D. L. A. de Faria

Raman microspectroscopy of some iron oxides and oxyhydroxides

Hematite (α-Fe2O3), magnetite (Fe3O4), wustite (FeO), maghemite (γ-Fe2O3), goethite (α-FeOOH), lepidocrocite (γ-FeOOH) and δ-FeOOH were studied by Raman microscopy. Such compounds have already been studied by Raman spectroscopy, but there are some disagreements in the reported data. Here, Raman microscopy was employed to investigate the laser power dependence of the spectra of these oxides and oxyhydroxides. Low laser power was used for the reference spectra in order to minimize the risks of spectral changes due to sample degradation. The results obtained show that increasing laser power causes the characteristic bands of hematite to show up in the spectra of most of the compounds studied whereas the hematite spectrum undergoes band broadening and band shifts.

Raman Spectroscopic Analysis of Ancient Egyptian Pigments

The application of FT-Raman spectroscopy and visible Raman microscopy to the non-destructive analysis of pigment specimens excavated from Tell el Amarna by Flinders Petrie in the 1890s has provided information about the chemical composition of the materials used by XVIIIth Dynasty artists in the New Kingdom at the time of King Akhenaten, c. 1340 BC. Comparison of the Raman spectra of the samples labelled red and yellow ochre with documented, archival material from geological collections provided a clear indication of the materials used in the iron(III) oxide/hydroxide system, including α-hematite, goethite, maghemite, magnetite and lepidocrocite. The yellow-orange specimen labelled realgar proved to be a mixture of realgar and pararealgar; since the specimen had been sheltered from light since its excavation, this could indicate that the ancient Egyptian artists recognized the colour variation and may have used this to effect in their decorations. A specimen of yellow ochre contained goethite, α-FeO.OH, with particles of crystalline, highly ordered graphite; in contrast, the red ochre specimens contained amorphous carbon particles.

Raman characterization of polyaniline induced conformational changes

Abstract Conformational changes induced by temperature and secondary doping process, were followed by Raman resonance spectroscopy and ESR measurements. Raman results give complementary data about the secondary doping process showing that together with the structural change of the polymeric chains, there is also a chemical transformation of quinoid segments into scmiquinoid units. When the temperature is raised, changes in Raman spectra arc coincident with those observed in secondarily doped samples, showing in this way, the importance of polymer conformation in the conductive behaviour. ESR measurements confirm the increasing amount of free radicals when the PANI/CSA films are treated with m-cresol in good agreement with Raman results.

Raman spectroscopic study of 3000‐year‐old human skeletal remains from a sambaqui, Santa Catarina, Brazil

A Raman spectroscopic study of red-pigmented human bones from a 3000-year-old sambaqui burial was undertaken for the first time. Visible (633 nm) and near-infrared (1064 nm) excitation were used to characterize the pigment and its substrate; the red pigment is haematite, iron(III) oxide, which proved to be of a pure form and for which no previous heat treatment processing had been adopted. There is clear evidence in heavily pigmented areas of a ‘limewash’ layer which had been applied to the body of the deceased prior to treatment with ochre. Comparisons made with previous Raman studies of archaeological bone from a separate excavation indicate that mineralization of the present specimens is well advanced, with evidence of calcium carbonate incorporation into the hydroxyapatite phosphatic matrix. Copyright

THE INTERACTION BETWEEN POLYVINYLPYRROLIDONE AND I2 AS PROBED BY RAMAN SPECTROSCOPY

Abstract Polyvinylpyrrolidone (PVP) is known since long to interact with iodine producing a stable compound which has been largely employed as antiseptic owing to its iodophor property. Despite of the extensive number of studies involving such system, no attempts were made to investigate the low frequency region of the vibrational spectrum of PVP-I 2 . The characteristic vibrations of I 2 and its polyiodide derivatives (I 3 − and I 5 − ) give rise to strong peaks in the Raman spectrum which are observed in the region below 300xa0cm −1 . In this work the interaction of PVP and iodine is investigated from 80 to 1800xa0cm −1 using Raman spectroscopy. The spectra clearly shows the presence of I 3 − and I 5 − in a ratio that depends on the method used in the sample preparation. The PVP spectrum is not sensitive to the interaction, except by small shifts in the carbonyl band position towards higher wavenumbers, which seems to be a consequence of conformational changes caused by the halogen.

