efficiency (CE) and cycling performance. [2] In addition, the lithium polysulfides dissolution and Li dendrite growth also require a large amount excess electrolyte to achieve high performance, thus reducing the energy density. Extensive efforts have been devoted to suppress "shuttle" of lithium polysulfide. Among them, encapsulating sulfur cathode into porous host materials including porous carbon, [3] metal oxide/chalcogenide, [4] and conductive polymers [5] are the most effective method for suppressing "shuttle" effect. On the Li anode side, nanostructure design [6] or surface modification [7] has been also developed to suppress the dendritic Li growth.Different from separately nanostructured design of the electrodes, rational design and optimization of electrolytes are more effective, [8] which simultaneously suppress both lithium polysulfide shuttle and Li dendrite. [9] Recently, highly concentrated electrolyte (HCE) systems with unique solvation structure and functionality have been successfully developed for high performance Li-S batteries. For example, Suo et al. showed a new class of ultrahigh salt concentration electrolyte, which can effectively suppress the lithium dendrite growth and inhibit the polysulfide shuttle phenomenon in Li-S batteries. [2c] Qian et al. reported that the high-concentration electrolytes enabled the high-rate cycling of lithium metal with a high CE up to 99.1% without dendrite growth. [2a] These significant performance improvements were contributed to the strong restraining property for the solvents from the high-concentrated salts in electrolyte that efficiently control the reaction dynamics and Li 2 S n solubility synchronously. These exciting breakthroughs demonstrated that such unique HCE systems can offer new possibilities to address the shuttle effect and dendritic Li growth efficiently and simultaneously.Nevertheless, the usage of a large amount of expensive lithium salt in the HCE systems also lead to several disadvantages, including high cost, poor wettability, high viscosity, and low ionic conductivity. [10] To address these issues without scarifying the unique characteristics of HCE, a new kind of localized high-concentration electrolyte (LHCE) was proposed by using a rational cosolvent dilution in HCE system. The choice of the cosolvent in LHCE is critical for the performance of Li-S batteries. In Li-S battery electrolytes, ether-based solvents with high donor number were usually employed, which can effectively dissociate the Li + from anion and dissolve Li salts. However, the strong donating ability of such solvents can also facilitate the dissolution of long-chain polysulfide and amplify Rechargeable Li-S batteries are regarded as one of the most promising next-generation energy-storage systems. However, the inevitable formation of Li dendrites and the shuttle effect of lithium polysulfides significantly weakens electrochemical performance, preventing its practical application. Herein, a new class of localized high-concentration electrolyte (LHCE) enabled ...

We present a type of electronics that can be dissolved upon the presence of moisture within a controllable time scale.

The hepatitis delta virus ribozyme catalyzes an RNA cleavage reaction using a catalytic nucleobase and a divalent metal ion. The catalytic base, C75, serves as a general acid and has a pKa shifted towards neutrality. Less is known about the role of metal ions in the mechanism. A recent crystal structure of the pre-cleavage ribozyme identified a Mg2+ ion that interacts through its partial hydration sphere with the G25•U20 reverse wobble. In addition, this Mg2+ ion is in position to directly coordinate the nucleophile, the 2’-hydroxyl of U(-1), suggesting it can serve as a Lewis acid to facilitate deprotonation of the 2’-hydroxyl. To test the role of the active site Mg2+ ion, we replaced the G25•U20 reverse wobble with an isosteric A25•C20 reverse wobble. This change was found to significantly reduce the negative potential at the active site, as supported by electrostatics calculations, suggesting that active site Mg2+ binding could be adversely affected by the mutation. Kinetic analysis and molecular dynamics of the A25•C20 double mutant suggest that this variant stably folds into an active structure. However, pH-rate profiles of the double mutant are inverted relative to the profiles for wild-type ribozyme, suggesting that the A25•C20 double mutant has lost the active site metal ion. Overall, these studies support a model wherein the partially hydrated Mg2+ positioned at the G25•U20 reverse wobble is catalytic and could serve as a Lewis acid, a Brønsted base, or both to facilitate deprotonation of the nucleophile.

