Preferential Uniplanar Orientation of Cellulose Microfibrils Reinvestigated by the FTIR Technique

A simple detection method to observe the uniplanar orientation behavior of native cellulose microfibrils to the cell wall surface by using Fourier transform infrared (FTIR) spectroscopy in the transmission mode is reported. Four bands at 1372, 1355, 1337, and 1317 cm⁻¹ (the latter two have been mentioned previously by Liang and Marchessault (1960, J. Polym. Sci. 43: 85–100)) were found to be sensitive to such orientation: the two middle bands at 1355 and 1337 cm⁻¹ increase remarkably when the 0.60–61 nm lattice planes lie parallel to the cell wall surfaces. The reverse was true when the 0.53–54 nm lattice planes oriented preferentially. Polarization of the two bands at 1372 and 1355 cm⁻¹ was parallel, while that of the other two bands at lower wavenumbers, i.e., at 1337 and 1317 cm⁻¹, was perpendicular to the molecular axis of cellulose. These bands were assigned to OH-related motion, probably to in-plane OH bending, as reported by Maréchal and Chanzy (2000, J. Mol. Spectrosc. 523: 183–196).     

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     

Ambiguity in Assignment of Near Infrared Vibrational Bands for Polymerisation Monitoring of Epoxy System

The curing process of epoxy affects the chemical structure of the final network so mechanical and physical properties of the polymeric matrix for a composite may be modified according to the polymerisation conditions. This paper describes the ambiguity in assignment of reference bands to follow the cure of poly-epoxy reactive systems using a laboratory-made system which allows the coupling of dielectric analysis and Fourier Transform Near Infrared Spectroscopy (FTNIR). The dielectric measurements were obtained using interdigitated electrode. In situ monitoring of extent of reaction was carried out from room temperature up to 160 °C using fibre-optic FTNIR spectroscopy. For the DGEBA/MCDEA system the epoxy band at 6060 cm⁻¹ was chosen in preference to the band at 4530 cm⁻¹ as representative of the epoxy function evolution during polymerisation because a small unknown peak probably due to the hardener appears in the 4530 cm⁻¹ region. The bands at 4620 and 4680 cm⁻¹ assigned to aromatic combination bands and widely used as reference bands are not unique for this formulation hence the band at 5980 cm⁻¹ is used as reference. The Principal Components Analysis (PCA) shows clearly also that the bands at 4620 and 4680 cm⁻¹ vary during the polymerisation. Surprisingly, the band at 4530 cm⁻¹ is equivalent to the one at 6060 cm⁻¹ to calculate the conversion rate. It is probably due to the fact that the hardener band near 4530 cm⁻¹ follows the same behaviour as the epoxy band at 4530 cm⁻¹.     

Induced circular dichroism spectra of 2-(2,4,6-cycloheptatrien-1-ylidene)-4-cyclopentene-1,3-dione included inβ-cyclodextrin

The assignment of the absorption spectra of 2-(2,4,6-cycloheptatrien-1-ylidene)-4-cyclopentene-1,3-dione (1) is reported by measuring the induced circular dichroism spectra of the β-cyclodextrin complex with1. It is concluded from the signs of the induced circular dichroism bands that the first absorption band (17.1×10³–34.3×10³ cm^?1) is composed of three electronic transitions having perpendicular, parallel and perpendicular polarizations with respect to the long axis (z) of1. The second absorption band (34.3×10³–42.8×10³ cm^?1) is composed of two electronic transitions having parallel polarizations with respect to the long axis of1 and the third absorption band (42.8×10³–47.1×10³ cm^?1) has the transition dipole moment perpendicular to the long axis of1. Our experimental assignments are supported by CNDO/S CI calculations.     

