Coupling of Caged Molecule Dynamics to JG β-Relaxation: I

The paper (Sibik, J.; Elliott, S. R.; Zeitler, J. A. J. Phys. Chem. Lett. 2014, 5, 1968-1972) used terahertz time-domain spectroscopy (THz-TDS) to study the dynamics of the polyalcohols, glycerol, threitol, xylitol, and sorbitol, at temperatures from below to above the glass transition temperature Tg. On heating the glasses, they observed the dielectric losses, ε″(ν) at ν = 1 THz, increase monotonically with temperature and change dependence at two temperatures, first deep in the glassy state at TTHz = 0.65Tg and second at Tg. The effects at both temperatures are most prominent in sorbitol but become progressively weaker in the order of xylitol and threitol, and the sub-Tg change was not observed in glycerol. They suggested this feature originates from the high-frequency tail of the Johari-Goldstein (JG) β-relaxation, and the temperature region near 0.65Tg is the universal region for the secondary glass transition due to the JG β-relaxation. In this paper, we first use isothermal dielectric relaxation data at frequencies below 106 Hz to locate the "second glass transition" temperature Tβ at which the JG β-relaxation time βJG reaches 100 s. The value of Tβ is close to TTHz = 0.65Tg for sorbitol (0.63Tg) and xylitol (0.65Tg), but Tβ is 0.74Tg for threitol and 0.83Tg for glycerol. Notwithstanding, the larger values of Tβ of glycerol are consistent with the THz-TDS data. Next, we identify the dynamic process probed by THz-TDS as the caged molecule dynamics, showing up in susceptibility spectra as nearly constant loss (NCL). The caged molecule dynamics regime is terminated by the onset of the primitive relaxation of the coupling model, which is the precursor of the JG β-relaxation. From this relation, established is the connection of the magnitude and temperature dependence of the NCL and those of βJG. This connection explains the monotonic increase of NCL with temperature and change to a stronger dependence after crossing Tβ giving rise to the sub-Tg behavior of ε″(ν) observed in experiment. Beyond the polyalcohols, we present new dielectric relaxation measurements of flufenamic acid and recall dielectric, NMR, and calorimetric data of indomethacin. The data of these two pharmaceuticals enables us to determine the value of Tβ = 0.67Tg for flufenamic acid and Tβ = 0.58Tg or Tβ = 0.62Tg for indomethacin, which can be compared with experimental values of TTHz from THz-TDS measurements when they become available. We point out that the sub-Tg change of NCL at Tβ found by THz-TDS can be observed by other high frequency spectroscopy including neutron scattering, light scattering, Brillouin scattering, and inelastic X-ray scattering. An example from neutron scattering is cited. All the findings demonstrate the connection of all processes in the evolution of dynamics ending at the structural α-relaxation. © 2015 American Chemical Society

Revealing the rich dynamics of glass-forming systems by modification of composition and change of thermodynamic conditions

Secondary relaxations have been classified into two types, depending on whether they are related to the structural alpha-relaxation in properties or not. Those secondary relaxations that are related to the a-relaxation may have fundamental importance, and are called the Johari–Goldstein (JG) ß-relaxations. Two polar molecular glass-formers, one flexible and another rigid, dissolved in apolar host with higher glass transition temperature are studied by broadband dielectric spectroscopy at ambient and elevated pressure. The neat flexible glassformer diethylphthalate (DEP) has a resolved secondary relaxation which, unlike the a-relaxation, is insensitive to pressure and hence is not the JG ß-relaxation. In the solution, the JG ß-relaxation of DEP shows up in experiment and its relaxation time tß is pressure and temperature dependent like ta. The result supports the universal presence of the JG ß-relaxation in all glass-formers, and the separation between ta and tß is determined by intermolecular interaction. The rigid glass-former is cyano-benzene (CNBz) and its secondary relaxation involves the entire molecule is necessarily the JG ß-relaxation. The dielectric relaxation spectra obtained at a number of combinations of pressure and temperature at constant ta show not only unchanged is the frequency dispersion of the a-relaxation but also tß. The remarkable results indicate that the JG ß-relaxation bears a strong connection to the alpha-relaxation, and the two relaxations are inseparablewhen considering the dynamics of glass-forming systems. Experimentally, tau_alpha has been found to be a function of the product variables, T/rho^gamma, where rho is the density and gamma is a material constant. From the invariance of the ratio, tau_alphaa/tau_ß, to change of thermodynamic conditions seen in our experiment as well in other systems, it follows that tß is also a function of T/rho^gamma, with the same gamma at least approximately. Since the JG ß-relaxation is the precursor of the a-relaxation, causality implies that the T/rho^gamma-dependence originates from the JG ß-relaxation and is passed on to the alpha-relaxation

