Spectral Modifications Research Articles

FTIR investigations of phase transitions in an asymmetric azomethine liquid crystal

The liquid crystalline (LC) behavior of a literature-reported asymmetric azomethine compound (4-[4-(n-butyloxy)-benzylideneimino]-chlorobenzene, Cl.O4) was investigated by using optical polarized light microscopy, differential scanning calorimetry and medium-wide angle X-ray diffraction. FTIR in attenuated total internal reflection configuration was employed to study the microstructural changes occurring during phase transitions of the azomethine. Spectral modifications, associated with molecular conformation rearrangements, allowing the change of the molecular shape from a LC organization to another, have been found. The spectral analysis gave significant evidences for the different phase transitions, thus proving the efficiency of such method for investigating LC materials.

Green light effects on biological systems: a new biophysical phenomenon.

This paper reports a new phenomenon connected with the influence of green light (GL) on biological systems. Our experiments have revealed an antioxidant effect of GL on cells subjected to lethal doses of UV at the cellular level and a protective effect of GL on DNA denatured by UV, coupled with a structural modification of DNA macromolecules under GL irradiation, at the molecular level. Mouse melanocyte cultures are subjected to UV irradiations with L(50) fluxes of 16.0 J m(-2) s(-1). GL is obtained from a strontium aluminate pigment, which emits GL under UV activation. Cells grown in GL, prior to UV irradiation, present a clear surprising protective effect with surviving values close to the controls. A GL antioxidant effect is suggested to be mediated through GL influence on cellular water cluster dynamics. To test this hypothesis, reactive oxygen species (ROS) are determined in cell cultures. The results revealed a decrease of cellular ROS generation in the UV-irradiated samples protected by a previous 24 h of GL irradiation. At the DNA level, the same type of GL protection against UV damage is recorded by gel electrophoresis and by UV spectroscopy of the irradiated DNA molecules. Two physical methods, impedance spectroscopy and chronoamperometry, have revealed at the level of GL-irradiated DNA molecules spectral modifications that correlate with the UV spectroscopy results. The interaction between the chargeless photons and the field of water molecules from the cellular compartments is discussed in relation with the new field of macroscopic quantum coherence phenomena.

Unusual Photoinduced Response of mTHPC Liposomal Formulation (Foslip)

Liposomal formulations of meso-tetra(hydroxyphenyl)chlorin (mTHPC) have already been proposed with the aim to optimize photodynamic therapy. Spectral modifications of these compounds upon irradiation have not yet been investigated. The objective of this study was to evaluate photobleaching properties of mTHPC encapsulated into dipalmitoylphosphatidylcholine (DPPC) liposomes, Foslip. Fluorescence measurements in DPPC liposomes with different DPPC:mTHPC ratios demonstrated a dramatic decrease in fluorescence anisotropy with increasing local mTHPC concentration, thus suggesting strong interactions between mTHPC molecules in lipid bulk medium. Exposure of Foslip suspensions to small light doses (<50 mJ/cm(2)) resulted in a substantial drop in fluorescence, which, however, was restored after addition to the sample of a non-ionic surfactant Triton X-100. We attributed this behavior to photoinduced fluorescence quenching. This effect depended strongly on the molar DPPC:mTHPC ratio and was revealed only for high local mTHPC concentrations. The results were interpreted supposing energy migration between closely located mTHPC molecules with its subsequent dissipation by the molecules of photoproduct acting as excitation energy traps. We further assessed the effect of photoinduced quenching in plasma protein solution. Relatively slow kinetics of photoinduced Foslip response during incubation in the presence of proteins was attributed to mTHPC redistribution from liposomal formulations to proteins. Therefore, changes in mTHPC distribution pattern in biological systems would be consistent with changes in photoinduced quenching and would provide valuable information on mTHPC interactions with a biological environment.

Social context influences acoustic communication in zebra finches.

