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

Effect of Modified Phospholipid Bilayers on the Electrochemical Activity of a Membrane-Spanning Conjugated Oligoelectrolyte

The incorporation and electrochemical activity of a conjugated oligoelectrolyte (COE) in model phospholipid bilayers have been characterized using cyclic voltammetry and UV–vis absorption measurements. Several other modifiers were also incorporated into the phospholipid membranes to alter properties such as charge and alkyl chain disorder. Using potassium ferricyanide to measure charge transport, it was observed that bilayers that contained cholic acid, a negatively charged additive that also promotes alkyl chain disorder, had higher COE uptake and charge permeability than unmodified bilayers. In contrast, when the positively charged choline was incorporated, charge permeability decreased and COE uptake was similar to that of unmodified bilayers. The incorporation of cholesterol at low concentrations within the phospholipid membranes was shown to enhance the COE’s effectiveness at increasing membrane charge permeability without increasing the COE concentration in the bilayer. Higher concentrations of cholesterol reduce membrane fluidity and membrane charge permeability. Collectively, these results demonstrate that changes in phospholipid membrane charge permeability upon COE incorporation depend not only on the concentration in the membrane but also on interactions with the phospholipid bilayer and other additives present in the membranes. This approach of manipulating the properties of phospholipid membranes to understand COE interactions is applicable to understanding the behavior of a wide range of molecules that impart useful properties to phospholipid membranes

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

Using Reverse Osmosis Membranes to Couple Direct Ethanol Fuel Cells with Ongoing Fermentations

Separations in biological systems remain a challenging problem and can be particularly so in the case of biofuels, where purification can use a significant fraction of the energy content of the fuel. For small-molecule biofuels like ethanol, reverse osmosis (RO) membranes show promise as passive purifiers, in that they allow uncharged small molecules to pass through while blocking most other components of the growth medium. Here, we examine the use of RO membranes in developing biohybrid fuel cells, closely examining the case where a direct ethanol fuel cell (DEFC) is coupled with an ongoing yeast fermentation across an RO membrane. We show that, contrary to initial good performance, the acetic acid produced by the DEFC readily diffuses back across the RO membrane and kills the fermentation after a few days. We introduce an amelioration chamber where the acetic acid is converted to acetate ions. The RO membrane rejects the acetate ions due to their charge, preventing acetic acid buildup in the fermentation. We also show that some small, charged components of the fermentation such as amino acids are imperfectly rejected by RO membranes. Because of the high sensitivity of DEFCs to low concentrations (10s of μM) of amino acids, even a very slow diffusion of amino acids across the RO membranes can limit biohybrid fuel cell lifetimes

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