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k-Junctions are elaborated forms of kink turns with an additional helix on the nonbulged strand, thus forming a three-way helical junction. Two were originally identified in the structures of Arabidopsisand Escherichia colithiamine pyrophosphate (TPP) riboswitches, and another called DUF-3268 was tentatively identified from sequence information. In this work we show that the Arabidopsisand E. coliriboswitch k-junctions fold in response to the addition of magnesium or sodium ions, and that atomic mutations that should disrupt key hydrogen bonding interactions greatly impair folding. Using X-ray crystallography, we have determined the structure of the DUF-3268 RNA and thus confirmed that it is a k-junction. It also folds upon the addition of metal ions, though requiring a 40-fold lower concentration of either divalent or monovalent ions. The key difference between the DUF-3268 and riboswitch k-junctions is the lack of nucleotides inserted between G1b and A2b in the former. We show that this insertion is primarily responsible for the difference in folding properties. Finally, we show that the DUF-3268 can functionally substitute for the k-junction in the E. coliTPP riboswitch such that the chimera can bind the TPP ligand, although less avidly.

Wood-derived carbons have been demonstrated to have large specific capacities as the anode materials of lithium-ion batteries (LIBs). However, these carbons generally show low tap density and minor volumetric capacity because of high specific surface area and pore volume. Combination with metal oxide is one of the expected methods to alleviate the obstacles of wood-derived carbons. In this work, the composites of MnO loaded wood-derived carbon fibers (CF@MnO) were prepared viaa simple and environmentally friendly method, showing decreased specific surface area due to the generation of MnO nanoparticles on carbon fibers. Furthermore, the CF@MnO compostites exhibit superior electrochemical performance as anode materials of LIBs, which show high reversible capacity in the range of 529–734 mAh/g at a current density of 100 mA/g. The optimal CF@MnO product (MnO:carbon = 1:2) delivers reversible capacity of 734 and 265.3 mAh/g at current density of 100 and 2000 mA/g, respectively. Besides, the material presents outstanding stability with coulombic efficiency around 100% after 200 cycles at a high current density of 400 mA/g, revealing a potential as promising anode materials for high-performance LIBs.

Known ribozymes in contemporary biology perform a limited range of chemical catalysis, but in vitro selection has generated species that catalyze a broader range of chemistry; yet, there have been few structural and mechanistic studies of selected ribozymes. A ribozyme has recently been selected that can catalyze a site-specific methyl transfer reaction. We have solved the crystal structure of this ribozyme at a resolution of 2.3 Å, showing how the RNA folds to generate a very specific binding site for the methyl donor substrate. The structure immediately suggests a catalytic mechanism involving a combination of proximity and orientation and nucleobase-mediated general acid catalysis. The mechanism is supported by the pH dependence of the rate of catalysis. A selected methyltransferase ribozyme can thus use a relatively sophisticated catalytic mechanism, broadening the range of known RNA-catalyzed chemistry.

Organic materials with rich active sites are good candidates of high-capacity anodes in aqueous batteries, but commonly low utilization of active sites limits their capacity. Herein, two isomers, symmetric and asymmetric hexaazatribenzanthraquinone (s-HATBAQ and a-HATBAQ), with rich active sites have been synthesized in a controllable manner. It has been revealed for the first time that a sulfuric acid catalyst can facilitate the stereoselective formation of s-HATBAQ. Attributed to the reduced steric hindrance in favor of proton insertion as well as the amorphous structure conducive to electrochemical dynamics, s-HATBAQ exhibits 1.5 times larger specific capacity than a-HATBAQ. Consequently, the electrode of s-HATBAQ with 50% reduced graphene oxide (s-HATBAQ-50%rGO) delivers a record high specific capacity of 405 mAh g−1in H2SO4electrolyte. Moreover, the assembled MnO2//s-HATBAQ-50%rGO aqueous proton full batteries show an exceptional cycling stability at 25°C and can maintain ∼92% capacity after 1000 cycles at 0.5 A g−1at −80°C. This work demonstrates the controllable synthesis of isomers, showcases a wide-temperature-range prototype proton battery and highlights the significance of precise molecular structure modulation in organic energy storage.This paper describes the controllable synthesis of two isomeric conjugated small molecules in an archiral environment and their wide-temperature-range proton storage behaviors, and confirms the important role of steric hindrance in determining small-molecule electrochemical reactivity.

