Fourier Transform Raman Spectra Research Articles

The Efficiency of 10% Carbamide Peroxide Gel on Dental Enamel

This study investigated the effect of 10% carbamide peroxide gel on human tooth color, vibrational mode, and mineral loss. The exposed enamels were bleached for two weeks (six hours' bleaching and 18 hours' storage in distilled water per day). Color change was calculated from the CIE L*a*b* color values. Vibrational mode in Fourier transform Raman spectrum and mineral content were also estimated. The bleached enamels showed an apparent color change (deltaE* = 5.35). Within the test period, their whiteness increased linearly as the period increased. A slight decrease in Raman peak at 1068 cm(-1)--compared with the peak at 430 cm(-1)--was observed after bleaching. The total mineral content was decreased from 90.39 to 86.01 after bleaching. Also, the calculated Ca/P ratio decreased from 2.10 to 2.07. However, these changes were negligibly different from the enamels stored in distilled water except for a color change.

Vibrational study of dialkylphosphonates: di- n-propyl- and di- i-propylphosphonates by semiempirical and ab initio methods

Fourier transform infrared and Fourier transform Raman spectra of n-C 3H 7 and i-C 3H 7 dialkylphosphonates have been obtained. Semiempirical AM1 and the ab initio orbital molecular RHF/6-31G * theories have been used to study the molecular geometry, and the harmonic vibrational spectra with the purpose to assist the experimental assignments of these compounds. An extensive discussion on the assignment of the CC, CO, PO and PO stretching is carried out based on experimental data of compounds which have the propyl and isopropyl groups, as well as comparing the vibrational spectra of propane. Most of the RHF/6-31G * and AM1 results, once applied the appropriate scaling factor, showed an excellent agreement with the experimental wavenumbers. A few calculated frequencies related to CC and CO stretching do not agree well with the experimental trends.

Surface modification of TiO 2 nanoparticles by polyaniline

A composite of polyaniline (PAn) encapsulating titania (TiO 2) with nanometer size was prepared by the oxidating aniline hydrochloride with ammonium peroxodisulfate in the presence of TiO 2 nanoparticles. The obtained composite was characterized by Fourier-transform infrared spectra (FTIR), Fourier-transform Raman spectra, thermogravimetric analysis (TGA), wide-angle X-ray diffraction (WXRD) and scanning electron microscope (SEM). The conductivity was also investigated. FTIR and FT-Raman spectra measurements show that PAn and TiO 2 nanoparticles are not simply blended or mixed up, and a strong interaction exists at the interface of nano-TiO 2 and PAn. It is probably a composite at molecular level. TGA results suggests that PAn/nano-TiO 2 composite contains 10% PAn by mass. The conductivity of PAn/nano-TiO 2 composite has reached 2.9×10 −2 S cm −1 at 20 °C but the morphology and crystallinity of nano-TiO 2 were unchanged.

Polyaniline on surface modification of diatomite: a novel way to obtain conducting diatomite fillers

A conducting diatomite was obtained by polyaniline on surface modification of diatomite, and was characterized via Fourier-transform Raman spectra, UV-Vis absorption spectra, thermogravimetric analysis and scanning electron microscope, as well as conductivity. The results of spectroanalysis illustrate that polyaniline is not simply blended with diatomite. An interaction exists at the interface of diatomite and polyaniline, which may associate with hydrogen bond formed between the surface of diatomite with electronegativity and NH bond in polyaniline macromolecule. The results of thermogravimetric analysis suggest that the conducting diatomite only contains 8% polyaniline by mass, but its conductivity has reached 2.8×10 −2 S cm −1 at 20 °C.

