FTIR studies of calcium and sodium ionomers derived from an ethylene–methacrylic acid copolymer

A systematic study of the sodium and calcium salts of an ethylene–methacrylic acid copolymer is reported. Fourier-transform infrared spectroscopy (in the midinfrared region) is applied to the characterization of structural changes as a function of temperature and time of annealing. In the spectra of calcium ionomers, bands associated with carboxylate dimers are identified and assignments of specific spectral features to multiplets and clusters are discussed. The spectroscopic changes observed in the spectra of sodium ionomers differ somewhat from their calcium counterparts in that a single infrared band attributed to isolated carboxylate groups is observed. Assignments of specific bands to multiplets and clusters can, however, be made in a manner consistent with the interpretation of the spectra of calcium ionomers.     

Molecular dynamics simulation of liquid methanol. II. Unified assignment of infrared, Raman, and sum frequency generation vibrational spectra in methyl C-H stretching region

Vibrational spectra of methyl C-H stretching region are notoriously complicated, and thus a theoretical method of systematic assignment is strongly called for in condensed phase. Here we develop a unified analysis method of the vibrational spectra, such as infrared (IR), polarized and depolarized Raman, and ssp polarized sum frequency generation (SFG), by flexible and polarizable molecular dynamics simulation. The molecular model for methanol has been developed by charge response kernel model to allow for analyzing the methyl C-H stretching vibrations. The complicated spectral structure by the Fermi resonance has been unraveled by empirically shifting potential parameters, which provides clear information on the coupling mechanism. The analysis confirmed that for the IR, polarized Raman, and SFG spectra, two-band structure at about 2830 and 2950 cm(-1) results from the Fermi resonance splitting of the methyl C-H symmetric stretching and bending overtones. In the IR spectrum, the latter, higher-frequency band is overlapped with prominent asymmetric C-H stretching bands. In the depolarized Raman spectrum, the high frequency band at about 2980 cm(-1) is assigned to the asymmetric C-H stretching mode. In the SFG spectrum, the two bands of the splitted symmetric C-H stretching mode have negative amplitudes of imaginary nonlinear susceptibility χ(2), while the higher-frequency band is partly cancelled by positive imaginary components of asymmetric C-H stretching modes.     

Structural basis for the discrepancy of spectral behavior in C-H stretching band between steroids and long chain hydrocarbon compounds

The discrepancies of the spectral behavior for the C-H stretching band between some long chain hydrocarbon compounds and steroids were investigated. At low temperature, the C-H stretching bands exhibit complex fine structure in steroids but remain simple in long chain hydrocarbon compounds. MM3 molecular mechanics calculation indicates that, for long chain hydrocarbon compounds, the C-H groups vibrate with large scale coupling. There exist a few bands where the C-H groups vibrate in synchronous and inphase mode. Thus the variations of dipole moment for these bands are enhanced and the intensities are obviously stronger than others and cover other band in the spectra. This is just the reason why the C-H stretching bands are simple even at low temperature environment. Nevertheless, for the steroids, the C-H stretching bands vibrate with local coupling mode. The synchronous enhancement effect does not occur, the differences of intensities for various modes are not as large as those in long chain hydrocarbo     

Molecular understanding of the UCST-type phase separation behavior of a stereocontrolled poly(N-isopropylacrylamide) in bis(2-methoxyethyl) ether

The upper critical solution temperature (UCST)-type phase separation of an isotactic-rich poly( N-isopropylacrylamide) (PNiPA) in bis(2-methoxyethyl) ether (diglyme) has been investigated by turbidity measurement and infrared (IR) spectroscopy. The IR spectra of stereocontrolled PNiPAs in various solvents have clearly indicated that the amide I bands do not directly reflect the tacticity of the polymer. The relative intensity of the amide I bands changes depending upon the molecular environment around the amide groups of PNiPA, which is influenced by the tacticity. During the UCST-type phase separation of the isotactic-rich PNiPA in diglyme, the amide I band at around 1625 cm (-1) changes. To link the IR spectral change with the molecular information, quantum chemical calculations have been carried out for NiPA n-mers ( n = 1-4) with an isotactic stereosequence. The result has suggested that the amide I band at around 1625 cm (-1) arises from a helical structure formed by the isotactic stereosequences in the PNiPA main chain with the aid of intramolecular CO...H-N hydrogen bonding. The experimental IR spectra have revealed that the helical structures are unfolded as the temperature rises. The folding and unfolding of the isotactic sequences in the main chain may induce the thermal change in the solubility of the isotactic rich PNiPA in diglyme, resulting in the UCST-type phase separation of the solution.     

