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See detailAtomistic account of structural and dynamical changes induced by small binders in the double helix of a short DNA
Fresch, Barbara ULg; Remacle, Françoise ULg

in Physical Chemistry Chemical Physics [=PCCP] (in press)

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See detailMulti-scale modeling of mycosubtilin lipopeptides at the air/water interface: structure and optical second harmonic generation
Loison, Claire; Nasir, Mehmet Nail ULg; Benichou, Emmanuel et al

in Physical Chemistry Chemical Physics [=PCCP] (2014), 16

Monolayers of the lipopeptide mycosubtilin are studied at the air/water interface. Their structure is investigated using molecular dynamics simulations. All-atom models suggest that the lipopeptide is ... [more ▼]

Monolayers of the lipopeptide mycosubtilin are studied at the air/water interface. Their structure is investigated using molecular dynamics simulations. All-atom models suggest that the lipopeptide is flexible and aggregates at the interface. To achieve simulation times of several microseconds, a coarse-grained (CG) model based on the MARTINI force field was also used. These CG simulations describe the formation of half-micelles at the interface for surface densities up to 1 lipopeptide per nm2. In these aggregates, the tyrosine side chain orientation is found to be constrained: on average, its main axis, as defined along the C–OH bond, aligns along the interface normal and points towards the air side. The origin of the optical second harmonic generation (SHG) from mycosubtilin monolayers at the air/water interface is also investigated. The molecular hyperpolarizability of the lipopeptide is obtained from quantum chemistry calculations. The tyrosine side chain contribution to the hyperpolarizability is found to be dominant. The orientation distribution of tyrosine, associated with a dominant hyperpolarizability component along the C–OH bond of the tyrosine, yields a ratio of the susceptibility elements χ(2)ZZZ/χ(2)ZXX consistent with the experimental measurements recently reported by M. N. Nasir et al. [Phys. Chem. Chem. Phys., 2013, 15, 19919]. [less ▲]

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See detailCharacterization of the MgO2+ dication in the gas phase: electronic states, spectroscopy and atmospheric implications
Linguerri, Roberto; Hochlaf, Majdi; Baccus-Montabonel, Marie-Christine et al

in Physical Chemistry Chemical Physics [=PCCP] (2013), 15(3), 824-831

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See detailInfluence of the tyrosine environment on the second harmonic generation of iturinic antimicrobial lipopeptides at the air–water interface
Nasir, Mehmet Nail ULg; Benichou, Emmanuel; Loison, Claire et al

in Physical Chemistry Chemical Physics [=PCCP] (2013), 15

The second harmonic generation (SHG) response at the air–water interface from the tyrosine-containing natural iturinic cyclo-lipopeptides mycosubtilin, iturin A and bacillomycin D is reported. It is shown ... [more ▼]

The second harmonic generation (SHG) response at the air–water interface from the tyrosine-containing natural iturinic cyclo-lipopeptides mycosubtilin, iturin A and bacillomycin D is reported. It is shown that this response is dominated by the single tyrosine residue present in these molecules owing to the large first hyperpolarizability arising from the non-centrosymmetric aromatic ring structure of this amino acid. The SHG response of these iturinic antibiotics is also compared to the response of surfactin, a cyclo-lipopeptide with a similar L,D-amino acid sequence but lacking a tyrosine residue, and PalmATA, a synthetic linear lipopeptide possessing a single tyrosine residue but lacking the amino acid sequence structuring the cycle of the iturinic antibiotics. From the light polarization analysis of the SHG response, it is shown that the tyrosine local environment is critical in defining the SHG response of these peptides at the air–water interface. Our results demonstrate that tyrosine, similar to tryptophan, can be used as an endogenous molecular probe of peptides and proteins for SHG at the air–water interface, paving the way for SHG studies of other tyrosine-containing bioactive molecules. [less ▲]