Spectral Studies of a Polyaniline/Diatomite Composite

Polyaniline/diatomite composite was prepared by the oxidation of aniline in the presence of diatomite, and this composite was characterized by Fourier transform infrared spectra, Fourier transform Raman spectra, UV‐VIS absorption spectra and wide‐angle X‐ray diffraction, as well as conductivity. The results of spectral analysis illustrate that polyaniline is not simply blended with diatomite. An interaction exists at the interface of diatomite and polyaniline, which may be associated with hydrogen bonds formed between the surface of diatomite with electronegativity and N–H bonds in the polyaniline macromolecule. The result of wide‐angle X‐ray diffraction shows that polyaniline has no effect on the crystallizability of diatomite, but conductivity of the composite containing 8% polyaniline has reached 2.8 × 10− 2 S·cm− 1 at 20°C.

Fourier-transform Raman spectroscopic studies of chronological change in stromatolitic cores from Antarctic lake sediments

The Fourier transform-Raman spectra of two lacustrine sediment cores from Antarctic sites are reported. The Lake Hoare specimens were predominantly calcium carbonate, quartz and β-carotene, with chlorophyll and calcium sulphate being noted as minor components. No evidence was found for iron (III) oxide or oxy-hydroxide bands. The Lake Nella specimens, in contrast, contain chlorophyll and quartz predominantly, but the absence of β-carotene is noteworthy. Here, the presence of haematite and a haematite–goethite mixture have been identified, with weaker features such as those of scytonemin, characteristic of cyanobacterial mats. The Raman spectra indicate that two different types of lake chemistry have been operating and several reasons are proposed for this.

Doping-Induced Structural Changes of Conducting Polyalkoxythiophene on the Chemically Modified Gold Surface: An in Situ Surface Enhanced Resonance Raman Spectroscopic Study

In situ surface enhanced resonance Raman spectroscopy (SERRS) with excitation at 1064 nm has been used to monitor the dynamic changes in charge transfer, structure, and orientation during the redox doping of a self-assembled monolayer of conducting poly-3-(3‘-thienyloxy)propanesulfonate (P3TOPS) on a gold surface modified by 2-mercaptoethylamine (MEA). The SERRS spectra were compared with Fourier transform Raman spectra of solid 3TOPS monomer and with reduced and oxidized forms of P3TOPS in solution. The oxidative doping of P3TOPS has been carried out in the potential range between −0.3 and +0.7 V, vs Ag/AgCl. Our SERRS data indicate that the oxidation process goes through initial preferential generation of polaron charge carriers with followed generation of bipolarons at higher oxidation levels. At low doping levels, thiophene rings are more coplanar than at higher ones. The observed potential dependence of the normalized integrated SERRS intensities of P3TOPS in the range of the inter-ring stretch vibrations exhibits a bell-shaped curve with a maximum at 0 V. In the potential window from −0.1 to +0.1 V, the highest number of doped coplanar neighboring molecular units is achieved. Reorientation of alkoxy side chain closer to the surface normal starts at −0.1 V. At higher potentials applied, the trans → gauche conformational transformation of the alkoxy side chain was observed along with the massive growing number of bipolarons and simultaneous deplanarization of the polymer chain.

Natural variations and reproducibility of in vivo near‐infrared Fourier transform Raman spectroscopy of normal human skin

AbstractWe examined variations of in vivo near‐infrared Fourier transform Raman spectra on healthy human skin. Diurnal and day‐to‐day variation, variation between persons, variation between different spots in the same body region and variation in spectra obtained on the same spot was studied in 13 volunteers. In 140 volunteers we examined variations in Raman spectra caused by skin pigmentation. In our spectral analysis we concentrated on the wavenumbers and relative intensities of the water band around 3250 cm−1, the amide I and amide III bands in the regions around 1645–1680 and 1230–1300 cm−1, respectively, and on the wavenumbers of the strong bands at 1450 and 2940 cm−1 that were used as reference bands. The results showed a diurnal variation and interpersonal variation in relative water intensity. In relative amide I intensity there was a variation between persons and between repeated measurements on the same spot. Between persons the variation might arise from different hydration of proteins, but it is difficult to explain why this variation is seen when repeated measurements are made on the same spot. Day‐to‐day variations were seen in the relative amide III intensity. Variations in amide III band wavenumbers were seen between persons, probably because of different collagen structure. Pigmentation did not influence wavenumbers or intensities considerably, but a regression analysis showed a correlation between background height and pigmentation. The conclusion of our study is that Raman spectra obtained on healthy human skin are reproducible and show mostly small variations. Copyright © 2002 John Wiley & Sons, Ltd.

