135 research outputs found
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Chemistry and the Worm: Caenorhabditis elegans as a Platform for Integrating Chemical and Biological Research
This Review discusses the potential usefulness of the worm Caenorhabditis elegans as a model organism for chemists interested in studying living systems. C. elegans, a 1â
mm long roundworm, is a popular model organism in almost all areas of modern biology. The worm has several features that make it attractive for biology: it is small (<1000 cells), transparent, and genetically tractable. Despite its simplicity, the worm exhibits complex phenotypes associated with multicellularity: the worm has differentiated cells and organs, it ages and has a well-defined lifespan, and it is capable of learning and remembering. This Review argues that the balance between simplicity and complexity in the worm will make it a useful tool in determining the relationship between molecular-scale phenomena and organism-level phenomena, such as aging, behavior, cognition, and disease. Following an introduction to worm biology, the Review provides examples of current research with C. elegans that is chemically relevant. It also describes toolsâbiological, chemical, and physicalâthat are available to researchers studying the worm.Chemistry and Chemical Biolog
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Physical-Organic Chemistry: A Swiss Army Knife
âPhysical-organic chemistryâ is the name given to a subfield of chemistry that applies physical-chemical techniques to problems in organic chemistry (especially problems involving reaction mechanisms). âPhysical-organicâ is, however, also a short-hand term that describes a strategy for exploratory experimental research in a wide range of fields (organic, organometallic, and biological chemistry; surface and materials science; catalysis; and others) in which the key element is the correlation of systematic changes in molecular structure with changes in properties and functions of interest (reactivity, mechanism, physical or biological characteristics). This perspective gives a personal view of the historical development, and of possible future applications, of the physical-organic strategy.Chemistry and Chemical Biolog
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Influence of Fluorocarbon and Hydrocarbon Acyl Groups at the Surface of Bovine Carbonic Anhydrase II on the Kinetics of Denaturation by Sodium Dodecyl Sulfate
This paper examines the influence of acylation of the Lys-Δ-NH3+ groups of bovine carbonic anhydrase (BCA, EC 4.2.1.1) to Lys-Δ-NHCOR (R = âCH3, âCH2CH3, and âCH(CH3)2, âCF3) on the rate of denaturation of this protein in buffer containing sodium dodecyl sulfate (SDS). Analysis of the rates suggested separate effects due to electrostatic charge and hydrophobic interactions. Rates of denaturation (kAc,n) of each series of acylated derivatives depended on the number of acylations (n). Plots of log kAc,n vs n followed U-shaped curves. Within each series of derivatives, rates of denaturation decreased as n increased to 7; this decrease was compatible with increasingly unfavorable electrostatic interactions between SDS and protein. In this range of n, rates of denaturation also depended on the choice of the acyl group as n increased to 7, in a manner compatible with favorable hydrophobic interactions between SDS and the âNHCOR groups. As n increased in the range 7 < n < 14, however, rates of denaturation stayed approximately constant; analysis suggested that these rates were compatible with an increasingly important contribution to denaturation that depended both on the net negative charge of the protein and on the hydrophobicity of the R group. The mechanism of denaturation thus seems to change with the extent of acylation of the protein. For derivatives with the same net electrostatic charge, rates of denaturation increased with the acyl group (by a factor of 3 for n 14) in the order CH3CONHâ < CH3CH2CONHâ < (CH3)2CHCONHâ < CF3CONHâ. These results suggested that the hydrophobicity of CF3CONHâ is slightly greater (by a factor of <2) than that of RHCONHâ with similar surface area.Chemistry and Chemical Biolog
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Paper-based electroanalytical devices for accessible diagnostic testing
Microfluidic paper-based analytical devices (ÎŒPADs) use the passive capillary-driven flow of aqueous solutions through patterned paper channels to transport a sample fluid into distinct detection zones that contain the reagents for a chemical assay. These devices are simple, affordable, portable, and disposable; they are, thus, well suited for diagnostic applications in resource-limited environments. Adding screen-printed electrodes to the detection zones of a ÎŒPAD yields a device capable of performing electrochemical assays (an EÎŒPAD). Electrochemical detection has the advantage over colorimetric detection that it is not affected by interferences from the color of the sample, and can be quantified with simple electronics. The accessibility of EÎŒPADs is, however, limited by the requirement for an external potentiostat to power and interpret the electrochemical measurement. New developments in paper-based electronics may help loosen some of this requirement. This review discusses the current capabilities and limitations of EÎŒPADs and paper-based electronics, and sketches the ways in which these technologies can be combined to provide new devices for diagnostic testing.Chemistry and Chemical Biolog
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Formation of Bubbles in a Multisection Flow-Focusing Junction