Towards understanding ice nucleation by long chain alcohols

We demonstrate that infrared spectra of water covered by a film of heptadecanol show a continuous spectral shift, from a band characteristic of liquid water to one characteristic of ice, as the temperature is ramped from -10 to -17 degrees C. Experiments with pure water and water covered by films of long chain alkanes showed no such spectral shift. Analysis of the CH2 stretching features in the alcohols' absorbance bands reveals simultaneous structural changes within the alcohol film. We hypothesize that the spectral shift in the water band is due to an increasing fraction of water molecules participating in icelike clusters and that these clusters are stabilized by the influence of the flexible alcohol film.     

Fourier self-deconvolution in IR spectroscopy

Fourier self-deconvolution (FSD) is a mathematical means for reducing bandwidths, so that overlapped bands can be resolved from one another. The principles of FSD are described briefly, and examples are shown of how overlapped infrared spectra can be enhanced so as to greatly improve their information content. The disadvantages of FSD are discussed and it is shown how the method can be extended to extract individual components from a composite envelope of bands.     

Line shape distortion effects in infrared spectroscopy

This paper explores different phenomena that cause distortions of infrared absorption spectra by mixing of reflective and absorptive band shape components of infrared spectra, and the resulting distortion of observed band shapes. In the context of this paper, we refer to the line shape of the variations of the refractive index in spectral regions of an absorption maximum (i.e., in regions of "anomalous dispersion") as "dispersive" or "reflective" line shape contributions, in analogy to previous spectroscopic literature. These distortions usually result in asymmetric bands with a negative intensity contribution at the high wavenumber of the band, accompanied by a shift toward lower wavenumber, and confounded band intensities. In extreme cases of band distortions caused by the "resonance Mie" (RMie) mechanism, spectral peaks may be split into doublets of peaks, change from positive to negative peaks, or appear as derivative-shaped features.     

Intramolecular vibrational dynamics of diacetylene and diacetylene-d1 via eigenstate-resolved overtone spectroscopy

The high resolution spectra of several CH overtone bands in diacetylene and diacetylene-d₁ were measured using optothermally detected excitation of a collimated molecular beam. The first overtone of the acetylenic CH stretches in these two molecules were recorded in a single resonance scheme using a 1.5 μm color center laser. The second overtone spectra were taken using sequential infrared/infrared double resonance with a 3.0 and a 1.5 μm color center lasers. The perturbations in the spectra have been analyzed to obtain information about the nature and timescales of the underlying intramolecular vibrational redistribution processes. The uncovered dynamical features appear to be dominated by anharmonic couplings and exhibit regular, not chaotic, behavior. The first and second overtone spectra of diacetylene-d₁ are consistent with a coupling model which involves coupling through a doorway state and then subsequent coupling to the bath. In diacetylene, a combination band was also recorded which, in the local mode picture, is equivalent to putting two quanta in one acetylenic CH stretch and one quanta at the other end of the molecule. Comparison of this spectrum with the spectrum obtained by putting three quanta in the same CH stretch, is consistent with earlier observations that delocalized combination bands are less perturbed than nearly isoenergetic pure overtone states.     

