Experimental And Topological Determination of the Pressure-Temperature Phase Diagram of Racemic Etifoxine, a Pharmaceutical Ingredient with Anxyolitic Properties

International audienc

Fitting in a complex chi^2 landscape using an optimized hypersurface sampling

Fitting a data set with a parametrized model can be seen geometrically as finding the global minimum of the chi^2 hypersurface, depending on a set of parameters {P_i}. This is usually done using the Levenberg-Marquardt algorithm. The main drawback of this algorithm is that despite of its fast convergence, it can get stuck if the parameters are not initialized close to the final solution. We propose a modification of the Metropolis algorithm introducing a parameter step tuning that optimizes the sampling of parameter space. The ability of the parameter tuning algorithm together with simulated annealing to find the global chi^2 hypersurface minimum, jumping across chi^2{P_i} barriers when necessary, is demonstrated with synthetic functions and with real data

Thermal properties of halogen-ethane glassy crystals: Effects of orientational disorder and the role of internal molecular degrees of freedom

The thermal conductivity, specific heat, and specific volume of the orientational glass former 1,1,2-trichloro-1,2,2-trifluoroethane (CCl2F-CClF2, F-113) have been measured under equilibrium pressure within the low-temperature range, showing thermodynamic anomalies at ca. 120, 72, and 20 K. The results are discussed together with those pertaining to the structurally related 1,1,2,2-tetrachloro-1,2-difluoroethane (CCl2F-CCl2F, F-112), which also shows anomalies at 130, 90, and 60 K. The rich phase behavior of these compounds can be accounted for by the interplay between several of their degrees of freedom. The arrest of the degrees of freedom corresponding to the internal molecular rotation, responsible for the existence of two energetically distinct isomers, and the overall molecular orientation, source of the characteristic orientational disorder of plastic phases, can explain the anomalies at higher and intermediate temperatures, respectively. The soft-potential model has been used as the framework to describe the thermal properties at low temperatures. We show that the low-temperature anomaly of the compounds corresponds to a secondary relaxation, which can be associated with the appearance of Umklapp processes, i.e., anharmonic phonon-phonon scattering, that dominate thermal transport in that temperature rangeThis work was financially supported in part by the Spanish Ministry of Science and Innovation (Grant Nos. FIS2014-54734-P, FIS2011-23488, and MAT2014-57866- REDT), by the Catalan Government (Grant No. 2014SGR- 0581) and by the Comunidad de Madrid through program NANOFRONTMAG-CM (No. S2013/MIT-2850), as well as by the joint NAS Ukraine and Russian Foundation for Basic Research project “Metastable states of simple condensed systems” (Agreement No. N 7/-2013

Colossal barocaloric effects near room temperature in plastic crystals of neopentylglycol.

There is currently great interest in replacing the harmful volatile hydrofluorocarbon fluids used in refrigeration and air-conditioning with solid materials that display magnetocaloric, electrocaloric or mechanocaloric effects. However, the field-driven thermal changes in all of these caloric materials fall short with respect to their fluid counterparts. Here we show that plastic crystals of neopentylglycol (CH3)2C(CH2OH)2 display extremely large pressure-driven thermal changes near room temperature due to molecular reconfiguration, that these changes outperform those observed in any type of caloric material, and that these changes are comparable with those exploited commercially in hydrofluorocarbons. Our discovery of colossal barocaloric effects in a plastic crystal should bring barocaloric materials to the forefront of research and development in order to achieve safe environmentally friendly cooling without compromising performance

Microscopic structures and dynamics of high- and low-density liquid trans-1,2-dichloroethylene

