Characterization of infrared and near-infrared absorptions of free alcoholic OH groups in hydrocarbon

We have demonstrated that the near-infrared and infrared absorptions in the 8000-3200 cm(-1) region of an OH group of 2-nonanol, 1-nonanol, etc., in n-heptane are excellently separated by subtraction without any serious interference down to very low concentrations at which OH groups are completely free. The separated sharp absorptions are assigned to the fundamental, combination, and overtone bands that are concerned with the OH stretching of free OH. Two components of a sharp overtone band around 7100 cm(-1), which are observed for primary and secondary alcohols, are assigned to coexisting internal rotational isomers of an OH group around the O-C bond. The frequencies of the OH stretching fundamental and overtone bands that are assigned to internal rotational positions are consistent for all the investigated alcohols, including methanol and tertiary butanol. Comparison of the separated spectrum of 2-nonanol in n-heptane with that in 1-chlorooctane or in carbon tetrachloride makes it clear that hydrocarbon is an inert solvent that does not disturb the intrinsic nature of an alcohol OH group. There actually exists a constant anharmonicity shift of 169-175 cm(-1) between the double frequency (2nu(OH)o) of the observed fundamental and the observed overtone frequency ([2nu(OH)]o) for free OH of various alcohols in n-heptane.     

Crystallization of polylactide and its stereocomplex investigated by two-dimensional fourier transform infrared correlation spectroscopy employing carbonyl overtones

The band origins and transitions of weak vibrational modes developed in the 3500 cm(-1) region of polylactide (PLA) spectra during crystallization are investigated. The band assignment to the OH stretching mode of terminal hydroxyls is unlikely because the trace amount of chain-ends is negligible considering the long chain of high molecular weight polymer. The band intensity can be enhanced for quantitative study by increasing the sample film thickness. The results show that the transition patterns of these bands mimic those of C=O stretching modes. Therefore, these are assigned to C=O overtones. Two bands associated with crystalline and amorphous characteristics are revealed during cold crystallization. The crystalline C=O bands of PDLA and its stereocomplex counterpart are located at 3510 cm(-1) and 3482 cm(-1), respectively, indicating a weaker C=O bond in the latter crystal structure. Two-dimensional Fourier transform infrared (2D-FT-IR) correlation spectroscopy is then applied to study the correlation between C=O overtones and the crystalline characteristic band located near 900 cm(-1). The transitions of the two vibrational modes observed in crystallization of the stereocomplex are in-phase with each other. This reflects an involvement of short-range hydrogen bonding in the stereocomplex crystal structure. In contrast, crystallization of PDLA shows that the C=O overtone varies prior to that of the C-H character, indicating that dipole-dipole force is a crystal-induced interaction.     

Application of infrared emission spectroscopy to the thermal transition of indium hydroxide to indium oxide nanocubes

Cubic indium hydroxide nanomaterials were obtained by a low-temperature soft-chemical method without any surfactants. The transition of nano-cubic indium hydroxide to cubic indium oxide during dehydroxylation has been studied by infrared emission spectroscopy. The spectra are related to the structure of the materials and the changes in the structure upon thermal treatment. The infrared absorption spectrum of In(OH)(3) is characterized by an intense OH deformation band at 1150 cm(-1) and two O-H stretching bands at 3107 and 3221 cm(-1). In the infrared emission spectra, the hydroxyl-stretching and hydroxyl-bending bands diminish dramatically upon heating, and no intensity remains after 200 °C. However, new low intensity bands are found in the OH deformation region at 915 cm(-1) and in the OH stretching region at 3437 cm(-1). These bands are attributed to the vibrations of newly formed InOH bonds because of the release and transfer of protons during calcination of the nanomaterial. The use of infrared emission spectroscopy enables the low-temperature phase transition brought about through dehydration of In(OH)(3) nanocubes to be studied.     