Vibrational assignment and structure of 4-amino-3-cyano-3-penten-2-one

Fourier transform infrared and Fourier transform Raman spectra of 4-amino-3-cyano-3-penten-2-one and its deuterated analogue have been obtained. Density functional theory (DFT) B3LYP and G96LYP calculations have been carried out with the purpose of understanding the vibrational spectra of this compound and its deuterated analogue. Vibrational wavenumbers calculated by B3LYP/6-31G ∗ (with a p shell added on the amine protons) force field are closed with the experimental results. The percentage of deviation of the bond lengths and bond angles gives a good picture of the normal modes, and serves as a basis for the assignment of the wavenumbers. The calculated geometrical parameters show a strong intramolecular hydrogen bond with a N⋯O distance of 2.605–2.622 Å. This bond length is about 0.04–0.06 Å shorter than that in its parent, 4-amino-3-penten-2-one (with no cyano substitution in the α-position). Experimental evidences also indicate presence of an intermolecular hydrogen bond in the solid state, completely, and in solution, partially.

On the ambiguity of self-modeling curve resolution: orthogonal projection approach analysis of the on-line Fourier transform-Raman spectra of styrene/1,3-butadiene block-copolymerization

The self-modeling curve resolution (SMCR) technique called orthogonal projection approach (OPA) was used to resolve a complex set of Fourier transform (FT)-Raman spectra acquired on-line during styrene/1,3-butadiene block-copolymerization. The routine application of OPA did not yield physically acceptable results and manual corrections of the erroneous parts of the styrene concentration profiles had to be employed to improve the resolved spectra and concentrations of the two monomers and polybutadiene. The failure of automatic resolution by OPA is due to the ambiguity of SMCR. This problem is convincingly illustrated in the present case wherein is shown that physically reasonable manual correction significantly improve the results. The present study demonstrates that the combination of an automatic method for curve resolution and a suitable, efficient spectroscopic set-up enables real-time monitoring of this industrially important polymer reaction better than any conventionally employed technique.

Fourier Transform Raman Spectroscopy of Honey

In this work we present the Fourier transform Raman spectra of several commercial samples of honey in different states, comprising nine crystallized and three fluid samples. The measured water content of the specimens bears no relationship to their fluid behavior. The relative intensities of the vibrational bands in the C–H stretching region of the FT-Raman spectra are found to be sensitive to the observed physical states of the specimens. Several observed vibrational bands in the region 500–1800 cm−1 could be identified as fingerprints of the two major components in honey, fructose, and glucose, and at least one vibrational band was characteristic of sucrose. A relationship between the bandshape of the C–H stretching bands of honey specimens and their fluid properties was noted; crystallized samples show a well-resolved distinctive spectrum in this region, whereas the fluid samples do not exhibit this pattern. Some minor differences in the FT-Raman spectra of the honey specimens are discussed in terms of composition (saccharides and water) and the fluid state of the samples.

Spectroelectrochemical Raman Study of Two End-Capped Sexithiophenes with Applications as Electroactive Molecular Materials

In this paper, the vibrational Fourier transform Raman spectra of two sexithiophenes with the end α-positions substituted with n-hexyl or n-thiohexyl groups are studied. We investigate the effects of the different side chains on the intramolecular π-electron delocalization in neutral state and the charged defects generated upon p-doping. Density functional theory and ab initio quantum-chemical calculations are performed on various oligothiophene model compounds as an aid in the interpretation of the experimental data. The analysis of the peculiar Raman features of these π-conjugated systems has been guided by formalism of the effective conjugation coordinate theory. The Raman study of this class of materials is a powerful tool to derive information about the delocalization of π-electrons in the pristine state and the charged species upon doping.