4 págs.; 3 figs.; PACS number s : 64.70.Ja, 61.05.fm, 61.20. p, 61.25.EmWe present a study of the dynamics and structural changes for trans-1,2-dichloroethylene between high- and low-density liquids using neutron-scattering techniques diffraction, small-angle neutron scattering, and time of flight spectroscopy and molecular-dynamics simulations. We show that changes in the short-range ordering of molecules goes along with a change in the molecular dynamics: both structure and dynamics of the highdensity liquid are more cooperative than those of the low-density liquid. The microscopic mechanism underlying the cooperative motions in the high-density liquid has been found to be related to the backscattering of molecules due to a strong correlation of molecular ordering. ©2010 The American Physical SocietyThis work was supported by the Spanish Ministry of Science and Technology Grants No. FIS2008-00837 and No. BES-2007-17418, by the Government of Catalonia Grant No. 2009SGR-1251 and by the European Commission MI3/FP7.Peer Reviewe

Formulation and characterization of mucoadhesive controlled release matrix tablets of captopril

The purpose of this study is to characterize controlled release matrix tablets of captopril and to find out the physicochemical properties that have an effect on the mucoadhesion process. The hydrophilic matrix tablets contain captopril, microcrystalline cellulose, barium sulfate, ascorbic acid, ethylcellulose N100, hydroxypropylmethylcellulose K15M, talc, magnesium stearate and colloidal silicon dioxide. The physicochemical properties of the formulations have been characterized using confocal microscopy, contact angle, and scanning electron microscopy. The potential mucoadhesion capabilities of the formulations were assessed measuring the surface free energy, the polar and dispersive forces, the spreading coefficients, the surface roughness, and the network structure of the hydrophilic matrix tablets. The results show that when the concentration of HPMC K15M increases, the spreading coefficients of polymer over mucus and mucus over polymer are more positive, thus increasing the contact between the matrix tablets with the mucus layer. The formulation that contains 15% of HPMC K15M is the formulation that presents a greater swelling capacity, a greater increase in surface roughness, and larger pores within the matrix. This formulation has a higher chain mobility and more free macromolecular chains able to diffuse in the mucus layer. Therefore, this formulation has the greatest potential mucoadhesion capability

Giant and Reversible Barocaloric Effect in Trinuclear Spin-Crossover Complex Fe3(bntrz)6(tcnset)6

A giant barocaloric effect (BCE) in a molecular material Fe3(bntrz)6(tcnset)6 (FBT) is reported, where bntrz = 4-(benzyl)-1,2,4-triazole and tcnset = 1,1,3,3-tetracyano-2-thioethylepropenide. The crystal structure of FBT contains a trinuclear transition metal complex that undergoes an abrupt spin-state switching between the state in which all three FeII centers are in the high-spin (S = 2) electronic configuration and the state in which all of them are in the low-spin (S = 0) configuration. Despite the strongly cooperative nature of the spin transition, it proceeds with a negligible hysteresis and a large volumetric change, suggesting that FBT should be a good candidate for producing a large BCE. Powder X-ray diffraction and calorimetry reveal that the material is highly susceptible to applied pressure, as the transition temperature spans the range from 318 at ambient pressure to 383 K at 2.6 kbar. Despite the large shift in the spin-transition temperature, its nonhysteretic character is maintained under applied pressure. Such behavior leads to a remarkably large and reversible BCE, characterized by an isothermal entropy change of 120 J kg−1 K−1 and an adiabatic temperature change of 35 K, which are among the highest reversible values reported for any caloric material thus far

Population Genetics of Trypanosoma evansi from Camel in the Sudan

Genetic variation of microsatellite loci is a widely used method for the analysis of population genetic structure of microorganisms. We have investigated genetic variation at 15 microsatellite loci of T. evansi isolated from camels in Sudan and Kenya to evaluate the genetic information partitioned within and between individuals and between sites. We detected a strong signal of isolation by distance across the area sampled. The results also indicate that either, and as expected, T. evansi is purely clonal and structured in small units at very local scales and that there are numerous allelic dropouts in the data, or that this species often sexually recombines without the need of the “normal” definitive host, the tsetse fly or as the recurrent immigration from sexually recombined T. brucei brucei. Though the first hypothesis is the most likely, discriminating between these two incompatible hypotheses will require further studies at much localized scales