Phase diagram of mechanically stretched DNA: The salt effect

The cations, in form of salt, present in the solution containing DNA play a crucial role in the opening of two strands of DNA. We use a simple non linear model and investigate the role of these cations on the mechanical unzipping of DNA. The Hamiltonian is modified to incoporate the solvent effect and the cations present in the solution. We calculate the melting temperature as well as the critical force that is required to unzip the DNA molecule as a function of salt concentration of the solution. The phase diagrams are found to be in close agreement with the experimental phase diagrams

Crystallization of hydrated and anhydrous salts in porous limestone resolved by synchrotron X-ray microtomography

ACLInternational audienceThe crystallization processes of two anhydrous salts (NaCl and Na 2SO4) and one hydrated (sodium sulfate) salt in the pore space of a natural building stone, Savonnières limestone, are studied. We imaged the salt solution distribution before and after crystallization and the solid crystal distribution in between repeated crystallization cycles using synchrotron X-ray microtomography. This technique proves to be very useful to study salt crystallization processes at the pore scale. The use of simultaneous phase-and-amplitude retrieval during X-ray tomographic reconstruction allows a clear segmentation of sodium sulfate solution and hydrated sodium sulfate crystals without the need for a dopant. Salt crystals can precipitate under unconfined as well as confined conditions in the multiple pore systems of Savonnières limestone, depending on their interconnection. Salt solution and salt crystals are located in mechanically weak zones of the limestone, which can be linked to damage patterns observed in this stone after repeated salt weathering cycles. The distribution and the process of pore filling by salt crystals that are revealed here advance the understanding of salt damage in porous media and may open ways to perform remediation. © 2014 Elsevier B.V. All rights reserved

Nucleation in aqueous NaCl solutions shifts from 1-step to 2-step mechanism on crossing the spinodal

In this work, we use large-scale molecular dynamics simulations coupled to free energy calculations to identify for the first time a limit of stability (spinodal) and a change in the nucleation mechanism in aqueous NaCl solutions. This is a system of considerable atmospheric, geological and technical significance. We find that the supersaturated metastable NaCl solution reaches its limit of stability at sufficiently high salt concentrations, as indicated by the composition dependence of the salt chemical potential, indicating the transition to a phase separation by spinodal decomposition. However, the metastability limit of the NaCl solution does not correspond to spinodal decomposition with respect to crystallization. We find that beyond this spinodal, a liquid/amorphous separation occurs in the aqueous solution, whereby the ions first form disordered clusters. We term these clusters as "amorphous salt". We also identify a transition from one- to two-step crystallization mechanism driven by a spinodal. In particular, crystallization from aqueous NaCl solution beyond the spinodal is a two-step process, in which the ions first phase-separate into disordered amorphous salt clusters, followed by the crystallization of ions in the amorphous salt phase. In contrast, in the aqueous NaCl solution at concentrations lower than the spinodal, crystallization occurs via a one-step process, as the ions aggregate directly into crystalline nuclei. The change of mechanism with increasing supersaturation underscores the importance of an accurate determination of the driving force for phase separation. The study has broader implications on the mechanism for nucleation of crystals from solutions at high supersaturations

In vitro screening of four genotypes of citrus for salt tolerance : S08P07

Soil and water salinity is an important abiotic stress that can affect both production and quality of citrus. The use of tolerant rootstocks in these conditions would be the solution the most used. The objective of this study was to compare in vitro behavior of four citrus genotypes in terms of tolerance to salinity. The genotypes used were 'Cleopatra' mandarin, 'Chios' mandarin, 'Shamouti' orange and 'Star Ruby' grapefruit. Salt tolerance was evaluated by determination of callus and suspension cells growth, the fresh and dry weight, water content and chloride ion content after one month of culture in solid and liquid media supplemented with NaCl at different concentrations: 50, 100, 150 and 200 mM. At 0 mM NaCl, the results revealed that callus of the four genotypes tested have a similar behavior in term of tolerance to salinity as the suspension cells. However, a differential behavior was observed at high salt concentrations depending on genotypes and the nature of medium. (Texte intégral

An experimental and computational investigation of structure and magnetism in pyrite Co1−x_{1-x}Fex_xS2_2: Chemical bonding and half-metallicity

Bulk samples of the pyrite chalcogenide solid solutions Co$_{1-x}$Fe$_x$S$_2$ 0 <= x <= 0.5, have been prepared and their crystal structures and magnetic properties studied by X-ray diffraction and SQUID magnetization measurements. Across the solution series, the distance between sulfur atoms in the persulfide (S$_2^{2-}$) unit remains nearly constant. First principles electronic structure calculations using experimental crystal structures as inputs point to the importance of this constant S-S distance, in helping antibonding S-S levels pin the Fermi energy. In contrast hypothetical rock-salt CoS is not a good half metal, despite being nearly isostructural and isoelectronic. We use our understanding of the Co$_{1-x}$Fe$_x$S$_2$ system to make some prescriptions for new ferromagnetic half-metals.Comment: 8 pages including 9 figure

A Novel Biostimulant, Belonging to Protein Hydrolysates, Mitigates Abiotic Stress Effects on Maize Seedlings Grown in Hydroponics

The main challenge to agriculture worldwide is feeding a rapidly growing human population, developing more sustainable agricultural practices that do not threaten human and ecosystem health. An innovative solution relies on the use of biostimulants, as a tool to enhance nutrient use ef\ufb01ciency and crop performances under sub-optimal conditions. In this work a novel biostimulant(APR\uae,ILSAS.p.A.,ArziganoVI,Italy), belongingtothegroupofproteinhydrolysates, wassuppliedtomaizeseedlingsinhydroponicanditseffectswereassessedincontrolconditionsand in the presence of three different kinds of stresses (hypoxia, salt and nutrient de\ufb01ciency) and of their combination. OurresultsindicatethatAPR\uae issolubleandisabletoin\ufb02uencerootandshootgrowth depending on its concentration. Furthermore, its effectiveness is clearly increased in condition of single or combination of abiotic stresses, thus con\ufb01rming the previously hypothesised action of this substance as enhancer of the response to environmental adversities. Moreover, it also regulates the transcription of a set of genes involved in nitrate transport and ROS metabolism. Further work will be needed to try to transfer this basic knowledge in \ufb01eld experiments

Viscosimetric studies of water and water-salt solution of polyethylene glycol

The complex analysis of a state of PEG macromolecules of various molecular weights in water and water-salt solutions is carried out. Temperature factors, the constants characterizing intermolecular interaction in these systems are defined. The intrinsic viscosity is defined with the use of the various linear extrapolation equations. Influence of temperature and electrolytes on thermodynamic properties in PEG – water and PEG – water-salt solution systems is shown