Amyloid fibrils playing a critical role in disease expression, have recently been found to exhibit the excellent mechanical properties such as elastic modulus in the order of 10 GPa, which is comparable to that of other mechanical proteins such as microtubule, actin filament, and spider silk. These remarkable mechanical properties of amyloid fibrils are correlated with their functional role in disease expression. This suggests the importance in understanding how these excellent mechanical properties are originated through self-assembly process that may depend on the amino acid sequence. However, the sequence-structure-property relationship of amyloid fibrils has not been fully understood yet. In this work, we characterize the mechanical properties of human islet amyloid polypeptide (hIAPP) fibrils with respect to their molecular structures as well as their amino acid sequence by using all-atom explicit water molecular dynamics (MD) simulation. The simulation result suggests that the remarkable bending rigidity of amyloid fibrils can be achieved through a specific self-aggregation pattern such as antiparallel stacking of β strands (peptide chain). Moreover, we have shown that a single point mutation of hIAPP chain constituting a hIAPP fibril significantly affects the thermodynamic stability of hIAPP fibril formed by parallel stacking of peptide chain, and that a single point mutation results in a significant change in the bending rigidity of hIAPP fibrils formed by antiparallel stacking of β strands. This clearly elucidates the role of amino acid sequence on not only the equilibrium conformations of amyloid fibrils but also their mechanical properties. Our study sheds light on sequence-structure-property relationships of amyloid fibrils, which suggests that the mechanical properties of amyloid fibrils are encoded in their sequence-dependent molecular architecture.
Abstract. PM 1.0 , PM 2.5 , and PM 10 were sampled at Gosan ABC Superstation on Jeju Island from August 2007 to September 2008. The carbonaceous aerosols were quantified with the thermal/optical reflectance (TOR) method, which produced five organic carbon (OC) fractions, OC1, OC2, OC3, OC4, and pyrolyzed organic carbon (OP), and three elemental carbon (EC) fractions, EC1, EC2, and EC3. The mean mass concentrations of PM 1.0 , PM 2.5 , and PM 10 were 13.7 µg m −3 , 17.2 µg m −3 , and 28.4 µg m −3 , respectively. The averaged mass fractions of OC and EC were 23.0 % and 10.4 % for PM 1.0 , 22.9 % and 9.8 % for PM 2.5 , and 16.4 % and 6.0 % for PM 10 . Among the OC and EC sub-components, OC2 and EC2+3 were enriched in the fine mode, but OC3 and OC4 in the coarse mode. The filterbased PM 1.0 EC agreed well with black carbon (BC) measured by an Aethalometer, and PM 10 EC was higher than BC, implying less light absorption by larger particles. EC was well correlated with sulfate, resulting in good relationships of sulfate with both aerosol scattering coefficient measured by Nephelometer and BC concentration. Our measurements of EC confirmed the definition of EC1 as char-EC emitted from smoldering combustion and EC2+3 as soot-EC generated from higher-temperature combustion such as motor vehicle exhaust and coal combustion (Han et al., 2010). In particular, EC1 was strongly correlated with potassium, a traditional biomass burning indicator, except during the summer, when the ratio of EC1 to EC2+3 was the lowest. We also found the ratios of major chemical species to be a useful tool to constrain the main sources of aerosols, by which the five air masses were well distinguished: Siberia, Beijing, Shanghai, Yellow Sea, and East Sea types. Except Siberian air, the continental background of the study region, Beijing plumes showed the highest EC1 (and OP) to sulfate ratio, which implies that this air mass had the highest net warming by aerosols of the four air masses. Shanghai-type air, which was heavily influenced by southern China, showed the highest sulfate enhancement. The highest EC2+3/EC1 ratio was found in aged East Sea air, demonstrating a significant influence of motor vehicle emissions from South Korea and Japan and less influence from industrial regions of China. The high ratio results from the longer residence time and less sensitivity to wet scavenging of EC2+3 compared to EC1, indicating that soot-EC could have greater consequence in regionalscale warming.
A globally imminent shortage of freshwater has been demanding viable strategies for improving desalination efficiencies with the adoption of cost-and energy-efficient membrane materials. The recently explored 2D transition metal dichalcogenides (2D TMDs) of near atomic thickness have been envisioned to offer notable advantages as highefficiency membranes owing to their structural uniqueness; that is, extremely small thickness and intrinsic atomic porosity. Despite theoretically projected advantages, experimental realization of near atom-thickness 2D TMD-based membranes and their desalination efficiency assessments have remained largely unexplored mainly due to the technical difficulty associated with their seamless large-scale integration. Herein, we report the experimental demonstration of high-efficiency water desalination membranes based on few-layer 2D molybdenum disulfide (MoS 2 ) of only ∼7 nm thickness. Chemical vapor deposition (CVD)-grown centimeter-scale 2D MoS 2 layers were integrated onto porous polymeric supports with well-preserved structural integrity enabled by a water-assisted 2D layer transfer method. These 2D MoS 2 membranes of near atomic thickness exhibit an excellent combination of high water permeability (>322 L m −2 h −1 bar −1 ) and high ionic sieving capability (>99%) for various seawater salts including Na + , K + , Ca 2+ , and Mg 2+ with a range of concentrations. Moreover, they present near 100% salt ion rejection rates for actual seawater obtained from the Atlantic coast, significantly outperforming the previously developed 2D MoS 2 layer membranes of micrometer thickness as well as conventional reverse osmosis (RO) membranes. Underlying principles behind such remarkably excellent desalination performances are attributed to the intrinsic atomic vacancies inherent to the CVD-grown 2D MoS 2 layers as verified by aberration-corrected electron microscopy characterization.
Abstract. The Mass Absorption Cross section (MAC) andAbsorptionÅngström Exponent (AAE) have been commonly estimated for ambient aerosols but rarely for black carbon (BC) or organic aerosol (OA) alone in the ambient conditions. Here, we provide estimates of BC (and OA) MAC and AAE in East Asian outflow, by analyzing field data collected at the Gosan ABC super site. At this site, EC (and OC) carbon mass, the aerosol absorption coefficient at 7 wavelengths and PM mass density were continuously measured from October 2009 to June 2010.We remove the absorption data with significant dust influence using the mass ratio of PM 10 to PM 2.5 . The remaining data shows an AAE of about 1.27, which we suggest represent the average carbonaceous aerosol (CA) AAE at Gosan.We find a positive correlation between the mass ratio of OC to EC and CA AAE, and successfully increase the correlation by filtering out data associated with weak absorption signal. After the filtering, absorption coefficient is regressed on OC and EC mass densities. BC and OA MACs are found to be 5.1 (3.8-6.1) and 1.4 (0.8-2.0) m 2 g −1 at 520 nm respectively. From the estimated BC and OA MAC, we find that OA contributes about 45 % to CA absorption at 520 nm. BC AAE is found to be 0.7-1.0, and is probably even lower considering the instrument bias. OA AAE is found to be 1.6-1.8. Compared with a previous estimate of OA MAC and AAE near biomass burning, our estimates at Gosan strongly suggest that the strongly-absorbing so-called brown carbon spheres are either unrelated to biomass burning or absent near the emission source.
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