Porphyrin intercalation into a layered niobate derived from K4Nb6O17

The incorporation of guest species into two-dimensional inorganic structures can lead to materials with interesting chemical, catalytic, electronic, optical or mechanical properties. Concerning porphyrins and metalloporphyrins intercalation compounds, nanostructured materials have been obtained and evaluated in studies about photoprocess and catalytic reactions in confined media. The intercalation of bulky species such porphyrins into layered niobates is not easy to perform due to their high layer charge densities when compared to other layered materials. In this work we describe a method for TMPyP [5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H, 23H-porphyrin] intercalation into a layered niobate derived from K4Nb6O17. The potassium precursor was converted into the acidic-exchanged form and then intercalated with n-butylamine to produce an expanded material that was later used in the production of a dispersion containing exfoliated niobate sheets. The niobate dispersion was dropped into a porphyrin solution originating an organic-inorganic hybrid composite of formula TMPyP0.35H0.6K2Nb6O17·3H2O. XRD data suggest a tilted arrangement of the TMPyP ring with respect to the layers. Spectroscopic data (uv-visible absorption, fluorescence and resonance Raman) showed that TMPyP is intercalated in a non protonated form and that the interaction with the niobate layers surface is weak, corroborating with the proposed tilted orientation in the interlayer region.

Romano-British wall-paintings. II: Raman spectroscopic analysis of two villa sites at Nether Heyford, Northants

Abstract We report the analysis of 31 fragments of Roman wall-paintings from two adjacent villa sites near Northampton, which date from about 1800 years b.p . The specimens comprise pigments which are still attached to their substrate, affording an opportunity for the examination of interaction. The palette is rather restricted to a predominance of red (with shades varying from pink through to deep red), white and grey colours, with yellow, blue, brown and green being only rarely observed. This contrasts with Romano-British villa specimens from other sites where a more extensive palette has been recognised.

Raman spectra of human skin and nail excited in the visible region

The characterization of human tissues for biomedical purposes using spectroscopic techniques is of growing interest owing to the richness of the information that they provide. Particularly in the case of skin (stratum corneum) and nail, fluorescence has been a drawback to the use of Raman spectroscopy with excitation in the visible and even in the red region, thus making the excitation in the near-infrared region and the use of interferometric equipment essential. n n n nThis paper reports for the first time the Raman spectra of the outermost layer of human skin and nail excited at 632.8 nm. The initially strong fluorescent background was photobleached and the residual emission was rejected by spatial filtering. The spectra obtained are in full agreement with previously reported data. The feasibility of excitation in the visible region increases the possibilities of using Raman spectroscopy as a tool in skin and nail investigations. Copyright

RAMAN MICROSPECTROSCOPY OF PHTHALOCYANINE INTERCALATES : TETRASULPHONATED COBALT AND NICKEL PHTHALOCYANINES IN LAYERED DOUBLE HYDROXIDE

Tetrasulfonated cobalt and nickel phthalocyanines (CoPcTs and NiPcTs, respectively) intercalated in layered double hydroxide (LDH) were studied by Raman microscopy. In the case of the cobalt complex the investigation included the supported sample in which the phthalocyanine is not within the LDH galleries but on its outer surfaces. The interaction of CoPcTs with the surface (in both intercalated and supported samples) caused band shifting and changes in the relative intensities of some bands. The results for the intercalated compound are in agreement with x-ray data, showing that the phthalocyanine assumes an edge-on orientation in the LDH galleries electrostatically bound through the sulfonate groups, with negligible participation of the π-electrons. This is not the case for supported CoPcTs, since the shift and changes in the relative intensity of the 1546 cm-1 peak are consistent with variations in the pyrrole ring charge, as expected for a flat orientation with respect to the surface. The spectral behavior of NiPcTs does not follow that of CoPcTs. The Raman spectrum suggests that the nickel complex intercalates as an aggregate, which is confirmed by diffuse reflectance data and x-ray diffraction.

Raman spectra of poly(2-pyridinium hydrochloride-2-pyridylacetylene)

Poly(2-pyridinium hydrochloride-2-pyridylacetylene) (P2EPH) is a water-soluble conjugated polymer that is fluorescent when excited in the visible region. The problems associated with this fluorescence have been overcome, thus permitting a Raman spectroscopic investigation of P2EPH. The fluorescence was avoided by recording spectra with excitation in the UV region (244 nm); for spectra excited with a visible laser, silver colloids, electrodes and pellets were used to minimize the fluorescent background. The obtained results allowed an improvement in the band assignment of the P2EPH vibrational spectra and strongly suggested a higher content of the non-protonated pyridine moiety than previously reported. Copyright