bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some specific features of spreading at the molecular scale: Wetting transition and molecular self‐assembly
Authors: Valignat M. P. , Cazabat A. M. , Tiberg F. 
Published: July 2012

AbstractProfiles of microdroplets spreading on solid surfaces are studied in the molecular range of thickness using spatially resolved ellipsometry. Surface induced layering leads to stepped profiles for nonvolatile liquids, the thickness of the successive molecular layers giving information on the configuration of the molecules at the solid surface. For example, the worm‐like molecules of polydimethylsiloxane (PDMS) lay flat on the substrate, while the bulk configuration is a coil. On the same way, surfactant molecules behave differently on hydrophobic and hydrophilic surfaces.After a general discussion of drop behaviour on finite or infinite substrates, we present two examples illustrating the specificity of the molecule‐surface interactions. The first case could be referred to as a “wetting transition”: A hydrophobic layer is grafted on a high energy surface, and the liquids are a series of PDMS. The lighter oils wet the surface, the heavier do not. The approach to transition is clearly observed in the droplets shape: The thickness of the film which grows at the bottom of the drop increases when transition is approached and diverges at transition, where the liquid becomes nonwetting. This is the “pancake” first predicted by de Gennes.The second case concerns nonionic trisiloxane surfactants, which do not wet the substrates, but build an extended autophobic film on it. The profile of the film strongly depends on the surface energy: it looks like a “sand pile” on high‐energy surfaces, but the molecules self‐assemble into a perfect bilayer on low‐energy ones. These phenomena are understood by considering the chemical structure of the molecules, and the dynamics of the films is related to the “superspreading” properties of these surfactants.
Critical adsorption of fluids and the equivalence of extraordinary to normal surface transitions
Authors: Diehl H. W. 
Published: July 2012

AbstractThe current understanding of the critical adsorption of fluids on walls or interfaces is reviewed, with the emphasis put on a description of what can be learned from field‐theoretic renormalization group (RG) approaches. In particular, results of a recent RG calculation of the universal order‐parameter profile are presented. The prototypical continuum model describing critical adsorption is a standard semi‐infinite ϕ4 model with surface terms ∫ dS(−1/2g0ϕ2‐h1ϕ). For h1, = 0, this model describes surface phase transitions called ordinary, special, and extraordinary depending on whether the surface enhancement g0 is less than, equal, or greater than a certain critical value. For typical chemical systems one expects g0 to be subcritical and h1 to be nonvanishing. Under those conditions the model describes a so‐called normal surface transition or, equivalently, critical adsorption of fluids. The critical behavior at this normal transition (and hence at critical adsorption) is the same as at the extraordinary transition. This can be shown by an explicit mapping of appropriate lattice models.
The potentiality for tm elevation of dipalmitoylphosphatidylcholine liposomes
Authors: Fernández Marta S. 
Published: July 2012

AbstractIn a previous article from this laboratory [M.S. Fernández and E. Calderón, Ber. Bunsenges. Phys. Chem. 95, 1669 (1991)], the interfacial acid‐base ionization of dipalmitoylphosphatidylcholine (DPPC) was studied by applying the concept of potentiality for tm elevation to experimental results of the increase in the phase transition temperature of DPPC liposomes upon incorporation of cationic stearylamine, at different bulk pH values. In this way, an intrinsic interfacial pK of 4 was determined for the phosphodiester group of DPPC. In this work, a modified form of the theoretical treatment developed previously, is applied to the analysis of the ionization of the same phospholipid using data from the literature for the phase transition temperatures (tm) of lamellar phases of DPPC mixed with cetyl alcohol at neutral and acidic pH, as compared to tm values of pure DPPC liposomes. The intrinsic interfacial pK of lecithin phosphate determined in this way is 3.75, very close to that found using stearylamine as an additive. The similarity between the intrinsic interfacial pK values for lecithin phosphate group estimated from the pH dependent tm shifts induced in DPPC bilayers by additives with quite different polar groups such as stearylamine and cetyl alcohol, gives additional support to the concept of potentiality for tm elevation as correlated with the dissociation degree of DPPC bilayers, that we proposed previously.
Monolayers, critical layers and wetting films in a liquid‐liquid‐solid system undergoing a wetting transition. Experimental study
Authors: Privat M. , Amara M. , Hamraoui A. , Sellami H. , Mear A. M. 
Published: July 2012