Abstract: Stable picosecond dissipative soliton pulses were observed in an ytterbium-doped fiber laser employing a high-quality mixture of BP/SnSe2-PVA saturable absorber (SA). The modulation depth, saturation intensity, and non-saturable loss of the mixture of BP/SnSe2-PVA SA were measured with values of 5.98%, 18.37 MW/cm2, and 33%, respectively. Within the pump power range of 150–270 mW, stable dissipative soliton pulses were obtained with an output power of 1.68–4 mW. When the minimum pulse duration is 1.28 ps, a repetition rate of 0.903 MHz, center wavelength of 1064.38 nm and 3 dB bandwidth of 2 nm were obtained. The maximum pulse energy of 4.43 nJ and the signal-to-noise ratio up to 72 dB were achieved at pump power of 270 mW. The results suggest that the BP/SnSe2-PVA mixture SA has outstanding nonlinear saturable absorption characteristics and broad ultrafast laser applications. Graphical Abstract:

Light-harvesting lanthanide ions (Ln3+) doped NaYF4inks could provide polychromatic patterns for opposing counterfeiting commodity infestation because of their distinctive upconversion photoluminescence (UPL) properties. Herein, three kinds of core-triple-shell Ln3+ions doped NaYF4upconversion nanocrystals (UCNCs) are synthesized through modified high-temperature coprecipitation, which demonstrate excellent UPL properties of independent emitting colors under 808 or 980 nm laser excitation. Additive mixing three kinds of 808 nm emitted red-green-blue (RGB) UCNCs colloid solution can precisely regulate the emissions of the suspension for achieving full-color display. The as-obtained RGB three-primary colors induced by 808 nm laser accomplish broader color gamut than traditional standard RGB (sRGB) model and printing cyan-magenta-yellow (CMY) model. In addition, various China zodiac patterns and complex multicolor images are printed by the as-formulated UCNCs inks through screen printing technology. The printed patterns present colorful and polychromatic sequential toning visualization patterns under 808 nm excitation, while present another succession of gradually changed versatile patterns under 980 nm excitation. As a proof of concept, transparent polyvinyl chloride (PVC) self-adhesive anti-counterfeiting label is attached to the bottle of wine package for practical application. The demonstration of multiple model patterns of Chinese zodiac and poetry images based on these core-tripleshell UCNCs can be selected as a conceivable substitute of traditional single model patterns, underlining the full-color anti-counterfeiting level. 镧系离子掺杂的NaYF4油墨由于其独特的上转换光致发光特性可以被应用到防伪领域. 本文首先通过高温共沉淀法合成了三种核-壳结构的镧系离子掺杂的NaYF4上转换纳米材料, 它们在808和980 nm激光激发下均可以表现出差异性的上转换荧光性能. 其次, 通过物理混合808 nm激发的不同颜色的悬溶液红绿蓝, 可以调节混合液的发光颜色, 实现全彩色显示. 808 nm激发产生的颜色可以实现比sRGB和印刷CMY颜色空间模型更宽的色域. 最后, 我们使用传统丝网印刷技术印刷出中国十二生肖图案和其他大面积的复杂图像, 印刷图案在808 nm激发下可以呈现出一组多色连续的图案, 同时在980 nm激发下也可呈现出另一组逐渐改变的多色图案, 而且,印刷在透明聚氯乙烯PVC标签的图案可以附在酒瓶包装上, 实现酒瓶包装的防伪. 基于NaYF4的双模式荧光图案可以替代传统单模式荧光图案, 实现高水平的全色防伪及安全编码.

Extensive studies have been carried out to use carbon nanofibers/tubes (CNF/Ts) to reinforce cementitious materials because of their extraordinary properties (mechanical, electrical, energy storage). However, the high surface area of CNF/Ts makes them difficult to disperse in cementitious materials homogenously, leading to inefficient use of CNF/Ts. In this study, an eco-friendly method is proposed to functionalize CNFs so that they can be easily dispersed into cementitious materials. This method uses a plant-based biomolecule, tannic acid (TA), to modify CNFs. Compared with existing chemicals used to functionalize CNFs, TA is ubiquitous, renewable, and non-toxic. Experimental studies show that the TA can be successfully coated onto the surface of CNFs, making them stabilized in the water-based solution. SEM analysis suggests that a better dispersion of CNFs was achieved in the hydrated cement paste with TA functionalization compared to the one prepared with pristine CNFs. The homogenous dispersion also makes the nanofibers available to fill the nanopores, leading to a densified microstructure, as proved by MIP analysis. As a result, significant improvement in the mechanical properties of cement mortar has been achieved by using TA functionalization.