Influence of the Water Content on the Diffusion Coefficients of Li⁺ and Water across Naphthalenic Based Copolyimide Cation-Exchange Membranes

The transport of lithium ions in cation-exchange membranes based on sulfonated copolyimide membranes is reported. Diffusion coefficients of lithium are estimated as a function of the water content in membranes by using pulsed field gradient (PFG) NMR and electrical conductivity techniques. It is found that the lithium transport slightly decreases with the diminution of water for membranes with water content lying in the range 14 < λ < 26.5, where λ is the number of molecules of water per fixed sulfonate group. For λ < 14, the value of the diffusion coefficient of lithium experiences a sharp decay with the reduction of water in the membranes. The dependence of the diffusion of lithium on the humidity of the membranes calculated from conductivity data using Nernst–Planck type equations follows a trend similar to that observed by NMR. The possible explanation of the fact that the Haven ratio is higher than the unit is discussed. The diffusion of water estimated by 1H PFG-NMR in membranes neutralized with lithium decreases as λ decreases, but the drop is sharper in the region where the decrease of the diffusion of protons of water also undergoes considerable reduction. The diffusion of lithium ions computed by full molecular dynamics is similar to that estimated by NMR. However, for membranes with medium and low concentration of water, steady state conditions are not reached in the computations and the diffusion coefficients obtained by MD simulation techniques are overestimated. The curves depicting the variation of the diffusion coefficient of water estimated by NMR and full dynamics follow parallel trends, though the values of the diffusion coefficient in the latter case are somewhat higher. The WAXS diffractograms of fully hydrated membranes exhibit the ionomer peak at q = 2.8 nm⁻1, the peak being shifted to higher q as the water content of the membranes decreases. The diffractograms present additional peaks at higher q, common to wet and dry membranes, but the peaks are better resolved in the wet membranes. The ionomer peak is not detected in the diffractograms of dry membranes.The authors acknowledge financial support provided by the DGICYT (Dirección General de Investigación Cientifíca y Tecnológica) through Grant MAT2011-29174-C02-02

Research on Brake Disk Heat Dissipation Rib Arrangement Spacing for High-speed Railway Train

Objective As the design speed of trains reaches 400 km/h level, the flow field environment under the train becomes more complex, highlighting the issues such as increased brake disc resistance and power consumption. It is imperative to conduct in-depth research on the optimal arrangement spacing of train brake disc heat dissipation ribs at this speed level. Method Using a cylindrical heat dissipation rib structure as the basis, a model is established through finite element simulation, inputting relevant parameter values. Four calculation conditions are set for the center-to-center distance (dc) circumferentially between adjacent heat dissipation ribs, and five calculation conditions are set radially for the distance (dr) between adjacent heat dissipation ribs. Various dc and dr values are calculated respectively for their impact on brake disc temperature rise, resistance, and heat dissipation power. It is aimed to determine recommended values for both dc and dr. Result & Conclusion When dr equals 40 mm (i.e. the ratio of the distance between the heat dissipation ribs and the brake disc edge to the brake disc diameter is 0.75), the brake disc temperature rise reaches the lowest value, indicating the optimal performance of brake disc. For heat dissipation ribs with a diameter equal to half of dc, the brake disc demonstrates the best overall performance

Structural basis for two-step glucose trimming by glucosidase II involved in ER glycoprotein quality control

AbstractThe endoplasmic reticulum (ER) has a sophisticated protein quality control system for the efficient folding of newly synthesized proteins. In this system, a variety of N-linked oligosaccharides displayed on proteins serve as signals recognized by series of intracellular lectins. Glucosidase II catalyzes two-step hydrolysis at α1,3-linked glucose–glucose and glucose–mannose residues of high-mannose-type glycans to generate a quality control protein tag that is transiently expressed on glycoproteins and recognized by ER chaperones. Here we determined the crystal structures of the catalytic α subunit of glucosidase II (GIIα) complexed with two different glucosyl ligands containing the scissile bonds of first- and second-step reactions. Our structural data revealed that the nonreducing terminal disaccharide moieties of the two kinds of substrates can be accommodated in a gourd-shaped bilocular pocket, thereby providing a structural basis for substrate-binding specificity in the two-step deglucosylation catalyzed by this enzyme.</jats:p

Preparation and properties of covalently cross-linked sulfonated poly(sulfide sulfone)/polybenzimidazole blend membranes for fuel cell applications

To improve the radical oxidative stability, a series of covalently cross-linked blend membranes have been prepared from a sulfonated poly(sulfide sulfone) with 80% degree of sulfonation (SPSSF80) and a polybenzimidazole with pendant amino groups (H2N-PBI) using glycidyloxypropyltrimethoxysilane (KH-560) and bisphenol A diglycidyl ether (BADGE) as cross-linkers. The resulting cross-linked membranes show increased tensile strength but slightly decreased elongation at break compared with the plain SPSSF80. The radical oxidative stability of the blend membranes is significantly improved due to the synergic action of the covalent cross-linking and the presence of the PBI component. For example, the cross-linked membrane with the composition of SPSSF80/H2N-PBI/KH-560 = 7/1/3 started to break into pieces after being soaked in Fenton’s reagent for 98 min, which is about 4 times longer than that (20 min) of the plain SPSSF50 (degree of sulfonation = 50%). The covalent cross-linking is also essential to suppress membrane swelling and to enhance membrane water stability. The KH-560-cross-linked blend membranes tend to show higher proton conductivities at low relative humidities than the BADGE-cross-linked one due to the hydrophilic silica network in the former. At fully hydrated state, the cross-linked membranes generally show high proton conductivities comparable with that of Nafion112®. </jats:p

Remodeling of the Oligosaccharide Conformational Space in the Prebound State To Improve Lectin-Binding Affinity

We developed an approach to improve the lectin-binding affinity of an oligosaccharide by remodeling its conformational space in the precomplexed state. To develop this approach, we used a Lewis X-containing oligosaccharide interacting with RSL as a model system. Using an experimentally validated molecular dynamics simulation, we designed a Lewis X analogue with an increased population of conformational species that were originally very minor but exclusively accessible to the target lectin without steric hindrance by modifying the nonreducing terminal galactose, which does not directly contact the lectin in the complex. This Lewis X mimetic showed 17 times higher affinity for the lectin than the native counterpart. Our approach, complementing the lectin-bound-state optimizations, offers an alternative strategy to create high-affinity oligosaccharides by increasing populations of on-pathway metastable conformers