References of "Journal of Physical Chemistry B"
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See detailUltraviolet Laser Induced Hydrogen Transfer Reaction: Study of the First Step of MALDI In-Source Decay Mass Spectrometry
Asakawa, Daiki; Calligaris, David ULg; Smargiasso, Nicolas ULg et al

in Journal of Physical Chemistry B (2013), 117(8), 2321-2327

The early mechanisms of matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) are described herein. MALDI-ISD is initiated by the hydrogen transfer from excited matrix molecules to the ... [more ▼]

The early mechanisms of matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) are described herein. MALDI-ISD is initiated by the hydrogen transfer from excited matrix molecules to the carbonyl oxygen of the peptide backbone, which is followed by a radical-induced cleavage, producing the c′/z• fragment pair. As expected, the use of 2,5-DHB or 1,5-DAN was efficient to induce MALDI-ISD, and the strongest intensity of MALDI-ISD fragments was observed when laser shots were performed on matrix crystals. In contrast, the hydrogen radical transfer reaction was suppressed by using ionic liquid and amorphous structure of 2,5-DHB and 1,5-DAN mixture as a matrix. Our results suggest that the hydrogen transfer occurs on the matrix crystal during the dissipation of the laser energy and before desorption, following ISD fragments formed in the MALDI plume. [less ▲]

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See detailA Nanobody Binding to Non-amyloidogenic Regions of the Protein Human Lysozyme Enhances Partial Unfolding but Inhibits Amyloid Fibril Formation.
de Genst, EJ; Chan, PH; Pardon, Els et al

in Journal of Physical Chemistry B (2013)

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See detailLiquid Crystalline Phases Induced by the Hydroxyl Group Stereochemistry of Amphiphilic Carbohydrate Bicatenary Derivatives
Razafindralambo, Hary ULg; Richel, Aurore ULg; Paquot, Michel ULg et al

in Journal of Physical Chemistry B (2012), 116(13), 3998-4005

Liquid-crystals (LC) may exist in different phases depending upon the orientational and positional orders of molecules in the material. Here, we demonstrate that the class of LC state induced by ... [more ▼]

Liquid-crystals (LC) may exist in different phases depending upon the orientational and positional orders of molecules in the material. Here, we demonstrate that the class of LC state induced by amphiphilic carbohydrate bicatenary derivatives is strictly a hydroxyl group stereochemistry-dependent. This statement results from the experimental and theoretical investigations of surface film (2D) and bulk solid (3D) thermal behavior of synthetic stereoisomers n-tetradecyl (-D-n-tetradecyl) galacto- and gluco-pyranosiduronate, with an axial (GalA-C14/14) or equatorial (GlcA-C14/14) hydroxyl group at the fourth carbon, respectively. Surface pressure-area isotherms (283 K to 310 K), differential scanning calorimetry thermograms (223 K to 573 K), and polarized optical textures (298-363 K) reveal that GlcA-C14/14 organizes as a smectic LC-like phase (positional or lateral order) whereas the analogous stereoisomeric GalA-C14/14 behaves as a nematic LC-like phase (orientational order). Thermodynamic investigations and molecular dynamics models computed under similar temperature conditions provide consistent data with physical properties resulting from experimental approaches. [less ▲]

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See detailMulti-Scale Simulation of the Simian Immunodeficiency Virus Fusion Peptide.
Crowet, Jean-Marc ULg; Parton, Daniel L.; Hall, Benjamin A. et al

in Journal of Physical Chemistry B (2012)

Fusion peptides of type I fusion glycoproteins are structural elements of several enveloped viruses which enable the fusion between host and virus membranes. It is generally suggested that these peptides ... [more ▼]