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See detailBubble bouncing at a clean water surface
zawala, jan; Dorbolo, Stéphane ULg; Vandewalle, Nicolas ULg et al

in Physical Chemistry Chemical Physics [=PCCP] (2013), 15

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See detailMorphological and opto-electrical properties of solution deposited Platinum counter electrode for low cost dye sensitized solar cells
Thalluri, Venkata Visveswara Gopala Kris ULg; Décultot, Marc ULg; Henrist, Catherine ULg et al

in Physical Chemistry Chemical Physics [=PCCP] (2013), 15

Although Platinum (Pt) is a rare and very expensive material, Pt counter electrodes are still very commonly used for reaching high efficiencies in dye-sensitized solar cells (DSCs). The use of alternative ... [more ▼]

Although Platinum (Pt) is a rare and very expensive material, Pt counter electrodes are still very commonly used for reaching high efficiencies in dye-sensitized solar cells (DSCs). The use of alternative cheaper catalyst materials did not yet yield to equivalent efficiencies. In this work, we tried to understand how to reduce the amount of deposited Pt-material and simultaneously to deliver higher DSC performances. We systematically compared the properties of Pt-counter electrodes prepared by simple solution deposition methods such as spray-coating, dip-coating, brushing with reference to the Pt-electrodes prepared by sputtering onto fluorine doped-tin oxides (FTOs). The morphological and structural characterizations of the deposited Pt-layers were performed by atomic force microscopy (AFM) and scanning electron microscope (SEM). The composition of Pt-material was quantified by using SEM electron dispersive x-ray (EDX) mapping measurements are further compared with optical transmission measurements. Also contact angle and sheet resistance measurements were performed. By taking Pt-layers composition, morphology and structural factors into account 9.16% efficient N3 dye based DSCs were assembled. The DSCs were subjected to various opto-electrical characterization techniques like current-voltage (I-V), external quantum efficiency (EQE), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and transient photo voltage (TPV) measurements. The obtained experimental data suggest that the Pt counter electrodes prepared by solution deposition methods can also reach to high DSC device performances with a consumption of very less amount of Pt material compared with sputtered Pt-layers. This process also proves that higher DSC performances are not limited to the usage of sputtered Pt-layer as counter electrode. [less ▲]

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See detailMonolayer Properties of Uronic Acid Bicatenary Derivatives at the Air-Water Interface: Effect of Hydroxyl Group Stereochemistry Evidenced by Experimental and Computational Approaches
Razafindralambo, Hary ULg; Richel, Aurore ULg; Wathelet, Bernard ULg et al

in Physical Chemistry Chemical Physics [=PCCP] (2011), 13(33), 1529115298

By screening uronic acid-based surfactant interfacial properties, the effect of the hydroxyl group stereochemistry (OH-4) on the conformation of bicatenary (disubstituted) derivatives at the air–water ... [more ▼]

By screening uronic acid-based surfactant interfacial properties, the effect of the hydroxyl group stereochemistry (OH-4) on the conformation of bicatenary (disubstituted) derivatives at the air–water interface has been evidenced by experimental and computational approaches. Physical and optical properties of a monolayer characterized by Langmuirfilmbalance, Brewster angle microscopy, and ellipsometry at 20°C reveal that the derivative of glucuronate (C14/14–GlcA) forms a more expanded monolayer, and shows a transition state under compression, in the opposite to that of galacturonate (C14/14–GalA). Both films are very mechanically resistant (compression modulus > 300m Nm-1) and stable (collapse pressure exceeding 60mNm-1), while that of C14/14–GalA exhibits a very high compression modulus up to 600mNm-1 like films in the solid state. Computational approaches provide single and assembly molecular models that corroborate the molecule expansion degree and interactions data from experimental results. Differences in the molecular conformation and film behaviours of uronic acid bicatenary derivatives at the air–water interface are attributed to the intra-H-bonding formation, which is more favourable with an OH-4 in the axial (C14/14–GalA) than in the equatorial position (C14/14–GlcA). [less ▲]

