Capillary-Induced Ge Uniformly Distributed in N-Doped Carbon Nanotubes with Enhanced Li-Storage Performance

Germanium (Ge) is a prospective anode material for lithium-ion batteries, as it possesses large theoretical capacity, outstanding lithium-ion diffusivity, and excellent electrical conductivity. Ge suffers from drastic capacity decay and poor rate performance, however, owing to its low electrical conductivity and huge volume expansion during cycling processes. Herein, a novel strategy has been developed to synthesize a Ge at N-doped carbon nanotubes (Ge at N-CNTs) composite with Ge nanoparticles uniformly distributed in the N-CNTs by using capillary action. This unique structure could effectively buffer large volume expansion. When evaluated as an anode material, the Ge at N-CNTs demonstrate enhanced cycling stability and excellent rate capabilities

Precision and accuracy of single-molecule FRET measurements - a multi-laboratory benchmark study

Single-molecule Förster resonance energy transfer (smFRET) is increasingly being used to determine distances, structures, and dynamics of biomolecules in vitro and in vivo. However, generalized protocols and FRET standards to ensure the reproducibility and accuracy of measurements of FRET efficiencies are currently lacking. Here we report the results of a comparative blind study in which 20 labs determined the FRET efficiencies (E) of several dye-labeled DNA duplexes. Using a unified, straightforward method, we obtained FRET efficiencies with s.d. between ±0.02 and ±0.05. We suggest experimental and computational procedures for converting FRET efficiencies into accurate distances, and discuss potential uncertainties in the experiment and the modeling. Our quantitative assessment of the reproducibility of intensity-based smFRET measurements and a unified correction procedure represents an important step toward the validation of distance networks, with the ultimate aim of achieving reliable structural models of biomolecular systems by smFRET-based hybrid methods

Method development for next-generation single-molecule fluorescence technologies

We report two categories of method improvements for single-molecule fluorescence measurements, i.e., improvements on surface passivation and on binding assays, and an artificial minimal system to mimic and study cotranscriptional RNA folding in vitro. In the second chapter, we report a surface passivation method based on dichlorodimethylsilane (DDS)–Tween-20 for in vitro single-molecule studies, which, under the conditions tested here, more efficiently prevented nonspecific binding of biomolecules than the standard poly(ethylene glycol) surface. The DDS–Tween-20 surface was simple and inexpensive to prepare and did not perturb the behavior and activities of tethered biomolecules. It can also be used for single-molecule imaging in the presence of high concentrations of labeled species in solution. In the third chapter, we demonstrate that the use of the single-molecule centroid localization algorithm can improve the accuracy of fluorescence binding assays. Two major artifacts in this type of assay, i.e., nonspecific binding events and optically overlapping receptors, can be detected and corrected during analysis. The effectiveness of our method was confirmed by measuring two weak biomolecular interactions, the interaction between the B1 domain of streptococcal protein G and immunoglobulin G, and the interaction between double-stranded DNA and the Cas9–RNA complex with limited sequence matches. This analysis routine requires little modification to common experimental protocols, making it readily applicable to existing data and future experiments. Vectorial folding of RNA during transcription can produce intermediates with distinct biochemical activities. In the fourth chapter, we design an artificial minimal system to mimic cotranscriptional RNA folding in vitro. In this system, a presynthesized RNA molecule begins to fold from its 5‘-end, as it is released from a heteroduplex by an engineered helicase that translocates on the complementary DNA strand in the 3‘-to-5‘ direction. This chemically stabilized, “superhelicase“ Rep-X processively unwinds thousands of base pairs of DNA. The presynthesized RNA enables us to flexibly position fluorescent labels on the RNA for single-molecule fluorescence resonance energy transfer analysis and allows us to study real-time conformational dynamics during the vectorial folding process. We observed distinct signatures of the maiden secondary and tertiary folding of the Oryza sativa twister ribozyme. The maiden vectorial tertiary folding transitions occurred faster than Mg2+-induced refolding, but were also more prone to misfolding, likely due to sequential formation of alternative secondary structures. In the fifth chapter, we examine the Fusobacterium ulcerans ZTP riboswitch using the novel superhelicase-based vectorial folding assay. The RNA folds under kinetic control, when it is released in a 5‘-to-3‘ direction by helicasefacilitated heteroduplex unwinding. Changing the average unwinding speed and introducing artificial pausing sites tune the folding outcome. Realtime observation of heteroduplex unwinding and riboswitch folding shows non-native structural intermediates, which could explain some of the leaky readthrough detected in transcription termination assays