During communication, a signal conveys information between an emitter and a receiver, but indirect receivers can eavesdrop on the interaction. In birds, communication has been demonstrated to often be under the influence of this eavesdropping. Social species show complex communication networks where audience drives individual behaviors. Zebra finches (Taeniopygia guttata) are gregarious songbirds that live in social groups and form life‐long pair‐bonds. Previous studies showed that the vocal behavior of males highly depends on this audience effect. Males show mate calls preference over other female calls in the presence of an established male‐female pair, but not in the presence of unmated male‐female or male‐male dyads. Males in social groups also show stronger vocal response to female calls than males in social isolation. In this study, we investigate whether female calls of varied social salience evoke differently male calling according to the audience. We show that social context modifies not only call rate in response to female calls of varied social salience, but also acoustic structure of evoked calls. Thus male distance calls are not stereotyped calls whose acoustic cues only convey bird’s identity. We propose that fine spectral modifications of the calls could carry information about the emitter motivation.

Inclusion complex of usnic acid with β-cyclodextrin: characterization and nanoencapsulation into liposomes

In this study β-cyclodextrin (β-CD) was used to improve usnic acid (UA) solubility and the inclusion complex (UA:β-CD) was incorporated into liposomes in order to produce a targeted drug delivery system for exploiting the antimycobacterial activity of UA. A phase-solubility assay of UA in β-CD at pH 7.4 was performed. An apparent stability constant of K1:1 = 234.5 M−1 and a complexation efficiency of 0.005 was calculated. In the presence of 16 mM of β-CD the solubility of UA (7.3 μg/mL) increased more than 5-fold. The UA:β-CD complex was prepared using the freeze-drying technique and characterized through infrared and 1HNMR spectroscopy, X-ray diffraction and thermal analyses. The UA:β-CD inclusion complex presented IR spectral modifications when compared with UA and β-CD spectra. 1HNMR spectrum of UA:β-CD inclusion complex showed significant chemical shifts in proton H5 located inside the cavity of β-CD (Δδ = 0.127 ppm), suggesting that phenyl ring moiety of UA would be expected to be included within the β-CD cavity, interacting with the H-5 proton. A change in UA from its crystalline to amorphous form was observed on X-ray, suggesting the formation of a drug inclusion complex. DSC analysis showed the disappearance of the UA fusion peak UA:βCD complex. No differences between the antimicrobial activity of free UA and UA:βCD were found, supporting the hypothesis that the complexation with cyclodextrin did not interfere with drug activity. Liposomes containing UA:βCD were prepared using hydration of a thin lipid film method with subsequent sonication. Formulations of liposomes containing UA:βCD exhibited a drug encapsulation efficiency of 99.5% and remained stable for four months in a suspension form. Interestingly, the encapsulation of UA:βCD into the liposomes resulted in a modulation of in vitro kinetics of release of UA. Indeed, liposomes containing UA:β-CD presented a more prolonged release profile of free usnic acid compared to usnic acid-loaded liposomes.

Tuning of the charge ordered state in the manganite thin films by internal or external strains

AbstractWe have investigated methods for tuning the charge ordered state in the R1–x Cax MnO3 (R = La, Pr) manganite thin films grown on different substrates (SrTiO3 (STO), LaAlO3 (LAO), SrLaGaO4 (SLGO) and SrLaAlO4 (SLAO)). We have studied thin films of the Pr1–x Cax MnO3 manganite under hydrostatic pressure for various doping levels in order to induce a delocalization of carriers and destroy the charge ordered state (CO). It appears that both doping and the strains from the substrate can alter the CO state and tune the electrical properties of the compound. We have also proved that the application of an external hydrostatic pressure induces similar spectral modifications to doping in the Pr1–x Cax MnO3 (LCMO) thin films. By our systematic Raman studies under varying external (temperature and pressure) and internal (interfacial strains and doping) conditions, we investigate certain modes and extract direct information about the amount of the Jahn–Teller (JT) distortions, the CO state, and the strain or pressure induced phase separation in the manganite thin films. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Study of protein–gold nanoparticle conjugates by fluorescence and surface-enhanced Raman scattering