Fusion peptides of type I fusion glycoproteins are structural elements of several enveloped viruses which enable the fusion between host and virus membranes. It is generally suggested that these peptides can promote the early fusion steps by inducing membrane curvature and that they adopt a tilted helical conformation in membranes. Although this property has been the subject of several experimental and in silico studies, an extensive sampling of the membrane peptide interaction has not yet been done. In this study, we performed coarse-grained molecular dynamic simulations in which the lipid bilayer self-assembles around the peptide. The simulations indicate that the SIV fusion peptide can adopt two different orientations in a DPPC bilayer, a major population which adopts a tilted interfacial orientation and a minor population which is perpendicular to the bilayer. The simulations also indicate that for the SIV mutant that does not induce fusion in vitro the tilt is abolished. [less ▲]

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See detailStabilized mixed micelles with a temperature-responsive core and a functional shell
Petrov, Petar; Tsvetanov, Christo B.; Jérôme, Robert ULg

in Journal of Physical Chemistry B (2009), 113(21), 7527-7533

Formation and stabilization of multiresponsive micelles with a mixed poly(ethylene oxide)/polyelectrolyte shell and a temperature-responsive poly(propylene oxide) core were studied. Various poly(ethylene ... [more ▼]

Formation and stabilization of multiresponsive micelles with a mixed poly(ethylene oxide)/polyelectrolyte shell and a temperature-responsive poly(propylene oxide) core were studied. Various poly(ethylene oxide)block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers were mixed with poly(acrylic acid)-block-poly(propylene oxide)-block-poly(acrylic acid) (PAA-PPO-PAA) or poly(dimethylaminoethyl methacrylate)-block-poly(propylene oxide)-block-poly(dimethylaminoethyl methacrylate) (PD-MAEMA-PPO-PDMAEMA) triblock copolymers. The micelles formed by binary mixtures of well-defined compositions at a specific pH were additionally stabilized by loading with pentaerythritol tetraacrylate (PETA), that was polymerized and cross-linked "in situ" with UV assistance. Depending on both the composition of the copolymers and the experimental conditions, either spherical or wormlike "stabilized polymeric micelles with a mixed shell" (SPMMS) were observed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The SPMMS that contained PAA blocks in the shell were pH-sensitive, such that a reversible transition from well-dispersed SPMMS to precipitate could be promoted. In contrast, the SPMMS with a PEO/PDMAEMA mixed shell remained well-dispersed in the 2-11 pH range. Finally, SPMMS were successfully exploited as templates for the preparation of Ag nanoparticles (Ag NPs). [less ▲]

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See detailImpacts of the carbonyl group location of ester bond on interfacial properties of sugar-based surfactants: experimental and computational evidences
Razafindralambo, Hary ULg; Blecker, Christophe ULg; Mezdour, Samir et al

in Journal of Physical Chemistry B (2009), 113

Interfacial properties of surfactants are dependent on the conformation adopted by the hydrophilic headgroup or/and the hydrophobic tail at the boundary limit of two immiscible phases. Here, we ... [more ▼]

Interfacial properties of surfactants are dependent on the conformation adopted by the hydrophilic headgroup or/and the hydrophobic tail at the boundary limit of two immiscible phases. Here, we demonstrate the impacts of the carbonyl group (-CO-) location of the ester bond of sugar-based surfactants by comparing some properties of two closely related esters, octyl glucuronate and glucose octanoate, at the air-water interface. The carbonyl group location influences the rate and extent of interfacial adsorption and the rheology properties of sugar esters at the air-water interface, which were evaluated by dynamic surface tension and complex surface viscoelastic measurements. Octyl glucuronate adsorbs the fastest at the air-water interface whereas glucose octanoate reduces the dynamic surface tension at the lowest value and exhibits the highest film viscoelasticity. Differences are attributed to molecular conformation constraints inducing relevant changes to the surface coverage kinetic capacity and the interaction strengths of the octyl sugar ester adsorbed films at the air-water interface. All of the results are supported by the minimum cross-sectional area values per molecule determined by both experimental and computational approaches. [less ▲]

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See detailComputational, Structural, and Mechanistic Analysis of the Electrochemically Driven Pirouetting Motion of a Copper Rotaxane
Periyasamy, Ganga ULg; Sour, A.; Collin, Jacques ULg et al

in Journal of Physical Chemistry B (2009), 113(18), 6219-6229

A mechanism for the electrochemically driven reorganization of a model copper [2]pseudorotaxane is proposed on the basis of density functional theory computations and validated by comparing to ... [more ▼]