Infrared spectroscopic characterization of oriented polyamide 66: Band assignment and crystallinity measurement

Having found much ambiguity in the infrared band assignments for polyamide 66 (PA66), we revisited some of these assignments before using infrared spectroscopy to assess microstructure changes resulting from multiple thermal treatments. We discovered that earlier assignments of the 1144 and 1180 cm⁻¹ bands to the amorphous (noncrystalline) phase were incorrect, whereas the bands at 924 and 1136 cm⁻¹ can be attributed unambiguously to the noncrystalline phase. We also confirmed that PA66 bands at 936 and 1200 cm⁻¹ are crystalline bands. The normalized absorbance of the 1224‐cm⁻¹ fold band increases in proportion to crystallinity, indicating that chain folding is the predominant mechanism of thermal crystallization in PA66. We demonstrated that infrared spectroscopy can be used to estimate the degree of crystallinity of PA66, and two methods were explored. One is a calibration method in which the band ratio of 1200 and 1630 cm⁻¹ is plotted against crystallinity measured by density. The other is an independent infrared method based on the assumption that PA66 satisfies a two‐phase structure model. The crystallinity determined by the independent infrared method showed good agreement with the crystallinity obtained from density measurements. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 516–524, 2000     

Vibrational spectroscopic characterization of the phosphate mineral hureaulite – (Mn,Fe)5(PO4)2(HPO4)2·4(H2O)

This research was done on hureaulite samples from the Cigana claim, a lithium bearing pegmatite with triphylite and spodumene. The mine is located in Conselheiro Pena, east of Minas Gerais. Chemical analysis was carried out by Electron Microprobe analysis and indicated a manganese rich phase with partial substitution of iron. The calculated chemical formula of the studied sample is: (Mn_3.23, Fe_1.04, Ca_0.19, Mg_0.13)(PO₄)_2.7(HPO₄)_2.6(OH)_4.78. The Raman spectrum of hureaulite is dominated by an intense sharp band at 959 cm⁻¹ assigned to PO stretching vibrations of HPO₄²⁻ units. The Raman band at 989 cm⁻¹ is assigned to the PO₄³⁻ stretching vibration. Raman bands at 1007, 1024, 1047, and 1083 cm⁻¹ are attributed to both the HOP and PO antisymmetric stretching vibrations of HPO₄²⁻ and PO₄³⁻ units. A set of Raman bands at 531, 543, 564 and 582 cm⁻¹ are assigned to the ν₄ bending modes of the HPO₄²⁻ and PO₄³⁻ units. Raman bands observed at 414, and 455 cm⁻¹ are attributed to the ν₂ HPO₄²⁻ and PO₄³⁻ units. The intense A series of Raman and infrared bands in the OH stretching region are assigned to water stretching vibrations. Based upon the position of these bands hydrogen bond distances are calculated. Hydrogen bond distances are short indicating very strong hydrogen bonding in the hureaulite structure. A combination of Raman and infrared spectroscopy enabled aspects of the molecular structure of the mineral hureaulite to be understood.     

High-resolution infrared analysis of seven fundamental bands of gaseous isothiazole between 750 and 1500 cm−1

The gas phase IR spectrum of isothiazole, C₃H₃NS, between 550 and 1700 cm⁻¹ was recorded with a resolution of ca. 0.003 cm⁻¹. The rotational structure of seven fundamental bands in the region 750–1500 cm⁻¹ has been assigned and analysed by the Watson Hamiltonian model. A number of local resonances in the bands have been identified and explained qualitatively in terms of Coriolis interactions. For each band upper state spectroscopic constants, including band center, rotational constants, and quartic centrifugal distortion constants are given. From observed crossings due to resonances we locate the weak bands ν₉(A′) and ν₁₃(A′) at 1041.9(2) and 642.0(3) cm⁻¹, respectively. The anharmonic frequencies have been determined using a cc-pVTZ basis set, at the MP2 and B3LYP levels; the two theoretical methods give very similar results for rotational constants, anharmonic band center frequencies and distortion constants, and many of these are in good agreement with experiment.     

Confirmation of the presence of imine bonds in thermally cured polyimides

Model compounds for imines formed during the thermal curing of short chain polyimides have been synthesized and characterized. These compounds have imine bonds (C?N) formed by the nucleophilic attack of primary amines on imide carbonyls. The C?N stretching mode appears at 1649–1664 cm^?1 in the Raman and infrared spectra of these compounds and the band assigned to the carbonyl mode in an imide ring with an imine bond appears near 1740 cm^?1. These compounds have been prepared and characterized to verify the conclusions of a previously reported study in which bands observed in thermally cured short chain polyimides at 1656 and 1742 cm^?1 were assigned as the C?N and associated C?O modes, respectively. It has also been confirmed that the C?N stretching mode in the imide model compounds is inherently IR weak and can only be seen if the concentration of imine species is high. © 1993 John Wiley & Sons, Inc.     