We investigate the direct interaction between bovine serum albumin (BSA) protein and the surface of gold nanoparticles (GNPs) of different shapes (nanospheres and nanorods) by using localized surface plasmon resonance (LSPR) spectroscopy, fluorescence spectroscopy and surface-enhanced Raman scattering (SERS). The spectral modifications observed in LSPR bands of GNPs after mixing with BSA are consistent with the formation of protein–GNPs bioconjugates. While the monitoring of fluorescence quenching of tryptophan residues from BSA in the presence of GNPs is exploited for determining the binding constant ( K b) and the numbers of binding sites ( n), the SERS data allow us to reveal some specific molecular groups involved in conjugation.

Comparison of experimental and computational neutron spectroscopy at a 14 MeV neutron generator facility

At any neutron production facility, the energy spectrum at any meaningful distance from the target will be modified. For the case of a facility used to provide reference irradiations of electronics and other devices at various target-to-device distances it is important to have knowledge of these spectral modifications. In addition, it is desirable to have the ability to generate near real-time measurement capability. Advances in neutron metrology have made it possible to determine neutron energy spectra in real time to high levels of accuracy. This paper outlines a series of experimental measurements and theoretical calculations designed to quantify the scattering effects for a 14 MeV neutron generator facility, and makes appropriate recommendations for near real-time measurements of these fields.

Molecular and supramolecular chirality in gemini‐tartrate amphiphiles studied by electronic and vibrational circular dichroisms

This contribution presents an application of electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) to study the molecular and supramolecular chirality in assemblies of gemini-tartrate amphiphiles. Nonchiral dicationic n-2-n amphiphiles (n = 14-20) can self-organize into right- or left-handed structures upon interacting with chiral tartrate counterions. Micellar solutions can also be obtained for shorter alkyl chains (n = 12). First, the conformation of tartrate counterions has been investigated in various environments (micellar solutions and chiral ribbons). ECD and VCD spectra recorded in micellar solutions are independent from the solvent and from the nature of the cations (sodium, cetyl-trimethylammonium, or dimeric surfactant 12-2-12) used and are representative of the anticonformation of the tartrate dianions. On the other hand, drastic changes in the ECD and VCD spectra have been observed in multilayered chiral assemblies of 16-2-16 tartrate. These strong spectral modifications are associated with the chiral arrangement of the tartrate molecules at the surface of the bilayers. Moreover, chirality transfer from counterions to achiral amphiphiles has been clearly evidenced by VCD since circular dichroism has been observed on vibrations related to alkyl chains and gemini headgroups. Finally, ECD and VCD experiments were performed varying the enantiomeric excess of the tartrate. The ECD and VCD intensities do not vary linearly with the enantiomeric excess of the anion and different behaviors have been observed from the two spectroscopic methods: ECD intensities are correlated to the pitch of the ribbons, whereas the VCD intensities are correlated to the dimension of the chiral ribbons.

Salt Effects on the Structure of Water Probed by Attenuated Total Reflection Infrared Spectroscopy and Molecular Dynamics Simulations

We study aqueous solutions of alkaline chlorides (NaCl, KCl, RbCl and CsCl) with a combination of attenuated total reflection infrared (ATR-IR) spectroscopy and molecular dynamics (MD) simulations using the TIP4P-Ew water model (Horn et al., J. Chem. Phys. 2004, 120, 9665), covering concentration ranges between 0.1 and 6 M. Spectral modifications in the OH stretch region are evaluated and correlated to the various salts and salt concentrations. By taking the difference spectra between the spectral line shapes of aqueous salt solutions and those of pure water, we specifically focus on the small quasi-"free OH" band appearing at the highest wavenumbers in the spectra. This free-OH feature is found constantly at 3650 cm(-1) for all salts and salt concentrations, but it shows a characteristic intensity depending on the chosen cation. In the order from Na(+) to Cs(+), the free OH intensity decreases compared to that of pure water. To interpret the experimental results, we performed MD simulations for similar salt solutions. The experimentally observed effects can be correlated with structural alterations indicated by differences between the site-site pair correlation functions of water in aqueous salt solutions and those of pure water.