A mechanism for the electrochemically driven reorganization of a model copper [2]pseudorotaxane is proposed on the basis of density functional theory computations and validated by comparing to experimental results. We investigate in detail the ligand reorganization around the Cu ion from a 4 to 5 coordination number that follows the conversion of the oxidation state from +1 to +2. It is found that for both the oxidation and the reduction processes the rearrangement proceeds in a concerted fashion via a single transition state. Energy paths involving stable decoordinated-coordinated intermediates are computed to be higher in energy. The cyclic voltammogram simulated using the computed transition theory state rate constants in solvent medium is in good agreement with the experimental voltammogram. Further, we report on the computed concentration change of stable (Cu-4(+), Cu-5(2+)) and metastable species (Cu-4(2+), Cu-5(+)) during single cyclic voltammetry (CV) cycle as a function of the applied voltage or time (the subscripts 4 and 5 refer to the coordination number of the copper center). [less ▲]

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See detailConformational and interfacial analyses of K3A18K3 and alamethicin in model membranes.
Kouzayha, Achraf; Nasir, Mehmet Nail ULg; Buchet, René et al

in Journal of Physical Chemistry B (2009), 113

The involvement of membrane-bound peptides and the influence of protein conformations in several neurodegenerative diseases lead us to analyze the interactions of model peptides with artificial membranes ... [more ▼]

The involvement of membrane-bound peptides and the influence of protein conformations in several neurodegenerative diseases lead us to analyze the interactions of model peptides with artificial membranes. Two model peptides were selected. The first one, an alanine-rich peptide, K3A18K3, was shown to be in R-helix structures in TFE, a membrane environment-mimicking solvent, while it was mostly -sheeted in aqueous buffer as revealed by infrared spectroscopy. The other, alamethicin, a natural peptide, was in a stable R-helix structure. To determine the role of the peptide conformation on the nature of its interactions with lipids, we compared the structure and topology of the conformational-labile peptide K3A18K3 and of the R-helix rigid alamethicin in both aqueous and phospholipid environments (Langmuir monolayers and multilamellar vesicles). K3A18K3 at the air-water interface showed a pressure-dependent orientation of its -sheets, while the R-helix axis of alamethicin was always parallel to the interface, as probed by polarization modulation infrared reflection absorption spectroscopy. The -sheeted K3A18K3 peptide was uniformly distributed into DPPC condensed domains, while the helical-alamethicin insertion distorted the DPPC condensed domains, as evidenced by Brewster angle microscopy imaging of the air/interface. The -sheeted K3A18K3 interacted with DMPC multilamellar vesicles via hydrophilic interactions with polar heads and the helical-alamethicin via hydrophobic interactions with alkyl chains, as shown by infrared spectroscopy and solid state NMR. Our findings are consistent with the prevailing assumption that the conformation of the peptide predetermines the mode of interaction with lipids. More precisely, helical peptides tend to be inserted via hydrophobic interactions within the hydrophobic region of membranes, while -sheeted peptides are predisposed to interact with polar groups and stay at the surface of lipid layer [less ▲]

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See detailTemperature responsive complex coacervate core micelles with a PEO and PNIPAAm corona
Voets, Ilya K.; Moll, Puck M.; Aqil, Abdelhafid et al

in Journal of Physical Chemistry B (2008), 112(35), 10833-10840

In aqueous solutions at room temperature, poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP38-b-PEO211 and poly(acrylic acid)-block-poly(isopropyl acrylamide), PAA55-b-PNIPAAm88 ... [more ▼]