Near infrared fourier transform Raman spectroscopy of human artery

We report the first near IR FT-Raman spectroscopy of normal diseased human artery. In normal human aorta, two bands at 1669 cm⁻¹ and 1452 cm⁻¹ dominate the spectrum and can be assigned to protein amide I and C-H in-plane bending vibrations, respectively. Weaker bands are also observed between 1250 and 1350 cm⁻¹. Non-calcified atherosclerotic lesions with a large amount of necrotic debris below the tissue surface show a relative increase in the intensity of the 1452 cm⁻¹ band. In atherosclerotic aortas which contain calcified deposits several hundred microns below the tissue surface, a strong 961 cm⁻¹ band is observed due to the symmetric stretch of phosphate groups in the calcified salts. The results show that this method provides the capability to probe biological substituents several hundred microns below the tissue surface.     

The use of polarised Fourier transform Raman spectroscopy in morphological studies of uniaxially oriented PEEK fibres—some preliminary results

The use of Raman spectroscopy to measure crystallinity in uniaxially oriented poly(aryl ether ether ketone) (PEEK) fibres is discussed. It is shown that previously reported measurements based upon the 1608:1597 cm⁻¹ band intensity ratio are affected by molecular orientation, and as such their application to anisotropic samples must be regarded with caution. The use of the crystallinity-sensitive carbonyl bandhead frequency seems to be less sensitive to molecular orientation and so may be applicable to oriented samples—further work is required to calibrate this measurement with oriented samples of known crystallinity. Some preliminary data on the polarisation properties of the 1597 cm⁻¹ ring mode intensity in PEEK fibre bundles is also presented. These data suggest that the band displays perpendicular rather than parallel character with respect to the fibre long axes. Possible reasons for this effect are discussed. The Raman data indicate that molecular orientation is present in both melt-spun and drawn fibres. The spun fibres appear to be amorphous, but drawing induces significant crystallisation.     

NMR and vibrational spectroscopic study of the order and mobility in polycarbonate and polycarbonate — poly(ethylene oxide) blends

Time dependence of the gel formation in toluene solutions of polycarbonate (PC) was investigated by two-dimensional Fourier-transform infrared (2D FT-IR) correlation spectroscopy. The 2D correlation approach reveals that there are at least three bands in the C=O stretching region. The intensity increase of the band at 1771 cm⁻¹ occurs later compared with the onset of the intensity changes of the bands at 1778 and 1765 cm⁻¹ corresponding to amorphous and crystalline-like domains, respectively. The band at 1771 cm⁻¹ is assigned to the chain conformations occurring in the partial-order regions accompanying crystalline-like domains. Splitting of the signals of aromatic carbons in the solid-state ¹³C CP/MAS NMR spectra of semicrystalline PC and PC-PEO blends indicates restricted mobility resulting from the fixed ordering due to partial crystallinity of PC itself and from blending of PC with PEO. The decreasing mobility of PC with the increasing content of highly mobile PEO in the blends was proved by the dipolar dephasing rates obtained in the ¹H-¹H CRAMPS (combined rotation and multi-pulse spectroscopy) NMR experiments.     

Induced circular dichroiism spectra of benz[b]anthracene included inβ-cyclodextrin

The assignment of the absorption spectra of benz[b]anthracene (1) is reported by measuring the induced circular dichroism spectra of the -cyclodextrin complex with1. It is concluded from the signs of the induced circular dichroism bands that the first absorption band (20.4–30.9×10³ cm^–1) has the transition dipole moment perpendicular to the long axis and the second absorption band (30.9–37.2×10² cm^–1) has the transition dipole moment parallel to the long axis of1. Our assignments are in complete agreement with earlier assignments. The induced circular dichroism spectra exhibit Cotton splittings at 19.1×10³ and 42.8×10³ cm^–1. It can be concluded from Cotton splittings of the induced circular dichroism spectra that the association of two 1:1 inclusion complexes forms a ground-state dimer.     