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See detailStereocontrol of attosecond time-scale electron dynamics in ABCU using ultrafast laser pulses: a computational study
Mignolet, Benoît ULg; Gijsbertsen, A.; Vrakking, M. J. J. et al

in Physical Chemistry Chemical Physics [=PCCP] (2011), 13(18), 8331-8344

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See detailImplementing quantum algorithms in hyperfine levels of ultracold polar molecules by optimal control
Pellegrini, Philippe; Vranckx, Stéphane; Desouter, Michèle ULg

in Physical Chemistry Chemical Physics [=PCCP] (2011), 13

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See detailThe role of the support in COads monolayer electrooxidation on Pt nanoparticles : Pt/WOx vs. Pt/C.
Micoud, Fabrice; Maillard, Frédéric; Bonnefont, Antoine et al

in Physical Chemistry Chemical Physics [=PCCP] (2010), 12

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See detailZwitterionic i-motif structures are preserved in DNA negatively charged ions produced by electrospray mass spectrometry
Rosu, Frédéric ULg; Gabelica, Valérie ULg; Joly, Laure ULg et al

in Physical Chemistry Chemical Physics [=PCCP] (2010), 12

DNA cytosine-rich strands can fold into an intercalated motif (i-motif) structure. The i-motif is formed by mutually intercalated duplexes containing proton-mediated C-H(+)-C (cytosine-proton-cytosine ... [more ▼]

DNA cytosine-rich strands can fold into an intercalated motif (i-motif) structure. The i-motif is formed by mutually intercalated duplexes containing proton-mediated C-H(+)-C (cytosine-proton-cytosine) base pairs. Negatively charged ions of DNA i-motifs produced by electrospray mass spectrometry are therefore zwitterionic if the base pairing motif is preserved in the gas phase. Here we used IRMPD spectroscopy and ion mobility spectrometry to assess whether i-motif structures were preserved in the gas phase. We first investigated the IRMPD spectral signature of the tetramer [dC(6)](4), which can only be formed via C-H(+)-C base pairing, compared to the single strand dC(6). The IR signature of i-motif formation is an apparent broadening of the band at 1650 cm(-1). DFT calculations show this apparent broadening is actually due to blue-shifts of the NH(2) scissoring modes and red shifts of C[double bond, length as m-dash]O stretching modes. We then investigated the gas-phase conformations of the telomeric sequence d(CCCAAT)(3)CCC, that can form an intramolecular i-motif, by performing IRMPD spectroscopy and ion mobility spectrometry as a function of the charge state. We show that the negative ions of the lowest charge states correspond to a preserved i-motif structure. This is the first demonstration of the native extraction of solution-phase zwitterionic nucleic acids using negative electrospray ionization. [less ▲]

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See detailFirst-principles study of the dynamical and nonlinear optical properties of urea single crystals
Hermet, Patrick ULg; Ghosez, Philippe ULg

in Physical Chemistry Chemical Physics [=PCCP] (2010), 12

Raman and infrared spectra of urea single crystals have been calculated using the density functional theory. This allowed us to assign the remaining experimental low-frequency phonon modes. Then, we have ... [more ▼]

Raman and infrared spectra of urea single crystals have been calculated using the density functional theory. This allowed us to assign the remaining experimental low-frequency phonon modes. Then, we have determined the sign of the second-harmonic nonlinear optical susceptibility coefficient in urea to be negative, clarifying a long debate in the literature. Finally, we computed for the first time the electro-optic coefficients of urea. We found that the electronic and ionic contributions have a similar order of magnitude and an opposite sign, yielding a smaller value than that expected, and necessitating further experimental clarifications. [less ▲]

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See detailControlled full adder-subtractor by vibrational computing
Bomble, L.; Lauvergnat, D.; Remacle, Françoise ULg et al

in Physical Chemistry Chemical Physics [=PCCP] (2010), 12(48), 15628-15635

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See detailLiMSO(4)F (M = Fe, Co and Ni): promising new positive electrode materials through the DFT microscope
Frayret, Christine; Villesuzanne, Antoine; Spaldin, Nicola et al

in Physical Chemistry Chemical Physics [=PCCP] (2010), 12(47), 15512-15522

A theoretical study of the lithium intercalated LiMSO(4)F and deintercalated MSO(4)F systems, where M = Fe, Co and Ni has been performed within the framework of density functional theory. Beyond ... [more ▼]

