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Spectroscopy Techniques (spectroscopy + techniques)
Selected AbstractsThe influence of cholesterol on the interaction of HIV gp41 membrane proximal region-derived peptides with lipid bilayersFEBS JOURNAL, Issue 19 2007Ana S. Veiga A small amino acid sequence (LWYIK) inside the HIV-1 gp41 ectodomain membrane proximal region (MPR) is commonly referred to as a cholesterol-binding domain. To further study this unique and peculiar property we have used fluorescence spectroscopy techniques to unravel the membrane interaction properties of three MPR-derived synthetic peptides: the membrane proximal region peptide-complete (MPRP-C) which corresponds to the complete MPR; the membrane proximal region peptide-short (MPRP-S), which corresponds to the last five MPR amino acid residues (the putative cholesterol-binding domain) and the membrane proximal region peptide-intermediate (MPRP-I), which corresponds to the MPRP-C peptide without the MPRP-S sequence. MPRP-C and MPRP-I membrane interaction is largely independent of the membrane phase. Membrane interaction of MPRP-S occurs for fluid phase membranes but not in gel phase membranes or cholesterol-containing bilayers. The gp41 ectodomain MPR may have a very specific function in viral fusion through the concerted and combined action of cholesterol-binding and non-cholesterol-binding domains (i.e. domains corresponding to MPRP-S and MPRP-I, respectively). [source] Strong seasonal disequilibrium measured between the oxygen isotope signals of leaf and soil CO2 exchangeGLOBAL CHANGE BIOLOGY, Issue 11 2010LISA WINGATE Abstract The oxygen isotope composition (,18O) of atmospheric CO2 is among a very limited number of tools available to constrain estimates of the biospheric gross CO2 fluxes, photosynthesis and respiration at large scales. However, the accuracy of the partitioning strongly depends on the extent of isotopic disequilibrium between the signals carried by these two gross fluxes. Chamber-based field measurements of total CO2 and CO18O fluxes from foliage and soil can help evaluate and refine our models of isotopic fractionation by plants and soils and validate the extent and pattern of isotopic disequilibrium within terrestrial ecosystems. Owing to sampling limitations in the past, such measurements have been very rare and covered only a few days. In this study, we coupled automated branch and soil chambers with tuneable diode laser absorption spectroscopy techniques to continuously capture the ,18O signals of foliage and soil CO2 exchange in a Pinus pinaster Aït forest in France. Over the growing season, we observed a seasonally persistent isotopic disequilibrium between the ,18O signatures of net CO2 fluxes from leaves and soils, except during rain events when the isotopic imbalance became temporarily weaker. Variations in the ,18O of CO2 exchanged between leaves, soil and the atmosphere were well explained by theory describing changes in the oxygen isotope composition of ecosystem water pools in response to changes in leaf transpiration and soil evaporation. [source] Reactivity of selected volatile organic compounds (VOCs) toward the sulfate radical (SO4,)INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2001Ch. George Rate constants for a series of alcohols, ethers, and esters toward the sulfate radical (SO4,) have been directly determined using a laser photolysis set-up in which the radical was produced by the photodissociation of peroxodisulfate anions. The sulfate radical concentration was monitored by following its optical absorption by means of time resolved spectroscopy techniques. At room temperature the following rate constants were derived: methanol ((1.6 ± 0.2) × 107 M,1 s,1); ethanol ((7.8 ± 1.2) × 107 M,1 s,1); tert -butanol ((8.9 ± 0.3) × 105 M,1 s,1); diethyl ether ((1.8 ± 0.1) × 108 M,1 s,1); MTBE ((3.13 ± 0.02) × 107 M,1 s,1); tetrahydrofuran (THF) ((2.3 ± 0.2) × 108 M,1 s,1); hydrated formaldehyde ((1.4 ± 0.2) × 107 M,1 s,1); hydrated glyoxal ((2.4 ± 0.2) × 107 M,1 s,1); dimethyl malonate (CH3OC(O)CH2C(O)OCH3) ((1.28 ± 0.02) × 106 M,1 s,1); and dimethyl succinate (CH3OC(O)CH2CH2C(O)OCH3) ((1.37 ± 0.08) × 106 M,1 s,1) where the errors represent 2,. For the two latter species, we also measured the temperature dependence of the corresponding rate constants. A correlation of these kinetics with the bond dissociation energy is also presented and discussed. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 539,547, 2001 [source] A funerary rite study of the Phoenician,Punic necropolis of Mount Sirai (Sardinia, Italy)INTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 2 2010G. Piga Abstract A recent excavation in the Phoenician,Punic necropolis of Mount Sirai, located in the southwestern part of Sardinia, Italy, has brought to light a number of tombs contextually attributed to a period from the early 6th to early 5th century BC, which is simultaneous with the beginning of the Carthago influence in Sardinia. Among the interred burials recently brought to light, the skeletal remains, sometimes of two superposed bodies, are found in a primary position and with fine anatomic connection. Some of the bones were visually stained, suggesting they were possibly subjected to fire treatment. In order to ascertain more objectively whether the bodies were subjected to burning, the bones from all the tombs were investigated by powder X-ray diffraction (XRD) and Fourier Transform infra-red (FT-IR) spectroscopy techniques. After excluding the role of important diagenetic effects, from line broadening/sharpening analysis of hydroxylapatite in the bones according to the Rietveld method, it was evaluated that the bodies were probably subjected to a temperature regime from 300 to 700°C. These data were supplemented and confirmed by an analysis of the splitting factor (SF) of apatite phosphate peaks in the infra-red spectrum of the bones. Our results indicate the existence of a rite intermediate between incineration and inhumation. This sort of ,semi-combustion', perhaps limited to the period of the early 5th century BC, appears to be peculiar just to this site. Copyright © 2008 John Wiley & Sons, Ltd. [source] Generalized Diffusion Tensor Imaging (GDTI): A Method for Characterizing and Imaging Diffusion Anisotropy Caused by Non-Gaussian DiffusionISRAEL JOURNAL OF CHEMISTRY, Issue 1-2 2003Chunlei Liu For non-Gaussian distributed random displacement, which is common in restricted diffusion, a second-order diffusion tensor is incapable of fully characterizing the diffusion process. The insufficiency of a second-order tensor is evident in the limited capability of diffusion tensor imaging (DTI) in resolving multiple fiber orientations within one voxel of human white matter. A generalized diffusion tensor imaging (GDTI) method was recently proposed to solve this problem by generalizing Fick's law to a higher-order partial differential equation (PDE). The relationship between the higher-order tensor coefficients of the PDE and the higher-order cumulants of the random displacement can be derived. The statistical property of the diffusion process was fully characterized via the higher-order tensor coefficients by reconstructing the probability density function (PDF) of the molecular random displacement. Those higher-order tensor coefficients can be measured using conventional diffusion-weighted imaging or spectroscopy techniques. Simulations demonstrated that this method was capable of quantitatively characterizing non-Gaussian diffusion and accurately resolving multiple fiber orientations. It can be shown that this method is consistent with the q-space approach. The second-order approximation of GDTI was shown to be DTI. [source] Synthesis and characterization of novel polyimide/SiO2 nanocomposite materials containing phenylphosphine oxide via sol-gel techniqueJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Canan Kizilkaya Abstract In this article, a series of novel polyimide/silica (PI/SiO2) nanocomposite coating materials were prepared from tetraethoxysilane (TEOS), ,-glycidyloxypropyltrimethoxysilane (GOTMS), and polyamic acid (PAA) via sol-gel technique. PAA was prepared by the reaction of 3,3,,4,4,-benzophenone tetracarboxylic dianhydride (BTDA) and bis (3-aminophenyl) phenyphosphine oxide (BAPPO) in N -methyl-2- pyrrolidone (NMP). BAPPO was synthesized hydrogenation of bis (3-nitrophenyl) phenyphosphine oxide (BNPPO) in the presence of Pd/C. The silica content in the hybrid coating materials was varied from 0 to 20 wt %. The molecular structures of the composite materials were analyzed by means of FT-IR and 29Si-NMR spectroscopy techniques. The physical and mechanical properties of the nanocomposites were evaluated by various techniques such as, hardness, contact angle, and optical transmission and tensile tests. These measurements revealed that all the properties of the nanocomposite coatings were improved noticeable, by the addition of sol-gel precursor into the coating formulation. Thermogravimetric analysis showed that the incorporation of sol-gel precursor into the polyimide matrix leads to an enhancement in the thermal stability and also flame resistance properties of the coating material. The surface morphology of the hybrid coating was characterized by scanning electron microscopy (SEM). SEM studies indicated that nanometer-scaled inorganic particles were homogenously dispersed throughout the polyimide matrix © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Phosphonic acid functionalized polyethylene glycol and derivativesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Mohamed Essahli Abstract This article describes the functionalization of polyethylene glycol, mono or bifunctional, and a nonionic surfactant by phosphonic acids without the need for protection of the functional group. The functionalization is performed in two steps, first an esterification by thioglycolic acid, secondly a radical addition of vinyl phosphonic acid on the thiol group. All products were obtained quantitatively and characterized by 1H-, 13C-, 31P-NMR spectroscopy techniques, MALDI, and step-by-step chemical titrations. Enhanced thermal properties were found while phosphonylating polyethylene glycol, particularly when the sulfur atom was oxidized into a sulfone group. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Facilities for high-pressure research with the diamond anvil cell at GSECARSJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2005Guoyin Shen An overview of facilities for high-pressure research with the diamond anvil cell (DAC) at the GeoSoilEnviroCARS (GSECARS) sector at the Advanced Photon Source (Argonne, Illinois) is presented. There are three operational experimental stations (13-ID-C, 13-ID-D and 13-BM-D) where DAC instrumentation is installed for various types of experiments at high pressure and extreme temperature conditions. A fourth station (13-BM-C) is under construction and will be operational in 2006. While most X-ray diffraction experiments have been undertaken with powder samples so far, there is a growing demand for single-crystal diffraction (SCD) at high pressure. As one of the principal components at GSECARS, SCD is currently under rapid development. Other relevant techniques have also been developed for obtaining complementary information from powder or single-crystal samples at high pressure. For example, an on-line Brillouin system is installed and operational at 13-BM-D for acoustic velocity and single-crystal elasticity determinations. In addition, various X-ray spectroscopy techniques (e.g. X-ray emission and X-ray Raman) are employed for measuring electronic and magnetic properties. Future developments are discussed with the DAC program at GSECARS. [source] Preparation of NiAl2O4/SiO2 and Co2+ -Doped NiAl2O4/SiO2 Nanocomposites by the Sol,Gel RouteJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2006I. Prakash NiAl2O4/SiO2 and Co2+ -doped NiAl2O4/SiO2 nanocomposite materials of compositions 5% NiO , 6% Al2O3, 89% SiO2 and 0.2% CoO , 4.8% NiO , 6% Al2O3, 89% SiO2, respectively, were prepared by a sol,gel process. NiAl2O4 and cobalt-doped NiAl2O4 nanocrystals were grown in a SiO2 amorphous matrix at around 1073 K by heating the dried gels from 333 to 1173 K at the rate of 1 K/min. The formations of NiAl2O4 and cobalt-doped NiAl2O4 nanocrystals in SiO2 amorphous matrix were confirmed through X-ray powder diffraction, Fourier transform infrared spectroscopy, differential scanning calorimeter, transmission electron microscopy (TEM), and optical absorption spectroscopy techniques. The TEM images revealed the uniform distribution of NiAl2O4 and cobalt-doped NiAl2O4 nanocrystals in the amorphous SiO2 matrix and the size was found to be ,5,8 nm. [source] Kinetics of Core-Shell Nanoparticle Formation by Two-Dimensional Nuclear Magnetic ResonanceMACROMOLECULAR RAPID COMMUNICATIONS, Issue 11 2009Alaitz Ruiz de Luzuriaga Abstract We have studied the kinetics of polymeric nanoparticle formation for poly(styrene- block -4-vinylpyridine) [P(S- b -4-VPy)], chains in a non-selective solvent using 1,4-dibromobutane (DBB) as a cross-linker by means of different nuclear magnetic resonance (NMR) spectroscopy techniques. The kinetic process was followed using 1H, 13C, and 2-D Heteronuclear Single Quantum Correlation (HSQC) NMR experiments. The kinetic data obtained from 2-D HSQC and 1H NMR experiments were in good agreement between them, proving the reliability of the 2-D HSQC NMR technique for the in situ study of the kinetics of core-shell nanoparticle formation. A value of 1.5,×,10,5 s,1 was determined for the apparent kinetic constant of the P(S- b -4-VPy)-DBB core-shell nanoparticle formation process. [source] A simple approach for phase-modulated single-scan 2D NMR spectroscopyMAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2005Nikolas Salisbury Andersen Abstract Conventional NMR spectroscopy techniques require long acquisition times due to the recovery time between the repeated excitations necessary for each increment of the evolution times in the indirectly detected dimensions. Here we outline a pulse sequence element for gradient-assisted ultrafast multidimensional NMR spectroscopy using frequency-modulated ,chirp' pulses to generate phase-modulated magnetization in an indirectly detected spectral dimension. The potential of this sequence element is demonstrated by acquiring a correlation spectroscopy (COSY) spectrum in 96 ms. This new pulse sequence element is an extension of ultrafast spectroscopy techniques based on the generation of amplitude modulation of the NMR signal in the indirectly detected spectral dimensions. The use of phase modulation instead of amplitude modulation helps broaden the applicability and may provide an increase of sensitivity in some experiments due to the ability to distinguish between positive and negative frequency offsets relative to the carrier frequency of the sequence element. Copyright © 2005 John Wiley & Sons, Ltd. [source] Modulation spectroscopy on a single self assembled quantum dotPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2007S. Seidl Abstract We present high resolution modulation spectroscopy on single quantum dots and discuss briefly the differences to other spectroscopy techniques. We use this technique to study the excitonic fine structure while charging the quantum dot and applying mechanical strain to it. We also show that the fine structure can be used as a polarization analyzer. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Quasi-localized low-frequency vibrational modes of disordered solids: Study by single-molecule spectroscopyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2004A. V. Naumov Editor's Choice of this issue of physica status solidi (b) is the article [1] by Andrei V. Naumov et al. This paper is Part II (Part I see [2]) of a study on elementary excitations in glasses, presented at the 11th International Conference on Phonon Scattering in Condensed Matter, St. Petersburg, 25,30 July 2004. For his outstanding talk, Naumov received the new physica status solidi Young Researcher Award which was bestowed for the first time at this conference. The cover picture is a sketch of a glass with a single impurity molecule and one hypothetical quasi-localized vibrational mode. The broadening and shift of the chromophore spectral line are caused by the interaction with this mode. Andrei V. Naumov is senior scientific researcher and deputy head of the Molecular Spectroscopy Department of the Institute of Spectroscopy, Troitsk. His main research interests are experimental and theoretical studies of low-temperature dynamics of amorphous solids (glasses, polymers etc.) via high resolution laser selective spectroscopy techniques. The second Editor's Choice is an article by E. A. Eliseev and M. D. Glinchuk [3]. Eugene A. Eliseev is scientific researcher at the Frantsevich Institute for Problems of Materials Science of the Ukrainian National Academy of Sciences, Kiev. His research areas are the theory of size and correlation effects in ferroelectric materials as well as modelling of disordered ferroelectrics properties. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Two mechanisms of 1D2 fluorescence quenching of Pr3+ -doped Y2SiO5 crystalPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2003Yu. V. Malyukin Abstract In Y2SiO5:Pr3+ crystals (0.1 at%, 0.3 at%, 0.6 at% , and 1.8 at% Pr3+) characterized by the existence of two types of Pr3+ optical centers, the energy transfer has been investigated using time-resolved site-selective spectroscopy techniques. The results obtained show that at certain conditions there are two different mechanisms of fluorescence quenching of the excited 1D2 states of Pr3+ ions. At 0.3 at% Pr3+ and under the excitation of 1D2 states as the result of 3P0 , 1D2 nonradiative relaxation, the phonon-assisted energy transfer from 1D2 states of the I-type Pr3+ ions to the II-type ones has been found. The nonexponential part of donor fluorescence decay was described by the law t0.5. and the transfer efficiency exhibits a strong temperature dependence in the range of 1.5,80 K. At the direct selective excitation of the 1D2 states of one type Pr3+ optical centers it was possible to observe only their own fluorescence which quenched at a concentration above 0.6 at% Pr3+. The donor fluorescence decay was not fit by the law t0.5 and the quenching efficiency was characterized by the square-loaw dependence on the concentration and a very poor dependency on the temperature. The analysis of some models allows us to assume, that in this case, the cooperative quenching of the 1D2 states of both type Pr3+ optical centers can take place. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical spectra of Tm3+ -doped YAl3(BO3)4 single crystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007E. Cavalli Abstract Flux grown YAl3(BO3)4 (YAB) crystals doped with Tm3+ have been characterised by optical spectroscopy techniques. The absorption and emission spectra in the UV-VIS-NIR region have been measured at 10 and 298 K. The visible emission decay profiles have been measured at room temperature. The low temperature spectra have been used to obtain the energy level scheme of the optically active ion in YAB. The Judd-Ofelt parametrization scheme has been applied to the analysis of the room temperature absorption spectra in order to evaluate the intensity parameters, the branching ratios and the radiative lifetimes of the emitting states. These have been compared with the experimental values. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Low temperature structural transformations of dilute KTa1,xNbxO3: x = 0.018, quantum superparaelectric or reentrant glass scenario?PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005V. A. Trepakov Abstract Impurity induced structural transformations are studied for KTa1,xNbxO3 with x = 0.0018 (KTN-1.8) by low-frequency linear and non-linear dielectric spectroscopy techniques. Nb admixture leads to the appearance of a sharp ,,(T) maximum accompanying the ferroelectric phase transition at TC , 27 K, and a glass-like state formation at lower temperatures. The linear permittivity evidences properties inherent to systems being near the quantum-mechanical displacive limit and shows the long range polar order with macroscopic polarization formation at ,27 K. This conclusion was proven by nonlinear polarization response stuidy under dc electric field action, which evidenced also the proximity of the three-critical point. Above 27 K, the nonlinearity increases at cooling in accordance with the Devonshire theory for the paraelectric phase of conventional ferroelectrics. Below 27 K, the random distribution of Nb5+ ions and related system's inhomogeneities provoke a new low temperature phase state formation, which can be treated as reentrant polar-glass. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis, crystal structure and spectroscopic properties of a novel carbacylamidophosphate: N -(3-nitrobenzoyl)- N,,N,,-bis(tert -butyl)phosphoric triamideACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2009Khodayar Gholivand The new compound N -(3-nitrobenzoyl)- N,,N,,-bis(tert -butyl)phosphoric triamide was synthesized by reacting 3-nitrobenzoyl phosphoramidic dichloride and tert -butyl amine, and characterized by multinuclear (1H, 13C and 31P) NMR and FTIR spectroscopy techniques. Structural and conformational properties were analyzed using single-crystal X-ray diffraction, vibrational spectra and theoretical calculations. The crystal structure contains three symmetry-independent disordered molecules, connected via intermolecular N,H...O=P and N,H...O=C hydrogen bonds to form a centrosymmetric hexameric chain extended along the [2,1,] direction. The disorder is mainly caused by rotation of the tert -butyl groups around the C,N bonds. [source] CLIMATE FORCINGS AND THEIR INFLUENCE ON ALPINE HISTORY AS RECONSTRUCTED THROUGH THE APPLICATION OF SYNCHROTRON-BASED X-RAY MICROFLUORESCENCE ON LAYERED STALAGMITES*ARCHAEOMETRY, Issue 2 2005S. FRISIA Solar variability and volcanic activity strongly interact with climate and the environment. Synchrotron radiation X-ray microfluorescence (micro-XRF) to an annually laminated Alpine stalagmite confirmed that annual laminae result from hydrological variability and changes in the duration of soil microbial degradation. The latter is modulated by solar variability. At the centennial timescale, growth rate and solar activity appear to be correlated with temperature change, with low temperatures at solar minima. By combining micro-XRF and absorption spectroscopy techniques (XANES), we also found that speleothems are a new archive of aerosol sulphate related to volcanic activity. Peaks in S-concentration from c. 5.2 to 5.0 ka bp in an Alpine stalagmite suggest that multiple volcanic sulphate aerosol emissions enhanced Mid-Holocene summer cooling, thus favouring the preservation of the Alpine Iceman mummy in a persistent ice casket. [source] Synthesis of Symmetrical Multichromophoric Bodipy Dyes and Their Facile Transformation into Energy Transfer Cassettes,CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2010Altan Bozdemir Dr. Abstract Multichromophoric boron-dipyrromethene (Bodipy) dyes synthesized on phenylene-ethynylene platforms have been be converted to energy transfer cassettes in a one-step chemical transformation. Excitation energy transfer processes in these highly symmetrical derivatives were studied in detail, including time-resolved fluorescence spectroscopy techniques. Excitation spectra and the emission lifetimes suggest efficient energy transfer between the donor and acceptor chromophore. These novel energy transfer cassettes, while highlighting a short-cut approach to similar energy transfer systems, could be useful as large pseudo-Stokes shift multichromophoric dyes with potential applications in diverse applications. Fenilenetilen platformu üzerinde sentezlenen multikromoforik Bodipy boyarmaddeleri, tek basamakl, bir kimyasal transformasyonla enerji transferi kasetlerine dönü,türülmü,tür. Zaman ayr,ml, floresans spektroskopisi tekniklerinin de içinde bulundu,u yöntemlerle, yüksek simetri ö,eleri bulunduran bu türevlerdeki eksitasyon enerjisi transferi süreçleri ayr,nt,l, olarak çal,,,lm,,t,r. Eksitasyon spektrumlar, ve emisyon ömürlerindeki de,i,im, donör ve akseptör kromoforlar, aras,nda etkin bir enerji transferi oldu,unu dü,ündürmektedir. Bu yeni enerji transfer kasetleri, benzer enerji transfer sistemlerine kolay bir geçi, yolu göstermekle birlikte, pek çok farkl, alanda potansiyel uygulamalar, olabilecek, büyük pseudo-Stokes kaymas, de,erlerine sahip multikromoforik boyarmaddeler olarak da yararl, olabilirler. [source] | ||||||||||||||||||||||||||||