The formation of bubbles in a flow-focusing (FF) junction comprising multiple rectangular sections is described. The simplest junctions comprise two sections (throat and orifice). Systematic investigation of the influence on the formation of bubbles of the flow of liquid and the geometry of the junction identifies regimes that generate monodisperse, bidisperse, and tridisperse trains of bubbles. The mechanisms by which these junctions form monodisperse and bidisperse bubbles are inferred from the shapes of the gas thread during breakup: these mechanisms differ primarily by the process in which the gas thread collapses in the throat and/or orifice. The dynamic self-assembly of bidisperse bubbles leads to unexpected groupings of bubbles during their flow along the outlet channel.Chemistry and Chemical Biolog
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Uniform Amplification of Phage with Different Growth Characteristics in Individual Compartments Consisting of Monodisperse Droplets
Jeder Klon zÀhlt! Beim Phagen-Display gehen Klone, die das Phagenwachstum hemmende Liganden prÀsentieren, bei der VervielfÀltigung verloren. In monodispersen Emulsionen, die mithilfe eines einfachen Mikrofluidiksystems erzeugt wurden, ist die Konkurrenz zwischen langsam (S) und schnell (R) wachsenden Phagen abgemildert, sodass das R/S-VerhÀltnis beibehalten bleibt. Die konkurrenzfreie VervielfÀltigung von Phagen bewahrt Liganden, die im normalen Phagen-Display abhanden kommen.Chemistry and Chemical Biolog
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Use of Thin Sectioning (Nanoskiving) to Fabricate Nanostructures for Electronic and Optical Applications
This Review discusses nanoskivingâa simple and inexpensive method of nanofabrication, which minimizes requirements for access to cleanrooms and associated facilities, and which makes it possible to fabricate nanostructures from materials, and of geometries, to which more familiar methods of nanofabrication are not applicable. Nanoskiving requires three steps: 1) deposition of a metallic, semiconducting, ceramic, or polymeric thin film onto an epoxy substrate; 2) embedding this film in epoxy, to form an epoxy block, with the film as an inclusion; and 3) sectioning the epoxy block into slabs with an ultramicrotome. These slabs, which can be 30â
nmâ10â
ÎŒm thick, contain nanostructures whose lateral dimensions are equal to the thicknesses of the embedded thin films. Electronic applications of structures produced by this method include nanoelectrodes for electrochemistry, chemoresistive nanowires, and heterostructures of organic semiconductors. Optical applications include surface plasmon resonators, plasmonic waveguides, and frequency-selective surfaces.Chemistry and Chemical Biolog
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Ionic skin
Electronic skins (i.e., stretchable sheets of distributed sensors) report signals using electrons, whereas natural skins report signals using ions. Here, ionic conductors are used to create a new type of sensory sheet, called âionic skinâ. Ionic skins are highly stretchable, transparent, and biocompatible. They readily measure strains from 1% to 500%, and pressures as low as 1 kPa.Engineering and Applied Science
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Self-assembly of magnetically interacting cubes by a turbulent fluid flow
Previous work has demonstrated that combining mechanical vibration with magnetic interactions can result in the self-assembly of complex structures, albeit at low yield. Here we introduce a system where the yield of self-assembled structures is quantitatively predicted by a theoretical analysis. Millimeter-sized magnetic blocks, designed to form chains as their minimal energy state, are placed in a turbulent fluid flow. The distribution of chain lengths that form is quantitatively consistent with predictions, showing that the chain length distribution coincides with that of monomers or polymers in a thermal bath, with the turbulence strength parametrizing the effective temperature.Chemistry and Chemical Biolog
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Warning Signals for Eruptive Events in Spreading Fires
Spreading fires are noisy (and potentially chaotic) systems in which transitions in dynamics are notoriously difficult to predict. As flames move through spatially heterogeneous environments, sudden shifts in temperature, wind, or topography can generate combustion instabilities, or trigger self-stabilizing feedback loops, that dramatically amplify the intensities and rates with which fires propagate. Such transitions are rarely captured by predictive models of fire behavior and, thus, complicate efforts in fire suppression. This paper describes a simple, remarkably instructive physical model for examining the eruption of small flames into intense, rapidly moving flames stabilized by feedback between wind and fire (i.e., âwindâfire couplingââa mechanism of feedback particularly relevant to forest fires), and it presents evidence that characteristic patterns in the dynamics of spreading flames indicate when such transitions are likely to occur. In this model system, flames propagate along strips of nitrocellulose with one of two possible modes of propagation: a slow, structured mode, and a fast, unstructured mode sustained by windâfire coupling. Experimental examination of patterns in dynamics that emerge near bifurcation points suggests that symptoms of critical slowing down (i.e., the slowed recovery of the system from perturbations as it approaches tipping points) warn of impending transitions to the unstructured mode. Findings suggest that slowing responses of spreading flames to sudden changes in environment (e.g., wind, terrain, temperature) may anticipate the onset of intense, feedback-stabilized modes of propagation (e.g., âblowup firesâ in forests).Chemistry and Chemical Biolog
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