A theoretical study of the lithium intercalated LiMSO(4)F and deintercalated MSO(4)F systems, where M = Fe, Co and Ni has been performed within the framework of density functional theory. Beyond predictions of structural evolution and average voltages versus a lithium electrode, we have applied partial density of states and Bader's topological analysis of the electron density to the study of lithium deintercalation. Upon lithium extraction, charge rearrangement occurs for nickel between different d-orbitals, but with little net positive charge gain, while cobalt and iron atoms end up with a clear oxidized state. The participation of oxygen ions in accepting the electron of the lithium is thus enhanced for LiNiSO(4)F. However, this effect does not affect the long-range electrostatic interactions a lot in the lithiated phase, since the valence of all transition metals is very close due to initial lower oxidized state for the Ni atom in the host. It is found that this is not essentially a long-range electrostatic interaction within the lithiated phase but within the host which explains, at least partly, the increase in voltage by passing from Fe to Ni. Our results also shed light upon the possibility of getting an approximate evaluation of the local strain associated with delithiation from the atomic volume evolutions, which are also likely to affect the electrochemical potential. [less ▲]

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See detailDiblock polyampholytes at the silicon/water interface: adsorption at various modified silicon substrates
Mahltig, Boris; Jérôme, Robert ULg; Stamm, Manfred

in Physical Chemistry Chemical Physics [=PCCP] (2001), 3(19), 4371-4375

The adsorption behaviour of the ampholytic diblock copolymer poly(methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate), PMAA-b-PDMAEMA, was investigated on differently prepared silicon surfaces ... [more ▼]

The adsorption behaviour of the ampholytic diblock copolymer poly(methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate), PMAA-b-PDMAEMA, was investigated on differently prepared silicon surfaces. All adsorption experiments were performed from aqueous solutions as a function of pH. The polyampholyte amount adsorbed was determined ellipsometrically, while the topographies of the adsorbed polymer were investigated using scanning force microscopy (SFM). Three polyampholyte systems with similar molecular weight around 60000 g mol–1 and different block ratios were adsorbed on three different types of silicon substrates. Depending on the pretreatment the silicon substrates contained different isoelectric points (IEP) and hydrophobicity. The adsorbed amount, as a function of pH, was characterized by maxima and minima near the IEP of the polyampholytes. In the case of polyampholytes containing an IEP close to the IEP of the silicon substrates, the nature of the substrate strongly influenced the adsorption behaviour. Even a complete erasure of one adsorption maximum could be observed in some cases. In contrast to this, polyampholytes with an IEP in a pH area far away from the IEP of the substrates adsorbed in a quite similar manner on the different substrates. [less ▲]

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See detailAdsorption of polyampholyte copolymers at the solid/liquid interface: the influence of pH and salt on the adsorption behaviour
Mahltig, Boris; Walter, H.; Harrats, C. et al

in Physical Chemistry Chemical Physics [=PCCP] (1999), 1(17), 3853-3856

Polyampholytes are macromolecules that contain oppositely charged groups. We have studied the adsorption of the polyampholyte diblock copolymer poly(methacrylic acid)-block-poly((dimethylamino)ethyl ... [more ▼]

Polyampholytes are macromolecules that contain oppositely charged groups. We have studied the adsorption of the polyampholyte diblock copolymer poly(methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate), PMAA-b-PDMAEMA, on oxidized silicon surfaces. The amount of polymer adsorbed from aqueous solution of different pH and salt concentration was measured by ellipsometry. The influence of the added salts NaCl, Na2SO4 and CaCl2 was determined. In every case adsorption took place, although the polyampholyte and the substrate exhibit the same sign of net charge. For all types of salt, the adsorbed amount shows two maxima close to the isoelectric point (IEP) of the polymer as a function of pH. Directly at the IEP of the polyampholyte, no adsorption was found. The measured dependences can be explained by the adsorption of one or the other of the two blocks depending on acidity and ionic strength. Furthermore, the lateral structure of the dried films was investigated by scanning force microscopy (SFM). [less ▲]

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See detailQuantum mechanical statistical theories for chemical reactivity. Overlapping resonances
Desouter, Michèle ULg; Chapuisat, Xavier

in Physical Chemistry Chemical Physics [=PCCP] (1999), 1