Revealing covariance structures in fourier transform infrared and Raman microspectroscopy spectra: a study on pork muscle fiber tissue subjected to different processing parameters

The aim of this study was to investigate the correlation patterns between Fourier transform infrared (FT-IR) and Raman microspectroscopic data obtained from pork muscle tissue, which helped to improve the interpretation and band assignment of the observed spectral features. The pork muscle tissue was subjected to different processing factors, including aging, salting, and heat treatment, in order to induce the necessary degree of variation of the spectra. For comparing the information gained from the two spectroscopic techniques with respect to the experimental design, multiblock principal component analysis (MPCA) was utilized for data analysis. The results showed that both FT-IR and Raman spectra were mostly affected by heat treatment, followed by the variation in salt content. Furthermore, it could be observed that IR amide I, II, and III band components appear to be effected to a different degree by brine-salting and heating. FT-IR bands assigned to specific protein secondary structures could be related to different Raman C-C stretching bands. The Raman C-C skeletal stretching bands at 1,031, 1,061, and 1,081 cm(-1) are related to the IR bands indicative of aggregated beta-structures, while the Raman bands at 901 cm(-1) and 934 cm(-1) showed a strong correlation with IR bands assigned to a alpha-helical structures. At the same time, the IR band at 1,610 cm(-1), which formerly was assigned to tyrosine in spectra originating from pork muscle, did not show a correlation to the strong tyrosine doublet at 827 and 852 cm(-1) found in Raman spectra, leading to the conclusion that the IR band at 1,610 cm(-1) found in pork muscle tissue is not originating from tyrosine.     

Infrared and near-infrared spectral evidence for water clustering in highly hydrated poly(methyl methacrylate)

First, we developed quantitative analytical methods of water in poly(methyl methacrylate) (PMMA) in various hydrated states by utilizing the first combination and OH stretching bands of water at about 5240 and 3630 cm-1, respectively. Next, we investigated how the state of water depended on its quantity or the mole ratio of water to the CO (denoted as the H2O/CO ratio), which only interacts with water in PMMA, mainly on the basis of the band feature of the OH stretching bands. Below the H2O/CO ratio of 0.032, the contained water, which shows two clear bands at about 3630 and 3550 cm-1, is hydrogen-bonded to two C=O groups as C=O::H-O-H::O=C to form "the hydration core". The spectrum of the water that exceeds the ratio in question shows one broader band only, the frequency of which shifts downward with the increasing hydration. From detailed analysis of the behavior of the OH stretching and combination bands in relation to the H2O/CO ratio, we have concluded that the water that exceeds the hydration ratio becomes mobile to aggregate or "cluster" around hydrated sites rather than nonhydrated ones in the PMMA matrix, although the latter is much larger in population.     

Ab initio calculations of proline vibrations with and without water: consequences on the infrared spectra of proline-rich proteins

The infrared spectra of proline-rich proteins display a strong band in the 1450 cm(-1) region. In the literature, this band has been assigned either to the deformation modes of the CH(2) and CH(3) groups or to the CN stretching mode of proline residues. In order to establish the correct assignment of this band, the impact of proline vibrations in a polypeptide chain is studied and ab initio calculations are performed for a model molecule (I) containing a repeat unit of polyproline. A strong band is effectively calculated in the 1450 cm(-1) region and mostly assigned to CN stretching, whereas, due to the absence of the N-H bond, there is no amide II band. These results are in good agreement with the spectral features observed in the Fourier transform infrared (FT-IR) spectra of gliadins. Moreover, the spectral shifts calculated when a water molecule is complexed with (I) are consistent with the hydration effect observed in the experimental data.     

