Consumer Attitudes toward Freshness Indicators on Perishable Food Products

Consumer/Household Economics, Food Consumption/Nutrition/Food Safety,

Viscoplasticity and large-scale chain relaxation in glassy-polymeric strain hardening

A simple theory for glassy polymeric mechanical response which accounts for large scale chain relaxation is presented. It captures the crossover from perfect-plastic response to strong strain hardening as the degree of polymerization $N$ increases, without invoking entanglements. By relating hardening to interactions on the scale of monomers and chain segments, we correctly predict its magnitude. Strain activated relaxation arising from the need to maintain constant chain contour length reduces the $N$ dependence of the characteristic relaxation time by a factor $\sim \dot\epsilon N$ during active deformation at strain rate $\dot\epsilon$. This prediction is consistent with results from recent experiments and simulations, and we suggest how it may be further tested experimentally.Comment: The theoretical treatment of the mechanical response has been significantly revised, and the arguments for coherent relaxation during active deformation made more transparen

Tuning Nanocrystal Surface Depletion by Controlling Dopant Distribution as a Route Toward Enhanced Film Conductivity

Electron conduction through bare metal oxide nanocrystal (NC) films is hindered by surface depletion regions resulting from the presence of surface states. We control the radial dopant distribution in tin-doped indium oxide (ITO) NCs as a means to manipulate the NC depletion width. We find in films of ITO NCs of equal overall dopant concentration that those with dopant-enriched surfaces show decreased depletion width and increased conductivity. Variable temperature conductivity data shows electron localization length increases and associated depletion width decreases monotonically with increased density of dopants near the NC surface. We calculate band profiles for NCs of differing radial dopant distributions and, in agreement with variable temperature conductivity fits, find NCs with dopant-enriched surfaces have narrower depletion widths and longer localization lengths than those with dopant-enriched cores. Following amelioration of NC surface depletion by atomic layer deposition of alumina, all films of equal overall dopant concentration have similar conductivity. Variable temperature conductivity measurements on alumina-capped films indicate all films behave as granular metals. Herein, we conclude that dopant-enriched surfaces decrease the near-surface depletion region, which directly increases the electron localization length and conductivity of NC films

The [4+2]‐Cycloaddition of α‐Nitrosoalkenes with Thiochalcones as a Prototype of Periselective Hetero‐Diels–Alder Reactions—Experimental and Computational Studies

The [4+2]‐cycloadditions of α‐nitrosoalkenes with thiochalcones occur with high selectivity at the thioketone moiety of the dienophile providing styryl‐substituted 4H‐1,5,2‐oxathiazines in moderate to good yields. Of the eight conceivable hetero‐Diels–Alder adducts only this isomer was observed, thus a prototype of a highly periselective and regioselective cycloaddition has been identified. Analysis of crude product mixtures revealed that the α‐nitrosoalkene also adds competitively to the thioketone moiety of the thiochalcone dimer affording bis‐heterocyclic [4+2]‐cycloadducts. The experiments are supported by high‐level DFT calculations that were also extended to related hetero‐Diels–Alder reactions of other nitroso compounds and thioketones. These calculations reveal that the title cycloadditions are kinetically controlled processes confirming the role of thioketones as superdienophiles. The computational study was also applied to the experimentally studied thiochalcone dimerization, and showed that the 1,2‐dithiin and 2H‐thiopyran isomers are in equilibrium with the monomer. Again, the DFT calculations indicate kinetic control of this process

Reconciling Semiclassical and Bohmian Mechanics: II. Scattering states for discontinuous potentials

In a previous paper [J. Chem. Phys. 121 4501 (2004)] a unique bipolar decomposition, Psi = Psi1 + Psi2 was presented for stationary bound states Psi of the one-dimensional Schroedinger equation, such that the components Psi1 and Psi2 approach their semiclassical WKB analogs in the large action limit. Moreover, by applying the Madelung-Bohm ansatz to the components rather than to Psi itself, the resultant bipolar Bohmian mechanical formulation satisfies the correspondence principle. As a result, the bipolar quantum trajectories are classical-like and well-behaved, even when Psi has many nodes, or is wildly oscillatory. In this paper, the previous decomposition scheme is modified in order to achieve the same desirable properties for stationary scattering states. Discontinuous potential systems are considered (hard wall, step, square barrier/well), for which the bipolar quantum potential is found to be zero everywhere, except at the discontinuities. This approach leads to an exact numerical method for computing stationary scattering states of any desired boundary conditions, and reflection and transmission probabilities. The continuous potential case will be considered in a future publication.Comment: 18 pages, 8 figure