Raman scattering features of lead pyroantimonate compounds. Part I: XRD and Raman characterization of Pb2Sb2O7 doped with tin and zinc

AbstractYellow pyroantimonates PbSb, PbSbSn and PbSbZn were synthesized by solid‐state reactions at high temperature and characterized by X‐ray diffraction and Raman spectroscopy. The lattice size of cubic pyrochlores increases with Sn and Zn doping and with Pb overstoichiometry, indicating the replacement of Sb5+ by the larger cations. This fact permits the understanding of the corresponding Raman spectral modifications as a consequence of the changes in the local symmetry of the SbO polyhedra, justifying the exploitation of Raman spectroscopy to noninvasively identify structural modifications of pyroantimonate pigments in artworks. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Time-dependent degradation of biotic carbonates and the search for past life on Mars

Searching for traces of extinct and/or extant life on the surface of Mars is one of the major objectives for remote-sensing and in-situ exploration of the planet. In the present paper we study the infrared (IR) spectral modifications induced by thermal processing on differently preserved calcium carbonate fossils, in order to discriminate them from their abiotic counterparts. The main conclusion of this study is that the degree of alteration of the fossils, derived from IR spectral analysis, seems to be well correlated with the sample age, and that terrestrial fossils after a billion years are so altered that it becomes impossible to trace their biotic origin. Since it is reasonable to assume that the putative Martian fossils should be at least 3.5 billion years old, this would imply that our spectroscopic method could not be able to detect them, if their degradation rate were the same as that we have found in usual conditions for the terrestrial fossils. However, due to the different climate evolution of the two planets, there is the possibility of having two different degradation rates, much lower for Mars than for Earth, especially if the fossils are embedded in a protective layer, such as a clay deposit. In this case IR spectroscopy, coupled with thermal processing, can be a useful tool for discriminating between abiotic and biotic (fossil) carbonate samples collected on the Martian surface.

Infrared microscopy for the study of biological cell monolayers. I. Spectral effects of acetone and formalin fixation

Infrared spectroscopy of biological cell monolayers grown on surfaces is a poorly developed field. This is unfortunate because these monolayers have potential as biological sensors. Here we have used infrared microscopy, in both transmission and transflection geometries, to study air-dried Vero cell monolayers. Using both methods allows one to distinguish sampling artefactual features from real sample spectral features. In transflection experiments, amide I/II absorption bands down-shift 9/4 cm(-1), respectively, relative to the corresponding bands in transmission experiments. In all other spectral regions no pronounced frequency differences in spectral bands in transmission and transflection experiments were observed. Transmission and transflection infrared microscopy were used to obtain infrared spectra for unfixed and acetone- or formalin-fixed Vero cell monolayers. Formalin-fixed monolayers display spectra that are very similar to that obtained using unfixed cells. However, acetone fixation leads to considerable spectral modifications. For unfixed and formalin-fixed monolayers, a distinct band is observed at 1740 cm(-1). This band is absent in spectra obtained using acetone-fixed monolayers. The 1740 cm(-1) band is associated with cellular ester lipids. In support of this hypothesis, two bands at 2925 and 2854 cm(-1) are also found to disappear upon acetone fixation. These bands are associated with C-H modes of the cellular lipids. Acetone fixation also leads to modification of protein amide I and II absorption bands. This may be expected as acetone causes coagulation of soluble cellular proteins. Other spectral changes associated with acetone or formalin fixation in the 1400-800 cm(-1) region are discussed.