In aqueous solutions at room temperature, poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP38-b-PEO211 and poly(acrylic acid)-block-poly(isopropyl acrylamide), PAA55-b-PNIPAAm88 spontaneously coassemble into micelles, consisting of a mixed P2MVP/PAA polyelectrolyte core and a PEO/PNIPAAm corona. These so-called complex coacervate core micelles (C3Ms), also known as polyion complex (PIC) micelles, block ionomer complexes (BIC), and interpolyelectrolyte complexes (IPEC), respond to changes in solution pH and ionic strength as their micellization is electrostatically driven. Furthermore, the PNIPAAm segments ensure temperature responsiveness as they exhibit lower critical solution temperature (LCST) behavior. Light scattering, two-dimensional 1H NMR nuclear Overhauser effect spectrometry, and cryogenic transmission electron microscopy experiments were carried out to investigate micellar structure and solution behavior at 1 mM NaNO3, T = 25, and 60 °C, that is, below and above the LCST of 32 °C. At T = 25 °C, C3Ms were observed for 7 < pH < 12 and NaNO3 concentrations below 105 mM. The PEO and PNIPAAm chains appear to be (randomly) mixed within the micellar corona. At T = 60 °C, onion-like complexes are formed, consisting of a PNIPAAm inner core, a mixed P2MVP/PAA complex coacervate shell, and a PEO corona. [less ▲]

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See detailJoint theoretical experimental investigation of the electron spin resonance spectra of nitroxyl radicals: application to intermediates in in situ nitroxide mediated polymerization (in situ NMP) of vinyl monomers
Zarycz, Natalia; Botek, Edith; Champagne, Benoit et al

in Journal of Physical Chemistry B (2008), 112(34), 10432-10442

Density functional theory (DFT) calculations have been performed to address the structure of nitroxide intermediates in controlled radical polymerization. In a preliminary step, the reliability of ... [more ▼]

Density functional theory (DFT) calculations have been performed to address the structure of nitroxide intermediates in controlled radical polymerization. In a preliminary step, the reliability of different theoretical methods has been substantiated by comparing calculated hyperfine coupling constants (HFCCs) to experimental data for a set of linear and cyclic alkylnitroxyl radicals. Considering this tested approach, the nature of different nitroxides has been predicted or confirmed for (a) the reaction of C-phenyl-N-tert-butylnitrone and AIBN, (b) N-tert-butyl-α-isopropylnitrone and benzoyl peroxide, (c) tert-butyl methacrylate polymerization in the presence of sodium nitrite as mediator, and (d) for the reaction of a nitroso compound with AIBN. Values of HFCC experimentally determined have been confirmed by DFT calculations. [less ▲]

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See detailRaman scattering in crystalline oligothiophenes: A comparison between density functional theory and bond polarizability model
Hermet, P.; Izard, N.; Rahmani, A. et al

in Journal of Physical Chemistry B (2006), 110(49), 24869-24875

Raman intensity of intramolecular and lattice modes of crystalline alpha-bithiophene (alpha-2T) are investigated within density functional theory using a nonlinear response formalism. First, comparison ... [more ▼]

Raman intensity of intramolecular and lattice modes of crystalline alpha-bithiophene (alpha-2T) are investigated within density functional theory using a nonlinear response formalism. First, comparison between the calculated Raman spectrum and the experimental data allows the assignment of the main Raman lines over the whole frequency range. Then, a bond polarizability (BP) model, limited to first neighbors, is built. We show that, although the BP model cannot reproduce the changes of dielectric susceptibility under individual atomic displacements, it is accurate enough to reproduce the profile of the unpolarized nonresonant Raman spectrum of alpha-2T powder. Finally, the BP model, fitted on our first-principles results on alpha-2T, is applied with success to the alpha-quaterthiophene polymorph phases and alpha-sexithiophene, demonstrating on practical examples that first-principles and BP approaches are powerful complementary tools to calculate the nonresonant Raman spectrum of alpha-2T and make reasonable predictions on larger oligothiophenes. [less ▲]

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See detailUltrathin transparent conductive films of polymer-modified multiwalled carbon nanotubes
Bocharova, Vera; Kiriy, Anton; Oertel, Ulrich et al

in Journal of Physical Chemistry B (2006), 110(30), 14640-14644

Deposition of multiwalled carbon nanotubes modified by poly(2-vinylpyridine) (CNT-g-P2VP) from aqueous dispersions at low pH is an effective method to prepare homogeneous ultrathin films with a tunable ... [more ▼]

