-crystallized nylon 11 spectra

Abstract Melt-crystallized and deuterated nylon 11 are studied using dynamic two-dimensional FTIR spectroscopy in the region below 1500 cm −1 of the infrared spectrum. The splittings observed in the methylene rocking-amide V (760-640 cm −1 ) and methylene bending (1500-1400 cm −1 ) regions are explained on the basis of morphological features. These morphological assignments are corroborated by correlating methylene rocking-amide V and methylene bending regions with the morphological assignments of amide I-amide II (1680-1500 cm −1 ) region of nylon 11 established in an earlier work.

Dynamic Two-Dimensional Infrared Spectroscopy. Part I: Melt-Crystallized Nylon 11

Two-dimensional FT-IR spectroscopy has been used to study the N-H stretching and amide I/amide II region of melt-crystallized nylon 11 thin films on Teflon® substrates. Samples are dynamic mechanically oscillated at room temperature at a frequency of 11 Hz. A two-dimensional correlation analysis on the dynamic spectra indicates that the N-H stretching region splits into two peaks. Analysis of two-dimensional crossplots between the N-H stretching region and the amide I/amide II region shows that the prominent peak in the N-H stretching region (∼3300 cm−1) is similar in morphological character to the ordered peak of the amide I region. The amide II region resolves into two-ordered and one-disordered peak.