No abstract

The hammerhead ribozyme is a self-cleaving RNA broadly dispersed across all kingdoms of life. Although it was the first of the small, nucleolytic ribozymes discovered, the mechanism by which it catalyzes its reaction remains elusive. The nucleobase of G12 is well positioned to be a general base, but it is unclear if or how this guanine base becomes activated for proton transfer. Metal ions have been implicated in the chemical mechanism, but no interactions between divalent metal ions and the cleavage site have been observed crystallographically. To better understand how this ribozyme functions, we have solved crystal structures of wild-type and G12A mutant ribozymes. We observe a pH-dependent conformational change centered around G12, consistent with this nucleotide becoming deprotonated. Crystallographic and kinetic analysis of the G12A mutant reveals a Zn2+ specificity switch suggesting a direct interaction between a divalent metal ion and the purine at position 12. The metal ion specificity switch and the pH–rate profile of the G12A mutant suggest that the minor imino tautomer of A12 serves as the general base in the mutant ribozyme. We propose a model in which the hammerhead ribozyme rearranges prior to the cleavage reaction, positioning two divalent metal ions in the process. The first metal ion, positioned near G12, becomes directly coordinated to the O6 keto oxygen, to lower the pKa of the general base and organize the active site. The second metal ion, positioned near G10.1, bridges the N7 of G10.1 and the scissile phosphate and may participate directly in the cleavage reaction.

No abstract

Organic electrode materials are promising for green and sustainable lithium-ion batteries. However, the high solubility of organic materials in the liquid electrolyte results in the shuttle reaction and fast capacity decay. Herein, azo compounds are firstly applied in all-solid-state lithium batteries (ASSLB) to suppress the dissolution challenge. Due to the high compatibility of azobenzene (AB) based compounds to Li PS (LPS) solid electrolyte, the LPS solid electrolyte is used to prevent the dissolution and shuttle reaction of AB. To maintain the low interface resistance during the large volume change upon cycling, a carboxylate group is added into AB to provide 4-(phenylazo) benzoic acid lithium salt (PBALS), which could bond with LPS solid electrolyte via the ionic bonding between oxygen in PBALS and lithium ion in LPS. The ionic bonding between the active material and solid electrolyte stabilizes the contact interface and enables the stable cycle life of PBALS in ASSLB.

PurposeTo investigate the association between concomitant esotropia or concomitant exotropia and refractive error in preschool childrenMethodsA population-based sample of 5831 children aged 3 to 6 years was selected from all kindergartens in a representative county (Yuhuatai District, Nanjing, Jiangsu Province) of Nanjing, China. Clinical examinations including ocular alignment, ocular motility, visual acuity, optometry, stereopsis screening, slit lamp examination and fundus examination were performed by trained ophthalmologists and optometrists. Odd ratios (OR) and 95% confidence intervals (95% CI) were calculated to evaluate the association of refractive error with concomitant esotropia and concomitant exotropia.ResultsIn multivariate logistic regression analysis, concomitant esotropia was associated independently with spherical equivalent anisometropia (OR, 3.15 for 0.50 to <1.00 diopter (D) of anisometropia, and 7.41 for > = 1.00 D of anisometropia) and hyperopia. There was a severity-dependent association of hyperopia with the development of concomitant esotropia, with ORs increasing from 9.3 for 2.00 to <3.00 D of hyperopia, to 180.82 for > = 5.00 D of hyperopia. Concomitant exotropia was associated with astigmatism (OR, 3.56 for 0.50 to 1.00 D of astigmatism, and 1.9 for <0.00 D of astigmatism), myopia (OR, 40.54 for -1.00 to <0.00 D of myopia, and 18.93 for <-1.00 D of myopia), and hyperopia (OR, 67.78 for 1.00 to <2.00 D of hyperopia, 23.13 for 2.00 to <3.00 D of hyperopia, 25.57 for 3.00 to <4.00 D of hyperopia, and 8.36 for 4.00 to <5.00 D of hyperopia).ConclusionsThis study highlights the close associations between refractive error and the prevalence of concomitant esotropia and concomitant exotropia, which should be considered when managing childhood refractive error.