Discrimination and classification of beet and cane inverts in honey by FT-Raman spectroscopy

As a natural product, honey has been prone to adulteration. Adulteration of honey by substituting with cheap invert sugars is a critical issue in the honey industry. Fourier Transform (FT) Raman Spectroscopy was used to detect adulterants such as cane and beet invert in honey. FT Ra man spectrum of adulterated samples were characterized and the region between 200 and 1600 cm−1 (representing carbohydrates and amino acid fractions) was used for quantitative and discriminant analysis. Partial least squares, and principal component regression analysis were used for quantitative analysis while linear discriminant analysis and canonical variate analysis (CVA) were used for discriminant analysis. FT-Raman spectroscopy was efficient in predicting beet and cane invert adulterants (R2>0.91) in all three floral types of honey considered. Classification of adulterants in honey using CVA gave a minimum classification accuracy of about 96%.

Fourier-transform Raman and infrared spectroscopic analysis of dipyrrinones and mesobilirubins

The Fourier-transform Raman (FT-Raman), infrared (FT-IR), and UV-visible absorption spectra of four dipyrrinones and two mesobilirubins have been investigated in the solid state and in CH 2Cl 2 solutions. A detailed spectral analysis, assignment and discussion of these spectra are presented. The bands at 1735–1738, 1691–1707 and 1359–1377 cm −1 which were assigned to the stretching vibrations of the COC and COH and symmetric deformation of CH bonds, respectively, can act as a marker to distinguish the compounds of this class. The striking differences between the spectra of the compounds suggest that mesobilirubin XIIIα is tending to adopt as ridge-tile conformation, rather than linear conformation.

High‐resolution Fourier transform Raman spectra of the fundamental bands of 14N15N and 15N2

AbstractThe Fourier transform Raman spectra of the fundamental bands of 14N15N and 15N2 were measured with a resolution of 0.02 cm−1. Lines from all branches (O, Q, S) were observed and measured. The analyses of the wavenumbers yield improved values for the band origins ν0(14N15N) = 2291.33773(8) cm−1 and ν0(15N2) = 2252.07846(9) cm−1 and improved values for the rotational parameters of the ground state and the first excited state of the two molecules. The values obtained for 14N15N are B0 = 1.9236102(35) cm−1 and D0 = 5.3530(94) × 10−6 cm−1 and B1 − B0 = −0.01651064(86) cm−1 and D1 − D0 = 1.06(16) × 10−8 cm−1. For 15N2 the following values obtained are B0 = 1.8576250(36) cm−1, D0 = 4.9760(87), B1 − B0 = 0.01566657(99) cm−1 and D1 − D0 = 0.94(18) × 10−8 cm−1. The bond length calculated for all three isotopomers of molecular nitrogen shows a systematic decrease with increasing molecular mass. Copyright © 2001 John Wiley & Sons, Ltd.

Quantitative Analysis of Benzyl Modification in Waxy Maize Starch by Fourier Transform (FT) Raman Spectroscopy

ABSTRACTWaxy maize starch was chemically modified to varying benzylation levels and the degree of benzylation substitution was measured using a nuclear magnetic resonance (NMR) method. Fourier Transform (FT) Raman spectra of the chemically modified starches were acquired and aromatic C=C stretch Raman bands characteristic of the benzylation modification were used to derive a calibration curve for the Raman intensity of these marker bands versus the degree of benzylation substitution. The best‐fit linear regression to the plotted data gave a linear correlation coefficient of 0.997. The FT‐Raman technique provides a fast, nondestructive method for the measurement of the degree of benzylation substitution of modified waxy maize starches and should be applicable for use with benzylated starches from other botanical sources.

Probing the binding site of 800-nm bacteriochlorophyll in the membrane-linked LH2 protein of Rhodobacter capsulatus by local unfolding and chemical modification: evidence for the involvement of a betaHis20 residue.