Extended model for the interaction of dielectric thin films with an electrostatic force microscope probe

To improve measurements of the dielectric permittivity of nanometric portions by means of Local Dielectric Spectroscopy (LDS), we introduce an extension to current analytical models for the interpretation of the interaction between the probe tip of an electrostatic force microscope (EFM) and a thin dielectric film covering a conducting substrate. Using the proposed models, we show how more accurate values for the dielectric constant can be obtained from single-frequency measurements at various probe/substrate distances, not limited to a few tip radii

Electrostatic force microscopy and potentiometry of realistic nanostructured systems

We investigate the dependency of electrostatic interaction forces on applied potentials in Electrostatic Force Microscopy (EFM) as well as in related local potentiometry techniques like Kelvin Probe Microscopy (KPM). The approximated expression of electrostatic interaction between two conductors, usually employed in EFM and KPM, may loose its validity when probe-sample distance is not very small, as often realized when realistic nanostructured systems with complex topography are investigated. In such conditions, electrostatic interaction does not depend solely on the potential difference between probe and sample, but instead it may depend on the bias applied to each conductor. For instance, electrostatic force can change from repulsive to attractive for certain ranges of applied potentials and probe-sample distances, and this fact cannot be accounted for by approximated models. We propose a general capacitance model, even applicable to more than two conductors, considering values of potentials applied to each of the conductors to determine the resulting forces and force gradients, being able to account for the above phenomenon as well as to describe interactions at larger distances. Results from numerical simulations and experiments on metal stripe electrodes and semiconductor nanowires supporting such scenario in typical regimes of EFM investigations are presented, evidencing the importance of a more rigorous modelling for EFM data interpretation. Furthermore, physical meaning of Kelvin potential as used in KPM applications can also be clarified by means of the reported formalism.Comment: 20 pages, 7 figures, 1 tabl

Investigation of the relevant kinetic processes in the initial stage of a double-arcing instability in oxygen plasmas

A numerical investigation of the kinetic processes in the initial (nanosecond range) stage of the double-arcing instability was developed. The plasma-sheath boundary region of an oxygen-operated cutting torch was considered. The energy balance and chemistry processes in the discharge were described. It is shown that the double-arcing instability is a sudden transition from a diffuse (glow-like) discharge to a constricted (arc-like) discharge in the plasma-sheath boundary region arising from a field-emission instability. A critical electric field value of ∼10^7 V/m was found at the cathodic part of the nozzle wall under the conditions considered. The field-emission instability drives in turn a fast electronic-to-translational energy relaxation mechanism, giving rise to a very fast gas heating rate of at least ∼10^9 K/s, mainly due to reactions of preliminary dissociation of oxygen molecules via the highly excited electronic state O2(B^3) populated by electron impact. It is expected that this fast oxygen heating rate further stimulates the discharge contraction through the thermal instability mechanism.Fil: Mancinelli, Beatriz Rosa. Universidad Tecnológica Nacional. Facultad Regional Venado Tuerto; ArgentinaFil: Prevosto, Leandro. Universidad Tecnológica Nacional. Facultad Regional Venado Tuerto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Chamorro Garcés, Juan Camilo. Universidad Tecnológica Nacional. Facultad Regional Venado Tuerto; ArgentinaFil: Minotti, Fernando Oscar. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Kelly, Hector Juan. Universidad Tecnológica Nacional. Facultad Regional Venado Tuerto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin

Effect of entropy on the dynamics of supercooled liquids: New results from high pressure data

We show that for arbitrary thermodynamic conditions, master curves of the entropy are obtained by expressing S(T,V) as a function of TV^g_G, where T is temperature, V specific volume, and g_G the thermodynamic Gruneisen parameter. A similar scaling is known for structural relaxation times,tau = f(TV^g); however, we find g_G < g. We show herein that this inequality reflects contributions to S(T,V) from processes, such as vibrations and secondary relaxations, that do not directly influence the supercooled dynamics. An approximate method is proposed to remove these contributions, S_0, yielding the relationship tau = f(S-S_0).Comment: 10 pages 7 figure

Synthesis, in vitro activity and in vivo toxicity of the new 2,3-dinitrobutadiene derivative (1E,3E)-1,4-bis(2-naphthyl)-2,3-dinitro-1,3-butadiene