Size-dependent modifications of the first-order Raman spectra of nanostructured rutileTiO2

The crystallite-size-dependent Raman spectral modifications observed for a suite of rutile ${\text{TiO}}_{2}$ nanocrystals are analyzed and compared to the characteristics of the Raman spectra that were reported for nanoscale rutile ${\text{TiO}}_{2}$ domains/crystallites embedded in thin films. The strong ${E}_{g}$ and ${A}_{1g}$ modes display disparate size dependencies in the various rutile nanostructures. The redshifts of the Raman frequencies, asymmetric peak broadening, and intensity/linewidth ratio reductions with decreasing crystallite size observed for nanopowder samples are consistent with phonon confinement. The nonsystematic Raman spectral modifications that are inconsistent with phonon confinement documented for the nanoscale rutile within thin films suggest that intrinsic crystallographic or extrinsic matrix influences can interfere and overprint the confinement effects.

Timbre transposition based on time‐varying spectral analysis of continuous monophonic audio and precomputed spectral libraries

A sinusoidal model for solo musical sounds consisting of time‐varying harmonic amplitudes and frequencies allows for convenient temporal and spectral modifications. With a harmonic model, analysis frames can be grouped by fundamental frequency (F0) and then clustered in terms of their harmonic spectra. The resulting cluster centroid spectra are used as spectral libraries. When continuous audio monophonic passages are analyzed in the form of harmonic components, F0 vs. time data are used to guide the extraction of parameters from the sound in order to find appropriate library spectra for resynthesis. Two methods for finding appropriate spectra are: (1) best rms match with the incoming spectra and (2) best spectral centroid match. These give similar results, but centroid matching yields smoother spectra over time. Timbre transposition is performed by using a library that belongs to another instrument. We have found that when the target instrument has a unique timbral quality based on its spectrum, the synth...

Noise annoyance indicators for various industrial noise sources: Results and comparisons

Characterizing the environmental impact of an industrial plant goes through a better understanding of the noise annoyance caused by industrial noise sources, which are numerous and various. A first step was to construct a perceptive typology of various industrial noise sources from a categorization test and based on perceived similarities. Now, laboratory tests are carried out, for each perceptive category separately, through the same experimental procedure, by testing the influence of the sound pressure level and of the noise spectral characteristics (low frequency noise, tonal noiseœ) on noise annoyance. The effect of spectral modifications due to the noise propagation on noise annoyance is also assessed. Subjects have also to judge the annoyance induced by an ambient noise exposure, built with a background noise and an industrial noise for which the emergence level is controlled. Different types of background noises are studied. Through a statistical analysis, indicators are developed for each percepti...

Effect of Relativistic Plasma on Extreme-Ultraviolet Harmonic Emission from Intense Laser-Matter Interactions

Experiments were performed in which intense laser pulses (up to 9x10(19) W/cm(2)) were used to irradiate very thin (submicron) mass-limited aluminum foil targets. Such interactions generated high-order harmonic radiation (greater than the 25th order) which was detected at the rear of the target and which was significantly broadened, modulated, and depolarized because of passage through the dense relativistic plasma. The spectral modifications are shown to be due to the laser absorption into hot electrons and the subsequent sharply increasing relativistic electron component within the dense plasma.

Efeito higrotérmico em prepregs de fibra de vidro/epóxi por espectroscopia de luminescência