太阳CO 4.6微米红外成像观测

太阳红外光谱中蕴含着丰富的物理信息,其中CO 4.6μm波段是具有代表性的分子谱带,其形成于温度极小区附近,对研究太阳物理具有极其重要的意义。为获得CO 4.6μm波段太阳单色像,本文建立了一套全反射太阳红外成像观测系统。该系统采用定天镜跟踪引光,通过成像反射镜将太阳成像于3~5μm波段红外相机的焦平面上,该相机采用的是国产HgCdTe焦平面阵列器件。同时,为提高信噪比,提出了一种有效计算平场提取观测目标的方法,并利用该方法获得了CO 4.6μm波段的太阳单色像。     

Application of two‐dimensional near‐infrared (2D‐NIR) correlation spectroscopy to the discrimination of three species of Dendrobium

The objective of this paper was to apply two‐dimensional (2D) near‐infrared (NIR) correlation spectroscopy to the discrimination of three species of Dendrobium. Generalized 2D‐NIR correlation spectroscopy was able to enhance spectral resolution, simplify the spectrum with overlapped bands and provide information about temperature‐induced spectral intensity variations that was hard to obtain from one‐dimensional NIR spectroscopy. The FT‐NIR spectra were measured over a temperature range of 30–140°C. The 2D synchronous and asynchronous spectra showed remarkable differences within the range of 5600–4750 cm⁻¹ between different species of Dendrobium. Copyright © 2009 John Wiley & Sons, Ltd.     

Infrared laser spectroscopy of uracil and thymine in helium nanodroplets: vibrational transition moment angle study

Vibrational spectra are reported in the N-H stretching region for uracil and thymine monomers in helium nanodroplets. Each monomer shows only a single isomer, the global minimum, in agreement with previous experimental and theoretical studies. The assignment of the infrared vibrational bands in the spectra is aided by the measurement of the corresponding vibrational transition moment angles (VTMAs) and ab initio frequency calculations. The ambiguity in the VTMA assignment of the N3H band for the uracil monomer is explained by the presence of dimer bands, which are overlapped with the monomer band.     

Combination of Single Bead FTIR and Chemometrics in Combinatorial Chemistry: Application of the Multivariate Calibration Method in Monitoring Solid-Phase Organic Synthesis

The single bead FTIR method has been used in quantitative analyses of solid-phase organic synthesis (SPOS) such as the determination of reaction kinetics and conversion yield. These studies rely on data analysis methods to extract quantitative information from IR spectra. However, the IR spectrum of a solid-phase sample contains vibrational bands from the starting material, product, and the polymer support itself. The coexistence of multiple chemical components causes severe spectral overlaps and sometimes makes quantitative analysis extremely difficult. In some cases, it is impossible to extract qualitative and quantitative information from overlapped IR spectra. In this paper, we use partial least squares (PLS), a chemometrics method, to achieve qualitative and quantitative analysis of samples that generate severely overlapped IR spectra. The primary loading factor obtained from a PLS calculation only displays those spectral features that have undergone changes during a SPOS reaction. Disappearing and emerging organic functional groups generate negative and positive signals, respectively, in the primary loading factor, thus allowing qualitative analysis of the reaction with improved precision. The scores of the primary loading factors of spectra taken at various times during a reaction provide quantitative information allowing the study of the reaction kinetics directly on solid support. On the basis of the analysis of three diverse SPOS reactions, the PLS method has demonstrated the unique capability of extracting quantitative and qualitative information from the overlapped IR spectra. It is a powerful data analysis tool for the monitoring of SPOS reactions in combinatorial chemistry.     

Influence and correction of peak shift and band broadening observed by rank analysis on vibrational bands from variable-temperature measurements

Variable-temperature infrared (IR) spectra of cyclohexane and IR and Raman spectra of chlorocyclohexane have been investigated by graphic eigenvalue analysis. Thermal effects known as peak shift and band broadening combined with heteroscedastic noise in vibrational bands are found to have severe influence on the interpretation of the outcome of rank analysis. Methods for correction of frequency shifts and band broadening in the spectral profiles due to temperature variation are developed and tested.     

