SciCombinator

Discover the most talked about and latest scientific content & concepts.

192

 To quantify the cost effectiveness of a government policy combining targeted industry agreements and public education to reduce sodium intake in 183 countries worldwide.

Concepts: Nation, Policy, Government, Sovereign state

23

Landfills are the final stage in the life cycle of many products containing per- and polyfluoroalkyl substances (PFASs) and their presence has been reported in landfill leachate. The concentrations of 70 PFASs in 95 samples of leachate were measured in a survey of U.S. landfills of varying climates and waste ages. National release of PFASs was estimated by coupling measured concentrations for the 19 PFASs where more than 50% of samples had quantifiable concentrations, with climate-specific estimates of annual leachate volumes. For 2013, the total volume of leachate generated in the U.S. was estimated to be 61.1 million m3, with 79% of this volume coming from landfills in wet climates (> 75 cm/yr precipitation) that contain 47% of U.S. solid waste. The mass of measured PFASs from U.S. landfill leachate to wastewater treatment plants was estimated to be between 563 and 638 kg for 2013. In the majority of landfill leachate samples, 5:3 fluorotelomer carboxylic acid (FTCA) was dominant and variations in concentrations with waste age affected total estimated mass. There were six PFASs that demonstrated significantly higher concentrations in leachate from younger waste compared to older waste, while no PFAS demonstrated significant variation with climate.

Concepts: Climate, Waste picker, Waste management, Recycling, Sewage treatment, Anaerobic digestion, Leachate, Landfill

23

Although my research has no common theme or defining area, a coherence connects the diverse topics insofar as one project leads logically to another. Thus, studies on mechanisms of hydrogen exchange in amides and amidines led to the influence of hydrogen bonding and to NMR methods for chemical kinetics, including 2D-EXSY spectroscopy. Another connection was the OH(-)-catalyzed NH exchange in amines that had supported the hypothesis of stereoelectronic control. We therefore analyzed that hypothesis critically, tested it, found counterexamples, and proposed an alternative hypothesis. We next addressed one-bond NMR coupling constants in ethers and the reverse anomeric effect. The latter studies required a highly accurate NMR titration method that we developed to measure the additional steric bulk resulting from protonation of a substituent. This method is also applicable to measuring secondary isotope effects on acidity, and we could demonstrate that they arise from n-σ* delocalization, not from an inductive effect. Other studies included kinetic isotope effects for both dissociation and H exchange of aqueous NH4(+), for C-N rotation in amides, and for a hydride transfer. The role of hydrogen bonding led us to the rotation of NH4(+) within its solvent cage and then to the symmetry of hydrogen bonds.

Concepts: Physical organic chemistry, Atom, Lithium aluminium hydride, Acid, Covalent bond, Hydronium, Hydrogen, Oxygen

23

Hilary M. Chase1#, Junming Ho2#, Mary Alice Upshur1, Regan J. Thomson1, Victor S. Batista3, Franz M. Geiger1* 1Department of Chemistry, Northwestern University, Evanston, IL. 60208, United States; 2 Agency for Science, Technology and Research, Institute of High Performance Computing, 1 Fusionopolis Way #16-16 Connexis North, Singapore 138632; 3Department of Chemistry, Yale University, P.O. Box 208107, New Haven, CT. 06520, United States # These authors contributed equally to this work. *corresponding author: geigerf@chem.northwestern.edu (847) 467-6553 Abstract. The adsorption of α-pinene to solid surfaces is an important primary step during the chemical conversion of this common terpene over mesoporous materials, as well as during the formation of atmospheric aerosols. We provide evidence of tight and loose physisorbed states of α-pinene bound on amorphous SiO2 as determined by their adsorption entropy, enthalpy and binding free energies characterized by computational modeling and vibrational sum frequency generation (SFG) spectroscopy. We find adsorption is partially (40% - 60%) irreversible over days at 294-342 K and 1 ATM total pressure of helium, while the distribution of α-pinene orientation remains invariant with temperature and partial pressure of α-pinene. Using the Redlich-Peterson adsorption model in conjunction with a van’t Hoff analysis of adsorption isotherms recorded for up to 2.6 Torr α-pinene in 1 ATM total pressure of helium, we obtain ΔSads, ΔHads, and ΔGads values of -60 (±11) J mol-1K-1, -40 (±3) kJ mol-1, and -23 (±5) kJ mol-1, respectively. These values are in good agreement with DFT calculations based on configurational sampling from MD simulations. Our findings are expected to have direct implications on the conversion of terpenes by silica-based catalysts and for the synthesis of secondary organic aerosol (SOA) in atmospheric chambers and flow tubes.

Concepts: Pascal, Entropy, Chemistry, Torr, Trigraph, Thermodynamics, Adsorption, Pressure

23

In vitro reconstruction of an alveolar barrier for modeling normal lung functions and pathological events serve as reproducible, high-throughput pharmaceutical platforms for drug discovery, diagnosis, and regenerative medicine. Despite much effort, the reconstruction of organ-level alveolar barrier functions has failed due to the lack of structural similarity to the natural basement membrane, functionalization with specific ligands for alveolar cell function, the use of primary cells and biodegradability. Here we report a bipolar cultured alveolar-capillary barrier model of human primary cells supported by a basement membrane mimics of fully-synthetic bifunctional nanofibers. One-step electrospinning process using a bioresorbable polyester and multi-functional star-shaped polyethylene glycols (sPEG) enables the fabrication of an ultrathin nanofiber mesh with interconnected pores. The nanofiber mesh possessed mechanical stability against cyclic expansion as seen in the lung in vivo. The sPEGs as an additive provide bio-functionality to fibers through the conjugation of peptide to the nanofibers and hydrophilization to prevent unspecific protein adsorption. Biofunctionalized nanofiber meshes facilitated bipolar cultivation of endothelial and epithelial cells with fundamental alveolar functionality and showed higher permeability for molecules compared to microporous films. This nanofiber mesh for a bipolar cultured barrier have the potential to promote growth of an organ-level barrier model for modeling pathological conditions and evaluating drug efficacy, environmental pollutants, and nanotoxicology.