FTIR spectra of the 2ν4, ν4 + ν6 and 2ν6 bands of formaldehyde

High resolution IR spectra of the overtones and the combination band of the ν₄ and ν₆ modes of formaldehyde (2ν₄, ν₄ + ν₆ and 2ν₆) were measured in the region of 2200–2650 cm⁻¹ using FTIR. The combination band ν₄ + ν₆, whose dipole transition is forbidden from molecular symmetry, was observed due to the intensity borrowed from the other bands. The observed frequencies were analysed by a Hamiltonian in which A-type Coriolis interactions and Darling—Dennison interaction were taken into account. The ratio and the relative signs of the transition dipole moments of the overtone bands, μ_2ν4 and μ_2ν6, have been determined by analysing the intensity distribution of the vibration—rotation lines.     

A Raman and infrared spectroscopic study of the phosphate mineral laueite

A laueite mineral sample from Lavra Da Ilha, Minas Gerais, Brazil has been studied by vibrational spectroscopy and scanning electron microscopy with EDX. Chemical formula calculated on the basis of semi-quantitative chemical analysis can be expressed as (Mn²⁺_0.85,Fe²⁺_0.10Mg_0.05)_∑1.00(Fe³⁺_1.90,Al_0.10)_∑2.00(PO₄)₂(OH)₂·8H₂O.The laueite structure is based on an infinite chains of vertex-linked oxygen octahedra, with Fe³⁺ occupying the octahedral centers, the chain oriented parallel to the c-axis and linked by PO₄ groups. Consequentially not all phosphate units are identical. Two intense Raman bands observed at 980 and 1045 cm⁻¹ are assigned to the ν₁ PO₄³⁻ symmetric stretching mode. Intense Raman bands are observed at 525 and 551 cm⁻¹ with a shoulder at 542 cm⁻¹ are assigned to the ν₄ out of plane bending modes of the PO₄³⁻. The observation of multiple bands supports the concept of non-equivalent phosphate units in the structure. Intense Raman bands are observed at 3379 and 3478 cm⁻¹ and are attributed to the OH stretching vibrations of the hydroxyl units. Intense broad infrared bands are observed. Vibrational spectroscopy enables subtle details of the molecular structure of laueite to be determined.     

Morphology and Temperature Phase Transitions in α,ω-Alkanediols with Different Chain Lengths

A comparative analysis of phase transitions in diols with various chain lengths [(CH₂)₄₄(OH)₂ and (CH₂)₂₂(OH)₂] and changes in their absorption spectra with temperature have been investigated by DSC and FTIR. Analysis of the DSC data has led to the conclusion that the low-temperature phase transition of (CH₂)₂₂(OH)₂ in a solid state (T_s-s = 367.1 K) is a phase transition of the first order, while the high-temperature phase transition (T_m = 376.3 K) is of the second order, i.e., a transition of the order-disorder type. Splitting of the IR absorption bands into doublets at 720-730 cm⁻¹ and 1463-1473 cm⁻¹ indicates that crystalline subcells in the lamellae of both diols are orthorhombic lattices with the parameters typical of hydrocarbons. IR spectra showed that at the phase transition temperature T_s-s transformation of an orthorhombic subcell into a hexagonal one occurs. This type of molecular chain packing remains the same up to the melting temperature T_m. In a (CH₂)₄₄(OH)₂ diol, the ortho-hexagonal subcell transition occurs only at the melting temperature (390.0 K). The wide IR band in the region from 3000 cm⁻¹ to 3600 cm⁻¹ shows that end hydroxyl groups of diol molecules form, on the surfaces of lamellar crystals, long (polymer) regular sequences consisting of intermolecular hydrogen bonds.     