AbstractExperimental adsorption isotherms have been drawn for the water‐2,5 lutidine liquid system against silica, at several temperatures, on both sides of the liquid‐liquid coexistence curve and for the coexisting phases. In the two‐phase liquid system, perfect wetting, probably due to long range interactions is made by the water rich phase, whereas lutidine, probably due to chemical forces is preferentially adsorbed.In water rich monophases, at very low lutidine concentrations, lutidine forms monolayers on silica. Close to the phase separation, lutidine adsorption strongly increases and diverges for T→Tc, the critical temperature of the liquid system: a critical behaviour.In lutidine rich phases, adsorption behaviour is quite different, and Tw, the wetting transition temperature is the important parameter for the behaviour of the adsorption at coexistence.The set of experimental results is very similar to the results of the theoretical literature, and both can be used as a guide for further experimental exploration of the so‐called “prewetting” transition.
Electrotransport in ionic crystals: I. Application of liquid electrolyte theory
Authors: Janek J. , Martin M. , Yoo H. I. 
Published: July 2012

AbstractTransport of matter and charge in ionic crystals is only possible by the existence of irregular structure elements (defects) which are often charged relative to the crystal lattice. A comparison between the transport behaviour of a crystalline matrix containing such charged defects and a liquid electrolyte containing dissolved ions shows a lot of similarities. As is well known the transport properties of liquid electrolytes are strongly affected by interactions between the dissolved ions. We have applied the well elaborated concept of mixed electrolytes by Onsager and Fuoss which was originally devoted to liquid electrolytes to ionic crystals containing charged point defects. The equations of Onsager and Fuoss allow in principle the calculation of the concentration dependence of the phenomenological transport coefficients Lij of all charge carriers of n‐component electrolytes. We will use these equations to predict the transport behaviour of ionic crystals containing differently charged point defects.As examples we have calculated transport coefficients for electrolyte systems which can be regarded as models for the transition metal oxides Co1‐δO and Cu2‐δO. One major result concerns the magnitude of the cross effect between the ionic and electronic fluxes in those materials. The implications of these results with respect to experimental observations are discussed.
Influence of electrochemical activation and surface orientation on the photoresponse of single crystalline pyrite/electrolyte and pyrite/metal junctions
Authors: Büker K. , Alonso‐Vante N. , Scheer R. , Tributsch H. 
Published: July 2012

AbstractThe current/voltage curves of crystalline (100)‐ and (111)‐oriented surfaces of n‐pyrite/electrolyte and n‐pyrite/Pt junctions in darkness and under illumination are strongly influenced by cathodic hydrogen evolution before junction formation. Higher dark current and lower photocurrent on n‐pyrite (111)‐oriented surfaces in comparison to (100)‐oriented surfaces were obtained. The junction properties of the untreated surfaces change from a metal‐like behaviour to a rectifying one. During electrochemical treatment different etching patterns develop according to the exposed surface orientation. In the case of (111)‐oriented crystals these patterns are identified as new (100)‐surfaces. Quantum yields of ca. 0.7 at photon energies of 1.4 eV and almost similar photocurrent action spectra are obtained on n‐pyrite/electrolyte and n‐pyrite/metal junctions. The energetical position of the subbandgap response at 0.68 eV is not changed during etching. The increase of the quantum yield for photon energies higher than 1.4 eV on both types of junction points towards a reduction of surface recombination centers on etched samples. EBIC analysis on previously etched n‐pyrite in contact to vacuum deposited platinum films of 120 to 1000 Å thickness (Schottky barriers) indicate that the charge carrier collection efficiency is higher on etched areas. The role of surface recombination processes for photocurrent generation is demonstrated and discussed.
Observation of an H/D‐isotope exchange channel in the reaction D + H2CO
Authors: Dóbé S. , Oehlers C. , Temps F. , Wagner H. Gg. , Ziemer H. 
Published: July 2012

AbstractThe reactions of H and D atoms with H2CO,H + H2CO → H2 + HCO ,	(1)D + H2CO → HD + HCO ,	(2a)	→ HD + HDCO ,	(2b)were studied in an isothermal discharge flow reactor at room temperature with EPR detection of H and D atoms and LIF detection of HCO radicals. Simultaneous measurements of the absolute concentration‐versus‐time profiles of D, H, and HCO in the D + H2CO system established the occurrence of the H/D isotope exchange reaction (2b), which competes with the usually assumed direct H atom abstraction channel (2a). The room temperature rate constants of the two reaction channels were found to bek2a (296 K) = (1.9±0.5) × 1010 cm3/mol s ,k2b (296 K) = (1.5∓0.4) × 1010 cm3/mol s .
Vapor pressure determination of liquid PCl3 by the Knudsen effusion method
Authors: Matsumoto K. , Schönherr E. , Wojnowski M. 
Published: July 2012