Deposition of multiwalled carbon nanotubes modified by poly(2-vinylpyridine) (CNT-g-P2VP) from aqueous dispersions at low pH is an effective method to prepare homogeneous ultrathin films with a tunable CNTs density. A percolation threshold of 0.25 mu g/cm(2) and a critical exponent alpha = 1.24 have been found from dc conductivity measurements. The sheet resistance value agrees with the percolation theory for 2D films. According to AFM and electrical measurements, even when only 5% of the surface is covered by CNT-g-P2VPs, the sheet resistance is of the order of 1 M Omega/sq, which indicates that conductivity is imparted by a network of an ultralow density. When the film transmittance decreases down to similar to 70% at 550 nm, the occupied surface area is similar to 15% and sheet resistance falls down to similar to 90 k Omega/sq. These data show that undesired in-plane clustering does not occur upon the dispersion casting of the films and that high-quality networks of CNT-g-P2VPs are built up. The electrosteric stabilization of the CNT-g-P2VP dispersions in water at low pH is at the origin of this desired behavior. Although the multiwalled CNT films prepared in this work are less conductive and less transparent than the SWNTs films, they could find applications, e. g., in touch screens, reflective displays, EMI shielding, and static charge dissipation. [less ▲]

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See detailStructure of Silica Xerogels Synthesized with Organoalkoxysilane Co-reactants Hints at Multiple Phase Separation
Gommes, Cédric ULg; Basiura, Monika; Goderis, Bart et al

in Journal of Physical Chemistry B (2006), 110

The microstructure of hybrid silica xerogels synthesized by the base-catalyzed polymerization of tetraethoxysilane (TEOS) in ethanol in the presence of 3-aminopropyltriethoxysilane (AES) and of 3-(2 ... [more ▼]

The microstructure of hybrid silica xerogels synthesized by the base-catalyzed polymerization of tetraethoxysilane (TEOS) in ethanol in the presence of 3-aminopropyltriethoxysilane (AES) and of 3-(2-aminoethylamino)- propyltrimethoxysilane (EDAS) as co-reactants, and dried in subcritical conditions, is analyzed. A thorough structural characterization of the samples is performed combining nitrogen adsorption, small-angle X-ray scattering (SAXS), and transmission electron microscopy coupled with digital image analysis. The use of these methods shows that, for both co-reactants, the xerogels are made of macropores supported by filaments, with each filament being formed of smaller structures. The quantitative impact of the additive on each structural level is assessed. The data are compared with a previous time-resolved SAXS study conducted during the formation of the gels (J. Phys. Chem. B 2004, 108, 8983-8991). The results are analyzed in the framework of a double phase separation model. [less ▲]

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See detailCollective fluctuations in ordered fluids investigated by two-dimensional electron-electron double resonance spectroscopy
Fresch, Barbara ULg; Frezzato, Diego; Moro, Giorgio J. et al

in Journal of Physical Chemistry B (2006), 110

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See detailIn situ SAXS analysis of silica gel formation with an additive
Gommes, Cédric ULg; Blacher, Silvia ULg; Goderis, Bart et al

in Journal of Physical Chemistry B (2004), 108(26), 8983-8991

Time-resolved small-angle X-ray scattering (SAXS) measurements performed during the formation of tetraethyl orthosilicate (TEOS) based silica gels in alcohol with 3-(2-aminoethylamino ... [more ▼]

Time-resolved small-angle X-ray scattering (SAXS) measurements performed during the formation of tetraethyl orthosilicate (TEOS) based silica gels in alcohol with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) as an additive are reported. The measurements reveal no discontinuity of the nanostructure at the gel point. A chemically induced spinodal phase separation is found to give a coherent picture of the collected data. Increasing the amount of EDAS induces the phase separation on a smaller length scale, which finally leads to a modified gel morphology. The SAXS measurements and the electron micrographs associated with the dry gels could be interpreted in terms of the suggested wet gel formation mechanism. [less ▲]