Torsional transitions and barrier to internal rotation of 1,2-butadiene

The far i.r. spectrum of 1,2-butadiene (methyl allene) has been recorded in the gas phase from 370 to 40 cm⁻¹ with a resolution of 0.1 cm⁻¹. The methyl torsional fundamental has been observed for the first time at 154.3 cm⁻¹, along with some accompanying torsional hot bands. From these data the barrier to internal rotation has been calculated to be 556 cm⁻¹ (1.59 kcal/mol). Detailed K-structure has also been observed for both A—A and E—E torsional transitions and considered in the analysis. SCF calculations have been made for the structure and energies of conformers, so that both kinetic and potential constants for internal rotation have been obtained. The a′ skeletal fundamental is observed at 201.8 cm⁻¹ as a much stronger band than the torsional mode, and the a″ skeletal fundamental gives rise to an even stronger band at 319.8 cm⁻¹.     

Light-induced FTIR difference spectroscopy of photosynthetic charge separation between 9000 and 250 cm−1

The light-induced FTIR difference spectrum corresponding to photosynthetic charge separation between the dimeric bacteriochlorophyll primary donor (P) and the quinone Q_A in the reaction center of the photosynthetic bacterium Rhodobacter sphaeroides has been measured in the frequency range between 9000 and 250 cm⁻¹ using a DTGS detector. Upon extensive signal averaging, the noise level is reduced below 2×10⁻⁵ absorbance unit. The positive bands of the difference spectrum contribute much more than the negative ones over the whole frequency range investigated. In the region below 650 cm⁻¹, a number of bands of small amplitude are observed for the first time. The presence of a tail extending between 6000 and 3600 cm⁻¹ on the high-energy side of the electronic transition of P⁺ peaking at ≈2600 cm⁻¹ [J. Breton, E. Nabedryk, W.W. Parson, Biochemistry, 31 (1992) 7503–7510] is confirmed.     

A FTIR study of ethylene oxidation on an Ru/ZnO system

The interaction of ethylene with a highly dispersed and oxidized Ru/ZnO catalyst has been studied at room temperature (RT) by FTIR spectroscopy. A fast oxidative reaction at RT produces a glycolate-like species strongly adsorbed on the surface, and at the same time the depletion of a strong and narrow band assigned to an RuO surface group. The assignment of the spectrum of a C₂H₄O₂ complex, characterized by two intense bands at 1035 and 890 cm⁻¹ and by 10 other bands in the range 3000-700cm⁻¹, is performed on the basis of a C_2ν symmetry and confirmed by C₂D₄ oxidation data; this assignment is performed by comparison of our spectra with the literature data for ethylene glycol and related complexes. A long oxidative reaction at RT with formation of formate and carboxylate-like species at the expense of the glycolate was also observed.     

Study of the ν1, ν1 + ν3 and ν2 + ν3 infrared bands of ONCl

A type (ΔK_a = 0) rovibrational lines of the near-prolate asymmetric top ¹⁶O¹⁴N³⁵Cl have been assigned on high resolution Fourier transform spectra: 820 lines of the ν₁ band, centered around 1800 cm⁻¹, 435 lines of the ν₁ + ν₃ band, centered around 2131 cm⁻¹, and 257 lines of the ν₂ + ν₃ band, centered around 925 cm⁻¹. Least-squares calculations have been carried out over these lines, using the A reduced Watson's hamiltonian in I^r representation; r.m.s. standard deviations of 0.0016 cm⁻¹, 0.0016 cm⁻¹ and 0.006 cm⁻¹ have been respectively obtained, making it possible to measure molecular constants of the (001), (101) and (011) vibrational levels of ¹⁶O¹⁴N³⁵Cl.     

Raman Optical Activity of Glucose and Sorbose in Extended Wavenumber Range

Raman optical activity (ROA) is pursued as a promising method for structural analyses of sugars in aqueous solutions. In the present study, experimental Raman and ROA spectra of glucose and sorbose obtained in an extended range (50–4000 cm⁻¹) are interpreted using molecular dynamics and density functional theory, with the emphasis on CH stretching modes. A reasonable theoretical basis for spectral interpretation was obtained already at the harmonic level. Anharmonic corrections led to minor shifts of band positions (up to 25 cm⁻¹) below 2000 cm⁻¹, while the CH stretching bands shifted more, by ∼180 cm⁻¹, and better reproduced the experiment. However, the anharmonicities could be included on a relatively low approximation level only, and they did not always improve the harmonic band shapes. The dependence on the structure and conformation shows that the CH stretching ROA spectral pattern is a sensitive marker useful in saccharide structure studies.