AbstractThe vapor pressure of liquid PCl3 was determined by the Knudsen effusion method. The pressure was found to follow the relation log10 P[kPa] = −1800/T+7.371 between 240 and 278 K.
Crystal structures, molecular conformations, hydrogen bonds, and 35Cl NQR in some chloral hemiacetals
Authors: Hashimoto Masao , Isono Takahiro , Mano Koichi 
Published: July 2012

AbstractCrystal structures of chloral 4‐bromo‐, 4‐methyl‐, 2,4‐dichlorobenzylhemiacetals, and iso‐butylhemiacetal were determined by the single crystal X‐ray method at room temperature. Two modifications were found for the 2,4‐dichlorobenzyl derivative. A chiral chain of molecules formed by OH … O hydrogen bonds (H‐bonds) along a 21 axis is common to the crystals studied, except for iso‐butyl derivative where a centrosymmetric dimer is formed by H‐bonds. Conformation analyses were made using molecular mechanics. The crystal structures and IR spectra indicated that the H‐bonds in these crystals except for the 2,4‐dichlorobenzyl derivate were bifurcated ones. An intramolecular OH…Cl interaction was found in the iso‐butyl derivative. The relationship between the 35Cl NQR spectrum and the molecular structure are discussed.
A Nuclear magnetic resonance investigation of proton dynamics in α‐D‐glucose
Authors: Latanowicz L. , Reynhardt E. C. 
Published: July 2012

AbstractIt has been shown that the trans‐gauche rearrangement of the CH2OH group and the jump motion of an OH group proton between two equilibrium sites in a hydrogen bond are the motions contributing to the observed proton spin‐lattice relaxation times of anhydrous polycrystalline α‐D‐glucose.
Electrochemical oxidation of anthracenes on poly(vinylferrocenium) coated pt electrodes in acetonitrile
Authors: Gülce Handan , Özyörük Haluk , Yildiz Attila 
Published: July 2012

AbstractThe electrooxidation behaviour of anthracene and 9,10‐diphenylanthracene on poly(vinylferrocenium) coated Pt electrodes was investigated and compared with that on uncoated Pt surface using cyclic voltammetry in acetonitrile/0.1 M TBAP solutions. IR spectroscopy was used to detect the changes occurring in the structure after the electrode reaction. The formation of the quinone and hydroxy substituted type products was revealed if the electrode potential was cycled between + 1.50 and 0.00 V. The catalytic oxidation of anthracene rings were observed if the potential cycling was kept between + 1.50 V and −2.30 V.
From vesicles to micelles
Authors: Schönfelder E. , Hoffmann H. 
Published: July 2012

AbstractOn the system soybean lecithin (Epicuron 200)/tetradecyldimethylaminoxide C14DMAO/water the aggregation behavior of mixtures composed of surfactant and phospholipid in a dilute solution was studied. The lipid was dispersed into water as vesicles, which were prepared by sonication. By varying the surfactant‐to‐lipid‐ratio at a constant total concentration the whole spectrum of properties from vesicles to micelles with its transition properties could be investigated. Most of the measurements were carried out at a total concentration of 10 mM.Three different regions exist in this system: a micellar region on the surfactant rich side, a vesicular region on the lipid rich side and a two‐phase‐region between these two phases. In the micellar region there are spherical micelles, which grow to rodlike micelles with increasing molefraction of lipid XL. This region was investigated by electric birefringence, by rheology and by measuring the interfacial tension.In the lipid rich solution vesicles are the dominant structures. Vesicles in this region can exist with a large molefraction of surfactant. These vesicles were examined by electron microscopy, dynamic light scattering, electric birefringence and conductivity measurements. We found that the vesicles in the region XL = 1–0.27 will grow only a small amount with added surfactant. For XL<0.27 the vesicles grow rapidly.A two‐phase‐region exists between the micellar and the vesicular region. One of these phases contains nearly the whole amount of lipid and surfactant in a very small volume of the solution. In this phase the lipid and surfactant molecules are present in the form of rodlike micelles. The other phase contains almost pure water. The two‐phase‐region shows a very strong temperature dependence.
A kinetic study about the reactions of NH(X3Σ−) with hydrocarbons part 1: Saturated hydrocarbons and acetaldehyde
Authors: Röhrig Michael , Wagner Heinz Georg 
Published: July 2012