Concepts: Basement membrane, Fibers, Endothelium, In vivo, In vitro, Function, Lung, Epithelium

23

The catalytic activity of proteins is a function of structural changes. Very often these are as minute as protonation changes, hydrogen bonding changes, and amino acid side chain reorientations. To resolve these, a methodology is afforded that not only provides the molecular sensitivity but allows for tracing the sequence of these hierarchical reactions at the same time. This feature article showcases results from time-resolved IR spectroscopy on channelrhodopsin (ChR), light-oxygen-voltage (LOV) domain protein, and cryptochrome (CRY). All three proteins are activated by blue light, but their biological role is drastically different. Channelrhodopsin is a transmembrane retinylidene protein which represents the first light-activated ion channel of its kind and which is involved in primitive vision (phototaxis) of algae. LOV and CRY are flavin-binding proteins acting as photoreceptors in a variety of signal transduction mechanisms in all kingdoms of life. Beyond their biological relevance, these proteins are employed in exciting optogenetic applications. We show here how IR difference absorption resolves crucial structural changes of the protein after photonic activation of the chromophore. Time-resolved techniques are introduced that cover the time range from nanoseconds to minutes along with some technical considerations. Finally, we provide an outlook toward novel experimental approaches that are currently developed in our laboratories or are just in our minds (“Gedankenexperimente”). We believe that some of them have the potential to provide new science.

Concepts: Acid, Enzyme, Oxygen, Metabolism, Amino acid, Molecular biology, Hydrogen, Protein

23

Espresso coffee foam, called crema, is known to be a marker of the quality of espresso coffee extraction. However, the role of foam in coffee temperature has not been quantitatively clarified. In this study, we used an automatic machine for espresso coffee extraction. We evaluated whether the foam prepared using the machine was suitable for foam analysis. After extraction, the percentage and consistency of the foam were measured using various techniques, and changes in the foam volume were tracked over time. Our extraction method, therefore, allowed consistent preparation of high-quality foam. We also quantitatively determined that the foam phase slowed cooling of the liquid phase after extraction. High-quality foam plays an important role in delaying the cooling of espresso coffee.

Concepts: Coffee, Density, Espresso

23

Sulphiting agents are well-known food preservatives. The European legislation does not allow their addition in fresh meat preparations. Therefore this type of food products has often been verified. To high sulphite levels in food is a health safety risk, due to toxic effects that these compounds may exercise on humans. In this study the control activity as performed by an Italian accredited laboratory from 2013 to 2015, relating to determination of sulphites in meat products, is described. Six hundred and sixty-nine meat product samples were analysed. Both applied techniques, a screening method (malachite green test) and a confirmatory method (ion chromatography), were accredited. 43 samples resulted positive at screening test and 19 of these samples showed high sulphites concentrations, in the range 67.6 - 1437 mg kg(-1). The non-negligible percentage of positives (6.4%) and the high concentrations verified, confirmed that the control of sulphuring treatment of fresh meat preparations is an important task for organisations in charge of food inspections and control.

Concepts: Type I and type II errors, Nutrition, Chemistry, Sulfites, Sulfur, Preservative, Sulfur dioxide, Sulfite

23

Continuous Glucose Monitoring (CGM) systems could improve glycemic control in critically ill patients. We aimed to identify the evidence on the clinical benefits and accuracy of CGM systems in these patients. For this, we performed a systematic search in Ovid MEDLINE, from inception to 26 July 2016. Outcomes were efficacy, accuracy, safety, workload and costs. Our search retrieved 356 articles, of which 37 were included. Randomized controlled trials on efficacy were scarce (n = 5) and show methodological limitations. CGM with automated insulin infusion improved time in target and mean glucose in one trial and two trials showed a decrease in hypoglycemic episodes and time in hypoglycemia. Thirty-two articles assessed accuracy, which was overall moderate to good, the latter mainly with intravascular devices. Accuracy in critically ill children seemed lower than in adults. Adverse events were rare. One study investigated the effect on workload and cost, and showed a significant reduction in both. In conclusion, studies on the efficacy and accuracy were heterogeneous and difficult to compare. There was no consistent clinical benefit in the small number of studies available. Overall accuracy was moderate to good with some intravascular devices. CGM systems seemed however safe, and might positively affect workload and costs.

Concepts: Adverse event, Employee benefit, Clinical research, Pharmaceutical industry, Clinical trial, Effectiveness, Hypoglycemia, Randomized controlled trial

23

Diabetes mellitus causes microcirculatory rarefaction and may impair the responsiveness of ischemic myocardium to proangiogenic factors.

Concepts: Diabetes, Stroke, Diabetes mellitus