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See detailOrientation of Thiophenol Adsorbed on Silver Determined by Nonlinear Vibrational Spectroscopy of the Carbon Skeleton
Mani, A. A.; Schultz, Z. D.; Caudano, Y. et al

in Journal of Physical Chemistry B (2004), 108

The orientation of thiophenol adsorbed on silver is determined by comparing ab initio calculated and experimental sum-frequency generation (SFG) spectra measured between 9 and 20 µm using a tandem KTP ... [more ▼]

The orientation of thiophenol adsorbed on silver is determined by comparing ab initio calculated and experimental sum-frequency generation (SFG) spectra measured between 9 and 20 µm using a tandem KTP/CdSe optical parametric oscillator. The molecule S-C bond is tilted ~37° from the surface normal with the aromatic ring plane perpendicular to the surface. [less ▲]

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See detailSynthesis of large pore disordered MSU-type mesoporous silicas through the assembly of C16(EO)10 surfactant and TMOS silica source: Effect of the hydrothermal treatment and thermal stability of materials
Blin, J. L.; Léonard, Alexandre ULg; Su, B. L.

in Journal of Physical Chemistry B (2001), 105(26), 6070-6079

Decaoxyethylene cetyl ether [C 16(EO) 10] has been employed as templating agent for large pore disordered MSU-type mesoporous silicas synthesis. The effect of the hydrothermal treatment (heating time and ... [more ▼]

Decaoxyethylene cetyl ether [C 16(EO) 10] has been employed as templating agent for large pore disordered MSU-type mesoporous silicas synthesis. The effect of the hydrothermal treatment (heating time and temperature) on the textural properties, in particular, pore diameter of materials has been investigated. The obtained materials have been characterized by different techniques such as X-ray diffraction, scanning and transmission electron microscopy and nitrogen adsorption-desorption analysis. The thermal stability of the compounds is also evaluated. Our results show that the pore diameter depends strongly on the heating time and temperature. This is the result of a competition between the stretching of the surfactant chains, which can lead to the breakdown of the walls separating adjacent pores, and the reorganization of micelles with heating time and temperature. At higher temperature or for longer durations, a more extended surfactant molecular conformation can be obtained, which leads to materials with larger pore sizes. A reorganization of the micellar solution during the hydrothermal treatment in autoclave can also simultaneously occur to give materials with smaller pore diameter. It is found that compounds prepared with the nonionic surfactant exhibit an enhanced thermal stability compared to those synthesized with cetyltrimethylammonium bromide (CTMABr) as templating agent. This higher stability is related to the synthesis pathway and the structure of materials. [less ▲]

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See detailHigh Resolution Electron Energy Loss Spectroscopy Investigation of the Vibrational Structure and Order of an Octadecanethiol Monolayer on Gold Substrates
Duwez, Anne-Sophie ULg; Yu, Li-Ming; Riga, Joseph et al

in Journal of Physical Chemistry B (2000), 104

The vibrational spectra induced by electron beam from octadecanethiol monolayers adsorbed on gold are reported as a contribution to study in detail the structure of the layers, through an analysis of the ... [more ▼]

The vibrational spectra induced by electron beam from octadecanethiol monolayers adsorbed on gold are reported as a contribution to study in detail the structure of the layers, through an analysis of the interaction mechanisms between the electrons and these organic ultrathin films. To show the different spatial distribution of scattered electrons from dipole and impact interactions with the monolayer, angular distributions of elastic and inelastic scattered electrons were measured for various primary energies. The absolute electron scattering loss probabilities from both dipole and impact interactions were estimated for different vibrational modes. The study of these different mechanisms was first hampered by the poor order of the layers adsorbed on evaporated gold. It became therefore highly desirable to perform the experiments on a single-crystal substrate. Using Au(111) and Au(100) single crystals as substrates, it was possible to separate the spectral response from impact and dipole interacting electrons. A negative ion resonant behavior has been observed in the energy dependence of the electron scattering differential cross sections [less ▲]