AbstractThe reactions of NH in its electronic ground state with the hydrocarbons methane (1), ethane (2), propane (3) and with acetaldehyde (4) were investigated behind incident shock waves using narrow line width absorption detection of NH(X3Σ−). The experiments were performed with very low initial concentrations of HN3 which was used as NH source to reduce the influence of secondary reactions. Thus it became possible to measure kinetic data for the reactions of NH(X3Σ−) with hydrocarbons directly. The following rate constants were obtained:k1 = (9±3)·1013 exp (−(84±5) kJ mol−1/RT) cm3/ mol s	( 1150 K < T < 1500 K)k2 = (7±3)·1013 exp (−(70±5) kJ mol−1/RT) cm3/ mol s	( 1010 K < T < 1170 K)k3 = (6±3)·1013 exp (−(61±5) kJ mol−1/RT) cm3/ mol s	( 980 K < T < 1150 K)k4 = (5±3)·1013 exp (−(48±5) kJ mol−1/RT) cm3/ mol s	( 1000 K < T < 1200 K)The apparent energies of activation fit rather well into an Evans Polanyi plot. They correlate with the energies of activation of the corresponding reactions of O(3P) and therefore also with (CH2(X̃3B1) radicals.
A kinetic study about the reactions of NH(X3Σ−) with hydrocarbons part 2: Ethene, propene, and 2,3‐dimethyl‐2‐butene
Authors: Röhrig Michael , Wagner Heinz Georg 
Published: July 2012

AbstractThe reactions of NH in its electronic ground state with the alkenes ethene (1), propene (2), and 2,3‐dimethyl‐2‐butene (TME) (3) were investigated behind incident shock waves using narrow line width absorption detection of NH(X3Σ−). The experiments were performed with very low initial concentrations of HN3 which was used as NH source to reduce the influence of secondary reactions. Thus it became possible to measure kinetic data for the reactions of NH(X3Σ−) with these alkenes directly. The following rate constants were obtained for T>1000 K:C2H4: k1 = (1.8±0.4)·13 exp (−(56±4) kJ/mol/RT)	cm3/mol sC3II46: k2 = (3.3±1.0)·13 exp (−(50±4) kJ/mol/RT)	cm3/mol sTME: k3 = (4.1±1.5)·13 exp (−(40±6) kJ/mol/RT)The apparent energies of activation correlate well with the ionisation potentials of the alkenes and with the energies of activation of the corresponding reactions of O(3P) and can therefore be used for the extrapolation to the addition reactions of the higher alkenes. The reaction of NH(X3Σ−) with ethene proceeds via an intermediate triplet diradical ethylenimin which then decomposes into several reaction channels. For the reaction of propene and TME with NH(X3Σ−) a contribution of an abstraction reaction channel besides electrophilic addition cannot be excluded.
Kinetics of oxirane formation in the reaction of nitrate radicals with tetramethylethylene
Authors: Berndt T. , Böge O. 
Published: July 2012

AbstractThe kinetics of oxirane formation in the reaction of nitrate radicals with tetramethylethylene was investigated in a flow system at room temperature. Total pressure ranged from 5 to 1000 mbar. Using inert gas (He, N2) tetramethyloxirane only was detected as reaction product. In the case of synthetic air acetone also is formed in dependence of the system pressure. With increasing pressure the oxirane yield decreases and the acetone yield increases. Under tropospheric conditions 20% tetramethyloxirane was found.It is concluded that the oxirane observed results from the excited adduct formed in the electrophilic addition of the nitrate radical to the double bond. In the absence of O2 the quenched adduct radical formes oxirane in a thermal reaction also.Kinetic parameters were estimated.
On the metallic droplet model for successive ionization potentials of metal clusters ‐ relativistic electronic structure investigations of the icosahedral gold cluster Au55
Authors: Häberlen Oliver D. , Chung Sai‐Cheong , Rösch Notker 
Published: July 2012