The aim of this study was to investigate the function of betaHis20 in the spectral behavior of the 800-nm bacteriochlorophyll (Bchl) of the Rhodobacter capsulatus LH2 protein. In this context, the 800-nm Bchl of the membrane-linked LH2 was used as an intrinsic probe to follow the reversible, denaturant-elicited unfolding of the neighboring protein region. This band was reversibly shifted to approximately 770 nm by acidic pH, suggesting that the environment of the pigment, responsible for its native red shift, was significantly disturbed by the protonation of a chemical group. The reversible acid-induced blue shift was only observed in the presence of unfolding agents (urea and guanidinium chloride). Thus, dismantling of the protein structure facilitated exposure of the basic group to the medium. The acid-base titrations of the spectral shift indicated an apparent pK approximately 6.1, a value consistent with His imidazole being the protonatable group responsible for the acid-induced band shift. The pK values of free N-terminal amino groups are higher and not expected to be lowered by their local environment in the unfolded state of the protein. A similar blue shift of the 800-nm Bchl band was caused by the modifier diethyl pyrocarbonate, which is known to carboxylate the imidazole group of His and free amino groups. It is also shown that the Fourier transform Raman spectrum of diethyl pyrocarbonate-treated LH2 preparations lacks the weak mode at 1695 cm(-1), suggesting that it should be assigned to the B800 Bchl.

Density functional theory study of the Fourier transform infrared and Raman spectra of dichloro-bis(2,4-pentanedionate)tin(IV)

Fourier transform infrared and Fourier transform Raman spectra of dichloro-bis(2,4-pentanedionate)tin(IV) have been obtained. Density functional theory (DFT) BLYP calculations, have been carried out with the purpose of understanding the metal-ligand region spectra of this compound. Vibrational wavenumbers calculated by BLYP/6-31G* force fields are closed with the experimental results. The percentage of deviation of the bond lengths and bond angles gives a good picture of the normal modes, and serves as a basis for the assignment of the wavenumbers. The calculated geometrical parameters show slight differences compared with the experimental ones, and these differences can be explained by the different physical state of Sn(acac) 2Cl 2. The DFT-BLYP calculations assumed a free molecule in the gas phase. The experimental wavenumbers are obtained from the spectra of solid samples.

Fourier transform infrared and Raman spectra, vibrational assignment and ab initio calculations of terephthalic acid and related compounds

The Fourier transform infrared and Raman spectra of solid terephthalic acid, p-C 6H 4(COOH) 2, have been recorded, and the Fourier transform Raman spectra for the terephthalate anion were measured. The wavenumbers for the band positions have been calculated in order to assign them. Moller–Plesset (MP2) and Density functional theory (DFT) calculations have been carried out with Huzinaga–Dunning basis sets (DZV). Also, a normal coordinate analysis through the Wilson–El'yashevich method was performed. The differences between the calculated ab initio spectra and the spectra of the solid phase have been interpreted with respect to the different C 2h and C i local symmetry in the gas and in the solid phase, respectively, and considering also the formation of long-chains of terephthalic acid in the solid phase. In spite to the absence of experimental data for the cis conformation, calculations have been carried out and structural parameters and infrared intensities have been evaluated for the trans and cis conformations of terephthalic acid.

Noninvasive characterization of human stratum corneum of undiseased skin of patients with atopic dermatitis and psoriasis as studied by Fourier transform Raman spectroscopy.

Etiopathogenetic regulatory disorders of epidermal metabolism and the subsequent changes in the molecular pattern of the stratum corneum play an important role in the clinical differentiation of particular dermatoses (e.g., psoriasis, atopic dermatitis). In this study we present in vitro Fourier transform Raman spectra of the stratum corneum from healthy skin, as well as from clinically undiseased skin of the right heel of atopic and psoriatic volunteers. Differences in the averaged spectra were detected, particularly in the spectral ranges of 1112-1142 (lipid band), 1185-1220, and 1394-1429 cm(-1). By using the first derivative of the averaged spectra and/or a statistical evaluation of the spectroscopic data it was possible to distinguish the skin types examined.