Dynamic two-dimensional fluorescence correlation spectroscopy. Generalized correlation and experimental factors

Dynamic two-dimensional fluorescence correlation spectroscopy (2D FCS) is presented in the general form. Dynamic 2D FCS evaluates the time correlation function between two wavelength axes when an external perturbation is applied to the sample. It displays the vibronic features with similar time response functions in the synchronous correlation spectrum and the features with different time responses in the asynchronous correlation spectrum. The correlation analysis allows detailed assignments of the vibronic spectra of multicomponent samples. The emission-emission 2D FCS has proven to be able to resolve spectra with substantial overlaps, of species in equilibrium with each other, and of reacting species whose kinetic constants are linked and multiexponential. Similarly, the correlation analysis between excitation wavelengths allows the assignment of the excitation bands to fluorescent components. When a sinusoidal light source is used to excite the sample, the excitation-emission correlation requires the collection of only four spectra, two in-phase and two quadrature. The two-dimensional excitation-emission correlation analysis uncovers the association between the excitation and the emission vibronic features, enabling the complete assignment of the component spectra. The band associations and spectral assignments are facilitated by the two-dimensional phase map that is constructed from the synchronous and asynchronous correlation spectra. Spectral resolution can be optimized by varying the frequency of excitation and is not influenced by the detector phase angle used to collect the spectra. The resolution power of the 2D FCS is demonstrated with the retrieval of the anthracene emission spectrum from a pyrene-anthracene mixture when it contributes only 4% to the total fluorescence intensity.     

Dynamic rheo-optical characterization of uniaxially oriented polyamide 11

Dynamic mechanical analysis, coupled with polarized step-scan FTIR transmission spectroscopy, has been used to monitor the submolecular motional behavior of uniaxially oriented polyamide 11. The dynamic in-phase spectra depend upon the morphology of the samples as well as on the polarization direction of the infrared radiation. The lineshape features of the dynamic in-phase spectra and their relationship to sample deformation are analyzed on the basis of changes of the internal coordinates, the reorientation movement of several functional groups, and the thickness change of the film during the stretching cycle. Dynamic infrared spectra are helpful for deconvolution of overlapping bands on the basis of their different responses to the external perturbation, which sometimes cannot be resolved well by derivative spectroscopy or curve-fitting analysis. The lineshape features have been used to follow microstructural changes after isothermal heat treatment. Near the N H stretching frequency, two bands at 3270 cm⁻¹ and 3200 cm⁻¹ are resolved and analyzed in terms of Fermi resonance between the N H stretching fundamental mode and the overtone and combination modes of the amide I and II vibrations. The dynamic response of the N H stretching mode correlates with the modulation of hydrogen bond strength in uniaxially oriented PA-11. After thermal treatment at the highest temperature (190°C), the dynamic response in this region is mainly caused by the modulation of crystals. In amide I region, three bands at 1680 cm⁻¹, 1648 cm⁻¹, and 1638 cm⁻¹ are separated and assigned to hydrogen bond-free, hydrogen-bonded amorphous, and hydrogen-bonded crystalline regions, respectively. The dynamic responses of the hydrogen-bonded regions are more sensitive to external perturbation. Two components are found in the amide II region, and the band at 3080 cm⁻¹ is assigned to the overtone resonance of the component with perpendicular polarization. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2895–2904, 1998     

Extended tunnelling states in the benzoic acid crystal: infrared and Raman spectra of the OH and OD stretching modes

We compare Raman and infrared spectra of the nuOH/OD modes in benzoic acid crystal powders at 7 K. The extremely sharp Raman bands contrast to the broad infrared profiles and suggest adiabatic separation of hydrogen (deuterium) dynamics from the crystal lattice. There is no evidence of any proton-proton coupling term. The assignment scheme is consistent with a quasisymmetric double-minimum potential, largely temperature independent. Tunnel splitting is a major band shaping mechanism, in addition to anharmonic coupling with lattice modes. The proton/deuteron dynamics are rationalized with nonlocal pseudoparticles and extended states. We propose a symmetry-related damping mechanism to account for the broad infrared profiles, as opposed to the sharp Raman bands. We assign spectral features to distinct interconversion mechanisms based on either pseudoparticle transfer or adiabatic pairwise transfer. We establish close contacts with theoretical models based on first-principles calculations.     

Two-dimensional correlation analysis useful for spectroscopy, chromatography, and other analytical measurements.