Method development for next-generation single-molecule fluorescence technologies

We report two categories of method improvements for single-molecule fluorescence measurements, i.e., improvements on surface passivation and on binding assays, and an artificial minimal system to mimic and study cotranscriptional RNA folding in vitro. In the second chapter, we report a surface passivation method based on dichlorodimethylsilane (DDS)–Tween-20 for in vitro single-molecule studies, which, under the conditions tested here, more efficiently prevented nonspecific binding of biomolecules than the standard poly(ethylene glycol) surface. The DDS–Tween-20 surface was simple and inexpensive to prepare and did not perturb the behavior and activities of tethered biomolecules. It can also be used for single-molecule imaging in the presence of high concentrations of labeled species in solution. In the third chapter, we demonstrate that the use of the single-molecule centroid localization algorithm can improve the accuracy of fluorescence binding assays. Two major artifacts in this type of assay, i.e., nonspecific binding events and optically overlapping receptors, can be detected and corrected during analysis. The effectiveness of our method was confirmed by measuring two weak biomolecular interactions, the interaction between the B1 domain of streptococcal protein G and immunoglobulin G, and the interaction between double-stranded DNA and the Cas9–RNA complex with limited sequence matches. This analysis routine requires little modification to common experimental protocols, making it readily applicable to existing data and future experiments. Vectorial folding of RNA during transcription can produce intermediates with distinct biochemical activities. In the fourth chapter, we design an artificial minimal system to mimic cotranscriptional RNA folding in vitro. In this system, a presynthesized RNA molecule begins to fold from its 5‘-end, as it is released from a heteroduplex by an engineered helicase that translocates on the complementary DNA strand in the 3‘-to-5‘ direction. This chemically stabilized, “superhelicase“ Rep-X processively unwinds thousands of base pairs of DNA. The presynthesized RNA enables us to flexibly position fluorescent labels on the RNA for single-molecule fluorescence resonance energy transfer analysis and allows us to study real-time conformational dynamics during the vectorial folding process. We observed distinct signatures of the maiden secondary and tertiary folding of the Oryza sativa twister ribozyme. The maiden vectorial tertiary folding transitions occurred faster than Mg2+-induced refolding, but were also more prone to misfolding, likely due to sequential formation of alternative secondary structures. In the fifth chapter, we examine the Fusobacterium ulcerans ZTP riboswitch using the novel superhelicase-based vectorial folding assay. The RNA folds under kinetic control, when it is released in a 5‘-to-3‘ direction by helicasefacilitated heteroduplex unwinding. Changing the average unwinding speed and introducing artificial pausing sites tune the folding outcome. Realtime observation of heteroduplex unwinding and riboswitch folding shows non-native structural intermediates, which could explain some of the leaky readthrough detected in transcription termination assays

Ultrathin and Edge-Enriched Holey Nitride Nanosheets as Bifunctional Electrocatalysts for the Oxygen and Hydrogen Evolution Reactions

Exploring economically efficient electrocatalysts with good electrocatalytic activity is essential for diverse electrochemical energy devices. Series of ultrathin metallic nickel-based holey nitride nanosheets were designed as bifunctional catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). They exhibit improved catalytic properties owing to the inherent advantages of their plentiful active reaction sites resulting from the complete exposure of the atoms in the large lateral surfaces and from the edges of pore areas, together with expanded lattice spacing distance. This obtained three-dimensional conductive integral architecture can not only accelerate the electron transportation by the highly orientated crystalline structure but also facilitate the diffusion of intermediate and gases. In terms of the OER electrocatalytic properties, a quite low overpotential (300 mV) is required for the holey two-dimensional (2D) Ni3Fe nitride nanosheets to deliver a current density of about 100 A g-1, with an enhanced improvement over IrO2by a factor of nearly 25 times. The holey 2D Ni3Fe nitride nanosheets also exhibit enhanced catalytic performance toward the HER, with a tiny overpotential (233 mV) to achieve a current density of about 100 A g-1with much better kinetic properties in comparison to those of highly active Pt/C

3-D structured SnO2-polypyrrole nanotubes applied in Na-ion batteries

SnO2-coated polypyrrole (PPy) with a three-dimensional (3-D) structured nanotube network has been prepared via a facile hydrothermal method and tested as an anode material for Na-ion batteries. The crystalline SnO2 nanoparticles (less than 25 nm in size) are distributed uniformly on the surfaces of the PPy tubes. When it is used as an anode material for sodium-ion batteries (SIBs), the composite electrode can deliver a good reversible capacity of nearly 288 mA h g-1 when discharging at 100 mA g-1, with more than 69.1% capacity retention and stable coulombic efficiency of 99.6% after 150 cycles. The good electrochemical performance compared to the 151 mA h g-1 achieved by bare SnO2, which was fabricated by the same method in the absence of PPy, could be mainly attributed to the good dispersion of SnO2 on the 3-D matrix of PPy tubes, which facilitates the diffusion of Na+ ions and buffers the large volumetric changes during charge/discharge. Our results suggest that such SnO2/carbonaceous composites would be good anode candidates for SIBs