Antibacterial Activity of and Resistance to Small Molecule Inhibitors of the ClpP Peptidase

There is rapidly mounting evidence that intracellular proteases in bacteria are compelling targets for antibacterial drugs. Multiple reports suggest that the human pathogen Mycobacterium tuberculosis and other actinobacteria may be particularly sensitive to small molecules that perturb the activities of self-compartmentalized peptidases, which catalyze intracellular protein turnover as components of ATP-dependent proteolytic machines. Here, we report chemical syntheses and evaluations of structurally diverse β-lactones, which have a privileged structure for selective, suicide inhibition of the self-compartmentalized ClpP peptidase. β-Lactones with certain substituents on the α- and β-carbons were found to be toxic to M. tuberculosis. Using an affinity-labeled analogue of a bioactive β-lactone in a series of chemical proteomic experiments, we selectively captured the ClpP1P2 peptidase from live cultures of two different actinobacteria that are related to M. tuberculosis. Importantly, we found that the growth inhibitory β-lactones also inactivate the M. tuberculosis ClpP1P2 peptidase in vitro via formation of a covalent adduct at the ClpP2 catalytic serine. Given the potent antibacterial activity of these compounds and their medicinal potential, we sought to identify innate mechanisms of resistance. Using a genome mining strategy, we identified a genetic determinant of β-lactone resistance in Streptomyces coelicolor, a non-pathogenic relative of M. tuberculosis. Collectively, these findings validate the potential of ClpP inhibition as a strategy in antibacterial drug development and define a mechanism by which bacteria could resist the toxic effects of ClpP inhibitors.National Institutes of Health (U.S.) (Grant GM-101988

Population Impacts of \u3cem\u3eWolbachia\u3c/em\u3e on \u3cem\u3eAedes albopictus\u3c/em\u3e

Prior studies have demonstrated that Wolbachia, a commonly occurring bacterium capable of manipulating host reproduction, can affect life history traits in insect hosts, which in turn can have population-level effects. Effects on hosts at the individual level are predicted to impact population dynamics, but the latter has not been examined empirically. Here, we describe a biological model system based on Aedes albopictus (Asian tiger mosquito) that allows for measurement of population dynamics, which has not been accomplished in prior field trials or laboratory designs. The results demonstrate the studied populations to be robust and allow for persistent, closed populations with overlapping generations, which are regulated solely through density-dependent, intraspecific competition for limited resources. Using a novel experimental design, we compare populations that are either uninfected or infected with Wolbachia. The results show differences that include population size, eclosion rates, adult survivorship, and fecundity. The aposymbiotic populations were generally larger and adults longer lived relative to the infected populations. The outcome is discussed in context with naturally occurring Wolbachia invasions, proposed autocidal strategies, and the utility of the developed system as a biological platform for hypothesis testing and improved parameterization

Editorial: Nucleic Acids Research and Nucleic Acid Therapeutics

Nucleic Acids Research has recently commissioned the publication of a series of Survey and Summary articles that encapsulate the current ‘state of the art’ surrounding the creation, function, behavior and optimization of nucleic acid molecules that may be adopted for clinical applications

High Dietary Iron and Radiation Exposure Increase Biomarkers of Oxidative Stress in Blood and Liver of Rats

Radiation exposure and increased iron (Fe) status independently cause oxidative damage that can result in protein, lipid, and DNA oxidation. During space flight astronauts are exposed to both increased radiation and increased Fe stores. Increased body Fe results from a decrease in red blood cell mass and the typically high Fe content of the food system. In this study we investigated the combined effects of radiation exposure (0.375 Gy of Cs-137 every other day for 16 days for a total of 3 Gy) and high dietary Fe (650 mg Fe/kg diet compared to 45 mg Fe/kg for controls) in Sprague-Dawley rats (n=8/group). Liver and serum Fe were significantly increased in the high dietary Fe groups. Likewise, radiation treatment increased serum ferritin and Fe concentrations. These data indicate that total body Fe stores increase with both radiation exposure and excess dietary Fe. Hematocrit decreased in the group exposed to radiation, providing a possible mechanism for the shift in Fe indices after radiation exposure. Markers of oxidative stress were also affected by both radiation and high dietary Fe, evidenced by increased liver glutathione peroxidase (GPX) and serum catalase as well as decreased serum GPX. We thus found preliminary indications of synergistic effects of radiation exposure and increased dietary Fe, warranting further study. This study was funded by the NASA Human Research Project