While methods for polymer synthesis have proliferated, their functionality pales in comparison to natural biopolymers–strategies are limited for building the intricate network of noncovalent ...interactions necessary to elicit complex, protein-like functions. Using a bioinspired di(phenylalanine) acrylamide (FF) monomer, we explored the impact of various noncovalent interactions in generating ordered assembled structures. In this work, amphiphilic copolymers were synthesized that exhibit β-sheet-like local structure upon collapsing into single-chain assemblies in aqueous environments. Systematic analysis of a series of amphiphilic copolymers illustrated that the global collapse is primarily driven by hydrophobic forces. Hydrogen-bonding and aromatic interactions stabilize local structure, as β-sheet-like interactions were identified via circular dichroism and thioflavin T fluorescence. Similar analysis of phenylalanine (F) and alanine-phenylalanine acrylamide (AF) copolymers found that distancing the aromatic residue from the polymer backbone is sufficient to induce β-sheet-like local structure akin to the FF copolymers; however, the interactions between AF subunits are less stable than those formed by FF. Further, hydrogen-bond donating hydrophilic monomers disrupt internal structure formed by FF within collapsed assemblies. Collectively, these results illuminate design principles for the facile incorporation of multiple facets of protein-mimetic, higher-order structure within folded synthetic polymers.
In this article the main attention is paid to research into the narrator’s time and the autobiographical hero’s time in the Modern Russian autobiographical prose. First of all it gives outlines of ...the leading position of the time in the binarization of “time / space” and explanations for relationships of the narrator’s time and the autobiographical hero’s time. The epic time is described as the basic time of the narrator, which manifests itself mainly in two points - change or cessation of chronological movements of the hero. The biographical time is regarded as the dominant time of the autobiographical hero, in which growth and evolution of the hero occur. The study on intersection of the biographical time with historical, everyday and mythological times occupies a great place in the article.
Among many problems that determine current international migration of population, those that are associated with the phenomenon of “brain drain” are of particular importance and topicality. The ...authors express a fundamental disagreement with those who try to present this phenomenon as a “mutually beneficial process for all countries”, as well as with those Russian authors who identify “brain drain” with “internal transition of people from scientific sphere to real production, business and social sphere” indicating this transition as “internal brain drain”. Particular attention is paid to two modern features, namely: “brain drain” under conditions of demographic crisis and “brain drain” between member states of the EAEU.
The distribution and accumulation factors of heavy metals and metalloids (HMMs) in the bottom sediments of the Selenga river and its tributary Uda have been studied on the territory of Ulan-Ude. ...Their ecological and geochemical condition can influence the state of the lower reaches of the Selenga river and Baikal lake. We selected 3 background, 12 urban and 1 sample of bottom sediments downstream of the city. The main physical-chemical properties (pH, content of organic matter, iron oxides, granulometric composition) and the total content of HMMs in the samples were determined. The sediments of the Selenga and Udarivers are characterized by sandy and sandy-loamy granulometric composition, neutral reaction, low content of organic matter and Fe2O3. Upstream Ulan-Ude the rivershave a similar chemical composition of the sediments and are characterized by the dispersion and near-clark concentrations of the HMMs. Within the city and downstream, microelemental composition of the sediments has not significantly differ from the background one, this is due to their low sorption capacity and insignificant contamination of the precipitating suspended matter. Low-contrast geochemical anomalies were formed near the motorways (Mo, Cd, Bi), the oil storage facilities BuryatTerminal (W, Cu, Mo, As, Sb, Pb, Bi, Cd, Co, Ni), treatment plant (As, W, Bi), upstream of the aircraft plant (Cd) and below TPP-1 (W, V, Cd, Cu, Sb). The presence of correlations between the HMM content and the physico-chemical properties of the deposits indicates that the geochemical anomalies were formed also due to the sorption-sedimentation, chemisorption and biogeochemical barriers. The acid barrier is of great importance for the accumulation of an anionic Mo. The total HMM contamination of sediments within the city and downstream refers to the permissible level. The MPC in the sediments of the Selengariver was exceeded for As(in 1,5-3,4 times). Thus, in the UlanUde city and downstream, there are a weak man-made transformation and a low ecological danger of pollution of river sediments. The maximum contents of HMMs are localized on geochemical barriers near industrial enterprises and highways.
The feedstocks from biomass are defined and limited by nature, but through the choice of catalyst, one may change the deoxygenation outcome. We report divergent but selective deoxygenation of sugars ...with triethylsilane (TESH) and two fluoroarylborane catalysts, B(C6F5)3 and B(3,5-CF3)2C6H3)3 (BAr3,5‑CF3). To illustrate, persilylated 2-deoxyglucose shows exocyclic C–O bond cleavage/reduction with the less sterically congested BAr3,5‑CF3, whereas endocyclic C–O bond cleavage/reduction predominates with the more Lewis acidic B(C6F5)3. Chiral furans and linear polyols can be selectively synthesized depending on the catalysts. Mechanistic studies demonstrate that the resting states of these catalysts are different.
A “ter-ionic complex” composed of a tetracationic Ru(II) complex and two iodide ions was found to yield a covalent I–I bond upon visible light excitation in acetone solution. 1H NMR, visible ...absorption and DFT studies revealed that one iodide was associated with a ligand while the other was closer to the Ru metal center. Standard Stern–Volmer quenching of the excited state by iodide revealed upward curvature with a novel saturation at high concentrations. The data were fully consistent with a mechanism in which the Ru metal center in the excited state accepts an electron from iodide to form an iodine atom and, within 70 ns, that atom reacts with the iodide associated with the ligand to yield I2 •–. This rapid formation of an I–I bond was facilitated by the supramolecular assembly of the three reactant ions necessary for this ter-ionic reaction that is relevant to solar fuel production.
Stabilizing perovskite solar cells requires consideration of all defective sites in the devices. Substantial efforts have been devoted to interfaces, while stabilization of grain boundaries received ...less attention. Here, we report on a molecule tributyl(methyl)phosphonium iodide (TPI), which can convert perovskite into a wide bandgap one-dimensional (1D) perovskite that is mechanically robust and water insoluble. Mixing TPI with perovskite precursor results in a wrapping of perovskite grains with both grain surfaces and grain boundaries converted into several nanometer-thick 1D perovskites during the grain formation process as observed by direct mapping. The grain wrapping passivates the grain boundaries, enhances their resistance to moisture, and reduces the iodine released during light soaking. The perovskite films with wrapped grains are more stable under heat and light. The best device with wrapped grains maintained 92.2% of its highest efficiency after light soaking under 1-sun illumination for 1900 hours at 55°C open-circuit condition.
"Understanding Health Policy: A Clinical Approach is a book about health policy as well as individual patients and caregivers and how they interact with each other and with the overall health ...system."--Preface.
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