AbstractWe have carried out relativistic electronic structure calculations on the naked cluster Au55 in icosahedral geometry using the linear combination of Gaussian‐type orbitals density functional (LCGTO‐DF) method. The one‐electron level spectrum is discussed and compared to that of the jellium model which is able to reproduce the s‐type level manifold of Au55 only qualitatively. Furthermore, a series of successive ionization potentials and electron affinities of the cluster has been calculated. The remarkable agreement of the all‐electron LCGTO‐DF results with those of the metallic droplet model indicates that the naked cluster Au55 acts like an almost perfect electron reservoir. In this respect a gold particle of about 50 atoms may mark the onset of the metallic regime.
Investigation of the electronic spectra of arylidene‐, arylethylidene‐ and heterocyclicmethylene‐malononitriles. MNDO‐CI treatment
Authors: Moustafa H. , Hamed Maher M. , El‐Taher S. , Hilal R. 
Published: July 2012

AbstractThe electronic absorption spectra of some arylidene‐, arylethylidene‐ and heterocyclicmethylenemalononitriles have been investigated qualitatively and quantitatively. MNDO‐CI calculations were performed to predict the suitable conformer for the studied compounds. The conformer adopted by arylethylidene derivatives is found to be the non‐planar one, while the other two groups of compounds had the planar conformer. The observed transitions are assigned as charge transfer (CT), localized and delocalized according to the contribution of the various configurations in the CI‐states. The correspondence between the calculated and experimental transition energies was satisfactory.
The mitotic oscillator: Temporal self‐organization in a phosphorylation‐dephosphorylation enzymatic cascade
Authors: Romond P.‐C. , Guilmot J.‐M. , Goldbeter A. 
Published: July 2012

AbstractThe conditions for temporal self‐organization in the form of sustained oscillations are determined in a minimal cascade model previously proposed (A. Goldbeter, Proc. Natl. Acad. Sci. USA 88, 9107–9111 (1991)) for the mitotic oscillator driving the embryonic cell division cycle. The model is based on a phosphorylation‐dephosphorylation cascade involving cyclin and cdc2 kinase. In the first cycle of the cascade, cdc2 kinase is activated through dephosphorylation triggered by the accumulation of cyclin, while in a second cycle the activation of a cyclin protease is brought about through phosphorylation by cdc2 kinase. The fact that cyclin promotes the activation of cdc2 kinase while the latter enzyme triggers cyclin degradation introduces a negative feedback loop which is at the core of the periodic operation of the cascade. We analyze the mechanism of oscillatory behavior by constructing stability diagrams as a function of some of the main parameters of the model. Investigated in turn are the roles of negative feedback and of phosphorylation‐dephosphorylation thresholds. Such thresholds arise from the phenomenon of zero‐order ultrasensitivity associated with the kinetics of covalent modification cycles. An extension of the minimal model allows one to address the effect of additional phosphorylation‐dephosphorylation cycles and the possible role of autocatalysis by cdc2 kinase in the generation of periodic behavior. The analysis shows that the existence of thresholds as well as an increase in the number of cycles in the cascade favor the occurrence of sustained oscillations. The results further indicate that negative and positive feedback may both contribute to the repetitive activation of cdc2 kinase.
On the existence of bicontinuous cubic phases in dioleoylphosphatidylethanolamine
Authors: Erbes J. , Czeslik C. , Hahn W. , Winter R. , Rappolt M. , Rapp G. 
Published: July 2012

AbstractAqueous dispersions of 1,2‐dioleoyl‐sn‐glycero‐3‐phosphatidylethanolamine (DOPE) exhibit a well‐known phase transition from a lamellar liquid‐crystalline (Lα) to an inverted hexagonal (HII) phase as the temperature is raised above 13°C. Recently, it has been reported [1, 2] that a bicontinuous cubic phase can be induced in this system, when the lipid is rapidly cycled between these two phases. Their X‐ray diffraction results indicated that the cubic lattice is most consistent with either the Pn3m or Pn3 space group. In studies on similar systems [3, 4], two cubic phases could be detected in the Lα‐HII transition region, however. One aim of the present study was to investigate, if still further bicontinuous cubic phases can be induced in simple DOPE dispersions by changing the experimental conditions. Indeed, we found that two cubic lattices may be induced when the lipid system is cycled between –5 and 15°C more than thousand times. The second goal of the present investigation was to study the temperature dependence of the lattice parameters, the stability and transformations of these cubic phases over a wide temperature range. It has been discussed that the presence of cubic phases may be a general feature of HII‐forming lipids in the region of their lamellar to hexagonal phase transition region and that non‐lamellar lipid structures might play an important role as transient intermediates in biochemical processes.