Abstract Our interesting results on the antiproliferative (in vitro) and antitumour (in vivo) activities of (1E,3E)-1,4-bis(1-naphthyl)-2,3-dinitro-1,3-butadiene (1-Naph-DNB) have more recently induced us to design and synthesize some new 1,4-diaryl-2,3-dinitro-1,3-butadienes characterized by a common arylnitrobutadiene array but with different geometric and/or functional properties. This task was undertaken with the aim to obtain new compounds with an enhanced antiproliferative activity and, possibly, a different specificity with respect to the original (lead) compound. (1E,3E)-1,4-Bis(2-naphthyl)-2,3-dinitro-1,3-butadiene (2-Naph-DNB) is one of the molecules so obtained, a structural isomer of 1-Naph-DNB provided with a different spatial arrangement. When analyzed in vitro for its inhibition of cell proliferation 2-Naph-DNB showed a remarkable activity in the range of micromolar concentrations, with significant differences, with respect to 1-Naph-DNB, against some cell lines. Furthermore, it was able to significantly trigger apoptosis, to up-regulate p53, to block cells in the G2/M phase of the cell cycle and, finally, to slightly bind to DNA forming interstrand cross-links (ISCL). 2-Naph-DNB was then analyzed for its toxic activity in vivo in CD1 mice. This allowed the determination of toxicity parameters such as the lethal doses (LD) and the maximal tolerated dose (MTD) together with the definition of the spectrum of tissue alterations due to its administration i.v. Altogether our data suggest that the idea of modifying the geometry of the lead compound 1-Naph-DNB deserves further investigation aimed at synthesizing new molecules with similar chemical functionalities but with different spatial requirements, hopefully characterized by still enhanced activities in terms of inhibition of cell proliferation and apoptosis

Plantation de chênes méditerranéens avec accompagnement ligneux : amélioration de la forme mais réduction de la croissance

Une plantation expérimentale de chênes (Q. ilex, Q. pubescens) avec un accompagnement ligneux de pin d’Alep et de coronille a été réalisée afin d’analyser l’influence des espèces ligneuses accompagnatrices sur la survie, la croissance et la morphologie des chênes sur une période de sept années. La végétation au sol a été, soit enlevée, soit laissée en place, pour détecter une éventuelle facilitation indirecte. Les résultats montrent que ce sont les relations de compétition qui dominent. La survie est fortement réduite pour le chêne blanc sous coronille en raison d’une interception forte de la lumière. Pour les deux chênes, la croissance est toujours plus forte dans les témoins que dans les traitements avec accompagnement, même dans le système enherbé. L’accompagnement avec pin d’Alep est cependant plus favorable que le traitement avec coronille pour le développement initial des chênes. En revanche, la forme des chênes est améliorée par l’accompagnement : les plants sont plus élancés, présentent un houppier moins large et un port moins buissonnant. Sur la base de ces résultats, nous soulignons l’importance de bien identifier les objectifs poursuivis avant d’installer une plantation mixte (par exemple maximiser la croissance des espèces cibles, ou celle du mélange, améliorer la morphologie, etc.) et la nécessité d’une gestion active pour contrôler les effets potentiels indésirables de la végétation accompagnatrice sur les espèces cibles

Influenza A Virus Challenge Models in Cynomolgus Macaques Using the Authentic Inhaled Aerosol and Intra-Nasal Routes of Infection

Non-human primates are the animals closest to humans for use in influenza A virus challenge studies, in terms of their phylogenetic relatedness, physiology and immune systems. Previous studies have shown that cynomolgus macaques (Macaca fascicularis) are permissive for infection with H1N1pdm influenza virus. These studies have typically used combined challenge routes, with the majority being intra-tracheal delivery, and high doses of virus (> 107 infectious units). This paper describes the outcome of novel challenge routes (inhaled aerosol, intra-nasal instillation) and low to moderate doses (103 to 106 plaque forming units) of H1N1pdm virus in cynomolgus macaques. Evidence of virus replication and sero-conversion were detected in all four challenge groups, although the disease was sub-clinical. Intra-nasal challenge led to an infection confined to the nasal cavity. A low dose (103 plaque forming units) did not lead to detectable infectious virus shedding, but a 1000-fold higher dose led to virus shedding in all intra-nasal challenged animals. In contrast, aerosol and intra-tracheal challenge routes led to infections throughout the respiratory tract, although shedding from the nasal cavity was less reproducible between animals compared to the high-dose intra-nasal challenge group. Intra-tracheal and aerosol challenges induced a transient lymphopaenia, similar to that observed in influenza-infected humans, and greater virus-specific cellular immune responses in the blood were observed in these groups in comparison to the intra-nasal challenge groups. Activation of lung macrophages and innate immune response genes was detected at days 5 to 7 post-challenge. The kinetics of infection, both virological and immunological, were broadly in line with human influenza A virus infections. These more authentic infection models will be valuable in the determination of anti-influenza efficacy of novel entities against less severe (and thus more common) influenza infections