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See detailProbing Organization and Structural Characteristics of Alkanethiols Adsorbed on Gold and of Model Alkane Compounds through their Valence Electronic Structure: an Ultraviolet Photoelectron Spectroscopy Study
Duwez, Anne-Sophie ULg; Pfister-Guillouzo, G.; Delhalle, Joseph et al

in Journal of Physical Chemistry B (2000), 104

In this paper we report an ultraviolet photoelectron spectroscopy (UPS) study of saturated alkane chains in various configurations and conformations. The dependence of the valence spectra on molecular ... [more ▼]

In this paper we report an ultraviolet photoelectron spectroscopy (UPS) study of saturated alkane chains in various configurations and conformations. The dependence of the valence spectra on molecular structure characteristics has been assessed by comparing the results obtained from n-alkanethiol, R,ö-alkanedithiol, and R-cycloalkyl-ö-alkanethiol monolayers adsorbed on gold, and from gas-phase model alkane compounds. The differences between the spectra reflect directly the structural changes induced in the electronic structure of the alkane chains. We have determined the type of folding sequences adopted in a 1,12-dodecanedithiol monolayer. Angular dependent measurements and investigations on the photoelectron attenuation length have evidenced very fine structural differences between films obtained on deposited gold films, annealed gold films, and gold single crystals [less ▲]

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See detailTransmission and confocal fluorescence microscopy and time-resolved fluorescence spectroscopy combined with a laser trap: investigation of optically trapped block copolymer micelles
Gensch, Thomas; Hofkens, Johan; van Stam, Jan et al

in Journal of Physical Chemistry B (1998), 102(43), 8440-8451

Optical trapping was combined with transmission microscopy (TM), confocal and nonconfocal fluorescence scanning microscopy (CFSM and FSM, respectively), and confocal and nonconfocal time-resolved ... [more ▼]

Optical trapping was combined with transmission microscopy (TM), confocal and nonconfocal fluorescence scanning microscopy (CFSM and FSM, respectively), and confocal and nonconfocal time-resolved fluorescence spectroscopy (CTRFS and TRFS, respectively) to study latex particles and block copolymer micelles. Dye-labeled latex particles of various size, in polymer composite films as well as optically trapped in solution, were studied with CFSM to characterize the limits of the setup. CFSM revealed that the resolution in the x- and y-directions was near the theoretical limit, i.e., 200−250 nm. CTRFS on the labeled latex particles revealed that the decay time of the label was not influenced by the polymer matrix nor the optical trap. Poly(tert-butylstyrene-block-sodium methacrylate) micelles (diameter approximately 30−40 nm) in deuterated aqueous solutions could be optically trapped, this region of high copolymer micelle concentration being referred to as a trapped cluster. In the transmission images, trapped clusters of 1.5−2 μm diameter were detected. Fluorescence images were obtained using perylene as a fluorophore that is specifically dissolved within the block copolymer micelles. The size of the trapped cluster, estimated from TM and FSM images, increases with increasing irradiation time and power, respectively. In the TM images, the trapped cluster appears as a dark spot (low transmission) with a bright (high transmission) corona-like ring around it. The appearance of the corona is explained as a light deflection phenomenon; i.e., the trapped cluster acts as lens due to a lateral refractive index gradient. When the corona is taken into account when the diameter of the trapped clusters is calculated, a very good agreement is found between TM and FSM. Long irradiation times lead to the formation of large trapped clusters, which are stable for about 10 s, with diameters of several hundred nanometers, while, for short irradiation times, the trapped cluster is smaller and disappears within a time less than 1 s. With CFSM it could be shown that the trapped particle has a spot size of approximately 1.7 μm in the region of the IR laser focus, while the diameter extends up to 5 μm without using the confocal imaging capability. The reason for this is that the conditions for optical trapping are fulfilled not only in but also above and below the focal region. Due to the high numerical aperture, a dumbbell-like shape of the trapped cluster results. [less ▲]

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