Estimation of crystallinity in isotropic isotactic polypropylene with Raman spectroscopy

The Raman spectrum of isotactic polypropylene (iPP) has been found to exhibit vibrational peaks in the region of 750 to 880 cm(-1) that are sensitive to the degree of crystallinity. These features are broadly assigned to various modes of methyl group rocking, rho(CH2), and there have been various attempts to assess crystallinity based on the integrated intensities of these bands. Various vibrational analyses performed in the past in combination with experimental studies have concluded that the presence of crystalline order with trans-gauche conformation gives rise to a peak at 809 cm(-1), which is assigned to a rho(CH2) mode coupled with the skeletal stretching mode. However, the presence of additional peaks at 830 cm(-1), 841 cm(-1), and 854 cm(-1), within the same envelope, have been the subject of controversy. In this work isotropic films of iPP derived from the same precursor of identical tacticity have been subjected to various degrees of annealing and the integrated intensities of the Raman bands were measured. The results showed that true 3d crystallinity in isotropic iPP can only be expressed by the 809 cm(-1) band whereas the band at 841 cm(-1) corresponds to an uncoupled rho(CH2) fundamental mode and thus is a measure of the amorphous content. The less intense satellite bands at 830 cm(-1) and 854 cm(-1) of solid iPP cannot be distinguished from the 841 cm(-1) band in the melt and are generally considered as intermediate phases possibly related to non-crystalline components with 3(1)-helical conformations. Independent differential scanning calorimetry (DSC) crystallinity measurements were in broad agreement with the Raman measurements based on the normalized intensity of the 809 cm(-1) Raman band. By comparing the Raman with the DSC data a new value for the theoretical heat of fusion for the 100% crystalline iPP has been proposed.     

Transmission infrared spectroscopy as a probe of Nafion film structure: analysis of spectral regions fundamental to understanding hydration effects

Transmission infrared spectroscopy was applied to investigate properties of the perfluorosulfonated polymer Nafion. Measurements were made on thin films formed by casting the polymer from solution onto ZnSe windows. Effects of water vapor permeation were studied. A complex band structure between 1350 and 1100 cm(-1) was analyzed qualitatively by fitting the region to Gaussian functions. Features associated with vibrational modes of -CF(2) and -SO(3)(-) groups were identified and observed to be sensitive to film hydration. The intensities of bands for the -SO(3)(-) modes increased with film hydration, while bands assignable to -CF(2) modes decreased. The results were applied to interpret infrared difference spectra of Nafion and shed light on the complicated features that appear. Vibrational bands for water were also examined. In partially hydrated films, the stretching mode of the free -OH group for interfacial water present in pores and channels of the polymer and bands for hydrated proton clusters were detected.     

Extended range near-infrared imaging of water and oil in facial skin

Recently, near-infrared (NIR) imaging has been applied to detecting changes in skin hydration using the water OH band centered near 1460 nm. However, assigning changes in the intensity of the OH band near 1460 nm to changes in the skin's water content is complicated. Consequently, detection of small changes in facial skin water content is difficult. For highly sensitive imaging of facial skin water and oil, a near-infrared unit with a large detection range that includes the CH(3) and CH(2) stretching vibration modes at 1700-1800 nm and the strongest water bands centered near 1920 nm is required. In this study, an extended range indium gallium arsenide near-infrared camera was combined with a diffuse-illumination unit specifically developed for facial skin analysis. Images of water and oil in facial skin were obtained in real time using a combination of interference filters, such as 1950 ± 56 nm for water OH, 1775 ± 50 nm for oil CH, and 1300 ± 40 nm for background reflections. Clear near-infrared images were obtained with little mirror reflection. The water and oil content of facial skin could be evaluated even around the eyes, nose, and sides of the cheeks, which are areas that are difficult to analyze using current commercial devices. Differences were detected in the time-dependent changes of water and oil content in facial skin images obtained after the application of different types of moisturizer. The distribution of both water and oil in the facial skin could be visualized at the same time, and the images could be used to evaluate skin type and skin conditions.     

