Microscopic mechanism of protein cryopreservation in an aqueous solution with trehalose

In order to investigate the cryoprotective mechanism of trehalose on proteins, we use molecular dynamics computer simulations to study the microscopic dynamics of water upon cooling in an aqueous solution of lysozyme and trehalose. We find that the presence of trehalose causes global retardation of the dynamics of water. Comparing aqueous solutions of lysozyme with/without trehalose, we observe that the dynamics of water in the hydration layers close to the protein is dramatically slower when trehalose is present in the system. We also analyze the structure of water and trehalose around the lysozyme and find that the trehalose molecules form a cage surrounding the protein that contains very slow water molecules. We conclude that the transient cage of trehalose molecules that entraps and slows the water molecules prevents the crystallisation of protein hydration water upon cooling.DC, EGS, and HES thank the NSF chemistry Division for support (Grants CHE-1213217, CHE-0911389, and CHE-0908218). PG gratefully acknowledges the computational support reveived by the INFN RM3-GRID at Roma Tre University. (CHE-1213217 - NSF chemistry Division; CHE-0911389 - NSF chemistry Division; CHE-0908218 - NSF chemistry Division)Published versio

Fragile to strong crossover coupled to liquid-liquid transition in hydrophobic solutions

Using discrete molecular dynamics simulations we study the relation between the thermodynamic and diffusive behaviors of a primitive model of aqueous solutions of hydrophobic solutes consisting of hard spheres in the Jagla particles solvent, close to the liquid-liquid critical point of the solvent. We find that the fragile-to-strong dynamic transition in the diffusive behavior is always coupled to the low-density/high-density liquid transition. Above the liquid-liquid critical pressure, the diffusivity crossover occurs at the Widom line, the line along which the thermodynamic response functions show maxima. Below the liquid-liquid critical pressure, the diffusivity crossover occurs when the limit of mechanical stability lines are crossed, as indicated by the hysteresis observed when going from high to low temperature and vice versa. These findings show that the strong connection between dynamics and thermodynamics found in bulk water persists in hydrophobic solutions for concentrations from low to moderate, indicating that experiments measuring the relaxation time in aqueous solutions represent a viable route for solving the open questions in the field of supercooled water.Comment: 6 pages, 4 figures. Accepted for publication on Physical Review

Bird and mammal response to large-scale habitat mitigation for game species in the oil and gas fields of northwest Colorado

2016 Spring.Includes bibliographical references.To view the abstract, please see the full text of the document

Effect of hydrophobic solutes on the liquid-liquid critical point

Jagla ramp particles, interacting through a ramp potential with two characteristic length scales, are known to show in their bulk phase thermodynamic and dynamic anomalies, similar to what is found in water. Jagla particles also exhibit a line of phase transitions separating a low density liquid phase and a high density liquid phase, terminating in a liquid-liquid critical point in a region of the phase diagram that can be studied by simulations. Employing molecular dynamics computer simulations, we study the thermodynamics and the dynamics of solutions of hard spheres (HS) in a solvent formed by Jagla ramp particles. We consider the cases of HS mole fraction x = 0.10, 0.15 and 0.20, and also the case x = 0.50 (a 1:1 mixture of HS and Jagla particles). We find a liquid-liquid critical point, up to the highest HS mole fraction; its position shifts to higher pressures and lower temperatures upon increasing x. We also find that the diffusion coefficient anomalies appear to be preserved for all the mole fractions studied.Comment: 8 pages, 7 figures, 1 table. In press (Phys. Rev. E

Immigration Policy as Family Language Policy: Mexican Immigrant Children and Families in Search of Biliteracy

Aims and objectives/purpose/research questions: In this article we draw upon the ethnography of language planning and policy (LPP) to examine the complexities of how young Latino children with a recently deported parent engage with family language policies within their routine interactions. We explore the following questions. (1) How do US elementary school-aged children engage with, resist, and refashion family language and literacy policies alongside their parents in the face of parental deportations to Mexico? (2) How do children’s and parents’ experiences with monoglossic ideologies of schooling in the USA and Mexico shape family LPP and migratory decisions? Design/methodology/approach: The data come from a three-year ethnography on Mexican immigrant fathers and their elementary school-aged children conducted within the context of heightened deportations. Data and analysis: We focus on the case of eight-year-old Princess following her father’s deportation to examine how she articulated awareness of their counterpoint lives as she engaged in LPP alongside her mother. Findings/conclusions: Our findings reveal the unintended language education consequences of immigration policy as well as the complex ways that children discursively contribute to family LPP and migration decisions. Originality: This article uniquely highlights the complex interplay between immigration policy and LPP in the daily lives of mixed status Mexican immigrant families and the active roles that children play in shaping family language policy and migratory decisions. Significance/implications: We illustrate how children orient to monoglossic schooling ideologies as they prepare for and contest the possibilities of transnational schooling in Mexico and how limited opportunities to develop dynamic bilingualism or biliteracy in US schools shape families’ decisions. We argue that educational policy and classroom practices that open up ideological and implementational spaces to dynamically develop both languages are needed to better prepare children—especially those from undocumented families within a context of unprecedented deportations—for educational success on both sides of the border

The relaxation dynamics of a simple glass former confined in a pore

We use molecular dynamics computer simulations to investigate the relaxation dynamics of a binary Lennard-Jones liquid confined in a narrow pore. We find that the average dynamics is strongly influenced by the confinement in that time correlation functions are much more stretched than in the bulk. By investigating the dynamics of the particles as a function of their distance from the wall, we can show that this stretching is due to a strong dependence of the relaxation time on this distance, i.e. that the dynamics is spatially very heterogeneous. In particular we find that the typical relaxation time of the particles close to the wall is orders of magnitude larger than the one of particles in the center of the pore.Comment: 9 pages of Latex, 4 figure