Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb-Pb collisions at root s(NN)=2.76TeV

Peer reviewe

Modeling control and transduction of electrochemical gradients in acid-stressed bacteria

Summary: Transmembrane electrochemical gradients drive solute uptake and constitute a substantial fraction of the cellular energy pool in bacteria. These gradients act not only as “homeostatic contributors,” but also play a dynamic and keystone role in several bacterial functions, including sensing, stress response, and metabolism. At the system level, multiple gradients interact with ion transporters and bacterial behavior in a complex, rapid, and emergent manner; consequently, experiments alone cannot untangle their interdependencies. Electrochemical gradient modeling provides a general framework to understand these interactions and their underlying mechanisms. We quantify the generation, maintenance, and interactions of electrical, proton, and potassium potential gradients under lactic acid-stress and lactic acid fermentation. Further, we elucidate a gradient-mediated mechanism for intracellular pH sensing and stress response. We demonstrate that this gradient model can yield insights on the energetic limitations of membrane transport, and can predict bacterial behavior across changing environments

Correlated Diffusivities, Solubilities, and Hydrophobic Interactions in Ternary Polydimethylsiloxane–Water–Tetrahydrofuran Mixtures

Bulk thermodynamic and kinetic properties of mixtures are generally composition dependent, often in complicated ways, especially for partially miscible and multicomponent systems. Combined ¹H chemical shift, ¹H diffusion NMR, and surface forces analyses establish the compositional dependences of water solubility and self-diffusion in ternary polymeric polydimethyl­siloxane–water–tetrahydrofuran (THF) mixtures. The addition of THF significantly increases the solubility of water, while decreasing its diffusivity, in hydrophobic polydimethyl­siloxane. Minimum values for the self-diffusivities of both water and THF coincide with a minimum in the hydrophobic adhesion energy between silicone polymer thin films near the same binary composition of 0.20 mole fraction THF. Such interrelated diffusivities, solubilities, and hydrophobic interactions are analyzed with respect to hydrogen bonding among the constituent species to account for the bulk physical properties of technologically important mixtures of silicone polymers with water and/or cosolvents

Understanding and Promoting Molecular Interactions and Charge Transfer in Dye-Mediated Hybrid Photovoltaic Materials

The performances of hybrid organic–inorganic photovoltaics composed of conjugated polymers and metal oxides are generally limited by poor electronic coupling at hybrid interfaces. In this study, physicochemical interactions and bonding at the organic–inorganic interfaces are promoted by incorporating organoruthenium dye molecules into self-assembled mesostructured conjugated polymer–titania composites. These materials are synthesized from solution in the presence of surfactant structure-directing agents (SDA) that solubilize and direct the nanoscale compositions and structures of the conjugated polymer, dye, and inorganic precursor species. Judicious selection of the SDA and dye species, in particular, exploits interactions that direct the dye species to the inorganic–organic interfaces, leading to significantly enhanced electronic coupling, as well as increased photoabsorption efficiency. This is demonstrated for the hydrophilic organoruthenium dye N3, used in conjunction with alkyleneoxide triblock copolymer SDA, polythiophene conjugated polymer, and titania species, in which the N3 dye species are localized in molecular proximity to and interact strongly with the titania framework, as established by solid-state NMR spectroscopy. In contrast, a closely related but more hydrophobic organoruthenium dye, Z907, is shown to interact more weakly with the titania framework, yielding significantly lower photocurrent generation. The strong SDA-directed N3-TiO_<i>x</i> interactions result in a significant reduction of the lifetime of the photoexcited state and enhanced macroscopic photocurrent generation in photovoltaic devices. This study demonstrates that multicomponent self-assembly can be harnessed for the fabrication of hierarchical materials and devices with nanoscale control of chemical compositions and surface interactions to improve photovoltaic properties

Functionally Active Membrane Proteins Incorporated in Mesostructured Silica Films

A versatile synthetic protocol is reported that allows high concentrations of functionally active membrane proteins to be incorporated in mesostructured silica materials. Judicious selections of solvent, surfactant, silica precursor species, and synthesis conditions enable membrane proteins to be stabilized in solution and during subsequent coassembly into silica–surfactant composites with nano- and mesoscale order. This was demonstrated by using a combination of nonionic (<i>n</i>-dodecyl-β-d-maltoside or Pluronic P123), lipid-like (1,2-diheptanoyl-<i>s</i><i>n</i>-glycero-3-phosphocholine), and perfluoro-octanoate surfactants under mild acidic conditions to coassemble the light-responsive transmembrane protein proteorhodopsin at concentrations up to 15 wt % into the hydrophobic regions of worm-like mesostructured silica materials in films. Small-angle X-ray scattering, electron paramagnetic resonance spectroscopy, and transient UV–visible spectroscopy analyses established that proteorhodopsin molecules in mesostructured silica films exhibited native-like function, as well as enhanced thermal stability compared to surfactant or lipid environments. The light absorbance properties and light-activated conformational changes of proteorhodopsin guests in mesostructured silica films are consistent with those associated with the native H⁺-pumping mechanism of these biomolecules. The synthetic protocol is expected to be general, as demonstrated also for the incorporation of functionally active cytochrome <i>c</i>, a peripheral membrane protein enzyme involved in electron transport, into mesostructured silica–cationic surfactant films

Waxy Gels with Asphaltenes 2: Use of Wax Control Polymers

The effect of asphaltenes on the effectiveness of wax control polymers was studied using a model waxy oil and a set of polymers with controlled crystalline and polar/aromatic content. The effect of crystalline content was examined with a set of maleic anhydride copolymers with alkyl appendages of different lengths. Different polar and/or aromatic functionalities were incorporated into the maleic anhydride copolymers (MAC) and poly(ethylene butene) polymers to probe potential interactions with the asphaltenes. The performance of the polymers was measured by testing their effect upon precipitation temperature, gelation temperature, and yield stress. Some polymers provided little or no benefit. Others had significant effects, reducing precipitation temperatures up to 1.9 °C, gelation temperatures up to 37 °C, and yield stresses up to 2200-fold for solutions of 8 wt % wax. Polymer efficacy was almost entirely determined by the crystalline functionality incorporated into the polymer rather than the presence of polar functionality designed to target interactions with the asphaltenes. The performance of the polymers is attributed to the ability of the polymers to coprecipitate with the wax. Comparison with previously published results using the same wax showed that the selectivity of the MACs was strongly affected by wax concentration, not because the quantity of wax overwhelmed the polymer, but because the range of wax precipitation temperatures increased above that of the polymer. Comparison of the effect of polymers in solutions with and without asphaltenes showed that asphaltenes had different effects on polymer performance, depending on the property being measured (precipitation temperature, gelation temperature, or yield stress)