Two-dimensional correlation study of uniaxially drawn poly(ethylene terephthalate) films by using attenuated total reflection based dynamic compression modulation step-scan fourier transform infrared in combination with spectral simulation analysis by density functional theory

Attenuated total reflection (ATR) based dynamic compression modulation two-dimensional (2D) correlation studies of uniaxially drawn poly(ethylene terephthalate) (PET) films have been performed in combination with spectral simulation analysis by density functional theory (DFT). The dynamic 2D infrared (IR) correlation spectra in the region of the CCO stretching mode vibrations show four distinct correlation peaks located around 1290, 1265, 1248, and 1234 cm(-1). These bands can be clearly assigned to the combination bands or coupling modes of the CH in-plane bend of the benzene ring or the CH(2) deformation of the ethylene glycol unit, as well as CCO stretching vibrations, which are gauche conformer's characteristic bands, by DFT analysis. The sequential analysis of 2D correlation data shows that, upon applying the dynamic compression, the response of the side chain regions (ester groups) occurs first, followed by that of the backbone regions (benzene rings). The ATR based dynamic compression modulation 2D correlation spectroscopy in combination with DFT analysis can be a powerful tool for various polymer characterizations.     

Nature of hydrogen bonding of water molecules in aqueous solutions of glycerol by attenuated total reflection (ATR) infrared spectroscopy

Attenuated total reflection infrared (ATR-IR) spectroscopy was performed on glycerol/water solutions in order to gain a better understanding of the strong hydrogen bonding of glycerol as a humectant. The OH stretching band after eliminating the contribution of glycerol OH in the glycerol/water solutions was decomposed using three Gaussian components. With increasing glycerol concentrations up to 50 volume %, the decrease of the 3428 cm(-1) component (middle H-bond component) and the increase of the 3562 cm(-1) component (longer H-bond component) suggested the breaking of H bonds among water molecules. On the other hand, the 3242 cm(-1) component (shorter H-bond component) remained unchanged. It was expected that water molecules surrounding glycerol molecules are retained by strong H bonding between H atoms of water and O atoms in C-O of glycerol when aqueous solutions containing glycerol are introduced in human skin.     

Band analysis of temperature-dependent near-infrared spectra of oleic acid in the pure liquid state by the analytic geometric approach

The applicability of the band-stripping and complementary matching method has been demonstrated by the analysis of temperature-dependent near-infrared (NIR) absorption spectra in the 7500-6500 cm(-1) region of oleic acid (cis-9-octadecenoic acid) in the pure liquid state. This method is based on first derivative-second derivative pair (D1-D2) plots and a new concept called the complementary band, cBDi, created by subtracting all the rest of the bands, exclusive of the ith estimated band, eBDi, from an experimental spectrum. The degree of coincidence of both band shapes provides a suitable measure for the quality of fit for each individual component band. It has been confirmed from the present analysis of the NIR spectra of oleic acid measured over a temperature range of 16-79 degrees C that the change of the peak intensity of the component band at around 6915 cm(-1) due to the first overtone of an O-H stretching vibration of the monomer has two transition points around 35 and 55 degrees C. Moreover, the present study has provided new insight into the analysis of temperature-dependent spectral variations of oleic acid. Among the three temperature ranges, 16-35 degrees C, 35-55 degrees C, and 55-79 degrees C, in the first range the band near 6915 cm(-1) shows a slight increase and in the second range it has a linear intensity change with a slope of 0.002 a.u./degree C. In the third range, a rapid increase of the peak intensity is observed. This band exists even at 15 degrees C (just below the melting point) and shows a shift from 6910 to 6915 cm(-1) and a band narrowing from 85 to 80 cm(-1) (full width at half-height) over a temperature range of 16 to 79 degrees C. Furthermore, it has been found that there are two broad bands at around 6835 and 6778.     

Gold nanoparticle-based pH sensor in highly alkaline region at pH > 11: surface-enhanced Raman scattering study