O objetivo deste trabalho é o estudo do efeito higrotérmico em pré-impregnados (prepreg) não curados de fibra de vidro-resina epoxídica usando a técnica de espectroscopia eletrônica de luminescência em modo estacionário. O método de fluorescência extrínseca foi empregado utilizando-se a sonda 9- ácido antróico (9-AA), cujo comportamento fotofísico depende fortemente da polaridade do meio. As amostras foram submetidas a umidades relativas de 6 e 84% por meio da utilização de soluções aquosas saturadas de hidróxido de sódio a 34,5 °C e cloreto de potássio a 20,0 °C, em recipientes fechados, pelos períodos de tempo de 1 semana, 15 dias e 1 mês. As amostras submetidas à umidade relativa de 6% apresentaram aumento significativo das intensidades relativas dos espectros de fluorescência em relação à amostra referência. Este comportamento fotofísico foi atribuído à presença da forma protonada do 9-AA no meio devido à reticulação da matriz polimérica. Após 1 mês, o espectro de emissão apresenta uma diminuição da intensidade em seu máximo. Isto ocorreu provavelmente devido ao processo de plastificação da matriz polimérica promovido pela presença de água na matriz, confirmado pela análise gravimétrica. Os espectros de fluorescência extrínseca das amostras submetidas à umidade relativa de 84% apresentaram as seguintes modificações espectrais: a) decaimento da intensidade de emissão das curvas b e d; b) deslocamento da banda de emissão para a região do azul devido ao aumento do teor de água; e c) aparecimento de um ombro na banda de emissão em 424 e 472 nm. Este comportamento fotofísico foi atribuído ao deslocamento do equilíbrio químico da forma protonada para a forma ionizada do 9-AA, promovido pela entrada de umidade no material.

Circular dichroism of polynucleotides: Interactions of NiCl2 with poly(dA‐dT)·poly(dA‐dT) and poly(dG‐dC)·poly(dG‐dC) in a water‐in‐oil microemulsion

The thermal behavior of the synthetic, high molecular weight, double stranded polynucleotides poly(dA-dT).poly(dA-dT) [polyAT] and poly(dG-dC).poly(dG-dC) [polyGC] solubilized in the aqueous core of the quaternary water-in-oil cationic microemulsion CTAB|n-pentanol|n-hexane|water in the presence of increasing amounts of NiCl(2) at several constant ionic strength values (NaCl) has been studied by means of circular dichroism and electronic absorption spectroscopies. In the microemulsive medium, both polynucleotides show temperature-induced modifications that markedly vary with both Ni(II) concentration and ionic strength. An increase of temperature causes denaturation of the polyAT duplex at low nickel concentrations, while more complex CD spectral modifications are observed at higher nickel concentrations and ionic strengths. By contrast, thermal denaturation is never observed for polyGC. At low Ni(II) concentrations, the increase of temperature induces conformational transitions from B-DNA to Z-DNA form, or, more precisely, to left-handed helical structures. In some cases, at higher nickel concentrations, the CD spectra suggest the presence of Z'-type forms of the polynucleotide.

The Quadruplex−Duplex Structural Transition of Polyriboguanylic Acid

The vibrational infrared (IR) absorption and vibrational circular dichroism (VCD) spectral changes of polyriboguanylic acid (polyG) as a function of time, temperature and pH have been investigated to establish how changes in spectral features relate to the structural modifications of polyG. From the progression of IR and VCD spectral features with respect to time, it is observed that stabilization of the quadruplex structure at pH 6.4 (near-neutral environment) takes place within 5 days. This stabilization process is most clearly evidenced by a downshift of the carbonyl absorption band and the corresponding positive VCD couplet, from 1689 to approximately 1682 cm(-1) in time. Time-induced spectral modifications also indicated that, in an acidic environment (pH 3.1) and within a 5 day waiting period, polyG develops a duplex structure. An additional positive VCD couplet associated with an absorption band at 1589 cm(-1) is identified as a marker of the polyG duplex structure. From the progression of spectral features with respect to temperature at pH 6.4, it is found that heating induces structural changes that favor the formation of a duplex structure. This duplex structure, at pH 6.4, would not form at room temperature simply by the passage of time. When polyG is in an acidic environment (pH 3.1), heating accelerates the conversion to the duplex structure that could also be obtained with passage of time at that pH. On the basis of the comparison of experimental and quantum theoretical VCD spectra for polyG, the key spectral signature for the quadruplex form is considered to be a single positive VCD couplet, while the spectral signature for a duplex form is considered to contain an additional positive VCD couplet at a lower frequency.