Application of generalized two-dimensional (2D) correlation in various analytical fields is explored. 2D correlation is a powerful and versatile technique applicable to spectroscopy, chromatography, and other measurements. Construction of 2D spectra is relatively straightforward, requiring only a series of systematically varying analytical signals, like spectra or chromatograms, induced by an external perturbation applied to the system of interest. Perturbation can take many different forms, like change in temperature, pressure or concentration, chemical reactions, electrical or mechanical stimuli, and so on. A set of analytical signals collected under a perturbation are then converted to 2D correlation spectra, which provide rich and useful information about the presence of coordinated or independent changes among signals, as well as relative directions and sequential order of signal intensity variations. The signal resolution is also enhanced by spreading overlapped bands along the second dimension. Illustrative examples of 2D correlation are given for spectroscopic and chromatographic applications.     

Conformational behavior of poly(L-lactide) studied by infrared spectroscopy

This paper reports the analysis of the C=O stretching region of poly(L-lactide). This spectral band splits into up to four components, a phenomenon that a priori can be explained in terms of carbonyl-carbonyl coupling or specific interactions (such as C-H...O hydrogen bonding or dipole-dipole). Hydrogen bonding can be discarded from the analysis of the C-H stretching spectral region. In addition, low molecular weight dicarbonyl compounds of chemical structure similar to that of PLLA, such as diacyl peroxides, show a remarkable splitting of the carbonyl band attributed to intramolecular carbonyl-carbonyl coupling. Several mechanisms can be responsible for this behavior, such as mechanical coupling, electronic effects, or through-space intramolecular TDC (transition dipole coupling) interactions. Intermolecular dipole-dipole interactions (possible in the form of interchain TDC interactions) are proven to be of minor relevance taking into account the spatial structure of the PLLA conformers. The Simply Coupled Oscilator (SCO) model, which only accounts for mechanical coupling, has been found to predict adequately the relative intensity of the symmetric and asymmetric bands of dicarbonyl compounds. The dispersion curves predicted for PLLA by the SCO model also match those given by more general treatments, such as Miyazawa's first-order perturbation theory. Hence, the SCO model is adopted here as an adequate yet simple tool for the interpretation of band splitting caused by intramolecular coupling of polylactide. The four components observed in the C=O stretching band of semicrystalline PLLA are attributed to the four possible conformers: gt, gg, tt, and tg. The narrow bands observed for the interlamellar material are attributed to highly ordered chains, indicating the absence of a truly amorphous phase in the crystalline polymer. The interphase seems to extend over the whole interlamellar region, showing the features of a semiordered metastable phase. In amorphous PLLA, bands corresponding to gt, gg, and tt conformers also can be resolved by second derivative techniques, and curve-fitting results provide information about the conformational population at different temperatures.     

尼龙1010红外光谱的研究

本文研究了尼龙1010的红外光谱。观测了不同热处理样品的红外光谱变化和密度,并测定了拉伸样品的偏振红外光谱。应用因子群解析、简正振动类比,得到许多振动的对称类型、偏振光学性质及选律,进而对尼龙1010的红外光谱谱带做了初步归属,还用电子计算机分峰的方法得到一些新谱带,并就若干谱带展开了讨论.     

Infrared spectra and molar absorption coefficients of the 20 alpha amino acids in aqueous solutions in the spectral range from 1800 to 500 cm(-1)

In this work, we present the absorption spectra and molar coefficients of all 20 amino acids in aqueous solutions down to 500 cm(-1). The spectral region between 1200 and 500 cm(-1) was yet disregarded for protein infrared spectroscopy, mainly due to the strong H(2)O absorption. Absorption spectra were obtained mainly for physiological relevant pH region. Intense bands for aromatic amino acids, histidine and such with OH group could clearly be identified throughout the given spectral region. For sulfur-containing amino acids cysteine and methionine some strong bands besides the weak carbon-sulfur stretching vibration was shown. Effects of aqueous solution environment, pH, protonation states were discussed, together with previously reported data from theoretical approaches. With this complete set of spectral information application to proteins in the whole mid infrared region could be described precise and the potential of the lower spectral region to study typical cofactor ligands like histidine, shown.