A surface plasmon resonance spectroscopy study showed that citrate-reduced gold nanoparticles ( approximately 15 nm diameter, approximately 9 x 10(-9) M concentration, approximately 2 x 10(-2) M ionic strength) were found to be utilized as a colorimetric sensor by exhibiting a distinct color change at a highly alkaline pH > 11.5. Surface-enhanced Raman scattering (SERS) of 4-ethynylpyridine (4-EP) on gold nanoparticle surfaces indicated that the multiple peaks in the v(C identical withC) stretching bands should vary significantly in the highly alkaline region from pH 12 to 14. As the pH value increased, the v(C identical withC) stretching band intensity at approximately 2080 cm(-1) became stronger than that at approximately 2010 cm(-1). The pK(1/2) value was determined to be around 13 by the SERS titration of taking intensity ratios of I(2080) with respect to I(2010). Using SERS enhancements and conspicuous spectral changes, self-assembled monolayers (SAMs) of 4-EP on Au nanoparticles holds potential as a pH sensor for sensitive detection of the hydroxide OH(-) concentration at around pH 13 in an aqueous solution. The pH calibration from SERS titration of 4-EP is expected to have advantages in terms of higher alkaline detection limit and more precise measurements, if compared with the indigo carmine, the pK(1/2) value of which is 12.2.     

Spatial differentiation of sub-micrometer domains in a poly(hydroxyalkanoate) copolymer using instrumentation that combines atomic force microscopy (AFM) and infrared (IR) spectroscopy

Atomic force microscopy (AFM) and infrared (IR) spectroscopy have been combined in a single instrument (AFM-IR) capable of producing sub-micrometer spatial resolution IR spectra and absorption images. This new capability enables the spectroscopic characterization of microdomain-forming polymers at levels not previously possible. Films of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) were solution cast on ZnSe prisms, followed by melting and annealing to generate crystalline microdomains of different sizes. A tunable IR laser generating pulses of the order of 10 ns was used for excitation of the sample films. Short duration thermomechanical waves, due to infrared absorption and resulting thermal expansion, were studied by monitoring the resulting excitation of the contact resonance modes of the AFM cantilever. Dramatic differences in the room-temperature IR spectra are observed in the 1200-1300 cm(-1) range as a function of position on a spatial scale of less than one micrometer. This spectral region is particularly sensitive to the polymer backbone conformation. Such dramatic spectral differences have also been observed previously in bulk IR measurements, but only by comparing room-temperature spectra with ones collected at higher temperatures. Less dramatic, but significant, AFM-IR spectral differences are observed in the carbonyl stretching region around 1720 cm(-1) as a function of location on the sample. Two overlapping, but relatively sharp, carbonyl bands are observed near 1720 cm(-1) in more crystalline regions of the polymer, while a broader carbonyl stretching band appears centered at 1740 cm(-1) in the more amorphous regions. Using this spectral region, it is possible to monitor the development of polymer crystalline structures at varying distances from a nucleation site, where the site was generated by bringing a heated AFM tip close to a specific location to locally anneal the sample.     

Infrared spectroscopy of OD vibrators in minerals at natural dilution: hydroxyl groups in talc and kaolinite, and structural water in beryl and emerald

An infrared (IR) study of natural deuteration is conducted on minerals containing hydroxyl groups (talc and kaolinite) and channel-water-bearing minerals (beryl and emerald). In talc, the OD valence vibration is located at 2710 cm(-1), corresponding to OD groups surrounded by 3 Mg atoms. In kaolinite, the OD valence vibrations are located at 2671 cm(-1) (inner OD group), 2712, 2706, and 2700 cm(-1) (three inner-surface OD groups). In beryl and emerald, natural deuteration of channel water is observed for the first time by infrared microspectroscopy. In beryl from Minas Gerais (Brazil), the OD profiles are characterized by four bands at 2735, 2686, 2672, and 2641 cm(-1). In emeralds from Colombia and Brazil, the OD profiles are characterized by five or four bands, respectively, at 2816, 2737, 2685, 2673, and 2641 cm(-1) (Colombia) and 2730, 2684, 2672, and 2640 cm(-1) (Brazil). The band at 2816 cm(-1) can be assigned to -OD or OD(-), and bands at 2686-2684, 2673-2672, and 2641-2640 cm(-1) can be assigned to type-I and type-II HOD molecules. The band at 2737-2730 cm(-1) is partially disturbed by combination bands of the mineral. Such OD profiles are different from those obtained by artificial deuteration at higher OD dilution.     

Hydrogen-deuterium exchange in bovine serum albumin protein monitored by Fourier transform infrared spectroscopy, part II: kinetic studies

The set of infrared spectra recorded at different levels of hydrogen-deuterium (H/D) exchange as a function of time were processed using spectral decomposition. The most precise information about H/D exchange of the NH groups of the protein backbone was retrieved by observing the intensity change of the nearest C=O stretching vibration. The H/D exchange at the protein backbone begins with NH groups bonded to C=O with a characteristic frequency of 1683 cm(-1). These amide groups were initially free and are the first to accept H-bonds from water during the hydration process. The NH groups, which are connected to C=O groups with a characteristic band at 1657 cm(-1), exchange at a slower rate. For both populations the pairs of comparable exchange rates were calculated with rate constants of 10(-3) min(-1), 0.014 min(-1), 0.0046 min(-1), and 0.09 min(-1). The appearance of two different exchange rates for each population is a consequence of the distinct exposure of particular molecular groups to the solvent. Two additional bands sensitive to exchange are attributed to NH bending modes in the side chains and are located at 1610 cm(-1) and 1585 cm(-1). These NH groups undergo H/D exchange at the beginning of the exchange with exchange rates of 0.019 min(-1) and 0.17 min(-1), respectively. The calculated exchange rate for hydrating water molecules is 0.037 min(-1). The distribution of water's exchange rate is extremely broad and covers almost the entire interval of the time-dependent experiment. From the efficiency of the exchange (96%) it is evident that some parts of the protein are completely forbidden to water molecules.     

溶胶—凝胶制备TiO2／SiO2复合薄膜的FT—IR表征

ＦＴ－ＩＲ吸收谱用来研究具有多孔结构的ＴｉＯ２／ＳｉＯ２复合薄膜；薄膜在１２００ｃｍ＾－１有一较强的肩峰，其强度与峰位随热处理温度度而生变化。在９５５ｃｍ＾－１的吸收峰是由于Ｓｉ－Ｏ－Ｔｉ和Ｓｉ－ＯＨ的结果，并随着热处理 度的提高其吸收峰完全是Ｓｉ－Ｏ－Ｔｉ振动所引起的，其峰位随着ＴｉＯ２的增加，向低频区域移动。     

Fourier transform infrared and inelastic neutron scattering study of HY zeolites

A combination ofFTi.r. and INS spectroscopy is used in a vibrational study of the bending and stretching vibrations of the acidic hydroxyl groups of Y zeolites. The influence of the number of acidic Bro¨nsted sites and theSi/Al ratio is discussed. Out-of-plane hydroxyl bending modes are assigned to vibrations centered around 419 cm⁻¹ and in-plane hydroxyl bending modes are assigned to vibrations centered around 1089 cm⁻¹. Upon dealumination, these bands are shifted by approximately 30 cm⁻¹ to lower values. The less intense bands at 319,470,565,765, and 1130 cm⁻¹ are assigned to proton-coupled framework vibrations. Upon dealumination, the mode at 319 cm⁻¹ is shifted to lower frequencies and the modes at 565 and 1130 cm⁻¹ are shifted to higher frequencies.     

Transmittance Fourier transform infrared spectra of liquid water in the whole mid-infrared region: temperature dependence and structural analysis

Transmittance Fourier transform infrared (FT-IR) spectra of liquid water in the 4-80 degrees C temperature range are reported in the whole mid-infrared (MIR) region (4000-360 cm (-1)). The spectra were recorded by using a newly developed, home-made transmittance cell, working in light vacuum conditions (pressures of the order of 3-4 millibar). This permits the elimination of the aqueous vapor bands from the liquid spectra, particularly in the bending region, and the rapid collection of data without fluxing large amounts of nitrogen through the interferometer sample chamber. The temperature evolution of the OH stretching and HOH deformation bands is discussed in terms of Gaussian components analysis and a two-state model describing the equilibrium between different H-bond structures of liquid water. From this picture, structural and thermodynamic information about the hydrogen-bonding network of water is obtained.